In the mature Frigg/Heimdal area, located in Quadrant 25 in the Norwegian sector, ten discoveries have been made. Most of the area is covered by 3D. Such a dense database has proven favourable to multidisciplinary and Integrated approaches. The Integrated approach is the key to the evaluation of small petroleum accumulations at the Brent level in the area. The current geological model for the Brent Gp is based on High Resolution Sequence Stratigraphy, a method integrating a consistent biostratigrapical framework, coal petrography and coherent reservoir zonation and correlation. Improved techniques in organic geochemistry has enabled the definition of the origin of the reservoir hydrocarbons.
Detailed well information including ‘Diamage’ (core/electric log correlation), VSP and Walkaway VSP is of indisputable importance for well/seismic calibration and the seismic interpretation. The detection of subtle structural and stratigraphical features by seismic horizon attribute displays has been implemented on the new generation of work stations-SISMAGE@', the meeting point to merge the results from the different geo-disciplines involved in the Integrated approach. The various approaches together with improved 3D acquisition and processing have demonstrated that they, in an integrated form, contribute not only to reduce the timeframe for the exploration/appraisaI/development phase but also to lower the risk.
INTRO DUCTI0 N The FriggJHeimdal area, which bas reached a mature phase of exploration, is located in Quadrant 25 in the Norwegian sector of the North Sea (Fig. i) and consists of five blocks: 2511, 2512, 2513, 25/4 and 25/5, operated by Elf Petroleum Norge AIS. Since the allocation of the first blocks in 1969 (25/1 and 2) ten discoveries have been made. Most important are the Tertiary gas/condensate discoveries Frigg (183 billion Sm3 reserves) Heimdal (33 billion Sm3 reserves), North East Frigg and East Frigg made in the early seventies. They made up an important reserve basis (230 billion Sm3 of gas + condensate) on the Norwegian shelf.
The main reservoirs are of Early Eocene to Early Paleocene and Middle Jurassic age. Most important are the Frigg Formation (Early Eocene) and Heimdal (Late Paleocene) sandstones being part of a complex Paleocene/Lower Eocene submarine fan, deposited in the axial part of the Viking Graben east of the structurally higher Shetland Platform. The Tertiary structures are mainly formed by the sub-marine fan depositional topography and enhanced by the draping and differential compaction of the sands.
Some influence by differential Cenozoic subsidence occurs due to the fact that several of the fields are lying above deeply buried Jurassic highs.
