ENERGY POTENTIAL OF THE MILLUNGERA BASIN: A NEWLY DISCOVERED BASIN IN NORTH QUEENSLAND

Transcription

1 Lead author Russell Korsch ENERGY POTENTIAL OF THE MILLUNGERA BASIN: A NEWLY DISCOVERED BASIN IN NORTH QUEENSLAND R.J. Korsch 1, H.I.M. Struckmeyer 2, A. Kirkby 1, L.J. Hutton 3, L.K. Carr 1, K.L. Hoffmann 3, R. Chopping 1, I.G. Roy 1, M. Fitzell 3, J.M. Totterdell 2, M.G. Nicoll 1 and B. Talebi 3 1 Onshore Energy and Minerals Division Geoscience Australia GPO Box 378 Canberra ACT Petroleum and Marine Division Geoscience Australia GPO Box 378 Canberra ACT Geological Survey of Queensland Queensland Mines and Energy, Department of Employment, Economic Development and Innovation Level 1, 119 Charlotte Street Brisbane Qld 42 Russell.Korsch@ga.gov.au Heike.Struckmeyer@ga.gov.au Alison.Kirkby@ga.gov.au Laurie.Hutton@deedi.qld.gov.au Lidena.Carr@ga.gov.au Kinta.Hoffmann@deedi.qld.gov.au Richard.Chopping@ga.gov.au Indrajit.Roy@ga.gov.au Melanie.Fitzell@deedi.qld.gov.au Jennifer.Totterdell@ga.gov.au Malcolm.Nicoll@ga.gov.au Benham.Talebi@deedi.qld.gov.au ABSTRACT Deep seismic reflection surveys in north Queensland that were collected in 26 and 27 discovered a previously unknown sedimentary basin, now named the Millungera Basin, which is completely covered by a thin succession of sediments of the Jurassic Cretaceous, Eromanga-Carpentaria Basin. Interpretation of regional aeromagnetic data suggests that the basin could have areal dimensions of up to 28 km by 95 km. Apart from regional geophysical data, virtually no confirmed geological information exists on the basin. To complement the seismic data, new magnetotelluric data have been acquired on several lines across the basin. An angular unconformity between the Eromanga and Millungera basins indicates that the upper part of the Millungera Basin was eroded prior to deposition of the Eromanga- Carpentaria Basin. Both the western and eastern margins of the Millungera Basin are truncated by thrust faults, with well-developed hangingwall anticlines occurring above the thrusts at the eastern margin. The basin thickens slightly to the east, to a maximum preserved subsurface depth of ~3,37 m. Using sequence stratigraphic principles, three discrete sequences have been mapped. The geometry of the stratigraphic sequences, the post-depositional thrust margins, and the erosional unconformity at the top of the succession all indicate that the original succession across much of the basin was thicker by up to at least 1,5 m than preserved today. The age of the Millungera Basin is unknown, but petroleum systems modelling has been carried out using two scenarios, that is, that the sediment fill is equivalent in age to (1) the Neoproterozoic-Devonian Georgina Basin, or (2) the Permian Triassic Lovelle Depression of the Galilee Basin. Using the Georgina Basin analogue, potential Cambrian source rocks are likely to be mature over most of the Millungera Basin, with significant generation and expulsion of hydrocarbons occurring in two phases, in response to Ordovician and Cretaceous sediment loading. For the Galilee Basin analogue, potential Permian source rocks are likely to be oil mature in the central Millungera Basin, but immature on the basin margins. Significant oil generation and expulsion probably occurred during the Triassic, in response to late Permian to Early Triassic sediment loading. Based on the seismic and potential field data, several granites are interpreted to occur immediately below the Millungera Basin, raising the possibility of hot rock geothermal plays. Depending on its composition, the Millungera Basin could provide a thermal blanket to trap any heat which is generated. 3D inversion of potential field data suggests that the inferred granites range from being magnetic to non-magnetic, and felsic (less dense) to more mafic. They may be part of the Williams Supersuite, which is enriched in uranium, thorium and potassium, and exposed just to the west, in the Mount Isa Province. 3D gravity modelling suggests that the inferred granites have a possible maximum thickness of up to 5.5 km. Therefore, if granites with the composition of the Williams Supersuite occur beneath the Millungera Basin, in the volumes indicated by gravity inversions, then, based on the forward temperature modelling, there is a good probability that the basin is prospective for geothermal energy. APPEA Journal

2 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi KEYWORDS North Queensland, Millungera Basin, Carpentaria Basin, Eromanga Basin, sedimentary basins, petroleum potential, geothermal potential, deep crustal seismic, aeromagnetics, gravity, magnetotellurics. INTRODUCTION A previously unknown sedimentary basin in northwest Queensland, the Millungera Basin, was discovered in 26, as a result of a deep crustal seismic reflection survey. The basin is completely covered by the thin Jurassic Cretaceous Eromanga-Carpentaria Basin (part of the same depositional system separated by a basement high, the Euroka Ridge). The 26 seismic survey, conducted under a collaborative program between Geoscience Australia, the Geological Survey of Queensland, the Predictive Mineral Discovery Cooperative Research Centre and Zinifex, was planned to image the structure of the upper crust in the Mount Isa Province. Relatively short segments up to 35 km long of a sedimentary succession beneath the Eromanga Basin were observed first on two seismic lines (6GA-M4 and 6GA-M5; Hutton et al, 29a; Fig. 1). A second survey in 27, conducted under a collaborative program between Geoscience Australia, the Geological Survey of Queensland and AuScope, was designed to image the structure of the upper crust between Cloncurry in the Mount Isa Province and the Charters Towers region in northeast Queensland (Korsch and Huston, 29). One seismic line, 7GA-IG1 (Fig. 1), imaged a 65 km-wide section of the basin (Korsch et al, 29). Interpretation of aeromagnetic data suggests that the basin could have areal dimensions of up to 28 km by 95 km (Fig. 2). Apart from geophysical data, virtually no geological information exists on the basin. This paper documents the discovery of this new, subsurface sedimentary basin in northwest Queensland, and presents a preliminary discussion of its extent, likely character, and possible basin correlatives. Petroleum maturation modelling and geothermal modelling, based on a series of scenarios, has been undertaken to assess the possible energy potential of the basin. SEISMIC INTERPRETATION Seismic line 7GA-IG1 In the vicinity of seismic line 7GA-IG1, the Jurassic Cretaceous Carpentaria Basin is about 2 3 m thick, and the organic-rich Toolebuc Formation occurs at a depth of about 185 m. Below the Carpentaria Basin, the seismic profile identified a succession of flat-lying to gently-dipping sedimentary strata of unknown age, extending from common depth point (CDP) 6,5 to CDP 9,9 (Fig. 3). This succession, now termed the Millungera Basin, is interpreted to have been deposited on top of the Kowanyama Seismic Province (Korsch et al, 29). In the seismic section, the depth to the thickest part of the basin is about 1.5 s two-way travel time (TWT), or ~3,37 m (subsurface), calculated using the stacking velocities. Smaller areas of similar reflections have been identified farther to the northeast along 7GA-IG1, between about CDP 16,4 and CDP 17,, and may represent equivalent strata to the Millungera Basin (Korsch et al, 29). Interpretation of gravity profiles suggests that the basin deepens to the south, possibly reaching a maximum thickness of 4, m subsurface. There is a noticeable angular unconformity between the two basins (e.g. at about CDP 9,3), indicating that part of the Millungera Basin was eroded prior to deposition of the Carpentaria Basin, and, in places, there is also a marked angular unconformity between the basement of the Kowanyama Seismic Province (granite and metasedimentary rocks) and the base of the Millungera Basin (e.g. at about CDP 7,3; Fig. 3). Three distinct sedimentary sequences, which thicken slightly to the east, can be mapped in the seismic section using sequence stratigraphic principles. The lower two sequences are further subdivided at possible sequence boundaries (Fig. 3). At this stage, no attempt is made to interpret the lithology or composition of rocks that may be present in the succession, apart from noting that the sequences are considered to be entirely sedimentary. SEQUENCE 1 The basal sequence is highly reflective; multiple strong reflections occur through the entire unit and can be traced over most of the seismic section (Fig. 3). This implies the presence of different lithologies with contrasting acoustic impedances. The maximum thickness of this sequence is nearly 1, m, although sediments in the unit may be more compacted than the overlying sequences, and may have higher seismic velocities. The base of this sequence is unconformable on basement, for example, at about CDP 7,3 (Fig. 3). The base of the overlying Sequence 2 is interpreted to occur over the entire width of the basin in this seismic section (Fig. 3). SEQUENCE 2 The middle sequence mostly exhibits weak seismic reflectivity or is nonreflective, implying a relatively homogeneous lithology with little variation, although there are some discontinuous reflections towards the base of the sequence. The base of this sequence is interpreted to be immediately above the strong uppermost reflection in Sequence 1. Sequence 2 has a fairly uniform geometry, thickening slightly into the centre of the basin where it reaches a maximum thickness of up to 1,2 m. The unit is interpreted to be truncated at both the southwestern and northeastern ends of the section by the unconformity (sequence boundary) defining the base of the Carpentaria Basin (Fig. 3). SEQUENCE 3 The uppermost sequence is highly reflective, indicating the presence of different lithologies with contrasting 296 APPEA Journal 211

3 Energy potential of the Millungera Basin: a newly discovered basin in north Queensland 14 G U L F O F C A R P E N T A R I A Karumba Normanton 18 ETHERIDGE PROVINCE CARPENTARIA BASIN 7GA IG2 7GA GC1 GSQ Dobbyn 1 Canobie Depression 7GA IG1 RN1939 QUEENSLAND 2 6GA M3 B A RN17183 MOUNT ISA PROVINCE MILLUNGERA BASIN RN3527 JHR Gladevale Downs 1 Mount Isa Cloncurry 94MTI 1 6GA M4 RN GA M6 94MTI 2 PILGRIM FAULT JHR Glenbede Downs 1 JHR Rosevale Downs 1 RN3272 RN3276 RN3264 JHR Belfast 1 JHR Hampden Downs 1 Hughenden 1 km 22 BURKE RIVER STRUCTURAL BELT 6GA M5 EROMANGA BASIN BUO Denbigh Downs 1 Winton WA NT SA QLD NSW VIC TAS Millungera Basin Canobie Depression Mesozoic Cenozoic Etheridge Province Mount Isa Province Georgina Basin GA seismic lines Industry seismic lines Fault Limit of Galilee Basin Key drillholes Modelling site Town Figure 1. Simplified map of northwest Queensland showing the surface distribution of Cenozoic and Mesozoic sediments, the locations of the Neoproterozoic Ordovician Georgina Basin, and the Paleoproterozoic to Mesoproterozoic Mount Isa and Etheridge provinces. The interpreted subsurface distribution of the Millungera Basin and Canobie Depression are shown. Also shown are Geoscience Australia and industry seismic lines, as well as key drillholes. APPEA Journal

4 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi CARPENTARIA ETHERIDGE BASIN PROVINCE GSQ Dobbyn 1 Canobie Depression 7GA IG1 QUEENSLAND Mount Fort Bowen # # Mount Brown 2 MT. ISA PROVINCE MILLUNGERA BASIN JHR Gladevale Downs 1 Cloncurry 94MTI GA M4 JHR Glenbede Downs 1 5 km JHR Rosevale Downs GEORGINA BASIN 6GA M6 6GA M5 JHR Hampden Downs 1 JHR Belfast 1 EROMANGA BASIN WA NT SA QLD NSW VIC TAS Millungera Basin Canobie Depression GA seismic lines Industry seismic lines Fault # Key drillholes Town Mountain peak Figure 2. Grey scale, first vertical derivative of the total magnetic intensity data, showing the interpreted distribution of the Millungera Basin and the Canobie Depression, as well as key drillholes and seismic lines. 298 APPEA Journal 211

