Relinquishment Report

Transcription

1 Relinquishment Report P1790 Blocks 21/27a & 28/2a March 2013

2 P1790 Block 21/27a Relinquishment Report 1 General 1 2 Synopsis 3 3 Exploration Activities Wells Drilled Seismic Database 6 4 Prospectivity Analysis Reservoir Source Seal Trap Style Remaining Prospectivity 9 5 Reserves Summary 10 6 Clearance 12 7 References 13

3 List of figures 1.1 Licence Map Pilot Area Well Database Seismic and Well Coverage Map Inline Hydrocarbon Pore Thickness Map

4 List of tables 3.1 C o r e R e c o v e r y

5

6 [ 1 General Introduction This report documents the full relinquishment of licence P1790, UKCS blocks 21/27a & 28/2a. See Fig '0"E ± 0 8'0"E 0 10'0"E 0 12'0"E 0 12'0"E 0 14'0"E 0 16'0"E 21/27c 0 18'0"E 0 20'0"E 0 22'0"E 0 24'0"E 0 24'0"E 0 26'0"E 0 28'0"E 0 30'0"E 0 32'0"E 0 34'0"E 21/28c 21/27b BL A 2 10Z 10 FY NE 9Y 99Z 7 Y NE KE 4 21/28a '0"N Y 8Z ND DA FE UG H 21/27a 57 10'0"N 8 1 Bowhead /27d 57 6'0"N Pilot North Channel 3 T PILO Pilot Central Channel 5Z 6 5X 5Y Pilot Far South Channel '0"N Fulmar Lead SE Pilot Legend P '0"N Pilot South Channel 57 0'0"N 21/28b Harbour 1 1A 28/2b /2a 8 28/3 57 0'0"N Spinner 10 Km ELKE Western Platform Area 1:150,000 Bottlenose Coordinate System: ED 1950 UTM Zone 31N Projection: Transverse Mercator Datum: European 1950 False Easting: 500, False Northing: Central Meridian: Scale Factor: Latitude Of Origin: Units: Meter Updated December 2012 Fig. 1.1 Licence Map Licence Summary Licence Number P1790 Licence Round 26th Licence Type Traditional Block Number(s) 21/27a & 28/2a Operator / Partners % Enquest 100%

7 Commitments The work commitment at award was; to obtain 57km 2 of 3D seismic within the licence. Additionally, the drill or drop commitment was to drill one well to a depth of 1066 metres or to Top Balder, whichever is the shallower before the licence expiry. The seismic committment was fulfilled by the purchase of Western Geco's Q21 survey (2009 reprocessing) over the entire licence area and beyond, totalling km 2. This data has had a coloured inversion carried out on it. Therefore there are no outstanding work commitments on the licence. All wells on the licence have been plugged and abandoned.

8 [ 2 Synopsis Block 21/27a was originally awarded to Fina Petroleum and partners in the 10th licence round as part of licence P595. Fina drilled well 21/27-1A in 1989 which resulted in the Harbour oil and gas discovery. Later in the same year well 21/27-2 was drilled on what was to become the Pilot oil discovery. This was subsequently appraised by wells 21/27-3, 21/27-4 and 21/27a-5,X,Y,Z. In all, five wells and seven substantive well penetrations of the Tay Formation were drilled by Fina. The licence was subsequently taken by Venture Production, who drilled well 21/27a-6 in Following this well Venture relinquished the licence in April Enquest applied for and were awarded the licence in the 26th round (2010). The Pilot oil accumulation is well appraised and is well resolved on 3D seismic. Oil samples confirm the dense, viscous nature of the hydrocarbons present, minor gas accumulations are also present in localised four way dip closures e.g. 21/27a-5 and Harbour.The Pilot accumulation itself is a stratigraphic trap updip to the west, and is dip closed in other directions. Reservoir depths are typically around 2700 feet TVDSS. Three major hydraulic regions have been proven, in descending volumetric order these are: Pilot Main, Pilot South (21/27-4), and Harbour. Additionally, there are numerous minor 4 way dip closed features which have a hydrocarbon bearing seismic response. Enquest have conducted a substantial amount of work on the block including the following: Purchase of 2009 reprocessing of Western Geco 1997 survey Coloured inversion of previously mentioned data Re-assessment of fluid samples, including retesting of dead oil viscosity Log analysis for all wells Seismic interpretation and attribute analysis Construction of 3D static model Flow simulation for Pilot Main and South Economic evaluation Following this substantive technical work programme and revised cost estimates for a heavy oil development, economic analysis was not supportive of a development decision in the current cost environment. Other prospectivity on the block is in the form of the SE Pilot and Fulmar interpod leads. The SE Pilot lead did not share the same seismic character as encountered in Pilot and Harbour, and was not pursued further. Following the failure of Pilot to meet economic thresholds, the high risk Fulmar prospectivity was not pursued,

