Abstract Tullich Field, operated by Kerr-McGee Oil (UK) plc with 100% interest, lies in UK block 9/23a, to the southeast of Gryphon, and to the east of the Harding fields. The field is a subsea tie-back from a central manifold to the Gryphon ‘A’ FPSO (floating production, storage and offloading) facility. The southern part of the field was discovered by Hamilton in 1991–1992. Well 9/23a-27 and its sidetrack encountered thin oil and gas bearing sandstones of Lower Eocene age from the Balder Formation, which tested 570 bpd of 25.8 degree API oil. Kerr-McGee recorded a 3D seismic survey over the area in 1990, and in 1999 acquired a 3D OBC seismic survey over the Gryphon Field and the northern part of block 9/23a. The similarity of the inverted shear wave seismic data over the Gryphon Field and the northern part of block 9/23a was the catalyst for the further exploration and appraisal of the area. This led to an exploration drilling programme in 2001, which included the acquisition of full waveform shear sonic data and core. In July 2001, a separate discovery was made by Kerr-McGee with the drilling of 9/23a-29A, to the north of the 9/23a-27 wells. Thick oil bearing sandstones of excellent reservoir quality were encountered in the Balder Formation. The field was delineated between July and December 2001 by sidetracking 9/23a-29A and drilling the 9/23a-31 well. From a windowed extraction of peak amplitudes of the shear seismic data, it was noted that at Gryphon the high amplitudes corresponded to the presence of thick reservoir sandstones, whilst at Tullich it appeared that the high amplitudes related to a non-reservoir argillaceous sandstone sequence rather than the much thinner reservoir sandstones. These reservoir sandstones lie at different stratigraphic levels in the B2 unit of the Balder Formation but appear to be sufficiently in communication to act as a single reservoir unit. They are currently interpreted as sandstones deposited by turbidity currents which pinch out against the plunging nose of the Crawford Ridge. In order to take advantage of synergy with other work in the Gryphon area, a tight timeframe was imposed on the project. A four-well development drilling programme began immediately once the Department of Trade and Industry had given their approval of the Field Development Plan (FDP) in March 2002 and was completed by October 2002, with first oil achieved at the end of August 2002.

Abstract The Marathon-operated West Brae Field straddles Blocks 16/06a and 16/07a in the UK Central North Sea approximately 140 miles (225 km) NE of Aberdeen. The field was discovered in 1975 with drilling of exploration well 16/07-2. The West Brae reservoirs consist of Eocene Balder Formation and Upper Sele Formation Sandstones that were deposited in NW-SE trending submarine channels across the area. Development of the field commenced in April 1997 with first oil being achieved in October the same year. The field has been developed using sub-sea tie-back to the Brae A platform, which lies 5.6 miles (9 km) SE of the sub-sea manifold. Recoverable reserves are estimated to be 60 MMBBLs, of which some 23 MMBBLs had been produced by 31 December 1999.

Abstract A seismic stratigraphic analysis constrained by well and wireline log data has been undertaken on the Paleocene and earliest Eocene succession of the South Buchan Graben (Quadrants 20 and 21), Outer Moray Firth Basin (OMFB). Two principal sequences have been described relating to two regressive/transgressive second-order cycles of relative sea-level change. The Maureen, Andrew, Glamis Tuff and Balmoral sandstone members are expressed as a stacked set of lowstand basin floor fans separated by mudstone intervals representing four cycles of third-order relative sea-level change. The Sele and Balder formations contain both basinal and shelfal packages as an expression of two cycles of third-order relative sea-level change. The Forties Sandstone Member is deposited within highly mounded, levee-confined channels downlapped by a prograding slope succession with well-defined clinoforms and deltaic topsets attributed to the Dornoch and Beauly formations. The individual parasequences of the prograding wedge are related to higher-order eustatic fluctuations with incision and slope fans, attributed to the Cromarty Sandstone Member, deposited during periods of relative sea-level lowstand. It is demonstrated that through the integration of lithostratigraphic, seismic geomorphological and sequence stratigraphic analyses an understanding of depositional environments and the distribution of facies within them can be obtained. The identification of basinal and slope features with reservoir potential, along with an understanding of their chronostratigraphic relationship to sealing facies, play an important role in regional play fairway mapping and risk analysis in this area and beyond. Future prospectivity within mature basins, such as the OMFB, relies on subtle stratigraphic traps typical of lowstand systems tracts, where the main risk is associated with reservoir quality and containment.