MICROBIALLY ENHANCED OIL-RECOVERY FROM UNCONSOLIDATED LIMESTONE CORES

The enhanced recovery of residual oil from unconsolidated carbonate co res using microorganisms was examined in model cores packed with chips of Viola limestone. Vibrio aspartigenicus strain GSP-1, an acid produ cer, and Bacillus licheniformis strain JF-2, a surfactant producer, we re used as the test microorganisms. The primary hypothesis tested was that microbial treatment of a packed core system would result in the r ecovery of residual oil from the carbonate test system. After three tr eatments, 39-44% of the residual oil-in-place was recovered from packe d core systems after treatment with strain GSP-1. Two treatments with strain JF-2 resulted in a 27% recovery of the residual oil-in-place. M odification of the core matrix was indicated by the presence of calciu m in the core effluents and significant amounts of carbonate fines fou nd in the dissected cores, presumably caused by dissolution of the car bonate matrix by microbial acid end products of metabolism (microbial matrix acidizing). These results are encouraging since significant amo unts of crude oil were recovered in these systems with only a few trea tments, suggesting that microbially enhanced oil recovery (MEOR) in ca rbonate petroleum reservoirs could be efficient and economical.