A Mathematical Model for Microbially Enhanced Oil Recovery Process

Microbial-enhanced oil recovery (MEOR) has been considered as a promising technique to further increase oil recovery from petroleum reservoirs. Although the potential benefits of MEOR applications are considerable, engineering of oil recovery via the manipulation of microbial metabolism still remains an unproven concept rather than a highly desirable reality. One of the main reasons is that there are few tools appropriate to quantify the multiple metabolic and physical processes involved in the oil recovery. This study seeks to address the lack of tools by presenting a computational model for simulating coupled processes in MEOR systems with two mobile, immiscible fluids. The primary goal of MEOR is to reduce the residual oil saturation. The residual saturation changes as a function of the capillary number that defines the relative effect of viscous forces versus surface tension acting across an interface between oil and water. In all previous MEOR studies, no explicit relations between residual oil saturation and capillary number were incorporated into theoretical models although this concept is often used in commercial reservoir simulators to simulate interfacial tension (IFT) modification. In this study, a functional relation between residual oil saturation and capillary number is achieved through solution of a coupled biological (B) and hydrogeological (H) finite element model. The BH model is quite sophisticated and difficult to solve numerically, however, presentation of the model results is simple and straightforward. A robust implicit method that incorporates a number of cross couplings between the BH processes is developed to solve the BH model. The model results are presented as a simple relation between the residual oil saturation and the capillary number and are compared to data from a well-documented 123 78 J. Li et al.core-flooding experiment. The model is applied to perform parametric studies for different microbial flooding scenarios. The BH model incorporates a description of the evolution of porosity and permeability that depends on the combined effects of the interactions between the BH processes. The model is used to predict the enhancement of oil recovery in a simple homogeneous test case. The model results demonstrate that MEOR could enhance the oil recovery significantly if a larger capillary number (between 10 −5 and 10 −1 ) is achievable.

Section: Water Injectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Interactions of Microbial-Enhanced Oil Recovery Processes

Liu

Trefry

et al. 2010

“…Growth rate expressions for microorganisms are often the Monod expression based on the Michaelis-Menten enzyme kinetics and Langmuir expressions for heterogeneous catalysis (Chang et al 1991;Islam 1990;Nielsen et al 2003;Zhang et al 1992). The Monod expression is widely used, but it is still empirical regarding microbial growth.…”

Section: Bacterial Growth Consumption and Productionmentioning

confidence: 99%

“…and (ω b ρ w ) is the bacterial mass concentration of the water phase, Y sm is the yield of surfactant (m) on substrate (Nielsen et al 2003;Zhang et al 1992). Substrate is converted to either bacteria and surfactant.…”

Section: Bacterial Growth Consumption and Productionmentioning

confidence: 99%

1D Simulations for Microbial Enhanced Oil Recovery with Metabolite Partitioning

Nielsen¹,

Shapiro²,

Michelsen³

et al. 2010

We have developed a mathematical model describing the process of microbial enhanced oil recovery (MEOR). The one-dimensional isothermal model comprises displacement of oil by water containing bacteria and substrate for their feeding. The bacterial products are both bacteria and metabolites. In the context of MEOR modeling, a novel approach is partitioning of metabolites between the oil and the water phases. The partitioning is determined by a distribution coefficient. The transfer part of the metabolite to oil phase is equivalent to its "disappearance," so that the total effect from of metabolite in the water phase is reduced. The metabolite produced is surfactant reducing oil-water interfacial tension, which results in oil mobilization. The reduction of interfacial tension is implemented through relative permeability curve modifications primarily by lowering residual oil saturation. The characteristics for the water phase saturation profiles and the oil recovery curves are elucidated. However, the effect from the surfactant is not necessarily restricted to influence only interfacial tension, but it can also be an approach for changing, e.g., wettability. The distribution coefficient determines the time lag, until residual oil mobilization is initialized. It has also been found that the final recovery depends on the distance from the inlet before the surfactant effect takes place. The surfactant effect position is sensitive to changes in maximum growth rate, and injection concentrations of bacteria and substrate, thus determining the final recovery. Different methods for incorporating surfactant-induced reduction of interfacial tension into models are investigated. We have suggested one method, where several parameters can be estimated in order to obtain a better fit with experimental data. For all the methods, the incremental recovery is very similar, only coming from small differences in water phase saturation profiles. Overall, a significant incremental oil recovery can be achieved, when the sensitive parameters in the context of MEOR are carefully dealt with.

“…Chang et al (1991) proposed a one-dimensional model with a nonlinear equation which described the growth and decay of microbes on the rock surface, including bulk clogging and declogging effects. Another one-dimensional model was developed by Zhang et al (1992). In their work, the conservation equation for the sessile phase included biomass retention, detachment and growth.…”

Section: Introductionmentioning

confidence: 99%

Impact of Rock Heterogeneity on Interactions of Microbial-Enhanced Oil Recovery Processes

Liu

Trefry

et al. 2011

Residual oil saturation reduction and microbial plugging are two crucial factors in microbial-enhanced oil recovery (MEOR) processes. In our previous study, the residual saturation was defined as a nonlinear function of the trapping number, and an explicit relation between the residual oil saturation and the trapping number was incorporated into a fully coupled biological (B) and hydrological (H) finite element model. In this study, the BH model is extended to consider the impact of rock heterogeneity on microbial-enhanced oil recovery phenomena. Numerical simulations of core flooding experiments are performed to demonstrate the influences of different parameters controlling the onset of oil mobilization. X-ray CT core scans are used to construct numerical porosity-permeability distributions for input to the simulations. Results show clear fine-scale fingering processing, and that trapping phenomena have significant effects on residual oil saturation and oil recovery in heterogeneous porous media. Water contents and bacterial distributions for heterogeneous porous media are compared with those for homogenous porous media. The evolution of the trapping number distribution is directly simulated and visualized. It is shown that the oil recovery efficiency of EOR/MEOR will be lower in heterogeneous media than in homogeneous media, largely 123 374 J. Li et al. due to the difficulty in supplying surfactant to unswept low-permeability zones. However, MEOR also provides efficient plugging along high-permeability zones which acts to increase sweep efficiency in heterogeneous media. Thus, MEOR may potentially be more suited for highly heterogeneous media than conventional EOR.