9 3 Exploration Activities 3.1 Wells Drilled Well Database Extensive exploration and appraisal drilling has taken place in the area. Enquest have access to all data via CDA or well trades. Fig. 3.1 gives and overview of the well database. Well Field Status Date TD TD Fm Operator Core Velocities RFT 28/02-1 Narwhal Oil Triassic Arco Tay VSP Y 28/2a-2 Dry Hole Horda Venture No No No 28/03-1B Elke Oil Balder Murphy Tay Checkshot Y 28/04b-1A Dry Hole Zechstein Conoco No VSP No 28/04a-2 Dry Hole Rotliegendes Kerr McGee No No No 28/04a-3 Dry Hole Triassic Kerr McGee No VSP No 21/26-1D Dry Hole devonian Shell Zechstein Checkshot No 21/27-1A Harbour Oil and Gas Zechstein Fina Tay Checkshot Y 21/27-2 Pilot Oil Chalk Fina Tay Checkshot Y 21/27-3 Pilot Oil Chalk Fina Tay Checkshot Y 21/27-4 Pilot Oil Chalk Fina Tay Checkshot Y 21/27a-5 Pilot Oil and Gas Sele Fina Tay VSP Y 21/27a-5Z Pilot Oil and Gas 1998 Tay Fina No No No 21/27a-5Y Pilot Oil 1998 Tay Fina No No No 21/27a-5X Pilot Oil 1998 Tay Fina No No No 21/27a-6 Pilot Oil 2007 Tay Venture No No Y 21/27b-7 Blakeney Oil Chalk Wintershall Tay VSP Y 21/28-1 Feugh Oil and Gas Zechstein Mobil SWC Checkshot No 21/28a-2 Fyne Oil Zechstein Mobil Tay, Upper JurassCheckshot Y 21/28a-3 Oil Shows Chalk Mobil Tay Checkshot Y 21/28a-4 Oil and Gas Chalk Mobil Tay VSP Y 21/28a-5A Oil Shows Chalk Mobil Tay VSP Y 21/28a-6 Dandy Oil Chalk Mobil Tay VSP Y 21/28b-7 Dry Hole Triassic Unocal Tay VSP Y 21/28a-8 Dandy Oil Tor Monument Tay VSP Y 21/28a-8Z Dandy Oil and Gas Sele Monument No VSP Y 21/28a-9 Fyne Oil and Gas Chalk Antrim No VSP Y 21/28a-9Z Fyne Oil and Gas Sele Antrim No No No 21/28a-9Y Fyne Oil and Gas Sele Antrim No No No 21/28a-10 Fyne Oil and gas Antrim No VSP Y 21/28a-10Z Fyne Oil and gas Balder Antrim No No No 21/21-1 Dry Hole Chalk Mobil Tay VSP Y 21/22-1 Dry Hole Zechstein Texaco SWC VSP No 21/22-2 Dry Hole Zechstein Fina No VSP No Fig. 3.1 Pilot Area Well Database A considerable core database was acquired within the Pilot discovery, see table below. However, core recovery within the main reservoir sand is poor due to its highly unconsolidated nature.

