Forties Infill Drilling: A Case History Documenting an Extensive Infill Drilling Campaign Driven by 4-D Seismic Technology

Rose, Philip T. S., Stephen Adiletta, David Allard, Alistair Gray, Donald Keir, Apache North Sea Ltd, Aberdeen, United Kingdom

Apache North Sea Ltd embarked on a 30 well infill drilling campaign beginning in 2004 in the Forties Field after nearly 30 years and 2.5 billion barrels of oil production. Bypassed oil has been identified by interpretation of lithology, fluid and fluid difference seismic inver­sions derived from 3D seismic surveys, acquired in 1988, 1996 and 2000. Drilling targets were defined after integrating the seismic interpretations with individual well production / injection profiles and data acquired during the previous BP operated Forties infill drilling campaign of 1992 to 2001.

In this presentation the seismic processing methodology is briefly described and the cal­ibration to discovered hydrocarbon columns is illustrated. The seismic lithology volume, integrated with the well data, is used to define the key elements of the Forties Field reservoir architecture. This reservoir model is integrated with the 4D seismic fluid volumes, well log and production data to develop a model for the distribution of remaining hydrocarbons with­in the Forties Field.

To end 2004, 17 wells have been drilled and with 12 wells completed and on production. Approximately 25,000 BOPD production has been added to the field. The best well results (all with initial production rates between 3 and 6000 BOPD) were defined by strong oil anomalies on the 4D data and indications of a lack of sweep on the 4D difference volume.