Blocks: 53/15b, 53/19, 53/20, 54/11 & 54/16. Promote Licence P1252 Two Year Report

Transcription

1 Blocks: 53/15b, 53/19, 53/20, 54/11 & 54/16 Promote Licence P1252 Two Year Report Wintershall Noordzee BV October 2006

2 Contents Contents 1 List of Figures and Tables Licence details and work commitments Conclusions Seismic interpretation Depth conversion and mapping Well data Regional setting Occurrence and timing of hydrocarbons in the area Triassic Bunter Sandstone play Lower Cretaceous Spilsby Sandstone play Leman Sandstone play Namurian & Dinantian plays Leads & Volumetrics...10 Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 1

3 List of Figures and Tables List of Figures Figure 1: Location map of P1252 Promote Licence Figure 2: Seismic basemap of P1252 Promote Licence Figure 3: 2D seismic line ON Figure 4: Lead map of P1252 Promote Licence Figure 5: Geological setting of P1252 Promote Licence Figure 6: Stratigraphic column for P1252 Promote Licence Figure 7: Schematic summary of play types in P1252 Promote Licence Figure 8: Vitrinite reflectance depth trend for pre-cretaceous samples from wells in and near P1252 Promote Licence Figure 9: Base Cretaceous sub-crop map Figure 10: Base Cretaceous depth map Figure 11: Top Leman Sandstone depth map Figure 12: Top Dinantian Limestone depth map List of Tables Table 1: Depth conversion parameters... 4 Table 2: Well database P1252 Promote Licence and surroundings... 5 Table 3: GIIP of leads in P1252 Promote Licence Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 2

4 1. Licence details and work commitments Wintershall Noordzee BV acquired the Promote Licence (P1252) over block 53/15b, 53/19, 53/20, 54/11 & 54/16 (Figure 1) on 27 th April The firm commitment is: Within one year of the beginning of the Initial Term the Licencee shall obtain 900km of 2D seismic data and 2300km 2 of 3D seismic data relating to the Licenced Area. Additional work proposed by the Licencee: 1. Interpretation of 2D and 3D seismic data. 2. Study on occurrence and timing of hydrocarbons in the area. 3. Evaluation of prospectivity of the P1252 Licence area. The seismic was acquired by end All other necessary work is also fulfilled. A summary of the results is given in this report. 2. Conclusions Based on 2D and 3D seismic interpretation some 22 leads have been identified in the UK P1252 Promote Licence but unfortunately volumes are too small to justify economic development and/or they carry too high risk. Key risks are: 1. Trap definition over most of the leads. 2. Effectiveness of potential gas source rocks because of the burial and tectonic history (i.e. high risk on hydrocarbon generation and migration). 3. Presence of Carboniferous oil source rocks within the area is possible but remains speculative because lack of data. Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 3

5 3. Seismic interpretation The exploration potential evaluation of blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 started with the interpretation of the acquired 2D and 3D seismic data (Figure 2). The 2D data is in general of variable quality (Figure 3), whereas the 3D data quality is good to excellent. The synthetics of the wells within the 3D seismic area have been tied and based on these synthetics a total of 12 horizons was picked and interpreted (Table 1). 4. Depth conversion and mapping A regional velocity model is built covering the licences and the area around. The time horizons are gridded and subsequently depth converted in the model. The velocity functions applied for the depth conversion are given in Table 1. Interval Function Constants) V0 Grid values Base Tertiary v = v 0 + k*z k = 0.2 v 0 = surface Base intra Chalk Unc. v = v 0 + k*z k = 0.12 v 0 = 2784 Base Chalk v = v 0 + k*z k = 0.2 v 0 = 3152 Base Cretaceous Unc. v = v 0 + k*z k = 0.42 v 0 = 2048 Base Bunter Sandstone v = v int v int = 2858 Top Zechstein Z3 v = v int v int = 3220 Base Zechstein v = v int v int = 3560 Base Leman Sandstone v = v int v int = 3406 B. Carb. Barren Measures v = v int v int = 3180 B. Carb. Coal Measures v = v int v int = 3333 Top Dinantian Limestones v = v int v int = 3635 Table 1: Depth conversion parameters Structural time and depth maps are generated from the horizons confining the intervals of Table 1. In addition 3 additional horizons (Top Spilsby Sandstone, Top Bunter Sandstone and Top Hewett Sandstone) were generated through isochore mapping and partial interpretation. Maps of the primary and secondary objectives were used for prospect/lead evaluations. Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 4