5 Energy potential of the Millungera Basin: a newly discovered basin in north Queensland Figure 3. Migrated seismic section for part of seismic line 7GA-IG1 across the Millungera Basin showing (a) uninterpreted and (b) interpreted versions. Five sequence boundaries below the base Carpentaria unconformity have been mapped in the Millungera Basin. The display shows a vertical exaggeration of approximately two times over the horizontal scale, assuming an average crustal velocity of 6. km s -1. acoustic impedances. This sequence can be traced easily over the western part of the seismic section, but not in the eastern part, where intensity of deformation increases (Fig. 3). Based on the depth to the base of the basin at about CDP 9,7, this sequence is interpreted to occur in the core of the syncline at the northeast margin of the basin, and has a maximum preserved thickness of up to 8 m. It has been eroded completely at both the southwest end of the seismic line (about CDP 6,7) and in the hangingwall of a major thrust fault (about CDP 9,2; Fig. 3), and its base is defined as the strong reflection immediately above the nonreflective Sequence 2 (Fig. 3). STRUCTURE Both the northwestern and northeastern margins of the Millungera Basin are truncated by thrust faults (Fig. 3). The northwestern edge is defined by a southwest-dipping fault, which appears to be a backthrust off a larger, northeast-dipping fault. The northeast margin of the basin is truncated by a northeast-dipping thrust fault, which is a major basement structure (Korsch et al, 29). Although the western half of the basin is relatively undeformed, the eastern part of the basin has been cut by several, deep-penetrating, northeast-dipping thrust faults, with associated development of hangingwall anticlines (Fig. 3). The internal geometry of stratigraphic sequences, the post-depositional thrust margins, and the erosional unconformity at the top of the succession, all suggest that the original succession across much of the basin was thicker, by up to at least 1,5 m, than preserved today. Seismic lines 6GA-M4 and 6GA-M5 At the northern end of seismic line 6GA-M5 (Fig. 1), a series of subhorizontal seismic reflections identified below the Eromanga Basin have been interpreted as a stratigraphic succession. This section is underlain by a nonreflective zone, interpreted to be granite (Hutton et al, 29a). The stratigraphic succession has a similar reflective APPEA Journal

6 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi package to that seen in the Millungera Basin (reflective lower part, nonreflective middle part, reflective upper part; Fig. 4), and is considered to form part of this basin. At the southeastern end of seismic line 6GA-M4 (Fig. 1), a series of seismic reflections can be identified beneath the Eromanga Basin (Fig. 5) and has been interpreted by Hutton et al (29a) as a correlative of the succession in the Millungera Basin, as seen on seismic line 7GA-IG1. The sedimentary succession on seismic line 6GA-M4 is very thin (Fig. 5) and may represent only the basal part of the succession seen in seismic lines 7GA-IG1 (Fig. 3) and 6GA-M5 (Fig. 4). A nonreflective zone beneath the succession is interpreted as granite (Fig. 5). AREAL DISTRIBUTION A sedimentary succession is observed on two, and possibly three, seismic lines, and hence an attempt was made to map the areal extent of the basin using airborne magnetic data (Fig. 2). The margins of the basin were defined where strong magnetic trends in basement rocks, which include metamorphosed dolerite or basalt sills, were sharply truncated. Overall, the basin has low magnetic intensity, although south of seismic line 7GA-IG1 there are thin bands of higher magnetic intensity. These areas possibly represent sedimentary units that contain some magnetic material. Also, there are a few east west-trending dykes, particularly in the southern half of the basin. The initial outline shows a basin that extends over an area of ~28 km by 95 km, but this outline is speculative, particularly in the south, where seismic reflection lines are totally lacking (Fig. 1). Gravity data suggest that the sedimentary succession could occur as a series of disconnected sub-basins, but the similarity of the reflective packages seen on seismic lines 7GA-IG1 (Fig. 3) and 6GA-M5 (Fig. 4) suggest that the basin is likely to be more continuous. GEOPHYSICAL DATA AND MODELLING Inverse modelling of potential field data Three-dimensional inverse modelling of gravity and magnetic data was undertaken to provide further constraints on the geometry of the Millungera Basin, and its basement. Inverse modelling is where a computer algorithm calculates a model of physical properties (for example, densities or magnetic susceptibilities), such that this model reproduces the observed geophysical responses, subject to certain mathematical limitations. The University of British Columbia Geophysical Inversion Facility (UBC GIF) gravity and magnetic 3D inversion codes grav3d and mag3d (Li and Oldenburg, 1996, 1998a) were used to derive geologically unconstrained inversions for the region covered by the seismic transects. Vertical slices of the magnetic and gravity inversions were extracted along the CDP profile of seismic line 7GA-IG1 (Fig. 6). The inversions show the vertical distribution of densities and magnetic susceptibilities along the seismic line. They confirm the lower densities and magnetic susceptibilities of the basin succession, compared to the underlying basement (Fig. 6). In seismic line 7GA-IG1, the Millungera Basin overlies four prominent nonreflective zones up to.5 s TWT (1.5 km) thick, which were interpreted to be granite bodies (Korsch et al, 29). The western interpreted granite has low density and magnetic susceptibility, and is inferred to be non-magnetic, felsic granite. The two granites interpreted under the middle of the basin have higher densities and higher magnetic susceptibilities, and are inferred to be magnetic granite containing more mafic components. The eastern interpreted granite has low density and higher magnetic susceptibility, and is inferred to be magnetic, felsic granite. The sedimentary rocks in the Millungera Basin, as well as the overlying Eromanga-Carpentaria Basin, may have formed a thermal blanket above the granites, thus raising the possibility for a geothermal energy resource (see geothermal section below). Magnetotelluric survey A tensor magnetotelluric (MT) survey, with station intervals between 5 m and 5 m, was undertaken in the Mount Isa area in 29 (Fig. 7). A total of 24 stations were acquired along seven profiles in and around the Mt Isa Province. A dipole length of 1 m was used on each traverse. Data at each station were acquired during a period of 24 hours, measuring a frequency bandwidth between.1 Hz to 25 Hz. A previous MT survey was undertaken along seismic line 7GA-IG1 in 27 (Henson et al, 29a). Three of the new profiles, lines 5, 7 and 8 (Fig. 7), were acquired to provide additional information on the regional electrical resistivity distribution at depth in the northern part of the Millungera Basin. The MT method is a non-invasive, electromagnetic technique that measures naturally occurring electric (telluric) currents induced in the earth by natural variations in the Earth s magnetic field. These electric currents are influenced by rock properties, including rock type, porosity, permeability and temperature. Surveying involves measuring variations in the Earth s magnetic and electric fields using induction coils. Inversion algorithms are used to convert the readings to maps of electrical resistivity variations of the subsurface. 1D and 2D resistivity inversions of the apparent resistivity were undertaken for each site. The 1D inversions were run in the unconstrained mode using the Occam algorithm, with the results presented as depth-resistivity profiles for a layered earth model. The 2D resistivity cross sections were produced using all four components (transverse magnetic [TM] and transverse electric [TE] apparent resistivities and phases). The inversions were run using both modified P. Wannamaker (PWM) and R. Mackie (RLM) inversion codes. The PWM code tends to favour steeply dipping geologies, whereas the RLM code can accentuate anomalies with a horizontal aspect. The MT profiles show that the thin Carpentaria Basin is very conductive (Fig. 8). MT line 8 was acquired along the axis of the Millungera Basin, although at the northwestern end of the line the Argylla Formation of the Mount Isa Province is interpreted to occur beneath the Carpentaria Basin (Fig 8; stations 81 to 84). The moderately conduc- 3 APPEA Journal 211

7 Energy potential of the Millungera Basin: a newly discovered basin in north Queensland Figure 4. Migrated seismic section for the northern part of seismic line 6GA-M5 across the interpreted western edge of the Millungera Basin showing the (a) uninterpreted and (b) interpreted versions. The three stratigraphic sequences in the Millungera Basin interpreted on seismic line 7GA-IG1 (Fig. 3) are also interpreted on this seismic section. The displays show the vertical scale equal to the horizontal scale, assuming an average crustal velocity of 6. km s -1. APPEA Journal

8 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Figure 5. Migrated seismic section for the northern part of seismic line 6GA-M4 across the interpreted western edge of the Millungera Basin showing the (a) uninterpreted and (b) interpreted versions. Only a thin succession of the Millungera Basin is interpreted beneath the Eromanga Basin. The displays show the vertical scale equal to the horizontal scale, assuming an average crustal velocity of 6. km s -1. tive zone from about station 85 to the southeast end of the line is interpreted to represent the Millungera Basin. The southeastern half of line 8 has highly conductive basement (Fig. 8). Line 5 is parallel to, but to the southeast of, seismic line 7GA-IG1, with the southwest end of the line being near the Ernest Henry mineral deposit (Fig. 7). Beneath the Carpentaria Basin, the Mount Fort Constantine Volcanics (Mt Isa Province) is interpreted to occur between stations 5 and 54, and the Soldiers Cap Group (Mt Isa Province) between stations 58 and 511. The Mount Fort Constantine Volcanics is highly resistive, whereas the Soldiers Cap Group, which contains graphitic schists, is highly conductive (Fig. 8). The Millungera Basin is interpreted between stations 511 and 523, and is moderately conductive, above a significantly conductive basement. Line 7 is a shorter MT line to the northwest of seismic line 7GA-IG1 (Fig. 7). The western two-thirds of line 7 has been interpreted to cross the moderately conductive Millungera Basin beneath the thin, highly conductive Carpentaria Basin (Fig. 8). A resistive zone, centred under station 74, is interpreted possibly as granite beneath the Millungera Basin. A thick, resistive zone, between stations 77 and 712, rises to the surface at about station 711, near Mount Fort Bowen (Fig. 2). The moderately conductive signature, interpreted to represent the Millungera Basin, 32 APPEA Journal 211

9 Energy potential of the Millungera Basin: a newly discovered basin in north Queensland Figure 6. Vertical distributions of (a) densities and (b) magnetic susceptibilities along the CDP profile of seismic line 7GA-IG1 across the Millungera Basin, calculated from the inversion of the gravity and magnetic data for the region. The geological interpretation of the seismic line (Fig. 3; Korsch et al, 29) is overlain on the (c) density and (d) magnetic susceptibility sections. is seen to thin towards station 711 (Fig. 8). Overall, the Millungera Basin is seen to be moderately conductive on each of the three MT lines, whereas the basement is either highly resistive or highly conductive. DRILLHOLES Three shallow petroleum exploration wells have been drilled in the interpreted area of the Millungera Basin (Figs 1 and 2). JHR Glenbede Downs 1 was sited on a surface anticline, initially defined by Landsat imagery. Below the Eromanga Basin, the well penetrated almost 3 m of pink to cream-olive coloured quartz-rich sandstone to metaquartzite before terminating in the same rock type (JHR Oil and Gas Company, 1988a). It is uncertain whether these rocks are equivalent to the strata in the Millungera Basin or whether they are associated with the older succession in the Mount Isa Province. Nevertheless, the proximity of this well to the basin succession in seismic line 6GA-M5 suggests that the quartzite encountered in JHR Glenbede Downs 1 is likely to represent Sequence 3 imaged in the seismic section. APPEA Journal

10 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi CARPENTARIA BASIN 142 GSQ Dobbyn 1 Ç Esperanza Mammoth Canobie Depression RN1939 MT Line 7 7GA IG1 6GA M3 MT Line 8 A 2 QUEENSLAND B 21 MT Line 6 MOUNT ISA PROVINCE Ç Mount Isa Mount Isa Cloncurry Ernest Henry 6GA M4 94MTI 1 RN17183 Ç Ç MT Line 4 MT Line 5 E1 RN14338 MILLUNGERA BASIN RN3527 MT Line 3 94MTI 2 JHR Glenbede Downs 1 JHR Rosevale Downs 1 RN GA M6 PILGRIM FAULT BURKE RIVER STRUCTURAL BELT Ç MT Line 1-2 JHR Hampden Downs 1 RN3264 Merlin JHR Belfast 1 Ç EROMANGA BASIN Osborne Ç 6GA M5 Cannington BUO Denbigh Downs 1 WA NT SA RN3276 TAS QLD NSW VIC Millungera Basin Canobie Depression 75 km GA seismic lines Industry seismic lines Fault Ç Mine MT Site Key drillholes Modelling site Town Figure 7. Location of the sites of the 29 magnetotelluric stations in the Mount Isa region (solid white circles for individual stations), with seismic lines, on a background of the regional magnetic data. Lines 5, 7 and 8 in the upper right hand side cross the Millungera Basin. 34 APPEA Journal 211

11 Energy potential of the Millungera Basin: a newly discovered basin in north Queensland Figure 8. Magnetotelluric profiles for lines 5, 7 and 8, displayed to a depth of 18 km. Colour bar represents the level of resistivity. On line 7, MFB is the location of Mount Fort Bowen. APPEA Journal

