Evaluation of Microbial Systems in Porous Media for EOR

Abstract

Summary The use of microorganisms to enhance oil recovery has become a technically feasible technology for production from stripper wells (those that produce less than 10 B/D [1.6 m3/d]). As a result of microbial growth and the production of CO2 and/or chemicals, oil recovery can be effectively increased in certain reservoirs with temperatures and salinities hospitable to microorganisms. Research at the Natl. Inst, for Petroleum and Energy Research has led to development of laboratory facilities for evaluating microbial systems for microbial enhanced oil recovery (MEOR) applications. Results from microbial core studies using Berea sandstone have shown that bacteria can vary greatly in their ability to recover residual oil after waterflooding, giving from 7.5 to 71 % recovery efficiency. The type of core encapsulation did not affect oil recovery. Variations in rock permeability from 134 to 1,920 md indicated that some microorganisms may exhibit a better recovery efficiency in lower-permeability cores. The results also show that gas production by microorganisms is not the only factor affecting oil recovery; some bacteria that produce surfactants but no gas could provide equally efficient additional oil recoveries. Likewise, the type of surfactant also makes a difference; two species that produce surfactants can vary in recovery efficiency. Another contributing mechanism to microbial oil mobilization may be by increasing areal sweep efficiency from microbial growth. A comparison of oil recovery efficiencies between microorganisms using a medium-to-light-gravity oil (Delaware-Childers) and two heavy oils (Wilmington, CA, and Chaffee, CA) indicates that MEOR may be effective for heavy oils as well as light oils. Correlations are presented between the recovery efficiency of a particular microbial species and its ability to mobilize crude oil in etched-glass micromodels.