--> Organic Geochemical Indicators of Fluid Flow Processes and Oil Source in Eugene Island Block 330, by J. K. Whelan, M. C. Kennicutt, J. M. Brooks, and D. Schumacher; #90986 (1994).

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Abstract: Organic Geochemical Indicators of Fluid Flow Processes and Oil Source in Eugene Island Block 330

Jean K. Whelan, Mahlon C. Kennicutt, James M. Brooks, Deet Schumacher

A number of diverse geophysical, geological, and geochemical EI-330 observations from the Louisiana Gulf Coast Eugene Island 330 reservoirs support the "dynamic fluid injection hypothesis": that gas and oil are being injected into some of these reservoirs at the present time. Preliminary organic geochemical data for this "dynamic fluid injection" hypothesis are presented here:

1. Anomalously high gas and oil production from EI-330 reservoirs, in comparison to surrounding reservoirs.

2. Anomalously high C7 hydrocarbon F values for EI-330 oils considering their relatively low maturities.

3. Light n-alkanes superimposed on biodegraded whole oils in the shallow reservoirs. Light n-alkanes are highly biodegradable and must have been injected recently, after oil biodegradation of heavier n-alkanes had occurred.

4. High (nC3+nC4/nC17) ratios.

5. Temporal changes in whole oil and C7 compositions which occurred between 1985, 1988, and 1993.

6. Anomalously high vitrinite reflectance values near a fault thought to be one carrier of hot fluids from depth into the EI-330 reservoirs.

All of these observations are consistent with recent injection of fluids into some EI-330 reservoirs. In comparison, nearby SMI-128 samples on the other side of a salt ridge show none of these features.

Organic geochemical data are most consistent with a Cretaceous or Jurassic source for EI-330 oils followed by early migration and trapping under pressure beneath evaporitic layers, where thermal degradation would be retarded. Oil cracking to gas in deep reservoirs is proposed to drive episodic release of oil and gas through geopressure into the shallower productive EI-330 reservoirs.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994