Licence P1524 Relinquishment Report. RWE DEA June 2011

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1 1. Header Licence Number: P1524 Licence Round: 24 th 2007 Licence Type: Promote Blocks: 42/2b, 42/3, 42/4 Licencees: RWE Dea UK SNS Limited 70% (Op), Sterling Resources (UK) Limited 30% Work Programme: Reprocess 500 km of 2D seismic data. Drill or drop commitment at the end of Year 2 to drill a well to penetrate the Scremerston Formation (2600m). 2. Synopsis Licence P1524, comprising blocks 42/2b, 42/3 and 42/4, lies at the southern margin of the Dogger Shelf, to the north of the Breagh field (Figure 1). It was awarded in 2007 in the 24 th Licence Round. The firm work programme was to reprocess 500km of 2D seismic data, with a drill-or-drop decision at the end of Year 2. Following the mapping of the 2D seismic in 2009 it was concluded that the existing 2D seismic coverage was insufficient to determine if drilling of the Darach feature was warranted. This was due to its low structural relief and potential multiple culminations (Figure 2). Subsequently, it was agreed with DECC that the Licence could be continue into the second phase of the Initial Term by acquiring a new 3D seismic grid, with an associated contingent well obligation. 480 km 2 of 3D seismic data were acquired in August 2010 and processed by SIP to PreSTM (Figure 3). In addition, acoustic impedance inversion was done to try and differentiate between coals and limestones, within the Lower Carboniferous section, to aid the stratigraphic interpretation. As the 3D dataset did not include any well, a total of 25 2D seismic lines of various vintages (533 km) were also re-processed by SIP to provide well ties for the 3D seismic dataset (Figure 4). Interpretation and mapping of the new seismic data showed the Darach prospect to be a very low relief structural feature, with a combination top seal comprising Base Namurian shales (unproven effectiveness) and Zechstein evaporites. Closure to the northwest is weak. Hydrocarbon migration modelling indicates that any charge from the source kitchen to the south of Breagh / Crosgan is likely to bypass the Darach prospect area. Given the low relief closure, small GIIP volumes and concerns regarding charge, drilling of Darach was not warranted and the licence was surrendered with effect from 31/03/ Exploration activities The exploration activities carried out during the second half of the Initial Term of the licence were as follows: (1) Acquisition and processing of 480 km 2 of 3D data to PreSTM CGG acquired the 3D seismic survey in July/August 2010 (Figure 3).This was then processed by Seismic Image Processing (SIP) to PreSTM. Additional acoustic impedance inversion Page 1 of 10

2 processing of the 3D dataset was carried out to help in differentiating between coals and limestones within the Lower Carboniferous sequence. (2) Reprocessing 533 km of 2D data to PreSTM. There are no wells within the area of the new 3D dataset. Some 533 km of 2D data were therefore also reprocessed to provide a consistent dataset for tying in the offset wells (Figure 4). (3) Detailed Interpretation of the PreSTM dataset All of the significant Base Zechstein closures have been drilled in the immediate vicinity of licence P1524. Consequently, the remaining prospects / leads are formed by traps that rely on a combination of intra-carboniferous dip closures that subcrop the Base Zechstein at the Base Permian Unconformity (BPU). A basinal shale at the base of the Namurian may provide a top seal to any reservoir sandstones within the underlying Visean section (Figure 5). Extensive regional 2D interpretation has been carried out over the Greater Breagh area, which includes licence P1524. Figure 6 is a SW-NE oriented reprocessed 2D line that ties well 42/9-1 to the south of the licence area. The seismic shows that a significant event can be interpreted just beyond the TD of well 42/9-1. This event is interpreted as being Base Namurian and appears on the seismic as a strong trough above a series of black peaks. This Base Namurian marker has been mapped across the area and tied into wells that penetrated the deeper Visean section. To aid the depth conversion, eight seismic horizons were interpreted over the 3D dataset, from Seabed to Base Zechstein (Figure 7). Although this line is located on the northern flank of Darach, it serves to demonstrate the benign nature of the post BPU overburden and the gentle, persistent, shallowing of the Base Zechstein seismic event from SE to NW. In this area the Rotliegend is absent, so the Zechstein overlies the Carboniferous directly across the BPU. Well defined, dipping, intra-carboniferous events can be seen beneath the BPU and two prominent events were interpreted: Base Namurian, tied into the regional 2D interpretation and The deeper Fell Sandstone Figure 8 is a Base Namurian TWT map - a combined surface, with Base Zechstein completing the map in the areas where the Base Namurian subcrops the BPU. Over Darach, the Base Zechstein, is very flat and low relief, with minimal closure of 10 to 15 milliseconds and an obvious spill point to the northwest. (4) Hydrocarbon migration and charge studies A number of charge models were run to determine whether the Darach area could be charged. The most likely direction for charge is from the major source kitchen to the south of Breagh / Crosgan. Modelling indicates that when Breagh is overfilled it spills northwards via blocks 42/8 & 42/3, passing to the west of Darach. Charge from the west was also considered but again the model shows Darach to be bypassed. Charge from the east may be possible but there is a risk of diversion of charge towards Crosgan / Breagh, which would result in the Darach area being in a possible migration shadow. In summary, the Darach area appears to be in an unfavourable location as regards access to charge. Page 2 of 10