12 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi JHR Rosevale Downs 1 (Fig. 1) was sited on a surface anticlinal feature initially defined by Landsat imagery, intersected a 533 m-thick succession of the Eromanga Basin, and then 4 m of the Triassic Moolayember Formation and Warang Sandstone of the Galilee Basin. Below the thin Triassic succession of the Galilee Basin, the well penetrated about ~181 m of cream- to pink-coloured, quartz-rich sandstone to metaquartzite before terminating in material interpreted as granite (JHR Oil and Gas Company, 1988b). Examination of sand size cuttings, held at the Geological Survey of Queensland Core Store, for the unit intersected below the Galilee Basin, suggested that the basal granite is very similar to the cuttings of the quartz-rich sandstone. Wholerock geochemistry of a sample of the cuttings from the granite interval has SiO2 = 93.5%, confirming that it is actually a quartz-rich sandstone. JHR Hampden Downs 1 (Fig. 1) was sited on a surface anticlinal feature defined by Landsat imagery and, below the Eromanga Basin, it penetrated about ~188 m of pinkcoloured quartz-rich sandstone and metaquartzite before terminating in granite (JHR Oil and Gas Company, 1988c). Examination of the cuttings suggests that the basal granite is very similar to the cuttings of the metaquartzite, and this is confirmed by wholerock geochemistry of a sample of the cuttings from the granite interval, with SiO2 being 89.%. A fourth petroleum exploration well, JHR Belfast 1, is located about 3 km to the southeast of the inferred margin of the Millungera Basin (Fig. 1). This well intersected a thicker succession of the Eromanga Basin and then about 22 m of Triassic and late Permian rocks of the Galilee Basin, before penetrating about 168 m of pink to creamcoloured arkosic sandstone, and about 4 m of granite wash and granite (JHR Oil and Gas Company, 1988d). Again, wholerock geochemistry of a sample of the cuttings from the granite interval, with SiO2 = 87.4%, indicates that the granite is actually a quartz-rich sandstone. Cuttings from the section through the arkosic sandstone are very similar to the quartz-rich sandstone and metaquartzite in the three wells to the northwest of JHR Belfast 1. This implies that if those three wells penetrated into the Millungera Basin, then it is likely that JHR Belfast 1 also intersected the basin succession, suggesting that its areal boundary could be extended farther southeast than shown on Figures 1 and 2. Because JHR Rosevale Downs 1 and JHR Belfast 1 intersected the upper part of the Galilee Basin above the pink to cream-coloured quartz-rich sandstone, this implies that the sandstone is older than late Permian, at least in this part of the basin. Nevertheless, depending on the location in the Millungera Basin system, a drillhole could penetrate into any of sequences 1, 2 or 3, as seen in seismic line 7GA-IG1 (Fig. 3). GEOPHYSICAL WELL LOGS Petroleum exploration wells Geophysical well logs covering the succession inferred to represent the Millungera Basin in the four petroleum exploration wells (Fig. 9) generally bear little similarity to each other. An exception is the interval about 7 m thick in JHR Glenbede Downs 1, which has extremely similar natural gamma ray and electrical resistivity logs to a unit of almost identical thickness in JHR Belfast 1 (Fig. 9). The high gamma ray count in the logs is of interest, since it is not a typical response expected for quartz-rich sandstones. Sections of the gamma ray logs are relatively monotonous, for example JHR Rosevale Downs 1 and JHR Hampden Downs 1. Apart from JHR Belfast 1, all wells show a significant increase in electrical resistivity, possibly related to a decrease in porosity in the rocks below the Eromanga Basin. It is interesting to note that, in JHR Belfast 1, there is no significant difference in the electrical resistivity between the Permian Betts Creek beds of the Galilee Basin and the underlying sandstones, inferred to be part of the Millungera Basin (Fig. 9). Water bores More than 4 water bores drilled into the Eromanga- Carpentaria Basin, in the vicinity of the Millungera Basin have been logged geophysically (Habermehl, 21), although only a few of these bores penetrate the underlying Millungera Basin. Water bore RN17183, located close to seismic line 7GA-IG1 (Fig. 1), penetrated only 2 m below the Carpentaria Basin into basement (Habermehl, 21), presumably into the succession forming the Millungera Basin. This bore shows a significant increase in the gamma ray log, below the basal unconformity of the Carpentaria Basin (Fig. 1), which is consistent with the high gamma ray logs in the petroleum exploration wells. Near the southern margin of the basin, water bore RN3276 also showed a significant increase in gamma ray values below the basal unconformity of the Eromanga-Carpentaria Basin (Fig. 1). PRE-JURASSIC SEDIMENTARY ROCKS NEAR MILLUNGERA BASIN Two localities, close to seismic line 7GA-IG1, where pre- Jurassic rocks are exposed, occur on the Euroka Ridge at Mount Fort Bowen and at Mount Brown (Fig. 2). At Mount Fort Bowen, about 15 km northwest of the seismic line, a prominent cuesta about 3 km long consists of reddish-purple pebble conglomerate and pebbly sandstone dipping to the east-northeast at about 25º (Carter et al, 1961; Doutch et al, 197; Grimes, 1973). The well rounded clasts in the conglomerate are predominantly quartz, but also include siliceous siltstone, red jasper and rare felsic volcanic rocks. The sandstone is well sorted with hematitic cement, and consists predominantly of subrounded quartz and siliceous lithic clasts and subordinate fine-grained metasedimentary rocks and detrital muscovite and tourmaline. A detrital zircon population from a sandstone was dated by the U Pb method on the Geoscience Australia SHRIMP machine, and indicates a maximum depositional age of about 1,54 Ma (Carson et al, 211), suggesting that the rocks are derived partly from the Williams Batholith in the eastern part of the Mount Isa Province or the Forest Home Supersuite in the Etheridge Province. Palaeocurrent observations, such as cross bedding, suggest a transport direction from the south to southwest (Carter et al, 1961) and are con- 36 APPEA Journal 211

13 Energy potential of the Millungera Basin: a newly discovered basin in north Queensland Figure 9. Petroleum exploration well logs for natural gamma ray (GR) and electrical resistivity (LLD) for those wells that penetrated the uppermost part of the Millungera Basin. Note that only the lowermost part of the sedimentary succession above the Millungera Basin is shown. Note that the datum for the logs is the top of the succession in the Millungera Basin. Thus, the ages of the sediments immediately above the Millungera Basin are different in each well. Horizontal blue lines on the logs from JHR Glenbede Downs 1 and JHR Belfast 1 represent an inferred correlation between these wells. See Figure 1 for locations of wells. sistent with a source in the Mount Isa Province. Carter et al (1961) correlated the rocks at Mount Fort Bowen with the Quamby Conglomerate, which occurs in fault-bounded basins overlying the Mount Isa Province to the north of Cloncurry, and was considered to have been deposited between 1,58 Ma and 1,49 Ma by Evins et al (27). At Mount Brown, 15 km southeast of the seismic line, red sandstone and finer-grained rocks, referred to as quartzfeldspar-mica schist by Carter et al (1961), have dips to the northeast at 45 65º (Carter et al, 1961; Grimes, 1973). These rocks were considered by Carter et al (1961) to be older than those at Mount Fort Bowen, because they have a pronounced cleavage; these outcrops occur close to the eastern thrust margin of the Millungera Basin, if projected to the south from the seismic section. There is no age control on rocks from this locality. Purple, locally-foliated, sandstone and siltstone, similar to that observed at Mount Brown, contain aluminosilicate APPEA Journal

14 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Figure 1. Water bore logs of natural gamma ray for bores located within and adjacent to the Millungera Basin, which penetrated the basin or basement (for locations see Figure 1). MD = measured depth. Abbreviations refer to the tops of stratigraphic formations: Cz Cenozoic, wz weathered zone, Klm Mackunda Formation, Klr Normanton Formation, Kla Allaru Mudstone, Klo Toolebuc Formation, Klu Wallumbilla Formation, Klc Coreena Member, Kld Doncaster Member, Kco Cadna-Owie Formation, JKh Hooray Sandstone, Juw Westbourne Formation, Ja-Jmb Adori sandstone-birkhead Formation, Jlh Hutton Sandstone, Klg Gilbert River Formation, Jue Eulo Creek Group, Bas basement. 38 APPEA Journal 211

15 Energy potential of the Millungera Basin: a newly discovered basin in north Queensland spotting, occur below a 186 m succession of the Carpentaria Basin, and have been intersected recently in drillholes by Red Metal Limited at Taldora, about 25 km north of Mount Fort Bowen (Kary and Johnston, 29). These rocks are metamorphosed, strongly foliated in places, with sulfide mineralisation and alteration present in the cores. Detrital zircon from a sandstone sample from drillhole TD 82 was dated by Carson et al (211) by the U Pb method using the SHRIMP, and had a maximum depositional age of about 1,525 Ma. Geochronology on the rocks at Mount Fort Bowen and Taldora indicate that the rocks were deposited after the ~1,59 Ma Isan Orogeny, and hence are younger than the Soldiers Cap Group. Nevertheless, they are affected by a tectonic event of unknown age, which has produced the foliation at Mount Brown and Taldora. They correlate possibly with the Quamby Conglomerate (Evins et al, 27) to the northwest. Thus, at this stage, it is uncertain whether these rocks are part of the Millungera Basin, or whether they represent another previously unrecognised succession that overlies Paleoproterozoic rocks between the Mount Isa and Etheridge Provinces. Near the northeastern end of seismic line 7GA-IG1, the 1,552 Ma Croydon Volcanic Group (Black and McCulloch, 199) is disconformably overlain by the fluviatile Inorunie Group (Withnall et al, 1988) of unknown age. A detrital zircon population from a sandstone was dated by the U Pb method on the James Cook University laser ablation ICP MS machine, and indicates a maximum depositional age of ~1,65 Ma (R. Wormald, James Cook University, unpublished data), significantly older than the underlying Croydon Volcanic Group, and suggests that the rocks were derived from either, or both of, the Mount Isa Province and the Etheridge Province. AGE OF THE MILLUNGERA BASIN The age of the sedimentary rocks in the Millungera Basin is not known. The stratigraphic position of the Millungera Basin dates the succession as being younger than the deformed rocks of the Paleoproterozoic Soldiers Cap Group, which crop out in the Mount Isa Province to the west of the basin, and being older than the Late Jurassic Early Cretaceous Gilbert River Formation of the Carpentaria Basin, found in water bores in the vicinity of seismic line 7GA-IG1. If the wells JHR Rosevale Downs 1 and JHR Belfast 1 penetrated into the Millungera Basin, the succession in that area is older than the late Permian sedimentary rocks in these wells. U-Pb geochronology on detrital zircon from cuttings from the petroleum exploration wells was undertaken using the Geoscience Australia SHRIMP machine. Samples (JHR Glenbede Downs 1, pooled cuttings from ~ m) and (JHR Hampden Downs 1, pooled cuttings from ~ m) both have maximum depositional ages of about 1,555 Ma (Neumann and Kositcin, 211). Sample (JHR Rosevale Downs 1, pooled cuttings from ~ m) has a maximum depositional age of about 1,59 Ma, but contains four younger grains with individual ages of about 1,515 Ma, 1,17 Ma, 665 Ma and 545 Ma (Neumann and Kositcin, 211). All three samples have a dominant zircon age peak of ~1,77 1,75 Ma. These results suggest that at least most of the zircons were derived from local sources, either from the Mount Isa Province to the west or from the Etheridge Province to the east. Zircon from a sample of cuttings of granite at the bottom of JHR Gladevale Downs 1 (sample , pooled cuttings from ~ m), to the east of the Millungera Basin, has a SHRIMP U-Pb age of 347 ± 2 Ma (Neumann and Kositcin, 211) suggesting that either the basin is older than this age or, if the basin is younger, then the granite was not providing detritus to the basin at the time of deposition. Sedimentary basins in the vicinity, which may correlate with the Millungera Basin, include the Triassic Canobie Depression to the northwest, the Pennsylvanian (late Carboniferous) to Middle Triassic Galilee Basin to the south and southeast, the Late Devonian to Carboniferous Drummond Basin to the east, the Devonian Adavale Basin to the south, the Neoproterozoic to Devonian Georgina Basin to the southwest, and the Mesoproterozoic Isa Superbasin (Lawn Hill Platform and/or Roper Group) to the northwest. Here, we compare the Millungera Basin with the most adjacent basins, namely the Galilee and Georgina basins and the Canobie Depression. Comparison with Galilee Basin Results of petroleum exploration wells drilled in the 198s extended the interpreted northwestern edge of the Galilee Basin. The well BUO Denbigh Downs 1 (French, 1988; Fig. 1) intersected early Permian to Triassic units (Aramac Coal Measures to Warang Sandstone) of the Galilee Basin, before terminating in granite. The Early Middle Triassic Warang Sandstone was intersected in both JHR Rosevale Downs 1 (JHR Oil and Gas Company, 1988b) and JHR Gladevale Downs 1 (JHR Oil and Gas Company, 1988e; Fig. 1). An undifferentiated unit of multi-coloured, quartz-rich sandstone was identified in cuttings sampled beneath the Early Middle Triassic Warang Sandstone in JHR Rosevale Downs 1 (JHR Oil and Gas Company, 1988b), before terminating in granite. The Warang Sandstone is a formation in the upper part of the Galilee Basin, and is the ageequivalent of the Clematis Sandstone, Rewan Formation and lowermost Moolayember Formation of the eastern, central, and southern parts of the Galilee Basin. The petroleum exploration well JHR Glenbede Downs 1 is sited in the Millungera Basin, about 1 km east of seismic line 6GA-M5. According to the mud log observations, the well terminated in a thick succession of clear to brick redorange quartzite beneath the Eromanga Basin (JHR Oil and Gas Company, 1988a). This lithology is similar to that beneath the Warang Sandstone in JHR Rosevale Downs 1. The quartz-rich sandstone may be equivalent to early Permian formations of the lower Galilee Basin or, alternatively, it may represent an earlier phase of sedimentation. APPEA Journal

