Time-lapse seismic as a complementary tool for in-fill drilling

Time-lapse seismic data have improved the drainage understanding of the Gullfaks oil field and have resulted in several potential new in-fill drilling targets. The baseline survey was acquired in 1985, 1 year before production start-up. Since then, three more surveys have been acquired, one in 1995, one in 1996 and the last one so far in 1999. Key elements in the process of reducing the uncertainties are cross-disciplinary verifications and detailed geophysical analysis and modeling, where different saturation profiles are input to the model. Waterfront movements predicted by time-lapse seismic analysis have been confirmed by well observations. It is estimated that the recovery will most likely be increased by approximately 2% as a result of seismic monitoring, corresponding to a net value contribution of approximately US$100 million, assuming an oil price of US$15 per barrel.