1 Licence Number and Block Details

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2 Licence Number and Block Details 1 Licence Number and Block Details Table 1.1: Licence details. Licence Number: P1343 Licence Round: 23rd Round Licence Type: Traditional Block(s): 43/30b, 48/05a & 49/01b Table 1.2: Consortium details: Companies Equity (%) GDF Britain Ltd (Operator) Tullow Oil UK Ltd Endeavour Energy UK Ltd Shoot 45 km of long-offset 2D seismic data Carry out AVO, RAI and AI studies Work programme (Part 1) 2 Synopsis Following completion of the work programme, the licence area was surrendered in December 2007 at the end of the Initial Term. De-risking for the presence and position of reservoir sands in the identified leads from the results of the completed work programme, both seismic inversion and geological analogue studies, proved insufficient to proceed to a second term. 1

3 Exploration Activities 3 Exploration Activities The licence area is fully covered by 3D seismic surveys acquired between 1995 and 1999 and processed inhouse by Shell in 2001 as a pre-stack depth migration (PreSDM). A depth version of the data was used in structural mapping for the licence application, and the mapping methodology has subsequently remained essentially unchanged. It was recognised at the time of the application, however, that the cable length of between 3000m and 3600m of the 3D seismic surveys used as input for the PreSDM processing was suboptimal for sub-salt imaging and AVO studies, hence the work programme included the acquisition of 45 km of TGS long-offset 2D seismic data across the licence area. The TGS Nopec NSR05 2D data comprised four lines orientated southwest - northeast, with offsets of up to 8000m (NSR ; NSR ; NSR ; NSR ). Initial data quality proved to be disappointing, and dedicated reprocessing resulted in only a marginal data improvement. Parameter testing was carried out on line NSR , and an optimised processing sequence applied to all four lines. A 2D PreSDM trial resulted in improved imaging of the basal Zechstein event, but poor resolution at Carboniferous level. Character and event continuity of the Carboniferous section proved to be inferior to the 3D data, despite the long-offset contribution. Angle stacks of 5-15, and 25-35, together with PreSTM gathers, were generated to allow AVO analysis, but provided no conclusive evidence for AVO behaviour in the Carboniferous indicative of reservoir development. A key 2D line was converted to relative acoustic impedance (RAI) and compared with the equivalent line from the Shell PreSDM 3D data. A good quality tie to the 44/27-1 well had been achieved on both the 2D and 3D data. However, due to the poor response from the Carboniferous on the 2D data, there was virtually no additional information gained over the Stephanian target zone on the RAI section. The 3D was of better quality and it was possible to distinguish the tight sandstone in the Boulton Formation of the 44/26c-6 well (hard response) from the underlying shale (soft response). It was noted that a similar response was seen to the south of the salt wall on the southern flank of the Stephanian play fairway. The acoustic impedance volume had been calibrated to eight wells in the vicinity. However, due to the low frequency overlay that this introduced, it was not possible to see any meaningful response below the basal Zechstein evaporites in the potential target interval. It was concluded that an acoustic impedance volume in this situation added nothing to the interpretation process. Offshore geological analogue studies included reviewing available offset well data from the Silver Pit Basin with reference to GDF Suez's expanding chemostratigraphic and palynological database for Westphalian C/D and possible Stephanian sections. It is noteworthy that no younger Carboniferous penetrations appear to have been encountered than were available at the time of the licence appliation, hence no additional evidence for Stephanian prospectivity has come to light in the Silver Pit Basin. Onshore analogue studies centred largely on a field excursion in May 2006 to the Late Westphalian / Stephanian of the West Midlands (United Kingdom) organised by Besly Earth Science Limited with the participation of representatives from all licence holders. This allowed examination of the Westphalian C Etruria Formation and Westphalian D Halesowen Formation near Newcastle-under-Lyme and the Stephanian Salop Formation in the Wyre Forest area. While the Etruria Formation is the age equivalent of the Ketch Formation, the Halesowen is the direct correlative of the Boulton Formation. The Salop Formation can be considered as correlative of the younger formation that overlies the Boulton Formation, hardly penetrated and unnamed in the UK sector and forming the upper part of the Step Graben Formation in the Dutch sector. With the exception of the Halesowen Formation, exact correlations are uncertain, as the late Carboniferous succession is preserved in widely separated erosional relics in the cores of Variscan synclines, which preserve isolated fragments of different depositional systems. Sand bodies within the Salop Formation have similarities in depositional style and net-to-gross ratio to those in the 2

