Reservoir engineering of in-situ MEOR; impact of microbial community

Abstract

In this publication, we summarize and discuss the reservoir engineering aspects of applied in-situ MEOR technology. A nutrient formulation was developed to stimulate the targeted microorganisms in terms of its main metabolism with mixed acid fermentation. The incubation radius where the complete consumption of the injected nutrients takes place and the transport of metabolites and bacteria was estimated with well-known reservoir engineering equations, where the growth kinetics as well as retention characteristics were experimentally defined. Spontaneous imbibition experiments supported the contact angle measurements for the change of the wettability from intermediate to oil wet towards water wet. Observations in micromodels showed that bioplugging might be an effective conformance improvement mechanism in heterogeneous reservoirs. These two effects were also confirmed using sandpack and coreflood experiments. The effect of MEOR by the beneficial isolated community (IC) is higher compared to the reservoir community (RC). Therefore, using the IC (as applied mostly) for deciding on the fate of an application can yield overoptimistic conclusions for MEOR. If carbonates make up of even a small portion (1–2 % wt.) of the formation rock composition they act as pH buffers by reducing the negative impacts of a fermentation-induced pH drop and assure continuation of bacterial activity in the reservoir. The dissolution of carbonates as the result of this reaction is another contribution to MEOR causing pore volume increase. The results discussed above have been validated for the specific asset we are working on, for its microbiology, selected N and its reservoir characteristics.