Benefits of Two-boat 4D Acquisition - An Australian Case Study

In February 2007 Woodside acquired a two-boat, push reverse 4D monitor survey over the Enfield oil field in offshore Western Australia (Figure 1). Two-boat push reverse acquisition was used to maximize 4D repeatability and minimize 4D infill in a survey area known for strong, unpredictable currents. The source and receiver positional repeatability obtained in the monitor is good with a mean |Dsrc|+|Drec| of 27m at the target offset of 1900m. Survey infill is only 7% compared to a predicted infill of 30% to achieve the same 4D coverage with oneboat acquisition. Shortcomings of the two-boat push reverse technique include a large minimum near offset of around 500m and a receiver motion 4D error when matching to the conventional one boat baseline survey. An NRMS of 15% was obtained for the final processed data. Following the success of the 2007 Enfield survey, Woodside has proposed to acquire a second two-boat monitor survey on Enfield in early 2008.