16 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Comparison with Canobie Depression A relatively unexplored half graben, the Canobie Depression (Smart, 1973), lies about 25 km northwest of the Millungera Basin (Fig. 1). The half graben was delineated by the 1987 and 1988 Boomarra Seismic Surveys (Beahan and Barlow, 1987; Barlow and Dunster, 1988), and was sampled through the fully-cored stratigraphic bore, GSQ Dobbyn 1 (Williams and Gunther, 1989). The bore was drilled at SP 17 on Boomarra line 87BR-1, spudded into rocks of the Carpentaria Basin, and penetrated m of unnamed Middle Triassic terrestrial red beds that lie unconformably on metasedimentary rocks and metamorphic rocks inferred to be from the Proterozoic Soldiers Cap Group of the Mount Isa Province. It is possible that these red beds could be equivalent to the pink-coloured, quartz-rich sandstone seen in the cuttings from the petroleum exploration wells (see above). Detrital zircons from a metamorphosed sandstone from the basement below the unnamed Middle Triassic unit in GSQ Dobbyn 1 (depth ~839 m) was dated by Carson et al (211) by the U Pb method using the SHRIMP, and yielded a maximum depositional age of about 1,59 Ma; this is the age of rocks associated with the Isan Orogeny in the Mount Isa Province, and significantly younger than the Soldiers Cap Group. Filatoff and Price (1989) conducted a detailed palynological and source quality study on core samples from GSQ Dobbyn 1. Neither marine nor aquatic microfossils were identified in the assemblages prepared from three core samples from the Middle Triassic unit. The palynomorph Falcisporites, was present in all three samples, and is typical of microfloras in the Moolayember Formation from the Bowen Basin. Hence the unnamed Triassic unit is an age-equivalent of the Moolayember Formation. Similar to the Millungera Basin, the Canobie Depression lies unconformably below the regionally extensive Carpentaria Basin, suggesting there are possibly a number of unexplored residual basin depocentres throughout the area. The Middle Triassic stratigraphic control afforded by GSQ Dobbyn 1 indicates that deposition in the Canobie Depression occurred at the same time as the closing stage of Galilee Basin and, hence, the Millungera Basin, or at least its northern part, also could have formed at this time. The predominance of terrestrial red micaceous mudstones in the unnamed Triassic unit in GSQ Dobbyn 1 suggests poor source rock potential. Nevertheless, Filatoff and Price (1989) considered that the Triassic unit in the Canobie Depression was a source rock, owing to the moderately rich lipid content in three grey to dark grey mudstone beds. Also, thermal maturation reached the oil window higher up the stratigraphic column in this drill hole, as shallow as 4 m, in the overlying Toolebuc Formation. The hydrocarbon potential of the unnamed Triassic unit was deemed better than that of the Moolayember Formation farther south (Filatoff and Price, 1989), although this is dependent on the total thickness of the mudstones. If similar organic-rich mudstones had accumulated in the Millungera Basin, then its prospectivity would be encouraging. Spore colouration in the Middle Triassic unit up to the Toolebuc Formation succession of the Canobie Depression indicates that very early thermal maturity has been reached, but the rate of increase in maturation down the hole is low, suggesting a low geothermal gradient in the uppermost 9 m of the crust (Filatoff and Price, 1989). A temperature reading of 69ºC was measured at a depth 853 m, indicating a present-day geothermal gradient of 41ºC km -1. Comparison with Georgina Basin The first seismic image of the northeastern part of the Georgina Basin, known as the Burke River Structural Belt, was provided by seismic line 6GA-M6 (Hutton et al, 29b; Carr et al, 21; Fig. 1). The eastern part of this seismic line revealed a flat-lying package of reflections, defining a half graben thinning towards the east (see Fig. 2 in Carr et al, 21). Here, the basin is ~65 km wide, with the half graben geometry being bounded in the west by a rift border fault. It has a maximum thickness of ~2,8 m (calculated from stacking velocities). Interpretation of the stratigraphy is constrained by scattered outcrops in the vicinity of the seismic line. The lowermost sequence is interpreted to be the early Cambrian Mount Birnie beds. Based on well control from the nearby BMR Duchess 18 drillhole, the overlying Thorntonia Limestone is identified as a pair of strong seismic reflections. Stratigraphic units adjacent to the basin-bounding fault do not occur farther to the east, suggesting that they were either not deposited or have been eroded, with a major unconformity occurring above the Thorntonia Limestone (Southgate and Shergold, 1991). There has been intense inversion on the basin-bounding fault, with the strata rotated to steep dips (up to 75º). The zone of inversion is bounded to the east by the Pilgrim Fault, which is a reactivated basement fault. To the east of the Pilgrim Fault, the basin is essentially undeformed and preserves it original geometry. The general seismic configuration of the Georgina Basin in the Burke River Structural Belt is not dissimilar to that observed as the Millungera Basin in seismic line GA7-IG1; stratigraphically, both basins predate the Carpentaria Basin. The quartz-rich sandstones at the base of JHR Glenbede Downs 1 cannot be correlated with any of the Cambrian formations in the Burke River Structural Belt, but they might be equivalent to the Ordovician-Devonian Toko Group observed in the Toko Syncline farther to the south; this group contains quartz-rich to quartzofeldspathic sandstones. Alternatively, the sandstones could be equivalent to the Neoproterozoic Mopunga Group, which consists of arkosic sandstone, siltstone and conglomerate. To correlate the succession in the Millungera Basin with any further basins in the region would be highly speculative, considering the broad time span over which it could have developed. ECONOMIC POTENTIAL The economic potential and the depositional history of this new basin will not be known completely until the 31 APPEA Journal 211

17 Energy potential of the Millungera Basin: a newly discovered basin in north Queensland succession is intersected by exploration drilling. The emplacement of high-heat producing granites in the region may have produced an elevated geothermal gradient, which could result in increased source rock maturity or provide a source of geothermal energy. The hydrocarbon potential of the basin is uncertain. There are no confirmed lithological descriptions for the sedimentary rocks of the Millungera Basin. Hence, we can only speculate on the prospectivity of this unknown aged Proterozoic to Early Jurassic succession drawing on discoveries of oil, conventional gas, and coal seam gas from age-equivalent basins in the region. Strong reflections in the seismic sections may indicate coal beds, but until the basin extents, rock types and age are confirmed, the full potential of the basin remains speculative. If organic-rich beds have reached the oil window, the structurally more complex eastern side of the basin may contain petroleum traps. PETROLEUM SYSTEMS MODELLING Modelling of potential petroleum systems in the Millungera Basin was carried out using two scenarios for the most likely age of the sediment fill: Neoproterozoic to Devonian equivalents of the Georgina Basin or Permian Triassic equivalents of the Lovelle Depression, which is the western depocentre of the Galilee Basin. These scenarios were selected on the basis of the location of the Millungera Basin relative to the other basins, its structural style and event sequence, as well as the seismic signature of the succession. Both scenarios encompass two sites on seismic line 7GA-IG1 (Sites A and B; Fig. 1), chosen to model 1D burial histories (using IES Petromod 11), thermal histories, and generation and expulsion of hydrocarbons from postulated source rocks. Location A is close to the thickest, most deeply buried part of the basin, with the least amount of post-depositional erosion, whereas Location B is on the northwestern flank of the basin, where some of the units show clear thinning, and where significant amounts of section are likely to have been eroded (Fig. 11). The geological models are based on seismic line 7GA- IG1, using interval velocities at several points along the line to estimate depth of section. Inaccuracies relating to this estimated depth conversion are likely to be the largest source of errors in the modelling presented here. In all the models, the sediment-water interface (SWI) temperatures are based on calculations provided by the software for the present-day latitude of 22ºS. Present-day heat flow in the region of the Millungera Basin is in the vicinity of 8 mwm -2 (see geothermal section below), and was likely to have been high in the past, as indicated by hot granites interpreted to underlie the basin (Korsch et al, 29; Henson et al, 29b). Due to the paucity of hard data, a simple thermal history model invoking a constant heat flow of 8 mwm -2 was used in all the modelling. Scenario 1: Georgina Basin equivalent A possible stratigraphy for Scenario 1 assuming that the Millungera Basin is equivalent in age to the Georgina Basin has been inferred for seismic line 7GA-IG1 (Fig. 11), and is based on published data from the the Toko Syncline and the Burke River Structural Belt in the southeastern Georgina Basin (Jackson, 1982; Southgate and Shergold, 1991; Draper, 27; Ambrose and Putnam, 27; Boreham and Ambrose, 27; Radke 29). The postulated source rocks in the succession are the middle Cambrian Thorntonia Limestone and Arthur Creek Formation (Boreham and Ambrose, 27). SITE A The main input data for the modelling at Site A is shown in Table 1, and includes estimates of total organic carbon (TOC) content, reaction kinetics and initial hydrocarbon index (HI) for each source rock unit. The amount of erosion modelled for Site A includes an additional 5 m of sediment for the Toko Group, which was eroded during the Late Devonian to Mississippian (early Carboniferous) Alice Springs Orogeny, and an additional 5 m of sediment for the Allaru Mudstone which, subsequently, was eroded during the Late Cretaceous. The Thorntonia Limestone and the hot shale in the Arthur Creek Formation are considered to be the main potential source rocks. The choice of Type II kerogen kinetics (after Tissot et al, 1987) is based on their probable restricted shallow marine depositional environment. The main boundary conditions for geohistory modelling include paleowater depths, temperatures at the SWI, and heat flow through time (Table 2). The paleowater depths are based on the regional geology of the Georgina Basin, with most deposition likely to have occurred in shallow to very shallow water environments. Erosion during the Alice Springs Orogeny in the late Paleozoic was modelled as significant uplift. The burial history for Site A was modelled with deposition in the Neoproterozoic and Cambrian Ordovician, including 5 m of additional Ordovician sediment, and its subsequent uplift and erosion (Fig. 12a). Increasing the amount of sedimentation will result in earlier and more rapid kerogen transformation. A temperature overlay on the burial history plot for Site A shows that the modelled present-day temperature at 3 km depth is about 16ºC (Fig. 12b). The implied gradient is consistent with the predicted temperatures at 5 km depth on the OZTemp map (Gerner, 21). Overlaying the vitrinite maturity model on the burial history plot shows clearly that rapid burial during the late Cambrian to Early Ordovician brought potential middle Cambrian source rocks into the oil window, early in their burial history (Fig. 12c). They have probably been in the oil window since that time, and the Cretaceous burial appears to have had little effect. Thus, in this scenario for Site A, the potential middle Cambrian source rock layers are presently in the main oil to late oil window, and the Neoproterozoic to early Cambrian is gas mature. The predicted porosity versus depth graph for Site A shows that porosities of 2% or higher are predicted to a depth of about 1,5 m, and that porosities of 15%, or higher, are predicted down to about 2,5 m below base level (Fig. 12d). APPEA Journal

