Serica Energy (UK) Limited. P.1840 Relinquishment Report. Blocks 210/19a & 210/20a. UK Northern North Sea

Transcription

1 Serica Energy (UK) Limited P.1840 Relinquishment Report Blocks 210/19a & 210/20a UK Northern North Sea January 2013

2 1 Header Licence: P.1840 Round: Licence Type: 26th Round Traditional "Drill-or-Drop" after two years Block: 210/19a & 210/20a Operator/Partner %: Serica Energy (UK) Limited 100% Firm Work Programme (*): Contingent Work Programme (*): The Licencee shall obtain 485 km 2 of 3D seismic data. The licencee shall either (a) drill one well to 2390m or 30m below the top Dunlin Group, whichever is the shallower, or (b) elect to allow the licence to automatically cease at the end of the initial two-year "drill-or-drop" period. 2 Synopsis The P.1840 licence was awarded in the 26th Round as a Traditional Licence with 10th January 2011 as start date (Figure 2.1). The licence was awarded to Serica 100%. 0ᵒ 36 0 E 0ᵒ 48 0 E 1ᵒ E 1ᵒ E Field 61ᵒ E Serica 210/19a & 20a Home Sand North SE 61ᵒ E Brent East Home Sand North Brent South SW 61ᵒ E 0ᵒ 36 0 E 0ᵒ 48 0 E 1ᵒ E 1ᵒ E Figure 2.1 Blocks 210/19a and 210/20a (P.1840) Location Map 1 Header 1

3 Firm work commitment consisted of: 1. Obtaining 485 km 2 of 3D seismic data, and 2. A drill or drop commitment stating that the licensee shall either (a) Drill one well to 2390m or 30m below the top Dunlin Group, whichever is the shallower, or (b) Elect to allow the licence to automatically cease at the end of the initial two-year "drill-ordrop" period. The seismic work commitment was fulfilled and well planning was undertaken with the aim of drilling the SW Prospect, an analogue for the UK Northern North Sea Causeway Discovery. Technical studies undertaken on this prospect, such as amplitude studies aimed at identifying hydrocarbon-bearing reservoir, and fault seal studies aimed at reducing containment risk, were inconclusive. Despite Serica's efforts to attract a drilling partner, the SW Prospect remains undrilled, as do a number of other prospects in the block. Consequently, Serica elected to drop the licence in January Exploration Activities Serica has purchased a large volume of seismic data over the licence and adjacent areas, which more than satisfies the 3D seismic work commitment. These datasets have been merged and amplitude balanced to allow licence prospectivity to be put into a more regional framework. The seismic dataset is shown in Figure 3.1 and consists of: Western Original Processed Q D seismic survey covering the licence and surrounding areas: 320 km 2 Western Reprocessed Q D seismic survey covering the licence only: 184 km 2 Total-Fina Fugro Processed D seismic survey covering the Field and area to the north: 165 km 2 amplitudes balanced qualitatively across merge. Note Fugro data is a lot noisier Figure 3.1 Seismic and Well Database over Licence Area Serica wells (14 of 17 tied by 3D) Licence P1840 Fields & discoveries 3D data: time slice at 1.972s ( OWC) 2 Synopsis 2