4 Exploration Activities Ketch Formation reservoirs in the Silver Pit Basin, and may provide partial analogues for potential Stephanian reservoirs within the licence area. Reservoir connectivity of the Lower Ketch play was reviewed based on available well and field data from the Silver Pit Basin 4 Prospectivity Analysis Reservoir: Potential reservoirs lie in the Carboniferous Conybeare Group and range in age from Westphalian B to Stephanian. These are preserved below the Saalian Unconformity (Fig. 4.1) in a major synform bounded by NNW-SSE trending faults. The deepest reservoir of interest is the basal Westphalian B Murdoch Sandstone, represented as silty mouth-bar deposits overlain by stacked, low sinuosity channels. In the A, G and I leads, the main reservoir comprises Westphalian C/D Lower Ketch sands, which are believed to have been deposited in low sinuosity braided channels on a low-relief alluvial plain with a northern provenance. Fig. 4.1 Base Permian Unconformity depth map (ft TVDSS). Contour interval 100 ft 3

5 Prospectivity Analysis Sediments of Late Westphalian D - Stephanian age are considered as potential reservoirs in the Area 1, 2, 3/4 and 5 leads, where a section of up to 800 ft thickness younger than the Boulton Formation in the 44/26c-6 well is indicated from seismic mapping. Source: Coal beds of the Westphalian A Caister Coal Formation and Westphalian B Westoe Coal Formation provide a locally mature source rock. Additionally, coals in the Late Westphalian D section may provide a mature source. Seal: All the identified leads within the licence area rely for a seal on halites and shales of the Silverpit Formation directly overlying the Base Permian Unconformity. The possible local presence of Lower Leman Sandstone does not invalidate seal integrity, but the sandstone may act as a thief zone. Within the Carboniferous, additional sealing may be provided by shales within the Upper Ketch and Boulton Formations and by intra-stephanian shales. Trap type: Three Lower Ketch leads (A. G and I) and four leads from the Westphalian D /Stephanian play (Areas 1, 2, 3/4 and 5) were identified, and are indicated in Fig The Lower Ketch leads show dip / fault closure at the Base Permian Unconformity, possibly enhanced in the case of the G and I leads by a shale-prone Upper Ketch top seal. A Westphalian D / Stephanian reservoir bounded by surfaces 1845 ft and 1745 ft above the Top Upper Cleaver Formation and truncated by the Base Permian Unconformity is assumed in the definition of the other four leads. These rely on both an intra-carboniferous seat seal and an intra- Carboniferous top seal, in combination with the Base Permian Unconformity. Fig. 4.2 West Schooner leads map. Lower Ketch leads are shown in magenta and Westphalian D / Stephanian leads in orange. 4

6 Reserve Summary 5 Reserve Summary P50 GIIP figures remain unchanged from those quoted in the application document, namely 47, 19 and 62 bcf for the A, G and I leads respectively and 47, 167, 97 and 22 bcf for the Area 1, 2, 3/4 and 5 leads respectively. These used representative Lower Ketch reservoir parameters and a gas expansion factor from the close offset Schooner field. Risking of the Lower Ketch leads likewise remained unchanged at a Probability of Succcess of 0.42, 0.33 and 0.39 for the A, G and I leads respectively. In the case of the Westphalian D / Stephanian leads, however, minor derisking resulted in a Probability of Success ranging from 0.08 to Figures Figure 4.1: Base Permian Unconformity depth map (ft TVDSS) Figure 4.2: West Schooner leads map 7 Publication Clearance Both GDF Britain Ltd, as operator for the P1343 licence, and Tullow Oil UK Ltd and Endeavour Energy UK Ltd partners confim that DECC is free to publish this report and that third party ownership rights have been appropriately cleared for publication purposes. 5