MICROBIALLY ENHANCED OIL-RECOVERY FROM UNCONSOLIDATED LIMESTONE CORES

The enhanced recovery of residual oil from unconsolidated carbonate cores using microorganisms was examined in model cores packed with chips of Viola limestone. Vibrio aspartigenicus strain GSP-1, an acid producer, and Bacillus licheniformis strain JF-2, a surfactant producer, were used as the test microorganisms. The primary hypothesis tested was that microbial treatment of a packed core system would result in the recovery of residual oil from the carbonate test system. After three treatments, 39-44% of the residual oil-in-place was recovered from packed 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. Modification of the core matrix was indicated by the presence of calcium in the core effluents and significant amounts of carbonate fines found in the dissected cores, presumably caused by dissolution of the carbonate matrix by microbial acid end products of metabolism (microbial matrix acidizing). These results are encouraging since significant amounts of crude oil were recovered in these systems with only a few treatments, suggesting that microbially enhanced oil recovery (MEOR) in carbonate petroleum reservoirs could be efficient and economical.