4 In addition to the seismic data, Serica purchased well logs (wireline data) from all released exploration and appraisal wells drilled in the blocks and adjacent blocks. Fourteen of these seventeen wells are tied to the 3D seismic data. Most of the prospects and leads were adequately identified and mapped at the time of application, but their absolute and relative risks (and ranking) were not sufficiently defined. After evaluating all available data, post-award work focussed on: confirming the updip pinchout of the Upper Jurassic Home Sand Prospect, defining the continuity and fault juxtapositions of the faults that are interpreted to separate the Field (in Block 210/15 to the north of Serica's acreage) from the Southwest and Southeast prospects at Brent Sandstone (Middle Jurassic) level, evaluating the feasibility and value of acoustic impedance inversion (for fluid and lithology), and coherency volumes or spectral decomposition (for fault interpretation and Home Sand channel definition). 4 Prospectivity Analysis Serica's technical evaluation of the licence supports prospectivity at two stratigraphic levels, the Middle Jurassic Brent Sandstone and the Upper Jurassic Home Sandstone. Middle Jurassic Brent Sandstone 1. SW and SE Prospects The SW and SE Prospects are downthrown hanging-wall structural traps with well-defined reservoir, source and migration pathways (Figure 4.1). Top Brent: Depth 2011 Brent Depth Field SW Prospect SE Prospect terrace divided by cross-faults into several segments Brent E Prospect Brent S Prospect Figure 4.1 Top Brent Depth Structure Map showing SW, SE, Brent East and Brent South Prospects 3 Exploration Activities 3

5 Reservoir - The reservoir comprises fluvio-deltaic to shoreface sandstone of the Brent sequence which is widespread in this area. The best intervals are the older, channelized Etive Formation sandstone (if there is sufficient relief on the prospect) and channelized Ness Formation sandstone. The younger transgressive Tarbert Formation sandstone is also good quality in this area. Source - Rich, mature Kimmeridge Clay source rock is proven by numerous wells in close proximity to the licence with the main oil kitchen lying to the east. Migration pathways - The charge model is proven regionally and locally by the neighbouring Oil Field, located up-dip immediately north of the SW and SE prospects. Oil shows in several wells eleven to twelve kms from the known mature source kitchen indicates long-distance migration is possible with migration via sandstone interbeds within the Kimmeridge Clay, and "fill & spill" through the deeper Brent Sandstone fault blocks to the south-east. SW Containment - The SW Prospect is a downthrown hanging-wall structural trap. It is separated from the SE Prospect by a large-throw fault, with cross-fault (hanging-wall) seal provided along the north-eastern edge of the prospect by Lower Jurassic (Dunlin Group) shales (Figure 4.1, Figure 4.2 and Figure 4.3). Similar cross-fault (hanging-wall) seals with Brent Sandstones juxtaposed against the Dunlin Group are proven in the Western Isles (Rinnes-Melville) discoveries, which is the analogue for the SW Prospect. Fault Seal Analysis involving a seal assessment using published calibrations between seal capacity and shale gouge ratio predicts that the north-eastern edge of the prospect will be sealing. The spill point for the prospect is interpreted to be 2260m. Brent South SW SE Field NE Legend KCF Home Sand Base J71 Heather Brent Dunlin Zechstein Figure 4.2 SW-NE Seismic Line through SW and Brent South Prospects SE Containment- SE is a fault compartmentalised prospect consisting of three downthrown hanging-wall structural traps with Brent Sandstone against Brent Sandstone crossfault seals (Figure 4.1, Figure 4.2 and Figure 4.3). Although considered to be the main prospect risk, these cross-fault seals have been proven by recent drilling to be present in the UK Northern North Sea Causeway Discovery, which is the main analogue for the SE Prospect. The spill point for SE is mapped at 2520m and is interpreted to be separate from the southern tip of 4 Prospectivity Analysis 4