6 5. Well data Wells used for the seismic interpretation and various studies are listed in Table 2. A short interpretation is given on reason of failure (see also Figure 4 for location of wells). Well Year & Operator 53/ Arco 53/ Total 53/ Arco 54/ Amoco P Union Oil P Pennzoil P Conoco P Petro- Canada 2D/3D Shows Failure 3D 2D 2D 2D 2D C1 (and higher) in Leman Sst while drilling, tested water Minor C1 trip gas at Spilsby Sst. Gas shows (C1) at Spilsby Sst. Recent analysis by WINZ showed a gas saturation of 40%-50% Spilsby Sst. Inversion trap but without apparent closure. Reason why it was drilled in this location not clear. Possibly to test closure to the East (current Foxtrot lead) Combination of Spilsby Sst and Permo-Triassic Sst s. Fault-dip structure is not closing towards the NW. Combination of Spilsby Sst and Permo-Triassic Sst s. 4 way closure, inversion trap. Off-structure of current Kilo Lead. Combination of Spilsby Sst and Permo-Triassic Sst s. Faulted 4-way dip closure, inversion trap. Drilled below the closing contour of the Charlie lead cluster which spills towards the West. Leman Sst. Complex faulted structure, inversion trap. Leman is not closing towards NW. Down thrown fault block and not a trap. Doomed to be dry or mispositioned 2D C1 trip gas at Spilsby Sst. Combination of Spilsby Sst and Permo-Triassic Sst s. Faulted horst, inversion trap. Current 3D interpretation shows no closure to be present and spilling towards the West. 3D? Data not released. Zechstein & Leman Sst. Fault-dip closure, inversion trap. presumably dry because of juxtaposition to Spilsby Sst in the West. Unknown if Spilsby Sst is present at the trap location. If present than non-charging of the structure is the most likely reason for failure. If the Spilsby Sst is absent than the combination trap is an invalid structure. Important well to get data because of regional implication! Table 2: Well database P1252 Promote Licence and surroundings Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 5

