Abstract

In February 2007, Woodside acquired a two-boat, push reverse 4D monitor survey over the Enfield oil field offshore Western Australia (Figure 1). Two-boat push reverse acquisition maximizes 4D repeatability and minimizes 4D infill in a survey area known for strong, unpredictable currents. Significant survey planning and focused 4D field expertise resulted in excellent source and receiver positional repeatability with a mean |Dsrc|+|Drec| of 27 m at the target offset of 1900 m. Survey infill is only 7% compared to a predicted infill of 30% to achieve the same 4D coverage with conventional one-boat acquisition. Shortcomings of the two-boat push reverse technique include a large minimum near-offset of around 500 m 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. Due to the success of the 2007 Enfield survey, Woodside is planning a second two-boat monitor survey on Enfield and a two-boat 4D baseline survey on the neighboring Vincent Field in 2008. In this article, we discuss the results of the 2007 Enfield monitor survey and our thoughts on possible future improvements for two-boat acquisition.

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