18 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Figure 11. Schematic geological model assuming that the Millungera Basin is the equivalent in age to the Georgina Basin. The seismic section 7GA-IG1 has been depth converted using the interval velocities from several points along the seismic line. The modelling has calculated the kerogen transformation ratio and expulsion mass for the two main modelled source layers. At Site A, close to 6% of available kerogen in the Thorntonia source layer was transformed by the Early Devonian, whereas about 3% of the Arthur Creek source layer was transformed. Cretaceous burial caused a second, albeit minor phase of generation and expulsion of oil. The greater the Cretaceous deposition and erosion included in the model, the more significant this second phase of generation becomes. This is consistent with the results of Karajas (1994), who postulated at least two phases of oil generation in the southern Georgina Basin: an early phase (degraded to bitumen) and a later phase, which is generating relatively undegraded, aromatic-intermediate crude oil, to the present day. SITE B The main input data for the modelling at Site B is shown in Table 1. The main difference at this site to Site A is the reduced thickness of the stratigraphic section and increased erosion during the Devonian, as well as a less significant erosion event at the end of the early Cambrian. The boundary conditions used for Site B are the same as for Site A (Table 2), with the exception of the estimated elevations during the erosional phase. The burial history model for Site B (Fig. 13a) shows that the modelled source rock succession was buried to a maximum depth of about 1,3 m during the Paleozoic, whereas at Site A the maximum burial was about 2,5 m (Fig. 12a). The depth of burial corresponds to maximum burial temperatures of about 85 9ºC (Fig. 13b), as opposed to 125ºC for source rocks at Site A (Fig. 12b). Consequently, the modelled source rocks are only early mature for oil generation at present at Site B (Fig. 13c). The vitrinite maturity model for Site B reflects the significant erosion to the top of the inferred middle Cambrian succession. The predicted porosities for the whole stratigraphic section are above 2% (Fig. 13d). Modelling of generation and expulsion suggests that only about 3% of the kerogen in the source layer in the Thorntonia Limestone has been transformed into hydrocarbons, and that only minimal hydrocarbons were generated. It is unlikely that any of these would have been expelled from the source rock. Adjusting erosion amounts did not substantially change these results. The modelling 312 APPEA Journal 211

19 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Energy potential of the Millungera Basin: a newly discovered basin in north Queensland Table 1. Main input data for scenarios assuming that the Millungera Basin is an age equivalent of either the Georgina Basin or the Galilee Basin. Stratigraphic unit Lithology 1 Top Base Thickness Amount eroded Deposition from Deposition to Eroded from Eroded to Petroelum systems element Total organic carbon Kinetics 2 Hydrogen index (%) (m) (m) (m) (m) (Ma) (Ma) (Ma) (Ma) (%) (mghc/gtoc) Georgina Basin equivalent: Site A Alluvium overburden. none. Toolebuc-Allaru Lst (shaly) 5, Lst (org-rich) 2, Marl 2, Sst seal. none. Gilbert River Sst (qtz) 6, Slst (org-rich) 2, Sh 1, Cgl reservoir. none. Toko Sst 7, Sh 13, Slst 1, Lst 5, Glauc reservoir. none. Cockroach Lst (ooid) 4, Lst (org-rich) 2, Lst (shaly) 2, Slst 18, Sst 2 6 1, reservoir. none. Devoncourt-Arthur Creek Lst (shaly) 8, Slst 2 1,12 1, none. none. Arthur Creek hot shale Sh (org-rich) 9, Marl 1 1,745 1, source 8. Tissot 7. Thorntonia upper Dol (8), Slst (org-rich) 14, Sst 5, Chert 1 1,772 2, source 2. Tissot 6. Thorntonia source Sh (org-rich) 1 2,5 2, source 5. Tissot 6. Thorntonia lower Sst 8, Slst 2 2,55 2, source 2. Tissot 6. Thorntonia basal reservoir Sst 8, Slst 2 2,214 2, reservoir. none. Mount Birnie Sst 5, Slst (org-rich) 2, Dol 15, Sh 15 2,234 2, underburden. none. Mopunga Sst (qtz) 4, Slst (org-lean) 2, Sh 2, Cgl 1, Sst (wacke) 1 2,782 3, underburden. none. basement Granite (>1, Ma old) 7, Schist 15, Quartzite 15 3,25 3, underburden. none Georgina Basin equivalent: Site B Alluvium overburden. none. Toolebuc-Allaru Lst (shaly) 5, Lst (org-rich) 2, Marl 2, Sst seal. none. Gilbert River Sst (qtz) 6, Slst (org-rich) 2, Sh 1, Cgl reservoir. none. Toko Sst 7, Sh 13, Slst 1, Lst 5, Glauc reservoir. none. Cockroach Lst (ooid) 4, Lst (org-rich) 2, Lst (shaly) 2, Slst 18, Sst reservoir. none. Devoncourt-Arthur Creek Lst (shaly) 8, Slst overburden. none. Arthur Creek hot shale Sh (org-rich) 9, Marl source 8. Tissot 7. Thorntonia upper Dol (8), Slst (org-rich) 14, Sst 5, Chert source 2. Tissot 6. Thorntonia source Sh (org-rich) source 5. Tissot 6. Thorntonia lower Sst 8, Slst source 2. Tissot 6. Thorntonia basal reservoir Sst 8, Slst reservoir. none. Mount Birnie Sst 5, Slst (org-rich) 2, Dol 15, Sh underburden. none. Mopunga Sst (qtz) 4, Slst (org-lean) 2, Sh 2, Cgl 1, Sst (wacke) , underburden. none. basement Granite (>1, Ma old) 7, Schist 15, Quartzite 15 1,374 1, underburden. none Table continued next page. APPEA Journal

20 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Energy potential of the Millungera Basin: a newly discovered basin in north Queensland Table 1 (continued from previous page). Main input data for scenarios assuming that the Millungera Basin is an age equivalent of either the Georgina Basin or the Galilee Basin. Stratigraphic unit Lithology 1 Top Base Thickness Amount Eroded Deposition from Deposition to Eroded from Eroded to Petroelum systems element Total organic carbon Kinetics 2 Hydrogen index (%) (m) (m) (m) (m) (Ma) (Ma) (Ma) (Ma) (%) (mghc/gtoc) Galilee Basin equivalent: Site A Alluvium overburden. none. Toolebuc-Allaru Lst (shaly) 5, Lst (org-rich) 2, Marl 2, Sst seal. none. Gilbert River Sst (qtz) 6, Slst (org-rich) 2, Sh 1, Cgl reservoir. none. Moolayember Sh 4, Slst (org-lean) 3, Sst (qtz) seal. none. Warang Sst (qtz) 7, Sh 15, Slst (org-lean) , reservoir. none. Bandanna Sst (8), Slst (2) 1,2 1, seal 3. none. reservoir Slst (org-rich) 3, Sh (org-rich) 3, Sst (qtz) 2, Coal (silty) 2 1,745 1, reservoir 8. none. Colinlea 2 Sst (qtz) 65, Slst (org-rich) 15, Sh (org-rich) 1, Cgl 3, Coal (silty) 7 1,772 1, reservoir 3. none. organic rich layer 3 Sh (org-rich) 6, Slst (org-rich) 3, Sst 1 1,95 2, source 6. P&C 3. Colinlea 1 Sst (qtz) 65, Slst (org-rich) 15, Sh (org-rich) 1, Cgl 3, Coal (silty) 7 2,5 2, reservoir. none. organic rich layer 2 Sh (org-rich) 6, Slst (org-rich) 3, Sst 1 2,214 2, source 6. P&C 3. Aramac Slst (org-rich) 4, Coal (silty) 2, Sst (qtz) 2, Sh (org-rich) 2 2,234 2, source 3. P&C 3. organic rich layer 1 Sh (org-rich) 6, Slst (org-rich) 3, Sst 1 2,81 2, source 8. P&C 3. Jochmus Sst (clay-rich) 7, Tuff (felsic) 1, Sh 1, Cgl 1 2,85 3, underburden. none. basement 3,3 3, underburden. none. Galilee Basin equivalent: Site B Alluvium overburden. none. Toolebuc-Allaru Lst (shaly) 5, Lst (org-rich) 2, Marl 2, Sst seal. none. Gilbert River Sst (qtz) 6, Slst (org-rich) 2, Sh 1, Cgl reservoir. none. Moolayember Sh 4, Slst (org-lean) 3, Sst (qtz) seal. none. Warang Sst (qtz) 7, Sh 15, Slst (org-lean) reservoir. none. Bandanna Sst (8), Slst (2) seal. none. reservoir Slst (org-rich) 3, Sh (org-rich) 3, Sst (qtz) 2, Coal (silty) reservoir. none. Colinlea 2 Sst (qtz) 65, Slst (org-rich) 15, Sh (org-rich) 1, Cgl 3, Coal (silty) reservoir. none. organic rich layer 3 Sh (org-rich) 6, Slst (org-rich) 3, Sst source 8. P&C 3. Colinlea 1 Sst (qtz) 65, Slst (org-rich) 15, Sh (org-rich) 1, Cgl 3, Coal (silty) reservoir. none. organic rich layer 2 Sh (org-rich) 6, Slst (org-rich) 3, Sst source 6. P&C 3. Aramac Slst (org-rich) 4, Coal (silty) 2, Sst (qtz) 2, Sh (org-rich) source 3. P&C 3. organic rich layer 1 Sh (org-rich) 6, Slst (org-rich) 3, Sst source 8. P&C 3. Jochmus Sst (clay-rich) 7, Tuff (felsic) 1, Sh 1, Cgl , underburden. none. basement 1,374 1, underburden. none. Table notes: 1. Abbreviations: Lst limestone, Dol dolomite, Sst sandstone, Slst siltstone, Sh shale, Cgl conglomerate, Glauc glauconite, qtz quartzitic, org-rich organic rich. 2. Tissot Type II kerogen kinetics from Tissot et al (1987), P&C Type III kerogen kinetics from Pepper and Corvi (1995). 314 APPEA Journal 211

21 Energy potential of the Millungera Basin: a newly discovered basin in north Queensland Table 2. Boundary conditions for paleowater depth (PWD) and temperature of sediment-water interface (SWIT). Age PWD SWIT (Ma) (m) (ºC) Georgina Basin equivalent Sites A and B Age PWD SWIT (Ma) (m) (ºC) Galilee Basin equivalent Site A Age PWD SWIT (Ma) (m) (ºC) Galilee Basin equivalent Site B suggests that the middle Cambrian potential source rocks are mature in most of the Millungera Basin, where they are buried to depths greater than about 1, m (Fig. 14a). In summary, the above scenario assumes that the Millungera Basin is a Neoproterozoic Ordovician equivalent of the Georgina Basin, and potential middle Cambrian source rocks are likely to be mature over most of the Millungera Basin. Significant generation and expulsion probably occurred in two phases, in response to Ordovician and Cretaceous sediment loading (Fig. 14b). Phase 1 expulsion occurred after Neoproterozoic Cambrian trap formation, but before Devonian trap formation. Long preservation time and unroofing, therefore, are likely to be the major risks in the basin. Phase 2 expulsion occurred after the Devonian and during Late Cretaceous Holocene trap formation. Scenario 2: Galilee Basin equivalent A possible stratigraphy for Scenario 2, assuming that the Millungera Basin is equivalent in age to the Galilee Basin, has been inferred for seismic line 7GA-IG1 (Fig. 15). It is based on published data from the western Galilee Basin, particularly the Lovelle Depression (Jackson et al, 1981; Hawkins and Green, 1993; Radke 29). The postulated source rocks in the succession are the Permian Aramac Coal Measures and Betts Creek beds. Modelling was carried out at the two sites modelled in Scenario 1. SITE A The main input data for the modelling at Site A is shown in Table 1. The amount of erosion modelled for Site A includes an additional 1 m of Aramac Coal Measures, which was eroded during the mid-permian, an additional 3 m of Triassic Moolayember Formation, which was eroded during the Late Triassic (Hunter Bowen Orogeny), and an additional 8 m of Allaru Mudstone which, subsequently, was eroded during the Late Cretaceous. The Aramac Coal Measures and parts of the Betts Creek beds (Colinlea Sandstone and Bandanna Formation equivalent) are considered to be the main potential source rocks. The choice of Type III IV kerogen kinetics is based on their probable fluvial depositional environment. The main boundary conditions for the geohistory modelling include paleowater depths, temperatures at the sediment water interface (SWI), and heat flow through time (Table 2). The paleowater depths are based on the regional geology of the Galilee Basin, and most deposition is likely to have occurred in fluvial environments. Erosion during the last phase of the Hunter Bowen Orogeny in the Late Triassic was modelled as significant uplift. The burial history model for Site A reflects the very rapid deposition of the main sedimentary succession during the Permian to Early Triassic (Fig. 16a). A temperature overlay on the burial history plot for Site A shows that APPEA Journal

