Song Chenpeng, Chen Yulong, Wang Jiehao
National Inland Waterway Regulation Engineering Research Center, Chongqing Jiaotong University, Chongqing 400074, China.
Department of Energy and Mineral Engineering, EMS Energy Institute and G3 Center, Pennsylvania State University, University Park, Pennsylvania 16802, United States.
ACS Omega. 2020 Jun 9;5(24):14376-14383. doi: 10.1021/acsomega.0c00902. eCollection 2020 Jun 23.
Simple plugging of the high-permeability "thief zones" of oil reservoirs is the most plausible and also the most straightforwardly achievable approach to enhance sweep efficiency and oil recovery. is a representative microorganism with the ability to precipitate calcium carbonate (CaCO) enzymatic hydrolysis of urea in the presence of calcium ions. Microbially induced calcium carbonate precipitation (MICP) can cement and seal the granular and fractured media and thus can be used as a potential microbial plugging agent for the high-permeability zones of oil reservoirs. The following investigated the microscopic characteristics of MICP plugging and its efficacy in permeability reduction. The columns of near-spherical silica sand and angular silica sand with three separate granularities (40/60, 60/80, and 80/120 mesh) were used as artificial rock cores representing distinct pore sizes and pore characteristics to investigate the efficacy and microprocess of MICP plugging with different biotreatment periods. The results indicated that permeability is reduced significantly after only short periods of biotreatment. After eight cycles of MICP treatments, the permeability for each type of cores dropped by 54-90% of individual initial permeabilities. The measured CaCO content indicated that the decreasing rate in permeability with the increasing CaCO content experiences three contrasting stages, namely, slow decline, speedy decline, and plateauing. X-ray diffraction indicated that most of the generated CaCO crystals occur as vaterite with only a small amount of calcite. Imaging by scanning electron microscopy further revealed the microprocess of MICP plugging. Microorganisms first concentrate on the pore wall to secrete CaCO, forming a thin and large uniform layer of CaCO. Then, some nucleation sites of CaCO crystals will experience further preferential growth, resulting in large, dominant crystals that act as a plugging agent within the pore space. Compared to extracellular polymeric substances, which are currently the primary microbial plugging agent used to enhance sweep efficiency of oil reservoirs, bio-CaCO appears more effective in plugging in terms of its morphology, size, and growth characteristics.
简单封堵油藏的高渗透“窜流带”是提高波及效率和原油采收率最合理且最直接可行的方法。是一种具有在钙离子存在下使尿素发生酶促水解从而沉淀碳酸钙（CaCO₃）能力的代表性微生物。微生物诱导碳酸钙沉淀（MICP）可胶结和密封颗粒状及裂缝性介质，因此可作为油藏高渗透带潜在的微生物封堵剂。以下研究了MICP封堵的微观特征及其降低渗透率的效果。使用具有三种不同粒度（40/60、60/80和80/120目）的近球形硅砂柱和角形硅砂柱作为代表不同孔径和孔隙特征的人造岩心，以研究不同生物处理周期下MICP封堵的效果和微观过程。结果表明，仅经过短时间的生物处理，渗透率就显著降低。经过八轮MICP处理后，每种岩心的渗透率下降至各自初始渗透率的54 - 90%。测得的CaCO₃含量表明，渗透率随CaCO₃含量增加的降低速率经历三个不同阶段，即缓慢下降、快速下降和平稳阶段。X射线衍射表明，生成的CaCO₃晶体大部分为球霰石，只有少量方解石。扫描电子显微镜成像进一步揭示了MICP封堵的微观过程。微生物首先聚集在孔壁上分泌CaCO₃，形成一层薄而大的均匀CaCO₃层。然后，CaCO₃晶体的一些成核位点将经历进一步的优先生长，形成大的主导晶体，在孔隙空间中充当封堵剂。与目前用于提高油藏波及效率的主要微生物封堵剂胞外聚合物相比，生物CaCO₃在形态、尺寸和生长特性方面的封堵效果似乎更有效。