7 6. Regional setting The blocks 53/15b, 19, 20 and 54/11 & 16 are situated on the South Hewett Shelf, at the southern edge of the Winterton High (Figure 5). This high separates the Sole Pit Basin from the West Netherlands Basin. The area is dominated by the NW-SE running South Hewett inversion fault. This fault of Mesozoic age separates the Winterton High to the northeast from the South Hewett Shelf and London-Brabant Massif to the southwest. The Winterton High suffered from intense erosional events during the Late Jurassic (Mid and Late Kimmerian events). Thin Early Cretaceous Spilsby Sandstone was deposited in this area. To the south, the London-Brabant Massif is only covered by Late Cretaceous and younger rocks, resting unconformably on Carboniferous sediments. The area has either not experienced any major deposition, or the Permo- Triassic and Jurassic sediments have been removed by subsequent erosion. On the South Hewett Shelf, located in-between the London-Brabant Massif and the Winterton High, Permo-Triassic sediments were deposited and preserved. A stratigraphic column for the area is presented in Figure 6. The primary objectives in these southern blocks are the Triassic Bunter Sandstone, preserved in tilted fault blocks below the Base Cretaceous Unconformity, in combination with overlying Lower Cretaceous Spilsby Sandstone. Secondary objectives are the Lower Cretaceous Upper Speeton sands, Triassic Hewett Sandstone, Permian Leman Sandstone, Namurian Sandstone and Dinantian Limestone (Figure 7). 7. Occurrence and timing of hydrocarbons in the area Most likely source rock candidates for hydrocarbon charge in the promote licence area are Westphalian coals and possible basal Namurian Type II source rocks. Active, early gas mature, Tertiary kitchen areas for the coals have been identified in the Northeast of the area. Active, oil- and gas mature, Carboniferous to Mid-Jurassic kitchen areas for the basal Namurian source rocks have been identified in the Southwest of the area. From a basin-wide study, rich, oil-prone source rocks could be interpreted for the seismically-identified Namurian basinal shales and intercalations of marine bands in the Namurian section above. Based on the present day depths of burial the onset of early oil maturity is interpolated as 1500m, mid oil maturity as 2100m, late oil maturity as 2600m and the main gas window below 2900m for the licence area (Figure 8). These depths are shallow due to uplift following the controlling Mid Jurassic thermal event on the southern margin compared to equivalent maturity levels in the main Southern Permian Basin to the north. Measured data coupled with 1-D modelling demonstrated that maturation and oil expulsion has mainly taken place during a Mid-Jurassic high heat flow event. Towards the end of this event, prior to uplift and erosion, a large part of the licence area would then be oil-mature to late gas-mature at the top-namurian level. However, as Carboniferous-sourced oils are identified in the UK onshore and the in main Southern Permian Basin to the north only and none of the investigated stained samples from the licence area showed evidence for Carboniferous sourced oil the presence of Carboniferous oils trapped within the licence area remains speculative. Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 6

8 The oil and gas finds in the De Ruyter Field in Dutch offshore block P11, some 20 km to the East are the nearest commercial discoveries. The Lower Jurassic shales (Posidonia) present in the West Netherlands Basin east of the promote licence area are seen as the potential oil source. Oil migrated into this field via block P15 and goes from the Lower Jurassic source rock upward to the Lower Cretaceous claystones and westward along a 25 km conduit of sandstones from the Vlieland Sandstone Formation and the Main Buntsandstein Group. The possibility that the oil migrated further west into traps within the promote licence area is highly unlikely. Gas from the field is probably sourced from Carboniferous coals underneath and/or from the East. 8. Triassic Bunter Sandstone play This interval is the primary reservoir interval in blocks 53/19, 53/20, and 54/16, and a secondary target in blocks 53/15b and 54/11. Deposition of the Upper Bunter Sandstone was probably initiated by uplift of the London-Brabant Massif. The formation consists of mixed aeolian and fluvial coarse-grained sediments, channel and sheetflood sands. The basin-wide subsidence resulted in uniformly increasing thickness to the northeast. Erosional activity of the Late and Mid Kimmerian events reduced the original thickness. The thickness varies from 0 meter due to Base Cretaceous truncation to a maximum of 200 meters in blocks 53/19 and 53/20 as is shown on the Base Cretaceous sub-crop map (Figure 9). It also shows that in large part of the area the Upper Triassic is preserved. The Upper Triassic evaporates are a proven seal for the underlying Bunter Sandstone and Hewett Sandstone. The porosity of the Bunter Sandstone is strongly affected by the amount of burial. Based on well and seismic data a general trend of increasing porosity can be established from the deepest part in the West Netherlands Basin to the west. The licence area is situated in an area of very limited burial and reservoir porosity are expected to range from 10% to 20%, with the average skewed to the higher values. In blocks 53/15a, 53/19, 53/20 and part of 54/11 in the southwest of the area an upper Triassic syncline is seen. This would imply that potential Bunter Sandstone and Hewett Sandstone traps are sealed by upper Triassic evaporites. They constitute valid traps if they existed pre-inversion. In this way they could be effective traps for the hydrocarbons generated by the Carboniferous source during the Jurassic peak hydrocarbon generation. 9. Lower Cretaceous Spilsby Sandstone play The Spilsby Sandstone Formation although not deposited everywhere within the licence area is a primary target. The formation is known in the Dutch sector as the Vlieland Sandstone Formation. This basal sandstone is deposited on the Base Cretaceous Unconformity (Figure 10) and could reach as seen, in places in the Netherlands, a maximum thickness up to 300 meter. The Spilsby Sandstone encountered in the UK wells in Quadrant 53 and 54 and the Dutch wells along the Median Line, is a younger equivalent of the Vlieland Sandstone. At Early Cretaceous times the area of interest became submerged and the Spilsby Sandstone was deposited Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 7

