Optimization of Microbial Formulations for Oil Recovery: Mechanisms of Oil Mobilization, Transport of Microbes and Metabolites, and Effects of Additives

Abstract

ABSTRACT The mechanisms of oil mobilization by injection of microbial cells and nutrient have been studied to further develop an engineering methodology for optimizing formulations for oil recovery applications. An extensive laboratory study has been conducted to determine (1) the role of microbial cells and products in oil displacement, (2) the relative rates of transport of microbial cells and chemical products from the metabolism of nutrient in porous media, and (3) the effects of chemical additives on the oil recovery efficiency of microbial formulations. Oil displacement experiments were performed in Berea sandstone cores to compare the recovery efficiency of a formulation containing chemical products of microbial metabolism from which the cells had been removed by filtration with that of the original microbial formulation. The oil recovery efficiency of the microbial formulation was considerably greater than that of the solution of metabolic products without any cells. Previous m¡cromodel studies have indicated that the products of microbial metabolism were not as effective in mobilizing oil as was the microbial formulation. The results indicate that microbial cells play an important role in oil mobilization, probably by producing high localized concentrations of chemical products at the oil-brine interface. Additional oil displacement experiments were conducted in 4-foot-long Berea sandstone cores, and samples of in situ fluids were collected at various times at four intermediate points along the cores. The concentrations of metabolic products and microbes in the fluid samples were determined. The results showed that metabolic products transport through porous media at a faster rate than do microbes. The effects of additives on the oil recovery efficiency of microbial formulations were determined by conducting oil displacement experiments in 1-foot-long Berea sandstone cores. Sodium tripolyphosphate (STPP), a low-molecular-weight poly-acrylamide polymer, a lignosulfonate surfactant, and sodium bicarbonate were added to a microbial formulation at a concentration of 1 wt %. The effects of using these additives in a preflush prior to injection of the microbial formulation were also evaluated. Adding polymer, surfactant, or sodium bicarbonate increased the oil recovery efficiency of the microbial formulation, while STPP had a minimal effect. Injecting preflush formulations containing the additives also increased oil recovery efficiency of the microbial flood. The results of this investigation provide new insights into the mechanisms of oil mobilization of microbial formulations and engineering data that are useful in optimizing the design of microbial systems for oil recovery applications.