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