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The AAPG/Datapages Combined Publications Database

GCAGS Transactions


Gulf Coast Association of Geological Societies Transactions
Vol. 50 (2000), Pages 761-767

Post-Drilling Evaluation of Amplitude-Supported Prospects, Offshore Louisiana

Otis H. Walter


The identification of higher seismic reflection amplitudes as hydrocarbon indicators to support drilling prospects has a long and successful history. However, because wide ranges of subsurface conditions can produce higher amplitude reflections, the hope that the high amplitude is indeed related to hydrocarbons can go unfulfilled.

Several recent drilling examples from offshore Louisiana illustrate a cause other than hydrocarbon presence for the higher amplitude "bright spot" upon which the prospect was based. Post-drilling evaluations of these cases show a range of lithologic causes for the impedance contrasts. Specific examples illustrate a wet reservoir with high contrast at the base, a low impedance non-reservoir facies, and high impedance hard zones within the reservoir intervals.

For each case examined, a uniform template is applied showing the well logs, synthetic seismogram, and the seismic traces through the zone of interest. This process facilitates the identification of the actual cause of the higher amplitude and comparison between wells. It would be useful to develop a larger database, derived from this type of evaluation for an area or trend, as a source of analogs for modeling as well as a catalog of potential pitfalls and a tool for comparative risk assessment.

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