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Pushing the limits of resolution at Holstein

A case history from the deepwater Gulf of Mexico

BP, Houston, Texas, U.S.

Yannick Cobo

CGG, London, U.K.

Corresponding authors: E. Ekstrand, ekstraej@bp.com; A. Calvert (now at GMG-AXIS Geophysics, Denver, CO), ascalvert@axisgeo.com

The first 20% of the full text of this article appears below.

The high costs associated with production in deepwater have led to increased business support for acquisition and processing of high-quality seismic for field development. The relatively thin, stacked reservoirs discovered at Holstein Field, which contain significant recoverable hydrocarbon volumes (350 million boe), posed a challenge for development planning.

In this article we review our experience with acquiring and processing a high-density seismic survey to improve understanding of these reservoirs and optimize well placement. We discuss the challenges and lessons learned through the full cycle of the project focusing on issues related to planning and acquiring a high-resolution development survey that will also serve as a 4D baseline, multiples, time processing, and wave equation depth migration. This survey has proven its value at Holstein and the lessons learned are useful for others proposing or planning high-density surveys in any seismic environment.

	Background and the seismic problem

 
Holstein Field is 200 miles south of New Orleans in 4300 ft of water (Figure 1). Discovered and appraised in 1999, the BP operated field (Figure 2) is jointly owned with Shell and is one of the few recently discovered deepwater fields located completely above salt (Figure 3). Although the seismic environment is relatively benign compared to subsalt fields, Holstein's reservoir architecture presents its own challenges. The reservoirs consist of stacked sheet sands varying in thickness from 15 to 150 ft separated by shale layers of similar thickness. These sands exhibit a compensation stacking geometry where the total net thickness of adjacent gross units can remain almost constant but the relative proportions of sand thickness can vary significantly (Figure 3c). The sands act as independent reservoirs often with different pressures requiring wells to be targeted to individual units. Hydrocarbon column heights exceed 2500 ft with reservoir description of the steeply dipping structural . . . [Full Text of this Article]