Abstract: Organic Geochemistry of Fluids and Kerogens from DOE Drilling in Eugene Island 330 Reservoirs: Indicators of Fluid Flow Pathways

Jean Whelan, L. B. Eglinton, M. C. Kennicutt, III

Drilling has been carried out in Eugene Island 330 to test whether or not active fluid flow is occurring up faults into some reservoirs. Analyses of whole oils, gas, gasoline range hydrocarbons, and reservoir kerogens obtained during drilling will be presented. Parameters examined include:

(A) those diagnostic of recent remigration of hydrocarbons: light n-alkanes superimposed on biodegraded whole oil background, as has been found in shallow GA and HB reservoirs. The light n-alkanes are highly biodegradable so that if they are present along with biodegraded oils, they are indicative of very recent injection or remigration (within the last few years).

(B) Evidence of a recent evaporative fractionation event, or oil migration driven by sudden pressure release. The parameters diagnostic of the recently migrated, or the condensate end, of such an event are: high proportions of n-C₇ in the C₇ hydrocarbon fraction, high amounts of nC₃ and nC₄ compared to n-C₁₇, high gas to oil ratios, and low gas maturities as indicated by ethane and propane ^dgr¹³C analyses in gases.

(C) Compositions of hopane and sterane biomarkers, along with methyl phenanthrene ratios, to determine oil maturities and whether or not we are dealing with a single family of oils.

In addition, vitrinite reflectance measurements on whole rocks recovered during drilling will be described. These measurements are used to show zones of abnormally high kerogen maturations in comparison to surrounding sediments.

These elevated maturities may be due to exposure to hot fluids ascending the fault plane.

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