10 [ Table 3.1: Core Recovery Well Core Top Base Cut Recovered MD MD feet % 21/27-1A / / / /27a /27a

11 Well Core Top Base Cut Recovered Seismic Database An extensive seismic database was available for the evaluation, see table below. Survey Processing 2D/3D Notes AR28-91 Original & 2009 Repro 2D Angle stacks available AR28-95 Original & 2009 Repro 2D Angle stacks available F90/21 Original 2D PGS Megasurvey Original 3D Block 21/26 Coverage Western Geco Q21 3D Original 3D Covers 21/27 and 21/28 Western Geco Q21 3D Extension 2011 Reprocessing 3D Extension into 21/21 and reprocessed original area This is shown in map form in Fig 'W 0 00'E 0 04'E 0 08'E 0 12'E 0 16'E 0 20'E 0 24'E 0 28'E 0 32'E 0 36'E 0 40'E 0 44'E 0 48'E 21/26-1D 21/ /27a-5X 21/27a-5 21/ /27a-6 21/ / /2a-2 21/27b- 7 21/27-1A 28/2-1 21/ /28b-7 21/23a-8 21/23a-9 21/ /23a-4 21/24-7Y 21/24-7Z 21/28a-10Z 21/28a-5A 21/28a-2 21/28a-9 21/28a-3 21/28a-4 21/28a-8Z 21/28a-6 28/3-1B 28/4b-1A 21/ / /25 21/ /29a-6 21/29b-7 21/29a-8 21/29a-10Z 21/29a-5 21/29a-3 21/29b-2 21/29b-1 21/29b-4 28/4a Seismic Data Coverage Map m Yellow - Western Geco Q21 3D 1997 Original Blue Tags - Western Geco Q21 3D 1997 Reprocessed 2011 Coordinate System: European Datum 1950 Purple - PGS Megamerge UTM Zone: 31 North Lilac - Western Geco Q21 3D - 28/4 Extension Projection: Transverse Mercator 2D Surveys: F90, AR28-91, AR28-95, Elke Site Survey Red Polygon - 27th Round Application Area Fig. 3.2 Seismic and Well Coverage Map 21/27 21/28 28/2 28/3 21/29b-9 28/ 'N 57 10'N 57 08'N 57 06'N 57 04'N 57 02'N 57 00'N 56 58'N 56 56'N 56 54'N 56 52'N

12 [ 4 Prospectivity Analysis 4.1 Reservoir The Tay Sandstone Formation forms the reservoir in the Pilot and Harbour discoveries and is interpreted as being deposited in a deep-marine, turbiditic environment, as slope-edge fans (Jones, 2003). Reservoir quality is excellent. Within block 21/27, gross reservoir thicknesses of m and net to gross ratios of 85-90% are reported, and porosities average around 34%. Permeability is also excellent. Core plugs from exploration and appraisal wells show permeabilities exceeding 3500 md. The Eocene Tay Sandstone Formation is the proven, primary reservoir target in the area. Although there is the potential for the deposition of Upper Jurassic reservoirs on-block, this is currently seen as high risk, as a number of the salt pillow crests and intra salt-wall Mesozoic pods have been tested by drilling, and Block 21/27a lies outside of the documented Fulmar Sandstone fairway. The sporadic nature of such deposits would also make charge via a long distance model unlikely. Prospective reservoir intervals are therefore seen in the Paleocene and Eocene, where more regional sand fairways exist, providing a proven conduit for long distance migration from the kitchen area to the east. 4.2 Source The Kimmeridge Clay Formation is seen as the primary source rock for the area. However, it is thin or absent on-block, and where present, has not been buried sufficiently to generate hydrocarbons. Long distance migration is thus required to charge any potential structures. Tay Sandstone Member fairways extending westwards from this shelfal area are proven hydrocarbon migration routes.