3 4. Prospectivity analysis The primary play on P1524 are channel sandstones in the Carboniferous Yoredale Group, which form the main reservoir in Breagh to the south (Figure 9), sealed by Zechstein evaporites (proven) and intra-carboniferous shales (unproven). Source rocks are Namurian- Westphalian shales and coals from the Silverpit Basin to the south of Breagh. 4.1 Darach Prospect Darach is dependent on mapping a structure that combines dipping Base Namurian/Intra Carboniferous events that subcrop the Base Zechstein across the BPU (Figure 10). The Base Zechstein shows very weak low relief closure but this is enhanced beneath the Base Zechstein where the Base Namurian rolls over and subcrops the Base Zechstein on the flanks of the structure to the NE and SW. However in a NW-SE orientation (inline) on the 3D dataset the trapping mechanism is more difficult, with minimal dip closure shown on the PreSTM beneath a benign overburden (Figure 11). The lack of structural closure to the northwest is further demonstrated by a NW-SE arbitrary line (Figure 12). This line runs through the flat lying, low relief core of Darach in block 42/4 and across the critical spill point area to the northwest into block 42/3. No interpretation has been applied but the tie points to the 3D interpreted seismic are marked by appropriately coloured dots. This arbitrary line shows clearly the Base Namurian (red) subcropping the Base Zechstein (yellow) in the southeast. Overall the strata climb updip to the northwest. This is particularly clear at the Fell Sandstone level (pink) where the reflector rises steadily to the northwest, through a series of small anticlines. When the Base Namurian is depth converted, the resulting map (Figure 13) shows a small tight (realistic) closure at 7600 feet of 7.43 km 2 with a very small crestal area at 7400 feet in block 42/4. A larger, amorphous, closure at 7700 feet has an area of km 2 but this is very flat, and has major spill point problems to the west and northwest into Block 42/3. 5. Resources Summary Darach Prospect COS Mean P90 P50 P10 Whole Structure 11% GIIP (bcf) Table 1 Darach - Prospective GIIP Resources (bcf) 6. Clearance All of the seismic data contained in this report has either been shot and processed or purchased and reprocessed by the P1524 licensees and is therefore proprietary. The P1524 licensees have given their permission for the publication of these data. Page 3 of 10

4 7. Maps & Figures P /2b,42/3,42/4 Figure 1 Map showing the location of Licence P1524. Minimum GRV Figure 2 Base Zechstein Depth structure map (Oct 2009) based on 2D interpretation. Page 4 of 10

