考虑油藏环境因素和微生物因子的微生物采油数学模型

为研究油藏环境耦合作用下微生物驱技术提高采收率机理,建立了能全面反映微生物驱油过程的三维三相六组分数学模型,模型涉及的组分有油、气、水、微生物、营养物以及代谢产物。该模型综合考虑了微生物生长/死亡、营养消耗、产物生成、化学趋向性、对流扩散、油相黏度降低、吸附、解吸附以及油-水界面张力变化等特性。其中,微生物生长动力学方程以Monod模型为基础,考虑油藏环境因素对微生物生长模型的影响且微生物在地上与地下生长速率不一致;同时为了体现菌体对微生物驱油的作用,引入微生物因子到微生物驱油机理中。对微生物生长模型、微生物和营养物的混合溶液注入量、环境抑制系数、最大比生长速率以及微生物因子等进行分析的结果表明,通过完善后的微生物生长方程计算得出的产物浓度要比Monod模型低,但这两种微生物生长方程下的产物浓度的差异对最终采收率的影响较小;随着混合溶液注入量的增长,这两种微生物生长方程下的产物浓度差值和采收率提高幅度将增大;微生物因子对微生物驱油有较大的影响,不同微生物因子下提高原油采收率的绝对误差可高达24.53 %。

A mathematical model for microbial enhanced oil recovery considering reservoir environment and microbial factor

In this study, a 3D three-phase six-component mathematical model is established to fully reflect the microbial flooding process. The components of this model involve oil, gas, water, microbes, nutrients and metabolites. The model comprehensively involves such properties as microbial growth/death, nutrient consumption, metabolite production, chemotaxis, convection-diffusion, oil viscosity reduction, adsorption, desorption and oil-water interfacial tension change. Considering the effect of reservoir environmental factors on the microbial growth model and inconsistent growth rate of microbes on the ground and underground, the microbial growth kinetics equation is improved on a basis of Monod model. Meanwhile, in order to reflect the effect of bacteria on microbial flooding, a microbial factor is introduced into the mechanism of microbial flooding. Based on case studies, this paper conducts an analysis of the microbial growth model, microbe-nutrient mixed solution injection, environmental inhibition coefficient, maximum specific growth rate and microbial factors. The results show that the metabolite concentration calculated by the improved microbial growth kinetics equation is lower than that of Monod model, but the difference in metabolite concentration obtained using the two microbial growth equations has less effect on final oil recovery. With an increase in the injection amount of microbe-nutrient mixed solution, the difference in metabolite concentration and oil recovery in these two microbial growth equations will be improved. The microbial factor has a great impact on microbial flooding, and the absolute error under different microbial factors in oil recovery can reach up to 24.53 %.