22 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Energy potential of the Millungera Basin: a newly discovered basin in north Queensland 12a 12c Alluvium Toolebuc-Allaru Gilbert River Alluvium Toolebuc-Allaru Gilbert River Toko Toko Cockroach Cockroach 1 1 Depth (m) 2 Devoncourt-Arthur Creek Arthur Creek Hot Shale Thorntonia upper Thorntonia source Depth (m) 2 Devoncourt-Arthur Creek Arthur Creek Hot Shale Thorntonia upper Thorntonia source Thorntonia basal reservoir Thorntonia basal reservoir Mount Birnie Mount Birnie 3 Mopunga 3 Mopunga Proterozoic Proterozoic 6 4 Time (Ma) Time (Ma) 2 12b 8 C Immature ( ) Early oil (.55-.7) Main oil (.7-1.) Late oil (1.-1.3) Wet gas (1.3-2.) Dry gas (2.-4.) Alluvium Toolebuc-Allaru Gilbert River Toko Porosity (%) d 5 Alluvium Toolebuc-Allaru Gilbert River 1 Cockroach Temperature ( C) Porosity (%) Toko Depth (m) Time (Ma) Temperature ( C) Devoncourt-Arthur Creek Arthur Creek Hot Shale Thorntonia upper Thorntonia source Thorntonia basal reservoir Mount Birnie Mopunga Proterozoic % Depth (m) Temperature ( C) Cockroach Devoncourt-Arthur Creek Arthur Creek Hot Shale Thorntonia upper Thorntonia source Thorntonia basal reservoir Mount Birnie Mopunga Proterozoic Figure 12. Results from petroleum maturation modelling at Site A in the Millungera Basin, assuming the basin is the equivalent in age to the Georgina Basin. (a) Burial history plot, modelled with 5 m of erosion of Ordovician sediments during the Devonian Carboniferous Alice Springs Orogeny. (b) Temperature modelled with constant heat flow of 8 mwm -2, overlain on the burial history plot. (c) Vitrinite maturity overlain on the burial history plot. (d) Plot of predicted porosities and temperatures with depth. 316 APPEA Journal 211

23 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Energy potential of the Millungera Basin: a newly discovered basin in north Queensland 13a 13c Alluvium Alluvium Toolebuc-Allaru Toolebuc-Allaru Gilbert River Gilbert River Devoncourt-Arthur Creek Devoncourt-Arthur Creek Depth (m) Thorntonia source Thorntonia basal reservo Mount Birnie Depth (m) Thorntonia source Thorntonia basal reservoir Mount Birnie 1 1 Mopunga Mopunga Proterozoic Proterozoic Time (Ma) Time (Ma) 13b Immature ( ) Early oil (.55-.7) Main oil (.7-1.) Porosity (%) Alluvium Toolebuc-Allaru d 5 Alluvium Toolebuc-Allaru Gilbert River Temperature ( C) Devoncourt-Arthur Creek Porosity (%) Depth (m) Time (Ma) Temperature ( C) Thorntonia source Thorntonia basal reservo Mount Birnie Mopunga Proterozoic % Depth (m) Gilbert River Devoncourt-Arthur Creek Thorntonia source Thorntonia basal reservoir Mount Birnie Mopunga Proterozoic Temperature ( C) Figure 13. Results from petroleum maturation modelling at Site B in the Millungera Basin, assuming the basin is the equivalent in age to the Georgina Basin. (a) Burial history plot, modelled with 1,5 m of erosion of late Cambrian to Ordovician sediments during the Devonian Carboniferous Alice Springs Orogeny. (b) Temperature modelled with constant heat flow of 8 mwm -2, overlain on the burial history plot. (c) Vitrinite maturity overlain on the burial history plot. (d) Plot of predicted porosities and temperatures with depth. APPEA Journal

24 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Figure 14a. Location of the potential source kitchen, assuming the basin is the equivalent in age to the Georgina Basin. the modelled present-day temperature at 3 km is about 16ºC (Fig. 16b). Overlaying the vitrinite maturity model on the burial history plot shows clearly that rapid burial during the Permian to Early Triassic brought potential Permian source rocks into the oil window early in their burial history (Fig. 16c). The maturity modelling for Site A illustrates that the potential source rock layers are presently in the oil window and that the basal Aramac Coal Measures is in the gas window. These findings are consistent with Hawkins and Green (1993), who predicted a depth of about 1,2 m to the top of the oil window, but are higher than the maturities reported by Jackson et al (1981), although the wells examined by Jackson et al (1981) penetrated significantly less thickness of Aramac Coal Measures and late Permian to Triassic sediments. A plot of predicted porosity versus depth for Site A shows that porosities of 2% or higher are predicted to a depth of about 1,9 m, and of 15% or greater down to about 2,8 m below base level (Fig. 16d). The modelling has calculated the kerogen transformation ratio and expulsion mass for the two main modelled source layers in the lower and upper Aramac Coal Measures. At Site A, about 3% of available kerogen in the lower source layer was transformed by the Middle Triassic, associated with Early Triassic sediment loading. Minor kerogen transformation continued during the Late Triassic to middle Cretaceous. A second, more significant phase of transformation was triggered by Cretaceous sediment loading, resulting in a total of about 5% of the kerogen being transformed. The model predicts that oil was generated and expelled only during the early phase of generation, whereas gas has been generated and expelled since the Triassic. Only about 1% of the kerogen in the upper source layer has been transformed, with no generation and expulsion associated with the early loading. The model predicts that this source layer may have expelled gas since the Late Cretaceous. SITE B The main input data for the modelling at Site B is shown in Table 1. The main difference at this site to Site A is the reduced thickness of the stratigraphic section and increased erosion during the Triassic. The amount of additional deposition and erosion modelled for Site B includes a total of 8 m of erosion of the upper Permian to Lower Triassic section, which was eroded during the Late Triassic phase of the Hunter Bowen Orogeny. The boundary conditions used for Site B are shown in Table 2. The burial history model for Site B shows that the mod- 318 APPEA Journal 211

25 Energy potential of the Millungera Basin: a newly discovered basin in north Queensland elled source rock succession was buried to a maximum depth of about 1,2 m during the Early Triassic, whereas, at Site A, the maximum burial was about 2,8 m (Fig. 17a). A temperature overlay on the burial history plot for Site B shows maximum burial temperatures of about 7 75ºC (Fig. 17b), as opposed to 15ºC for the lower source layer in the Aramac Coal Measures at Site A. Consequently, at Site B, the modelled source rocks are predicted to be immature for oil generation at present, and only the underlying Jochmus Formation is marginally mature for oil generation (Fig. 17c). In summary, potential Permian source rocks are likely to be oil mature in the central Millungera Basin, but will be immature on the margins of the basin. The top of the oil window is predicted to occur at depths of about 1,1 1,4 m. Significant oil generation and expulsion probably occurred during the Triassic, in response to late Permian to Early Triassic sediment loading. Trap formation was probably at least partly concurrent with expulsion (Fig. 18), but unroofing and the long preservation time are still the major risks in the basin. Early generated oil may have been lost. Gas generation and expulsion is modelled to have occurred throughout the burial history of the basin, with a sharp increase in expulsion during the Late Cretaceous to Holocene in response to Cretaceous sediment loading. Trap configuration and timing would have been favourable for this expulsion phase. Thus, if the Millungera Basin is an equivalent of the Galilee Basin, the prospectivity for gas is rated high. POTENTIAL FOR GEOTHERMAL ENERGY Figure 14b. Proposed petroleum systems event chart for the Millungera Basin, assuming the basin is the equivalent in age to the Georgina Basin. A 3D geological model of the area was built to better understand the potential for geothermal energy in the Millungera Basin. The model included an interpreted distribution of the sediments in the basin and potential heat-producing bodies in the basement, and this was then used as a basis for thermal modelling to predict scenarios for temperatures at depth. Data used for this study included the national gravity and magnetic coverages of Australia, the 7GA-IG1, 6GA- M4 and 6GA-M5 seismic lines, and three heat flow data points located to the west of the study area. These reveal moderately elevated (7 8 mwm -2 ) to elevated (98 mwm -2 ) heat flow values. There are a number of water bores in the region of the Millungera Basin, some of which have been logged for temperature (Habermehl, 21; Fig. 19). These bores range in depth from m (subsurface), with most in the range 25 5 m deep. Several of the bores are artesian and instead have wellhead temperature measurements (Fig. 19). To obtain an estimate of the surface temperature and the regional geothermal gradient, a plot of bottom-hole temperature versus logged depth was constructed using all the logged boreholes in the area (Fig. 2). The bottom-hole temperatures plot on a reasonably straight line and reveal an elevated geothermal gradient of 6 km -1 in the study area, and an intercept of 31 C. The gradient is elevated in comparison to the global average of ~35 km -1, but also elevated when compared to the mean from the Eromanga APPEA Journal

26 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Figure 15. Schematic geological model assuming that the Millungera Basin is the equivalent in age to the Galilee Basin. The seismic section 7GA-IG1 has been depth converted using the interval velocities from several points along the seismic line. Basin of 48 km -1 (Polak and Horsfall, 1979). To better understand where the elevated groundwater temperatures occur in the study area, an average temperature gradient was calculated for each well by subtracting the surface temperature (taken to be 31 C, the intercept in Fig. 2), from the bottom-hole temperature, and dividing it by the logged depth (Fig. 2). These gradients are not likely to be purely conductive, and may not extend beyond the depth of the aquifer. Nevertheless, the data indicate that there is considerable variation in the temperature field across the study area. 3D gravity inversions The three seismic lines define regions of low reflectivity in basement (Figs 3 to 5). Some of these zones are coincident with negative gravity anomalies, and are interpreted as felsic intrusions. To define the potential extent of these intrusions in the basement, 3D gravity inversion modelling was carried out using programs developed by the University of British Columbia Geophysical Inversion Facility (UBC GIF; Li and Oldenburg, 1998a). Inversion modelling is a process in which iterative adjustments are made to a density model until there is an acceptable fit between the predicted response of the model and the observed gravity data (Meixner and Lane, 25). When physical property information is available, it is possible to make a reference model that will incorporate this information. The inversion can be forced to honour the property values, to within a specified upper and lower bound, at defined locations in the model. The inversion model used for this study consists of a mesh with a 2 km by 2 km horizontal and a 25 m vertical cell size. The smaller vertical cell size allowed vertical detail in the extent of the Millungera and Eromanga basins to be incorporated into the model. The response of the material beyond the limits of the inversion mesh was removed, using the method described by Li and Oldenburg (1998b). The method for building this model was based on that of Meixner and Holgate (29). The distribution of sediments in the Eromanga and Millungera basins was constrained using the seismic data and, where available, drilling data, and was used to construct a reference model for the 3D gravity inversion. Density values were assigned to the reference model depending on whether the cell occurs in the Eromanga Basin, Millungera Basin, or basement. 32 APPEA Journal 211

27 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Energy potential of the Millungera Basin: a newly discovered basin in north Queensland 16a Alluvium Toolebuc Formation Allaru Mudstone 16c Alluvium Toolebuc Formation Allaru Mudstone Gilbert River Formation Gilbert River Formation Moolayember Formation Moolayember Formation 1 Warang Sandstone 1 Warang Sandstone Depth (m) 2 Bandanna Formation Reservoir Colinlea Sandstone 2 Organic-rich layer 3 Colinlea Sandstone 1 Organic-rich layer 2 Depth (m) 2 Bandanna Formation Reservoir Colinlea Sandstone 2 Organic-rich layer 3 Colinlea Sandstone 1 Organic-rich layer 2 Aramac Coal Measures Aramac Coal Measures Organic-rich layer 1 Organic-rich layer 1 3 Jochmus Formation 3 Jochmus Formation Proterozoic Proterozoic 3 2 Time (Ma) Time (Ma) 1 16b Alluvium Toolebuc Formation Allaru Mudstone Immature ( ) Early oil (.55-.7) Main oil (.7-1.) Late oil (1.-1.3) Wet gas (1.3-2.) Gilbert River Formation Moolayember Formation Porosity (%) d 5 Alluvium Toolebuc Formation Allaru Mudstone 1 Warang Sandstone Temperature ( C) Gilbert River Formation Depth (m) Time (Ma) Temperature ( C) Bandanna Formation Reservoir Colinlea Sandstone 2 Organic-rich layer 3 Colinlea Sandstone 1 Organic-rich layer 2 Aramac Coal Measures Organic-rich layer 1 Jochmus Formation Proterozoic % Porosity (%) Depth (m) Temperature ( C) Moolayember Formation Warang Sandstone Bandanna Formation Reservoir Colinlea Sandstone 2 Organic-rich layer 3 Colinlea Sandstone 1 Organic-rich layer 2 Aramac Coal Measures Organic-rich layer 1 Jochmus Formation Proterozoic Figure 16. Results from petroleum maturation modelling at Site A in the Millungera Basin, assuming the basin is the equivalent in age to the Galilee Basin. (a) Burial history plot, modelled with 1 m of mid-permian and 3 m of Triassic erosion during phases of the Permian Triassic Hunter Bowen Orogeny. (b) Temperature modelled with constant heat flow of 8 mwm -2, overlain on the burial history plot. (c) Vitrinite maturity overlain on the burial history plot. (d) Plot of predicted porosities and temperatures with depth. APPEA Journal