9 as a transgressive sandstone at the base of the Lower Cretaceous. The older barrier sands were deposited along the margins of the West Netherlands Basin while progressively younger sands were deposited further west, onlapping onto the Winterton High. The sands are reworked delta front sands and offshore shoalbars. For gas prospects the play relies on generation and migration from a Carboniferous source. Although this source is present throughout the area, the effectiveness is the most important risk. For oil prospects the play relies on either long-distance migration from the Dutch Broad Fourteens basin (cf the De Ruyter oil field in P11) or on in-situ sourcing from possible Namurian hot shales. Top seal is the Lower Cretaceous Speeton Clay Formation which has a proven sealing capacity across many fields in the Dutch and UK offshore areas. For both oil and gas, the shale provides an adequate seal for Spilsby sand and subcropping pre-cretaceous accumulations. As it is present throughout the area top seal is considered low-risk. Spilsby traps formed during the late Cretaceous to early Tertiary are high risk in terms of timing with respect to hydrocarbon generation. 10. Leman Sandstone play The Lower Permian Leman Sandstone play consisting of aeolian dune sandstones is restricted to the southern half of the Southern North Sea gas province, because the reservoir facies passes northwards into contemporary playa lake mudstones and evaporites. The sandstone reservoir is present throughout the licenced area (Figure 11) and of high quality being proximal to the Hewett shelf and exposed to minimal burial. Although the Leman Sandstone traps in the area are in general considered to be invalid because of lack of top seal (absence of Zechstein salt), the play should not be ruled out completely; well 53/19-1 showed gas but tested water in the Leman Sandstone Formation. From seismic interpretation and well data it can be shown that the top seal formed by the Zechstein Group becomes thicker and more distal towards the NE where the Z3 dolomite develops more clearly and thicker anhydrite and clays occur thus increasing the top seal capacity. Whilst reservoir quality deteriorates towards the north, sealing capacity improves. Prospectivity is therefore limited to a narrow zone only. 11. Namurian & Dinantian plays On the southern flank of the basin, prograding Namurian deltas deposited sands and shales on the Dinantian slope. On regional seismic sections wedge-shape depositional structures have been identified in the deeper part of the Namurian sections that are potential stratigraphic Namurian traps. The pro-delta sandstone has proven in well 43/17-2 to have excellent reservoir potential. Higher along the Dinantian slope the coastal belt sand is a potential target. Due to lack of well control the reservoir development is very uncertain. The Dinantian Limestones are a potential secondary reservoir target, which is largely untested. Faulted structures and carbonate build-ups along the slope have been detected on seismic data in blocks 53/19 and 20 and 54/16. The general paleogeography for the Dinantian is one in which small clastic deltas prograded from south to north. Sandstones are expected to be mostly very fine to medium grained and were deposited in a variety of channel mouthbar settings; shales range from fully marine to non-marine Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 8

10 environments, the latter being associated with the delta-top coal. The limestone units represent marine flood events over the low lying deltas, causing the restriction of clastic input and the establishment of carbonate banks. Both plays are considered high-risk because the sourcing is complicated since pre- Dinantian sources are unknown from the area. Lateral sourcing is a possibility from the Westphalian coals or Namurian hot shales. Reservoir presence and quality are difficult to ascertain because of lack of well data and poor seismic. Because the Lower Carboniferous shelf-break is situated in the south western part of the Promote Licence (running NW-SE just south west of wells 53/18-1 and 53/19-1), reservoir quality in general is expected to increase from north east towards the south west. Sealing by the Namurian shales is considered low risk. Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 9