13 4.3 Seal Throughout the Western Platform, hydrocarbons accur in the uppermost Eocene (and Paleocene) reservoir unit. This suggests that intra-formation seals can be suspect, and the ultimate seal in the area is the regionally extensive Horda Formation claystones. Polygonal faulting in the overlying stratigraphy potentially compromises the integrity of the seal in certain cases; the failure of well 21/28b-7, which targeted the Tay Sandstone Member, is potentially attributable to this mechanism. 4.4 Trap Style Regionally, a number of structural and stratigraphic traps are developed within Eocene (and Paleocene) strata. To the north, the Blakeney, Feugh and Dandy discoveries are all four way dip closured traps that occur due to halokinesis within the underlying Zechstein evaporite sequence. The Elke discovery is similarly underlain by a salt high, although in this case the prospect lies on a NW-SE trending salt ridge. Stratigraphic trapping is also common in the area, particularly in the Eocene Tay Sandstone Formation fairway. Fig. 4.1 illustrates the up-dip westerly stratigraphic trap present adjacent to the 21/27-2 well in Pilot. Seismic Interpretation Inline 1354 (21/27-2 tie) W 21/ /27-1A (Offset) E Top Reservoir Supra Reservoir package Pinch out Base Reservoir Significant post-balder incised channel Balder to Base Reservoir Interval Discrete channelised turbidites. Differential compaction creates minor 4 way dip closures at reservoir level Near Top Balder. Partially eroded/not deposited over area Presentation Title 20 Fig. 4.1 Inline /27-2 Well Tie

14 [ 4.5 Remaining Prospectivity The SE Pilot lead identified by Enquest at the time of licence application does not exhibit a seismic character consistent with hydrocarbon fill. It is therefore suggested that the remaining prospectivity woth the licence is confined to the pre-cretaceous section, where substantial "interpods" are developed. Charge and reservoir development are the main risks for this play.

15 5 Reserves Summary Pilot and Pilot South Volumetric calculations have been undertaken for the Pilot discovery. A most likely STOIIP for Pilot and Pilot South combined of 263 MMstb was estimated, uncertainty assessments suggested a range of +/-8%. This is a relatively narrow range, and reflects the fact the discovery is well appraised and seismic imaging is of high quality. A hydrocarbon pore thickness map was created as part of the volumetric calculations, see Fig Fig. 5.1 Hydrocarbon Pore Thickness Map

16 [ As mentioned previously, the Pilot crude is particularly viscous. There is an extensive database of samples from RFT, well test, extraction from cuttings and estimates from NMR. The quality of the oil property estimates is variable to say the least. However, the last sample taken in the field, from well 21/27a-6, appears to be the most robust. The well's sole purpose was to obtain a sample for viscosity measurement, this yielded a best estimate of 409 centipoise at 87 degf and 1200 psig (reservoir temperature and pressure) following addition of a demulsifier. Other samples are of sufficient quality to be confident that there is a significant variation in viscosity within the discovery, with heavier oil being present in the 21/27a-5X well, and lighter oil to the south. A range of different viscosity models were used in the dynamic modelling work. Flow simulation work suggests a recovery factor of around 13% is possible, assuming long horizontal wells, water injection and an unconstrained liquid production rate. Harbour The volumes associated with the Harbour discovery (21/27-1A) are minor, around 9 MMstb STOIIP and 2.2 bcf GIIP are estimated. Flow simulation was not conducted for this accumulation. Some previous studies have suggested some continuity of hydrocarbon columns between Pilot and Harbour. This is not interpreted to be the case, rather a series of minor hydrocarbon accumulations in low relief 4 way dip closed features appear to be present, based on seismic response.

17 6 Clearance EnQuest gives permission for this report to be published.

18 [ 7 References Jones, E., Jones, R., Ebdon, C., Ewen, D., Milner, P., Plunkett, J., Hudson, G., and Slater, P Eocene in The Millenium Atlas: petroleum geology of the central and northern North Sea. Evans, D., Graham, C., Armour, A., and Bathhurst, P. (eds). Geological Society of London.