Experimental Studies of In-Situ Microbial Enhanced Oil Recovery

Experiments were conducted to study the feasibility of using microorganisms in EOR, particularly for the correction of permeability variation. The use of microorganisms requires the ability to transport viable cells as well as the nutrients required for cellular growth through reservoir formations. Nutrients such is glucose, peptone-protein, and phosphate and ammonium ions were transported through brine-saturated Berea sand-stone cores in amounts sufficient to suppose microbial growth. Viable bacterial cells were transported to through sandstone cores of 170-md permeability. Less than1% of the influent cell concentration was recovered in the effluent, indicating a high degree of cell retention inside the core. The addition of nutrients to these cores and subsequent incubation to allow for microbial growth resulted in permeability reductions of 60 to 80%. These data show that the growth of microorganisms significantly reduces the permeability of porous rock. permeability of porous rock. Introduction The major objective of this study is to investigate experimentally thepotential use of microorganisms in oil recovery. In this investigation, potential use of microorganisms in oil recovery. In this investigation, petroleum engineering and microbiology are used to understand the physical petroleum engineering and microbiology are used to understand the physical mechanisms of oil recovery by bacterial processes. One process under study is permeability reduction by the in-situ growth of bacteria as a proposed solution to reservoir heterogeneity problems, specifically permeability variation, that detrimentally affect the performance of waterflood and EOR projects. Numerous investigation have experimentally studied the plugging projects. Numerous investigation have experimentally studied the plugging effect of bacteria on Berea sandstone cores. However, their work dealt with injectivity problems resulting from wellbore plugging caused by bacteria. Theory Reservoir heterogeneity has a significant effect on the oil recovery efficiency of a waterflood or EOR process. The recovery efficiency ( )may be defined as a combination of a microscopic oil-displacement efficiency ( ) and volumetric sweep efficiency ( ). ............................(1) Permeability variation greatly influences the volumetric sweep efficiency Permeability variation greatly influences the volumetric sweep efficiency and its two-dimensional components of areal and vertical sweep efficiency. Reservoir selective plugging techniques developed in the past to modify permeability variations included a wide variety of plugging agents. The permeability variations included a wide variety of plugging agents. The application and success of these methods were limited. Meehan et al. demonstrated that additional oil recovery is possible if the channeling water in a waterflood can be immobilized. The residual oil saturation (ROS) remaining after waterflooding is apotential target for the application of a reservoir selective plugging potential target for the application of a reservoir selective plugging process using the in-situ growth of bacteria. The theoretical concept of process using the in-situ growth of bacteria. The theoretical concept of this process involves the introduction of viable bacteria in the aqueous displacing fluid to be injected into the high- permeability water-sweptzones. The selectivity is based on the experimental evidence that bacteria more readily, plug high-permeability zones since these zones receive a greater proportion of the fluid flow. Once the bacteria are in place, a designed volume of nutrients may be injected into the reservoir to support in-situ metabolism of the bacteria. The result of this metabolism is the production of cellular mass capable of initiating physical plugging. The production of cellular mass capable of initiating physical plugging. The physical plugging results in a reduction of original permeability mid can physical plugging results in a reduction of original permeability mid can be expressed as the ratio of impaired to original permeability. The resumption of injection will result in a diversion of the displacing fluid from plugged high-permeability zones to unswept zones and, thus, improvesweep efficiency. This reduces the ROS, decreases WOR, and increases theultimate recovery of oil in place. The success of an in-situ microbial plugging process depends on the ability to (1) transport the microorganisms plugging process depends on the ability to (1) transport the microorganisms throughout the reservoir rock stratum, (2) transport nutrients required for microbial growth and metabolism and (3) reduce the apparent permeability of the reservoir rock stratum as a result of microbial growth and metabolism. Description of Equipment and Processes Berea sandstone cores obtained from Cleveland Quarrics (Amherst, OH) werecut into cylinders 2 × 8 in. [5 × 20 cm] with a coring device. Cores were either steamcleaned for 2 weeks and then dried or used as received. Each core was coated with epoxy, cast in a resin mold (Evercoat Fiberglassresin), and cut into specified lengths. SPEJ p. 33