28 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Energy potential of the Millungera Basin: a newly discovered basin in north Queensland 17a 17c -5-5 Alluvium Toolebuc Formation Allaru Mudstone Alluvium Toolebuc Formation Allaru Mudstone Gilbert River Formation Gilbert River Formation Depth (m) 5 1 Bandanna Formation Reservoir Colinlea Sandstone 1 Aramac Coal Measures Organic-rich layer 1 Jochmus Formation Depth (m) 5 1 Bandanna Formation Reservoir Colinlea Sandstone 1 Aramac Coal Measures Organic-rich layer 1 Jochmus Formation 15 Proterozoic 15 Proterozoic 3 2 Time (Ma) 1 17b -5 Alluvium Toolebuc Formation Allaru Mudstone Gilbert River Formation Depth (m) 5 1 Bandanna Formation Reservoir Colinlea Sandstone 1 Aramac Coal Measures Organic-rich layer 1 Jochmus Formation 15 Proterozoic Time (Ma) Temperature ( C) Time (Ma) 1 Immature ( ) Early oil (.55-.7) Figure 17. Results from petroleum maturation modelling at Site B in the Millungera Basin, assuming the basin is the equivalent in age to the Galilee Basin. (a) Burial history plot, modelled with 12 m of erosion of the late early Permian Aramac Coal measures and 8 m of erosion of the late Permian to Triassic succession during phases of the Permian Triassic Hunter Bowen Orogeny. (b) Temperature modelled with constant heat flow of 8 mwm -2, overlain on the burial history plot. (c) Vitrinite maturity overlain on the burial history plot. 322 APPEA Journal 211

29 Energy potential of the Millungera Basin: a newly discovered basin in north Queensland Canobie Depression (! 19! ( (! QUEENSLAND GSQ (! Dobbyn 1 (! (! (! #* (! (! (! #* #* (! #* (! (! (!!! (!! ( 2 ( ( (! #* (! (! #* (! #* MILLUNGERA #*!! ( ( (! BASIN JHR Gladevale Downs 1 #* (! #* #* #* #* #* Cloncurry (! #* #* #* 6GA M4 94MTI GA M6 75 km #* #* JHR Glenbede Downs 1 JHR Rosevale Downs 1 #*#* 6GA M5 #* (! 7GA IG1 BUO Denbigh Downs 1 #* JHR Hampden Downs 1 JHR Belfast 1 (! #* #* #* NT QLD WA SA NSW VIC TAS Millungera Basin Canobie Depression GA seismic lines Industry seismic lines Fault Key drillholes Town Borehead temperature - artesian bores ( C) #* < 3 #* 3-4 #* 4-5 Temperature gradient - logged bores ( C/km) < 35 C/km C/km C/km C/km #* #* #* > C/km C/km > 85 C/km Figure 18. Proposed petroleum systems event chart for the Millungera Basin, assuming the basin is the equivalent in age to the Galilee Basin. Figure 19. Water bores logged for temperature in the Millungera Basin area, showing mean temperature gradient for logged bores, and borehead temperature for artesian bores. APPEA Journal

30 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Figure 2. Bottom-hole temperature versus depth for logged bores. REFERENCE MODEL The depth to the base of the Eromanga Basin is reasonably well constrained in the study area. Our modelling used a subset of the depth to basement dataset produced by Meixner (29). This dataset combines Queensland Department of Mines and Energy drillhole data, depth to basement interpretations from magnetic modelling, seismic refraction data, and basement outcrop data. Potential field data were used to provide an interpretation of the areal extent of the Millungera Basin (Fig. 2). This was used together with the seismic data to construct a surface representing the base of the Millungera Basin (Fig. 21). The seismic interpretations were converted to depth using velocities extracted from first breaks in the seismic reflection data, giving velocities of 2.2 and 5.2 km s -1, respectively. These velocities are similar to the interval velocities obtained from stacking velocities on these seismic lines. A velocity of 6. km s -1 was used for basement. An average density for sediments in the Eromanga Basin was obtained from density logs in petroleum exploration wells. No density logs were available for wells in the project area, although there are several in the surrounding region. These were used to determine an average density for sediments in the Eromanga Basin of 2,26 kgm -3. For the Millungera Basin, a density of 2,63 kgm -3 was calculated from the seismic velocity used for seismic depth conversion, using the empirical relationship derived by Gardner et al (1974). INVERSIONS The inversions were forced to honour the above density values, to within ±2 kgm -3 in the Eromanga and Millungera basins, by specifying upper and lower bounds in the reference model. For basement, a reference density of 2,72 kgm -3 was set, although the basement density was allowed to vary from 1,97 3,57 kgm -3. An initial gravity inversion was performed to define the distribution of low density regions in basement. Inversions tend to produce smoothly-varying density distributions. Therefore, to define the boundaries of all low density bodies in basement below the Millungera Basin, a series of isosurfaces were generated using a range of density cutoff values, encompassing successively larger volumes of low density. The method of Meixner and Holgate (29) was used to select isosurfaces that best defined the edges of the low density bodies. The average density values in the chosen isosurfaces range from 2,68 to 2,69 kgm -3. In addition, the isosurfaces extend to a maximum depth of 2 km. Because such a depth extent is not considered to be geologically realistic, and granite generally has a lower density than 2,68 2,69 kgm -3, the isosurfaces were truncated at shallower depths, and the material in the isosurfaces was defined to have a density of 2,62 kgm -3. Further inversion runs were performed to test different depth extents, in which they were forced to honour this density to within ±2 kgm -3. Five further inversions were performed, cutting off the depth of the bodies at 4, 6, 8, 1 and 12 km. The results of the inversions were inspected to determine an appropriate depth extent for each low density body. Where the depth extent of a body was too great, the inversion would compensate by putting high density material in the basement immediately below it. Likewise, where the depth extent was too small, the inversion would compensate by putting low density material below the body. Granite depths were defined by choosing depths that produced the most neutral result in the basement. In some cases, this required the depth of a body to be varied along its extent. The resulting model is presented in Figure 21. The model shows interpreted granites up to 5.5 km thick occurring beneath the Millungera Basin; this is thicker than the interpretation derived from seismic line 7GA-IG1 (Fig. 3), but is compatible with the granite interpreted beneath the Millungera Basin on seismic line 6GA-M4 (Fig. 5). Thermal modelling Forward prediction of temperatures was generated using a discretised version of the model in the GeoModeller code using the method described by Seikel et al (29). The grid used for thermal modelling was subsampled using a cell size of 4 km x 4 km x 25 m. Temperatures were solved by explicit finite difference approximation using a Gauss-Seidel iterative scheme, implemented until the sum of the residual errors fell below a specified threshold. Properties included in the output model consist of temperature, vertical heat flow, vertical temperature gradient and total horizontal temperature gradient. To compute a thermal model, the following inputs are required: surface temperature, basal heat flow, heat production rate of each lithology, and thermal conductivity of each lithology. The initial values for these inputs are estimated as follows. A surface temperature of 31 C was used. A constant basal heat flow of 4 mwm -2 was used, obtained from studies of heat production and heat flow in central Australia by McLaren et al (23). In the absence of any heat production data, sediments from the Eromanga and Millungera basins were attributed a low heat production 324 APPEA Journal 211

31 Energy potential of the Millungera Basin: a newly discovered basin in north Queensland Figure 21. Oblique perspective view of the 3D model of the Millungera Basin, basin sediments (yellow surface) and interpreted granites (pink surfaces). Viewed towards the north. rate of 1 μwm -3. Basement was attributed a heat production rate of 2 μwm -3. For interpreted granites, several scenarios were modelled. The most optimistic scenario used a heat production rate of 8 μwm -3. This value was obtained by taking the average chemical composition of granites from the Williams Supersuite of the Mt Isa Georgetown region (after Budd et al, 21), and calculating the heat production rate using the following formula: Heat generation (μwm -3 ) = ρ(8,31 x.35 x K 2 O x Th x U) / 1,,; where ρ = density in kgm -3 (for this study it was assumed to be 2,67 kgm -3 ): and K 2 O, Th, and U are the concentrations of in weight percent, ppm and ppm, respectively. Two other scenarios were modelled: a medium heat production scenario using a value of 5 μwm -3, equivalent to the mean composition for granites in the Mt Isa Georgetown area (Budd et al, 21), and a low heat production scenario, using 2 μwm -3. For sediments in the Eromanga Basin, available lithological logs were used, together with a compilation of published thermal conductivity values for sedimentary rocks (Beardsmore and Cull, 21, and references therein) to estimate a thermal conductivity of 2.3 WmK -1. All estimates were based on a weighted harmonic mean of all lithologies present. The thermal conductivity of granite was taken to be 3.1 WmK -1, obtained from L. Gow (Geoscience Australia, unpublished data 27). For basement, a thermal conductivity of 2.8 WmK -1 was used (also provided by L. Gow, Geoscience Australia, unpublished data, 27), taking a mean of lithology types likely to be present in the area. For the Millungera Basin, three possibilities were modelled. First, a value of 2.9 WmK -1 was obtained by taking the Georgina Basin as an analogue, and using its stratigraphy, together with published thermal conductivity measurements, to estimate a mean thermal conductivity for the basin. A second scenario was modelled using thermal conductivity of 2.6 WmK -1, about equivalent to a mix of 3% sandstone, 3% siltstone and 4% claystone. Finally, a scenario was modelled using a thermal conductivity of 2.3 WmK -1, similar to the thermal conductivity of sediments in the Eromanga Basin. In summary, a total of nine scenarios were modelled (Table 3). APPEA Journal

32 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi The results of the temperature modelling are shown as temperature slices at 5 km depth (Fig. 22a) and as surface heat flow (Fig. 22b). Five of the nine scenarios reveal elevated temperatures of over 19 C at 5 km depth in the lateral extent of the Millungera Basin. The maximum modelled temperature at this depth, in the extent of the basin, ranges from C, in the low-heat production scenarios, to C, in the high-heat production scenarios. The maximum modelled surface heat flow in this same area ranges from 8 82 mwm -2 for the low-heat production scenarios, to mwm -2 for the high-heat production scenarios. Interestingly, in the low-heat production scenarios, the temperature at 5 km depth is predicted to be about 12 C lower within the Millungera Basin than outside the basin. The main reason for this is that the input thermal conductivity for sediments in the Millungera Basin (2.9 WmK -1 ) is lower than that for basement (2.8 WmK -1 ). Although it is acknowledged that thermal conductivity values for the basin and basement were not based on direct measurements, the values are based on values from the published literature, and considered reasonable. The result highlights the fact that although sedimentary basins can provide a thermal blanket and, therefore, be quite prospective for geothermal energy, this is not necessarily the case. Conversely, it is possible for basement lithologies to have a sufficiently low thermal conductivity to trap significant heat at depth. Discussion The uncertainty in the composition of sediments in the Millungera Basin, granite and basement dictates that there is a high degree of variability in the results of the thermal modelling. This is without taking into account the uncertainty in the geometry of the Millungera Basin and its basement. It is clear that further work needs to be done to better constrain these inputs. Nevertheless, thermal modelling reveals interesting insights into the prospectivity of the basin. Firstly, in all of the high granite heat production scenarios, the models predict elevated temperatures at 5 km depth for the entire range of the trialled conductivity values for the Millungera Basin. Therefore, if granites with the composition of the Williams Supersuite occur beneath the Millungera Basin in the volumes indicated by gravity inversions, then, based on the forward temperature modelling, there is a good probability that the basin is prospective for geothermal energy. Secondly, in all of the medium- and high-heat production scenarios, the highest predicted temperatures (and heat flow values) in the Millungera Basin occur in the northwestern end of the basin, near the 7GA-IG1 seismic line, where the depth of the Millungera Basin is moderately well constrained. These scenarios are consistent with water temperature data, which reveals elevated temperature gradients in the northwestern Millungera Basin. In summary, although there is a high degree of uncertainty in the geothermal modelling carried out in the Table 3. Thermal property scenarios modelled for the Millungera Basin. All scenarios use a basal heat flow of 4 mwm -2 and a surface temperature of 31ºC. Scenario Thermal conductivity of sediments in Millungera Basin Millungera Basin, the promising results from this study suggest that the area certainly warrants further investigation. Thermal property measurements of sediments in the Millungera Basin, seismic lines to constrain its depth extent toward the south, and new heat flow measurements over the basin, would help reduce the uncertainty in future investigations. CONCLUSIONS Heat production rate of granite (WmK -1 ) (μwm -3 ) A new sedimentary basin identified from deep crustal seismic surveys has been named the Millungera Basin. Based on seismic data, it is possible to subdivide the basin into three major stratigraphic sequences of unknown age. Comparisons can be made with adjacent basins, such as the Permian Triassic Galilee Basin and the Neoproterozoic Devonian Georgina Basin, and several smaller sedimentary Mesoproterozoic to Paleozoic successions that overlie Paleoproterozoic rocks in the Mount Isa and Etheridge provinces. Petroleum systems modelling, using a Georgina Basin analogue, shows that potential middle Cambrian source rocks are likely to be mature in most of the Millungera Basin, with significant generation and expulsion of hydrocarbons occurring in two phases, in response to Ordovician and Cretaceous sediment loading. If a Galilee Basin analogue is modelled, potential Permian source rocks are likely to be oil mature in the central Millungera Basin, but immature on the basin margins. The top of the oil window is predicted to occur at depths of about 1,1 1,4 m. Significant oil generation and expulsion probably occurred during the Triassic, in response to late Permian to Early Triassic loading. Modelling suggests that generation and expulsion occurred throughout the burial history of the basin, with a sharp increase in expulsion during the Late Cretaceous to Holocene in response to Cretaceous loading, later than the most likely time of trap formation in the Late Triassic. Thus, if the Millungera Basin 326 APPEA Journal 211

