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Egypt Western Desert Petroleum Charge System as Defined by Oil Chemistry and Unmixing Analysis

Abrams, Michael A.*1; Thompson, Melissa 2; Collister, James 3
(1) EPT, Apache, Houston, TX.
(2) Apache Egypt, Cairo, Egypt.
(3) Consultant, Monrovia, CA.

Source rock analysis and maturity modeling in the Egypt Western Desert (WD) indicates there are multiple mature source rocks which could be expelling hydrocarbons over much of study area. The presence of highly variable oil characteristics suggests more than one charge system may be present but examination of reservoir crude oils chemistry indicates the fluids are derived from a single source facies. The oils have been generated over a broad range of organic maturities based on molecular characteristics. Secondary alteration mechanisms include water washing, biodegradation, and evaporative fractionation. Crude oils in the upper reservoirs tend to be most affected by biodegradation (less than rank 2) and water washing. Condensates and light crude oils in the oldest reservoirs appear to be the residual phase from fractional evaporation.

The broad variation in fluid properties and chromatogram character can be attributed to a multi end-member mixing system; early mature waxy oil, high maturity later volatile oil, low level biodegradation, migrated phase evaporative fractionation, and residual phase evaporative fractionation. A statistical “unmixing” algorithm was used to determine end member (EM) compositions and relative mixing proportions for each crude oil sample. Remigration and mixing of multi phase generation and alteration results in a reservoir fluid from multiple processes with no one reservoir oil being an end member but a mix of relative amounts of each end member. Examination of mixing proportions shows regional trends and changes within different reservoirs of a single field. The crude oil geochemical data and unmixing analysis do not support a simple two source rock scenario but a complex charge history from a single source rock.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California