--> ABSTRACT: Deepwater Gulf Of Mexico Piston Coring: Seepage Versus Anomalies Versus Background And Relationship To The Deepwater GoM Petroleum System, by Gary A. Cole, Rick Requejo, Joe DeVay, Alan Yu, Frank Peel, Jim Brooks, Bernie Bernard, John Zumberge, and Stephen Brown; #90906(2001)

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Gary A. Cole1, Rick Requejo2, Joe DeVay1, Alan Yu3, Frank Peel1, Jim Brooks4, Bernie Bernard4, John Zumberge5, Stephen Brown6

(1) BHP Petroleum, Houston, TX
(2) Geochemical Solutions International, Inc, Woodlands, TX
(3) BHP Petroleum, Hosuton, TX
(4) TDI-Brooks International Inc, Houston, TX
(5) GeoMark Research, Houston, TX
(6) GeoMark Research, Inc, Houston, TX

ABSTRACT: Deepwater Gulf Of Mexico Piston Coring: Seepage Versus Anomalies Versus Background And Relationship To The Deepwater GoM Petroleum System

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). A scale based on these early data identified anything <5000-10,000 fluorescence units as background, 10000-100000 as anomalies associated with seepage, and >100000 as seepage.

Using new 3D surveys, it is easier to locate seepage-related seabed features. With better defined seepage sites and an extensive geochemical database, the old scale for background versus anomaly versus seepage has changed. By correlating true seepage to reservoired oil, most "anomalies" are not related to seepage or to the reservoired oils, therefore, NOT related to the subsurface petroleum system.

Based on oil-to-seep correlations, we can demonstrate:

1. that most piston cores <30000-50000 fluorescence (on the old scale) represent background, 30000-100000 are anomalies, and >100000 are truthable seepage. 2. biomarker signatures of most cores with <100000 fluorescence do not correlate to the reservoired oils. 3. geographical differences exist. 4. a pervasive background biomarker signature is present across the GoM, related to either river discharge sediments containing extractable oil and/or organic matter, or possible sediment de-watering carrying an oil-like signature, unrelated to the subsurface petroleum system. 5. there is a distinct pattern related to the Mississippi fan. The "background signatures" appear to contain real oil, but do not correlate to the active true seepage.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado