Shell/BP enhance 4-D data quality

摘要

A case history from the Schiehallion geld (UKCS) demonstrates that careful planning and acquisition of a 4-D repeat/monitor towed streamer survey provides a significant improvement in 4-D repeatability. By ensuring that the source and receiver locations for baseline and monitor were repeated as closely as possible, Shell and BP were able to achieve a step-change improvement in geometrical repeatability. Comparison with the previous repeat survey, acquired 2 years earlier, shows a normalized root mean square (NRMS) improvement on brute stacks of between 0.1 and 0.2. After careful processing, the repeatability difference is reduced, but there is still a 0.1 to 0.15 improvement achieved by the new acquisition. A series of repeat towed streamer 4-D "monitor" surveys was conducted over three BP-operated West of Shetlands fields (Schiehallion, Loyal and Foinaven) in 1999, 2000 and 2002. With production start-up in 1998, these early surveys clearly revealed gas breakout around unsupported producers. This information was valuable to optimize injector locations in this first phase of field development. By 2003, pressure support had more or less been achieved in the field. The detection of the waterflood signal became of prime importance. However, simple modeling showed that its magnitude was only 50-75% of the gas breakout signal. Simply acquiring further surveys in a routine repeat 3-D manner would have compromised the detection of the 4-D effects. We needed to do something differently.