Print this pageDetailed 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.