Drilling using AvO to reduce uncertainties in D35 infill

Abstract

The 035 oil field in the Balingian province offshore Sarawak was discovered in 1983. It came on-stream in late 1994 and currently produces around 14,000 sth/d. An infill development drilling campaign has been planned for late 1997. A multidisciplinary study for the 035 field, including quantitative interpretation of the seismic for porefill prediction, was undertaken to support the development drilling. A high resolution 30 seismic survey was acquired over the 035 field in 1995. As the seismic data was of reasonably good quality, an AvO study was initiated. True amplitude near and far offset migrated sub-stacks were created, and amplitudes extracted at objective levels. AvO attributes were calculated and the responses at the infill target locations were evaluated by comparing the results with those observed at well locations. The results of this study showed that the brine-bearing and oil-bearing reservoirs have different AvO responses. Thus, the results gave an indication of the porefill at the reservoir level, and this in turn assisted in optimising the revisit target locations. In conclusion, AvO is aJ). additional tool that can be used in screening drilling targets and for risk management in a multidisciplinary team environment. The technique offers added information to reduce uncertainties as presented here in the 035 study.