Microbial Enhanced Oil Recovery: Interfacial Tension and Gas-Induced Relative Permeability Effects

Abstract

Potential mechanisms involved in microbial enhanced oil recovery (MEOR) from sandstone reservoirs are reviewed. Three phase relative permeability studies have shown that residual oil saturation can be reduced by the presence of gas in a water wet system. The production of biogenic gas to create a free gas phase can account for incremental oil recovery in MEOR processes. Reduction in interfacial tension between formation fluids can be caused by metabolic products. Also, bacterial plugging appears to preferentially occur in larger, high plugging appears to preferentially occur in larger, high permeability pores. As this occurs fluid is diverted into smaller pores permeability pores. As this occurs fluid is diverted into smaller pores causing an increase in fluid velocity within them. The changes in interfacial tension and fluid velocity combine to increase capillary number. Increases in capillary number are associated with reduction of residual oil saturation. Core experiments are related to the results of these studies. The methods discussed can partially account for additional oil recovery in an MEOR process. Introduction For the development of microbially enhanced oil recovery (MEOR) as a viable technology in the petroleum industry, it is important that the mechanisms involved in this process be understood. MEOR has the potential to recover a portion of the residual oil remaining after waterflooding portion of the residual oil remaining after waterflooding through changes brought about by metabolic activity. The changes include selective plugging of the reservoir and modification of the reservoir fluids and their saturations. This paper will address primarily the latter two of these. The goal of the authors is to expand the current body of knowledge on the microbial mechanisms involved in the MEOR process. However, the mechanisms discussed herein cannot account for all of the oil that has been produced from core experiments. EXPERIMENTS The experiments reported in this paper were conducted to provide information about the mechanisms of oil recovery caused by microbial activity within a core. Specifically, samples of microorganisms from well 1A-9 in the Southeast Vassar Vertz Sand Unit (SEVVSU), Payne County, Oklahoma were investigated for their potential in microbial enhancement of oil recovery. All experiments were performed using oil and brine taken from the SEVVSU. The NaCl salinity of the brine was 15%. The experiments were performed at reservoir temperature using the apparatus in Figure 1. The cores were prepared and experiments conducted using the techniques of prepared and experiments conducted using the techniques of Silfanus and Knapp, et al. The experiments were performed using the three step treatments described below. performed using the three step treatments described below. Consider an MEOR core flood with apparatus as shown in Figure 1. In this experiment a core is cleaned, dried, and flushed with brine, oil, and brine again, such that the final condition is a water wet core at residual oil saturation. The MEOR experiment is begun by an injection of nutrient rich brine containing bacteria. The experiment proceeds with three steps per treatment. First, the core is shut in and allowed to incubate. Second, the effluent end of the core is opened and fluids are produced under the influence of any internal driving force. Third, the core is flooded and fluids are produced under the influence of the flood. The displacing liquid is a nutrient rich brine which represents the carbon source for the next incubation. These three steps are repeated for each treatment. The effective permeability reduction factor (PRF) is defined as: ........................................(1) Petroleum Engineers processes, a series of nutrient treatments are used to Petroleum Engineers processes, a series of nutrient treatments are used to improve oil recovery. The incremental oil recovery associated with each nutrient treatment is the oil produced by the release of pressure caused by the in situ gas produced during incubation of the core with nutrients plus the oil that is produced by the injection of the subsequent treatment. P. 169

1D Simulations for Microbial Enhanced Oil Recovery with Metabolite Partitioning

“…We have specially restricted ourselves with this case of extremely efficient MEOR, in order to demonstrate the influence of the different physical phenomena and model approximations on the process. The recovery achieved in the laboratory studies is usually much lower (Chisholm et al 1990;Banat 1995;Zekri and Almehaideb 1999;Sen 2008). This is explained by the fact that normally the threshold concentrations, which should be obtained before the effect of surfactant takes place, are much higher than in our simulations.…”

“…Especially, the two first mechanisms are believed to have the greatest impact on recovery (Jenneman et al 1984;Bryant et al 1989;Chisholm et al 1990;Sarkar et al 1994;Desouky et al 1996;Delshad et al 2002;Feng et al 2002;Gray et al 2008;UTCHEM 2000). Islam (1990) presented a mathematical model for MEOR, where bacterial growth leads to plugging, reduction of oil viscosity and interfacial tension, and production of gas.…”

Microbial Enhanced Oil Recovery

“…In microbial enhanced oil recovery (MEOR), bacteria are regularly used because they show several practical features (Nielsen et al, 2010). Several publications state that oil recovery through microbial action takes place due to several mechanisms as follows Bryant et al 1989;Chisholm et al 1990;Sarkar et al 1994;Desouky et al 1996;Delshad et al 2002;Feng et al 2002;Gray et al 2008;Nielsen et al, 2010):…”

“…Particularly, the two first mechanisms are believed to have the greatest effect on improving oil recovery Bryant et al, 1989;Chisholm et al, 1990;Sarkar et al, 1994;Desouky et al, 1996;Delshad et al, 2002;Feng et al, 2002;Gray et al, 2008;Nielsen et al, 2010).…”

Chemical and Microbial Characterization of North Slope Viscous Oils to Assess Viscosity Reduction and Enhanced Recovery

“…The biogas formation also helps in maintaining the reservoir pressure (Chisholm et al, 1990). The alcohols produced act as solvents, resulting in reduction of oil viscosity.…”