11 12. Leads & Volumetrics Refer to Figure 4 when reading the volumetrics in the following table: Play Lead Segment data GIIP BCM GPOS Mean BCM Exp BCM Key Risks P90 P50 P10 Spilsby Sst Alpha s1 2D % Charge & Trap Spilsby Sst Alpha s2 2D % Charge & Trap Spilsby Sst Alpha s3 2D % Charge & Trap Spilsby Sst Bravo 3D % Charge Spilsby Sst Charlie s1 3D % Charge Spilsby Sst Delta 2D % Charge & Trap Spilsby Sst Echo 2D % Charge & Trap Spilsby Sst Foxtrot 2D % Charge & Trap Spilsby Sst Golf 2D % Charge & Trap Spilsby Sst Hotel 2D % Charge & Trap Spilsby Sst India 2D % Charge & Trap Spilsby Sst Juliette 2D % Charge & Trap Spilsby Sst Kilo 2D % Charge & Trap Spilsby Sst Lima 2D % Charge & Trap Bunter Sst Alpha b1 2D % Trap Bunter Sst Alpha b2 2D % Trap Bunter Sst Kilo 2D % Trap Bunter Sst Lima 2D % Trap Leman Sst Foxtrot 3D % Top Seal Dinantian Lmst* Dinantian Sst* Dinantian Lmst Alpha 2D % Alpha 2D % Foxtrot 3D % Trap, Reservoir & Source Trap, Reservoir & Source Reservoir & Source Table 3: GIIP of leads in P1252 Promote Licence *) Note that for the Dinantian Alpha lead two reservoir cases have been assessed: Sst and limestone reef build-up. This is an either/or situation and the two GIIP figures should not be summed. Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 10

12 Figure 1: Location map of P1252 Promote Licence Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 11

13 Figure 2: Seismic basemap of P1252 Promote Licence Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 12

14 Alpha Base Tertiary Base Chalk Base Cretaceous Top Rotliegend Top L.Bunter Top Zechstein Top Carboniferous Top Coal Measures Base Rot Top Namurian Top Dinantian Figure 3: 2D seismic line ON5 Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 13

15 Figure 4: Lead map of P1252 Promote Licence Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 14

16 Indefatigable Fault Zone Sole Pit Basin Broad Fourteens Basin IJmuiden High P10 P13 West Netherlands Basin UK NL O15 P16 Gas Field Oil Field Fault Winterton High 53/14 53/20 54/06 P5 Indefatigable Shelf LEMAN FIELD P8 South Hewett Fault Zone DE RUYTER FIELD P11 P15 P1252 Area South Hewett Shelf London Brabant High 5730 Figure 5: Geological setting of P1252 Promote Licence Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 15

17 Figure 6: Stratigraphic column for P1252 Promote Licence Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 16

18 Figure 7: Schematic summary of play types in P1252 Promote Licence Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 17

19 Figure 8: Vitrinite reflectance depth trend for pre-cretaceous samples from wells in and near P1252 Promote Licence Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 18

20 Figure 9: Base Cretaceous sub-crop map Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 19

21 Wintershall Noordzee B.V Base Cretaceous depth Map Foxtrot Golf / Charlie Echo 054/11-01 P UK 53 Promote License Kilo 053/ Bravo Alpha Hotel 053/18-01 P10-01 P10-04 Delta India P10-02 Juliette m Figure 10: Base Cretaceous depth map Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 20

22 Top Leman Sandstone depth map Foxtrot Figure 11: Top Leman Sandstone depth map Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 21

23 Top Dinantian Limestone depth map Foxtrot Alpha Figure 12: Top Dinantian Limestone depth map Blocks 53/15b, 53/19, 53/20, 54/11 & 54/16 Page 22