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The AAPG/Datapages Combined Publications Database

Indonesian Petroleum Association

Abstract


24th Annual Convention Proceedings (Volume 1), 1995
Pages 369-382

Bottom Cable 3-D Seismic Operations in the Transition Zone

Ezhar Manaf, Bambang Indroyono, Peter C. Johnson, James A. Musser

Abstract

The JJ 3-D transition zone seismic data was acquired from June to September 1994 in ARCO Indonesia's ONWJ concession. The survey covers 105 square kilometers with a fine spatial sampling for fault and sand body resolution. Because the shoreline, shallow water, and reefs in the area make streamer techniques unusable, a Patch 3-D design was developed with hydrophone cables on the seafloor and geophone cables on the beach to record data up to and under the shore, making this the first bottom cable 3-D survey in Indonesia. For economic and environmental reasons, explosive sources were not used, so shallow water shotpoints were very important. A shallow draft source boat was utilized to maximize source access into water as shallow as 80 cm. A carefully designed sleeve airgun array provided good quality data everywhere.

Because of the very shallow water, detailed bathymetry was needed to plan exactly how to maximize source coverage. Water depth changes of a few centimeters could affect whether or not source points could be acquired. Thus, it was necessary to measure tides and predict water depth at any time at each shotpoint as accurately as possible, allowing operational plans to maximize coverage and minimize unproductive time.

The flexible patch design was critical for adjusting to environmental conditions. Some shallow water areas were inaccessible to the source, but not to geophone stations. On one such patch, source and receiver line orientations were exchanged, maintaining continuous data coverage of the target objectives.

Hydrophone and geophone data often contribute to common gathers. Such trapes were carefully phase matched before stacking. Testing proved that the shallow water hydrophone and geophone data are almost exactly 90° out of phase, as expected. Final processing through migration yields a continuous, high quality image of the subsurface even under the shoreline.


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