6 W E SW SE Home Sandstone North Channel Legend KCF Home Sand Base J71 Heather Brent Dunlin Zechstein Figure 4.3 W-E Seismic Line through SE, SW and Home Sandstone North s 0 2km the Field by a W-E trending fault which offsets Brent against Dunlin in east but gets smaller westwards requiring Brent-Brent fault seal. Fault seal analysis has failed to reduce the risk on seal integrity in the SE Prospect. 2. Brent East and Brent South Prospects The Brent South and Brent East prospects are conventional tilted fault blocks which are clearly defined on 3D seismic data. The Field, 10 km away, is both the reservoir analogue and structural analogue for these prospects. As with the SW and SE prospects above, reservoir is provided by the Brent Group sandstones. Charge is from mature Kimmeridge Clay Formation, via up-dip migration from the basin to the east, and proven by the producing Field. Brent East Containment - Structural closure for the prospect is at 2520m, with a deeper structural closure interpreted at 2560m, if the NE-SW trending bounding fault seals against the Brent in the hanging wall. Thick Heather Formation shales provide proven regional top seal to the traditional tilted fault block Brent Sand play. This top seal is proven locally by the Field (Figure 4.1 and Figure 4.4). Brent South Containment - The prospect is dip closed down to 2200m without invoking a Brent- Brent seal on a small NW trending fault (Figure 4.1 and Figure 4.2). Maximum closure is constrained by sealing along this NW trending fault and Top Brent at 2243 m in the 210/20-1 dry hole. As with the Brent East Prospect, top seal is provided by the Heather Formation Shales. 4 Prospectivity Analysis 5

7 W E Brent East SW Legend KCF Home Sand Base J71 Heather Brent Dunlin Zechstein 0 2km Figure 4.4 W-E Seismic Line through SW and Brent East Prospects Upper Jurassic Home Sandstone Home Sandstone North Channel and Home Sandstone South s The Home Sandstone Member is a late Jurassic (Volgian) age sandstone encased within the Kimmeridge Clay Formation. It is locally derived from the East Shetland Platform to the west and is slightly younger than the Magnus Sandstone Member, which is itself derived from the NE and thins into the licence blocks. The two Home Sandstone channel prospects are well-defined high impedance units at the base of and within the Kimmeridge Clay Formation shales (J70 sequence) (Figure 4.5 and Figure 4.3). Rock Physics modelling was undertaken on these Home Sandstone amplitudes with the aim of determining fluid fill. However, the results are inconclusive as the AVO gradients were modelled to be similar for both oil and brine cases. Whilst AVO is not a useful technique here for discriminating fluid fill, the amplitudes have been used to predict the presence of the Home Sandstones and its likely thickness, and hence have reduced the risk on reservoir presence. Reservoir - The Home Sandstone comprises slope channel deposits trending NW-SE across the blocks, with porosities as seen in nearby wells of 25-30% and multi-darcy permeability. Source - Rich, mature Kimmeridge Clay Formation source rock is proven by wells in close proximity to the licence within the main oil kitchen lying to the east. Migration Pathways - The Home Sandstone channel prospects are interpreted to be charged via the SW prospect through cross-fault migration, when the SW prospect and the Home Sandstones are potentially juxtaposed across a NE-SW trending fault. Charge (migration) is considered to be the main risk for these prospects. Containment - The Kimmeridge Clay Formation provides regional top-seal and stratigraphic sideseal for the Home Sandstone channel prospects. This seal is proven locally by the Cladhan Discovery, and by the Magnus Field, Tybalt Discovery within the UK Northern North Sea. 4 Prospectivity Analysis 6

8 Base J71 Amplitude Map Field Base J71 Depth Map Field Home Sand North Home Sand North Home Sand South Home Sand South Home Sand Main Channel Figure 4.5 Base J71 Amplitude and Depth Maps to show Home Sandstone s 5 Reserves Recoverable resource estimates and geological risk for all prospects in the licence, based on Serica in-house evaluations, are tabulated below: Prospect Recoverable Resources (mmbo) P 90 P 50 P 10 Chance of Success (%) SW SE (north) SE (central) SE (south) Brent South Brent East Hone Sandstone North Channel Home Sandstone South Channel A location map showing all the prospects above can be found in Figure 2.1 and the relevant seismic sections are shown in Section 4 Prospectivity Analysis. 4 Prospectivity Analysis 7

9 6 Clearance It is hereby confirmed that DECC is free to publish the results contained in this relinquishment report and that all 3rd party ownership rights have been considered and appropriately cleared for publication purposes. 6 Clearance 8