Reservoir Engineering Analysis of Microbial Enhanced Oil Recovery

Abstract

Summary We assess processes for enhancing oil recovery by means of microbes (MEOR) from the perspectives of reservoir and reaction engineering. In this work, MEOR refers to recovering incremental oil by increasing displacement and/or volumetric efficiency; it does not include well stimulation treatments. MEOR processes address the same physical parameters as chemical enhanced oil recovery (EOR) processes; hence, they are subject to the same technical difficulties: identifying and locating the target oil and retention, dissipation, and consumption of chemicals in the formation. The essential difference between MEOR and chemical EOR resides in the method of introducing the recovery-enhancing chemicals into the reservoir. Although quantitative measures of microbial performance (reaction rates, stoichiometry, required product concentrations) are lacking, it is possible to demonstrate quantitative relationships between microbial performance, reservoir characteristics, and operating conditions (well spacing, injection rates, residual oil saturation). These relationships are the focus of this paper. From them, we conclude that MEOR is potentially a "high risk, high reward" process, depending on whether it can use residual oil as an in-situ carbon source for the production of recovery-enhancing chemicals. The reward in this case is that the difficulty and the logistical costs of implementing the process would approach those of implementing a waterflood. The risk is associated with the many and severe performance constraints that a microbial system would have to satisfy to take advantage of an in-situ carbon source. The current state of knowledge fails to provide satisfactory evidence that existing systems can meet the constraints identified in this study; thus, an ambitious program of research and development would be required to determine MEOR feasibility.