Plugging high-permeability zones within oil reservoirs is a straightforward approach to enhance oil recovery by diverting waterflooding fluids through the lower-permeability oil-saturated zones and thereby increase hydrocarbon displacement by improvements in sweep efficiency. Sporosarcina pasteurii (ATCC 11859) is a nitrogen-circulating bacterium capable of precipitating calcium carbonate given a calcium ion source and urea. This microbially induced carbonate precipitation (MICP) is able to infill the pore spaces of the porous medium and thus can act as a potential microbial plugging agent for enhancing sweep efficiency. The following explores the microscopic characteristics of MICP-plugging and its effectiveness in permeability reduction. We fabricate artificial rock cores composed of Ottawa sand with three separate grain-size fractions which represent large (40/60 mesh sand), intermediate (60/80 mesh sand), and small (80/120 mesh sand) pore sizes. The results indicate a significant reduction in permeability after only short periods of MICP treatment. Specifically, after eight cycles of microbial treatment (about four days), the permeability for the artificial cores representing large, intermediate, and small pore size maximally drop to 47%, 32%, and 16% of individual initial permeabilities. X-ray diffraction (XRD) indicates that most of the generated calcium carbonate crystals occur as vaterite with only a small amount of calcite. Imaging by SEM indicates that the pore wall is coated by a calcium carbonate film with crystals of vaterite and calcite scattered on the pore wall and acting to effectively plug the pore space. The distribution pattern and morphology of microbially mediated CaCO3 indicate that MICP has a higher efficiency in plugging pores compared with extracellular polymeric substances (EPSs) which are currently the primary microbial plugging agent used to enhance sweep efficiency.

中文翻译：

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微生物诱导碳酸钙封堵提高石油采收率

在油藏中封堵高渗透区是一种直接的方法，通过将水驱流体转移到渗透率较低的油饱和区来提高采收率，从而通过提高波及效率来增加碳氢化合物的驱替。Sporosarcina pasteurii (ATCC 11859) 是一种氮循环细菌，能够在给定钙离子源和尿素的情况下沉淀碳酸钙。这种微生物诱导的碳酸盐沉淀（MICP）能够填充多孔介质的孔隙空间，因此可以作为潜在的微生物堵塞剂来提高波及效率。下面探讨了 MICP 封堵的微观特征及其降低渗透率的有效性。我们制造由渥太华沙子组成的人工岩芯，具有三个独立的粒度部分，分别代表大（40/60 目沙子）、中（60/80 目沙子）和小（80/120 目沙子）孔径。结果表明仅在短时间 MICP 处理后渗透性显着降低。具体而言，经过 8 个微生物处理周期（约 4 天）后，代表大、中和小孔径的人工岩心的渗透率最大下降到个体初始渗透率的 47%、32% 和 16%。X 射线衍射 (XRD) 表明大多数生成的碳酸钙晶体以球霰石形式出现，只有少量方解石。SEM 成像表明，孔壁被碳酸钙膜覆盖，球霰石和方解石晶体散布在孔壁上，起到有效堵塞孔道的作用。微生物介导的 CaCO3 的分布模式和形态表明，与胞外聚合物 (EPS) 相比，MICP 具有更高的孔隙率，胞外聚合物是目前用于提高波及效率的主要微生物封堵剂。