33 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Energy potential of the Millungera Basin: a newly discovered basin in north Queensland Figure 22. Results of forward temperature modelling numbered by the heat production-thermal conductivity scenario as detailed in Table 3, displayed as (a) temperature at 5 km depth, and (b) surface heat flow. APPEA Journal

34 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi is an equivalent of the Galilee Basin, the prospectivity for gas is rated high. With regard to geothermal energy, several scenarios have been modelled. The results indicate that the basin has good potential for geothermal energy, if the granites can provide sufficient heat, and further work is warranted. Future studies, including drilling and seismic acquisition, are required to help determine the age, distribution and economic potential of the basin. ACKNOWLEDGEMENTS We thank the members of the North Queensland project team from Geoscience Australia, Geological Survey of Queensland and AuScope for their involvement in the interpretation of the deep seismic and related data. We also thank Riko Hashimoto and Dianne Edwards for reviewing the manuscript, Mark Livingstone for his support at the GSQ Core Store, Theo Chiotis and Veronika Galenic for their care in drafting the figures, Peter Milligan for the aeromagnetic image, and Simon van der Wielen for the water bore logs. Published with permission of the Chief Executive Officer of Geoscience Australia and the Director of the Geological Survey of Queensland. REFERENCES AMBROSE, G.J. AND PUTNAM, P.E., 27 Carbonate ramp facies and oil plays in the Middle/Late Cambrian, southern Georgina Basin, Australia. In: Munson, T.J. and Ambrose, G.J. (eds) Proceedings of the Central Australian Basins Symposium, Alice Springs, August, 25. Northern Territory Geological Survey, Special Publication 2, BARLOW, M.G. AND DUNSTER, J.N., 1988 Final report 1988 Carpentaria Basin seismic surveys, Authority to Prospect 373P, Queensland. Comalco Aluminium Limited, unpublished. (Open File Report, CR2346. Brisbane: Queensland Mines and Energy, Geological Survey of Queensland.) BEAHAN, P.L. AND BARLOW, M.G., 1987 Final report 1987 Carpentaria Basin seismic surveys, Authority to Prospect 373P, Queensland. Comalco Aluminium Limited, unpublished. (Open File Report, CR222. Brisbane: Queensland Mines and Energy, Geological Survey of Queensland.) BEARDSMORE, G.R. AND CULL, J.P., 21 Crustal Heat Flow: a guide to measurement and modelling. New York: Cambridge University Press. BLACK, L.P. AND McCULLOCH, M.T., 199 Isotopic evidence for the dependence of recurrent felsic magmatism on new crust formation: an example from the Georgetown region of Northeastern Australia. Geochimica et Cosmochimica Acta, 54, BOREHAM, C.J. AND AMBROSE, G.J., 27 Cambrian petroleum systems in the southern Georgina Basin, Northern Territory, Australia. In: Munson, T.J. and Ambrose, G.J. (eds) Proceedings of the Central Australian Basins Symposium, Alice Springs, August, 25. Northern Territory Geological Survey, Special Publication, 2, BUDD, A., WYBORN, L.A.I. AND BASTRAKOVA, I.V., 21 The metallogenic potential of Australian Proterozoic granites. Geoscience Australia, Record, 21/12. CARR, L.K., KORSCH, R.J., JONES, L.E.A. AND HOL- ZSCHUH, J., 21 The role of deep seismic reflection data in understanding the architecture and petroleum potential of Australia s onshore sedimentary basins. AP- PEA Journal and Conference Proceedings, 5, 4 pp. CARTER, E.K., BROOKS, J.H. AND WALKER, K.R., 1961 The Precambrian mineral belt of north-western Queensland. Bureau of Mineral Resources, Geology and Geophysics, Bulletin, 51. CARSON, C.J., HUTTON, L.J., WITHNALL, I.W., PER- KINS, W.G., DONCHAK P.J.T., PARSONS, A., BLAKE, P.R., SWEET, I.P. AND NEUMANN, N.L., 211 Summary of results: Joint GSQ-GA NGA geochronology project, Mount Isa region, Queensland Geological Record, in press. DOUTCH, H.F., MINGRAM, J.A., SMART, J. AND GRIMES, K.G., 197 Progress report on the geology of the southern Carpentaria Basin. Bureau of Mineral Resources, Geology and Geophysics, Record, 197/39. DRAPER, J., 27 Georgina Basin an early Palaeozoic carbonate petroleum system in Queensland. The APPEA Journal, 47 (1), EVINS, P.M., WILDE, A.R., FOSTER, D.R.W., McKNIGHT, S.W. AND BLENKINSOP, T.G., 27 Significance of monazite EPMA ages from the Quamby Conglomerate, Queensland. Australian Journal of Earth Sciences, 54 (1), FILATOFF, J. AND PRICE, P.L., 1989 GSQ Dobbyn No.1. APG Consultants, report N. 571/8. (Open File Report CR211. Brisbane: Queensland Mines and Energy, Geological Survey of Queensland.) FRENCH, J.V Denbigh Downs No. 1 well completion report for Petro Sources Inc. Open File Report CR Brisbane: Queensland Mines and Energy, Geological Survey of Queensland. GARDNER, G.H.F., GARDNER, L.W., AND GREGORY, A.R., 1974 Formation velocity and density the diagnostic basics for stratigraphic traps. Geophysics, 39 (6), GERNER, E.J., 21 OZTemp Interpreted temperature at 5 km depth image. Geoscience Australia. Accessed APPEA Journal 211

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37 Energy potential of the Millungera Basin: a newly discovered basin in north Queensland THE AUTHORS Russell Korsch is a group leader in the Onshore Energy and Minerals Division at Geoscience Australia and is responsible for the onshore petroleum and energy geodynamics components of the Australian Government s Onshore Energy Security Program. He has a BSc (hons), PhD and DipEd from the University of New England, with a background in structural geology and tectonics, and has been involved in understanding the evolution of sedimentary basins and in the geological and geodynamic interpretation of deep seismic data collected by Geoscience Australia and partners during several years. He is on the Executive of the Editorial Board of Australian Journal of Earth Sciences and a Fellow of the Geological Society of America. Member: PESA and the Geological Societies of Australia and New Zealand. Heike Struckmeyer is a principal research scientist in Geoscience Australia s Petroleum and Marine Division. She graduated from the University of Göttingen, Germany in 1981 and received a PhD from the University of Wollongong in Since joining Geoscience Australia in 1988, her work has been focused on the evolution and prospectivity of Australia s northern, northwestern, eastern and southern margins, and on regional basin analysis and petroleum systems modelling. In recent years, she has worked on projects in the Browse, Bight and Arafura Basins. Member: AAPG and PESA. Alison Kirkby graduated from the University of Auckland in 28 with an MSc in geology, in which she studied the magnetic and gravity characteristics of the Hauraki Rift in the central North Island of New Zealand. She joined Geoscience Australia in the same year, and now works in the geothermal project, where she is involved in the collection and processing of new heat flow data across the Australian continent. Laurie Hutton graduated from the University of Queensland in 1972, completing Honours the following year. Since then he has been involved in regional geological mapping in Queensland. From 1975 until 1981, he was involved in the geological mapping program at Mount Isa. In 24, he was awarded a Doctor of Philosophy for a thesis on mapping in the Pentland area of Queensland. From 24 29, he was involved in the remapping of the Mount Isa region. This project included deep crustal seismic profiling. During this project, the Millungera Basin was first discovered, and has since been the focus of other studies. Lidena Carr is a geologist for the Onshore Petroleum project in the Onshore Energy and Minerals Division at Geoscience Australia. She graduated from the Australian National University (ANU) majoring in geology and human ecology with BA/BSc (hons) in 24, and began working as a technical officer at the Research School of Earth Sciences (ANU). In 27, she joined Geoscience Australia with the then ACRES, before moving to her present position in early 29. Member: PESA and the Geological Society of Australia. Kinta Hoffmann graduated from James Cook University in 1984 with a BSc Geology (hons) researching the oil shale in the Toolebuc Formation. After working briefly for ESSO Minerals and as a curator of the JCU Geology Department, she joined the Geological Survey of Queensland in 1986 and has been involved in basin studies of the Cooper, Eromanga, Adavale, Surat and Bowen basins. She is now working with Geoscience Australia and ANU in collaborative marine geoscientific research off northeast Australia. Authors biographies continued next page. APPEA Journal

38 M. Fitzell, J.M. Totterdell, M.G. Nicoll and B. Talebi Continued from previous page. Richard Chopping joined Geoscience Australia in 25 after completing Honours in geophysics at the University of Tasmania. He has recently completed a MSc in earth physics at ANU. Initially sceptical as to the value of mineralogy and chemical alteration in understanding geophysical response, Richard has spent the last three years worrying about how chemical changes in rocks will change their geophysical response. Indrajit Roy is a project geophysicist in the Onshore Energy and Mineral Division, Geoscience Australia. His research interests are geophysical data processing, modelling and synthesis. He has been involved extensively in a wide range of geoscience research, which includes waveform inversion of seismic data, rock physics and reservoir characterisation, potential field data processing and modelling, and solid earth and environmental geophysics. He has conducted independent research on various scientific projects, supervised graduate students and offered various courses on geophysics. Member: ASEG, SEG and AGU. Melanie Fitzell joined the Geological Survey of Queensland in 23. She has worked on several regional mapping projects throughout Queensland and has developed an interest in 3D geological mapping and modelling. Melanie moved into the Energy Unit in late 28 to develop skills in seismic interpretation and basin analysis studies. Melanie was assigned to the Coastal Geothermal Energy Initiative team in mid 29. Jennie Totterdell is is a principal research scientist in Geoscience Australia s Petroleum and Marine Division and Project Leader of the Southern Frontiers Project. Since graduating from the Australian National University, Jennie has worked on a range of regional, thematic and basin studies at Geoscience Australia. In the last 1 years, her work has focused on offshore frontier basins, notably the Bight, Arafura and Browse basins. Her main areas of interest are the structural and stratigraphic evolution and petroleum potential of the southern Australian margin. Member: PESA. Malcolm Nicoll is a geoscience technologist in the Onshore Energy and Minerals Division at Geoscience Australia, and has a Diploma of Applied Science (Geoscience). He specialises in 3D data integration, model construction and visualisation technology. He joined Bureau of Mineral Resources in 1989 and has worked mainly on sedimentary basin studies and hard rock mineral terranes, and has also applied these skills in the geohazards and groundwater domains. Behnam Talebi completed his postgraduate studies in geothermal energy technology at the University of Auckland in New Zealand in In the past 17 years, he has been involved in a number of geothermal energy projects overseas from reconnaissance studies through to field exploration and development programs. In the past six years, he has been project manager for a 55MWe geothermal power development project in northwest Iran and led exploration, delineation and production drilling programs as well as field development and power plant construction. Behnam joined the Geological Survey of Queensland in September 29 as program leader for the Queensland Coastal Geothermal Energy Initiative program. 332 APPEA Journal 211