Detailed Microbial Reservoir
Characterization Identifies
Reservoir
Heterogeneities within a Mature Field in Oklahoma
TUCKER, JAMES D., DANIEL C. HITZMAN. and BROOKS A. ROUNTREE
A detailed Microbial Reservoir
Characterization (MRC) survey was conducted
over a mature producing field in Washington County, Oklahoma. The samples were
collected in a 330' grid pattern over the entire 720 acres of the study area.
MRC theory is dependent on observed rapid hydrocarbon microseepage and the
direct relationship between surface microbial populations and the pressure
regimes within the
reservoir
. Reduced microbial populations are located above
portions of the
reservoir
in direct communication with producers while elevated
populations are associated with injection. When a well is brought into
production, the
drive
mechanism changes from a vertically migrating buoyancy
force to horizontal gas streaming to low pressure sinks created within the
reservoir
in pressure communication with the producing wells. This change in
drive
mechanism causes rapid reduction of surface microbial populations and
defines
reservoir
drainages, radii and heterogeneities around producing wells.
Within single horizon producing fields, areas of elevated microbial values are
not in pressure communication with the producers and are isolated from the
producer by
reservoir
heterogeneities. Conversely, in areas where the
reservoir
is being repressured, as in a waterflood, microseepage is reestablished. The
microbial populations increase in response to increasing microseepage coming
from the portion of the
reservoir
in direct communication with the waterflood.
Low microbial counts within injection areas indicate depressured regions of the
reservoir
not in communication with injector and isolated by some heterogeneity.
All these patterns were observed in the study area and verified by recent infill
drilling.