Utilising Seismic and Pressure / Production Data to Predict and Locate Reserves Adjacent to the Borg Field
Authors: Helland-Hansen D. , Sirevaag T. , Myhrvold K. , Vikaunet T. 
Published: December 2007

The Borg Field is a stratigraphic trapped field of a shallow marine beachline system in the Tampen area of the Northern North Sea. The 30 MSm3 oil field is currently being developed with 2 injectors and 2 producers as a satellite field to the adjacent larger Tordis and Gullfaks Fields. As a result of the Upper Jurassic play, more reserves are possible to add as satellite developments. The Borg Field proves the Upper Jurassic Volgian-Ryazanian syn-rift deposit to be economically favourable. In the hunt for reserve replacement this play is expected to be important in the Tampen area, but however increasingly harder to predict and locate. The presence and location of additional reserves has been integration of multi-disciplinary data.

On the Borg Field pressure data acquired through RFT measurements in exploration wells indicated that the field was pressure depleted before production onset. By analysing pressure data from regional producing fields and exploration wells, this depletion is likely to be caused by production in the Statfjord Field to the Southwest. The oil migration into the Borg Field was interpreted to follow a route from the deep mature basin to the Statfjord Field and to the Borg Field along Upper Jurassic hanging-wall slumped and turbidite sand stones draped along the main Statfjord Fault. These were amalgamating with paleo-beachline sediments lining a restricted bay and finally connected to the Borg Field sandstone on the other side of the paleo-bay.

These sand stones can be partially mapped on seismic data and are encountered in exploration / appraisal wells and forms the likely path of pressure communication between the Borg Field and the Statfjord Field. These oil traps have a stratigraphic nature and both the location and size of the reservoir sands are difficult to map location and size of directly from the seismic, however the sands can be of economically importance due to their close proximity to nearby producing fields.

During seismic work on the Borg Field, a northern segment was observed detached from the southern segment by a fault zone. A paleo beachline and a delta fan could be predicted by seismic character and through AVO analysis these "seismic-geo-bodies" where likely to be "sand-filled".

The Borg Field was initially test produced for 6 months. During this test an influx of pressure was seen when the pressure dropped below the Statfjord Field, verifying earlier observations of pressure depletion from Statfjord, now being an influx. From analytical analysis of these data, the magnitude of the influx where calculated depending on pressure difference between the 2 fields. Well test analysis indicated that an additional volume was present outside of the main Borg Field.

Through data integration in a reservoir model and sensitivity testing through the history matching process the presence of an extra volume of 15 MSm^3 was predicted. This volume should be located to the north, to match timing and pressure of a production RFT, which corresponds to the seismic and geologic model. In addition a pressure influx from the Statfjord field mimicked by a pseudo injection well was required in order to math the final build up periods.

This prediction of volumes and location, has impact on the reservoir development of the southern segment, the timing and type of exploration / appraisal methods and possibly on infrastructure investment for the whole area.

The seismic methods utilised where verified by pressure analysis and can now be used to find similar type of sediments outside of the area "seen" by the production test.