5 42/4 Base Zechstein Depth Map 2D Dataset (March 2010) C.I. 50ft Survey Area Full Migration Figure 3 Darach 3D Survey Area over Blocks 42/3 and 42/4, acquired July Darach 3D 43/1 and 43/6-1 2D 43/6-1 3D Breagh 3D Crosgan 3D Figure 4 Darach 2D Reprocessed dataset and ties into Block 42/4. Page 5 of 10

6 Operator : Scale : 1: /15 1 Zechstein Depth GR 0 _ DT 140 _ 40 Operator : Scale : 1: /10A 1 Operator : Depth GR 0 _ DT 140 _ 40 41/10 1 Operator : MARATHON OIL UK LTD Scale : 1:4000 Depth GR DTLN 0 _ _ Namurian Scale : 1:4000 Depth GR 0 _ DT 140 _ ??? MLF Basinal Shale MLF Visean LLF DARACH /10 42/10a / /9 41/15 Figure 5 Regional Well data tie of Base Namurian. SW NE Darach prospect Base Namurian P1524 Figure 6 Reprocessed SW-NE 2D seismic line KM C tying 42/9-1 and correlating into block 42/4. Page 6 of 10

7 NW SE Top Chalk Base Chalk Top Bunter Top Zechstein Base Z h t i Base Fell Sst Figure 7 NW-SE Darach 3D Inline 1550 on the northern flank of the Darach structure. 42/4 C.I. 25msec Figure 8 Base Namurian TWT structure map, Darach 3D interpretation. Page 7 of 10

8 Kupf ersch iefer P7 P6b P6a P5b VG (-34) MM1 (-20) DA1 MP (-60) TD (-30) RN (-20) GV (-30) VG MM1 DA1 MP TD RN Oxford Limestone Dun Limestone true true True true true 3 mmscf/d 1 60/64" choke Breagh 42/13-2 Formations Reservoir Packages Zechsteinkalk Chemostrat Palyonology Uncertainty GR & Lithology MDbrt (ft) 7350 AT ohmm 200 RHOZ AT g/cc ohmm 200 NPHI DT AT90 45 dec µs/ft ohmm Palyonology Limestones TVDss (ft) 7200 Chronostratigraphy Lithostratigraphy (Onshore) Lithostratigraphy (Mid North Sea High) Stage Substage Group Formation Group Formation Namurian Visean Arnsbergian Pendleian Brigantian Asbian Yoredale Alston Tyne Limestone Farne Upper Limestone Middle Limestone Lower Limestone Scremerston Limestone Marker Beds Great Limestone Oxford Limestone Dun Limestone Breagh Reservoir Zones Zone 1 Zone 2, 3 & Holkerian Arundian Chadian Border Fell Sandstone Fell Sandstone 7750 Tournasian Courceyan Cementstone Cementstone Core Perforations Middle Limestone Lower Limestone DST Upper Channel Sands Upper Limestone/Mudstone Twin P eaks Limestones Oxford Twin Peaks Zone 1 Zone 2 DST 1 Lower Mixed Marine/Mire/Clastics Zone 3 Reservoirs Channel Sandstones in the late Visean & Lower Namurian (Low NG) Source Rocks Namurian-Westphalian shales and coals in Silverpit Basin Top Seal Zechstein evaporites (Proven) and intra-carboniferous shales (Unproven) Lower Clastics Zone Dun Figure 9 General Carboniferous Stratigraphy for Greater Breagh Area. Page 8 of 10

9 SW NE Base Namurian Fell Sst Darach Prospect Figure 10 Darach 3D interpreted crossline3050 across crest of structure. SE NW Base Namurian Fell Sst Darach Prospect area Figure 11 Darach 3D interpreted Inline 1300 across southern flank of structure. Page 9 of 10

10 SE NW Base Namurian subcrops Base Zechstein Figure 12 Arbitrary NW-SE Darach 3D line through core of structure showing general dip from NW to SE. Spill point area 42/4 Max closure of 7700ft from Realistic Closure of 7600ft from C.I. 50ft Figure 13 Base Namurian Depth structure map over Darach Prospect, Block 42/4 (Jan 2011). Page 10 of 10