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Cole, Gary A.1, Rick Requejo2, Alan Yu1, Jim Brooks3, Bernie Bernard3, John Zumberge4, Stephen Brown4
(1) BHP Petroleum, Houston, TX
(2) Geochemical Solutions International, Inc, Woodlands, TX
(3) TDI-Brooks International Inc, College Station, TX
(4) Geomark Research, Inc, Houston, TX

ABSTRACT: The Deepwater GoM Petroleum System: Seepage Distribution Using Piston Coring and Their Definition

In the early days of GoM piston coring, locations were chosen on a grid basis, or selected from loose 2D seismic surveys. Such locations resulted in some seepage “hits”, but the majority had either a background signature or an “anomalous” value that was between a true visible seep and background (using fluorescence intensity and UCM content). The problem was defining what truly typed to the petroleum system. Today, by using better finding techniques (e.g., 3D seismic seafloor amplitude extractions), the industry has higher hit rates since the seeps can be better imaged on the seafloor (e.g., mounds, amplitudes, etc.) Based on recent analysis of the piston coring database, a new interpretation scale has emerged.
Based on oil-to-seep correlations, we can demonstrate:
1. that most piston cores <30000-50000 fluorescence (old scale) represent background, 30000-100000 are anomalies, and >100000 are “clean” seepage. 2. Only clean seepage extracts type to reservoired oils. 3. biomarker signatures of most cores with <100,000 fluorescence do not correlate to the reservoired oils. 4. geographical differences exist. 5. a pervasive background biomarker signature is present across the GoM related to non-migrated oils. 6. there is a distinct pattern related to the Mississippi fan.
Using a rigorous approach when interpreting the detailed geochemical data from the piston cores, the “clean” seepage shows a regional trend that can be used to infer source rock type across the deepwater GoM. Because of the controls on the migration of oil and gas, true seepage should be predictable, whereas anomalies can be caused by different mechanisms not related to hydrocarbon seepage.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.