Effects of Stimulating Indigenous Bacteria in Oil Reservoirs on Relative Permeability Curves

Abstract

Abstract Laboratory studies show the existence of some strains of bacteria in field crude oils and formation waters. This work is concerned with studying the effect of indigenous bacterial activities on the relative permeability of samples from Egyptian fields. Such study is an original contribution to the knowledge of microbial enhanced oil recovery. Phase volume studies were carried out using two types of crude oils having different spores forming bacteria. The relative permeability experiments were conducted in sandstone cores. Some available nutrient solutions being used in the field tests were also used. Based on the phase volume measurements, it was found that the indigenous microbial growth was better after two days incubation time with 1% molasses concentration as a nutrient. Residual oil saturation was found to decrease with stimulating the indigenous bacteria in the crude oils by using 1% molasses concentration. Presence of 1% molasses concentration increases the relative permeability to oil. It was found also that crude oil A, which contains Clostridium sp. and Bacillus sp., gave better relative permeability curve behavior than that of crude oil B, which contains Bacillus sp. only. Salinity increase decreases the relative permeability to oil. In the presence or absence of molasses, no clear trend of absolute permeability on oil-water relative permeability curves was observed. The results obtained are discussed and analyzed in terms of the system phase variation, interfacial forces, wettability characteristics, hydrogen ion concentrations, viscosity effects, and mechanical and mineralogical analysis of the cores. Introduction The earliest realization that certain microbes might be useful for enhancement of petroleum recovery was made in 1926, when Beckman1 proposed that certain bacterial metabolites would assist in the release and transport of oil in the geological structure. Subsequent laboratory and field studies2–6 have shown that microorganisms can produce effective products similar to those described for chemical and miscible EOR processes. These products can assist in the release of oil from the capillary pores and can improve the sweep and displacement efficiencies so that:the microbial production of gases can improve the flow characteristics,the microbial production of solvents can reduce the interfacial tension,the microbial production of organic acids can result in the dissolution of carbonates in source rock and increase the rock permeability,The microbial production of polymers can increase the viscosity of the water in the waterfloods and/or plug the high-permeability zones of the reservoir rock and thus divert the reservoir fluids to previously unswept areas of the reservoir,and the microbial production of surface active compounds (surfactants) can reduce oil-water interfacial tension and cause emulsification, and can alter the wettability of the reservoir rock. Also, the microbial growth on rock pore surfaces can plug the high-permeability zones. Another important discovery is the ability of certain bacteria to eliminate paraffin deposition around the producing wells. During the last ten years, several studies on the microbial characteristics and metabolic activity of bacteria for improve oil recovery in the middle east area have been carried out.7–13 Based on these studies, MEOR should be able to recover up to 30 % of the residual oil under reservoir conditions.