微生物无固相钻井液固壁作用与机理研究

At present, borehole wall failure in loose or fractured formation is a tricky problem, an effective solution to this problem has a positive theoretical and practical significance. In view of the successful attempt of microbial consolidation technology that reinforce the loose rock and soil, applicant want to use this technique to solve the problem of borehole wall failure in loose or fractured formation. This project is based on solid-free drilling fluids, it is preferable to select some microbial species that could grow normally and have active metabolism in solid-free drilling fluids, and then construct microbial solid-free drilling fluids. On the basis of this, in order to clarify the temperature and pH range suitable for microbial growth in solid-free drilling fluids, the effects of drilling fluids temperature and pH on microbial growth and urease activity will be studied. The effect of borehole wall reinforced by microbial solid-free drilling fluids will be based on the change of the physical and mechanical properties of the artificial core treated by the microbial solid-free drilling fluids. Finally, the change of the mineral composition, microstructure and pore structure of the artificial core treated by microbial solid-free drilling fluids will be analyzed by means of correlation analysis and testing, and the mathematical model of the process that the microbial solid-free drilling fluids reinforce the borehole wall will be established for analyzing its mechanism deeply. The aim of this project is to explore a new way to solve the instability of borehole wall in loosening or fracture strata formation for laying a stronger theoretical and technical basis that steady the borehole wall.

当前，松散性、破碎性地层钻孔孔壁失稳是一个棘手的难题，有效解决这一难题具有积极的理论与现实意义。鉴于微生物固结技术在松散岩土体加固中的成功尝试，欲将这一技术用于解决松散性、破碎性地层孔壁失稳问题。该项目立足于无固相钻井液，首先优选出能够在无固相钻井液中正常生长且新陈代谢活跃的微生物种类，构建微生物无固相钻井液；在此基础上，研究钻井液温度、pH值对微生物生长及脲酶活性的影响，明确在无固相钻井液中适宜微生物生长的温度和pH值范围；根据被微生物无固相钻井液处理后人造岩心物理力学性能的变化，探究微生物无固相钻井液固壁作用；最后，通过相关分析测试手段，分析被微生物无固相钻井液处理后人造岩心的矿物成分、微观形貌、孔隙结构等特征的变化，建立微生物无固相钻井液固壁过程数学模型，深入分析其固壁机理。力图探索一条有效解决松散性、破碎性地层孔壁失稳的新途径，为稳定钻孔孔壁奠定更加坚实的理论与技术基础。

本项目针对松散破碎性地层易发生坍塌失稳这一工程技术难题，通过实验研究和理论分析相结合，将微生物固结技术引入到地质钻探领域，用于加固松散破碎地层，提高孔壁的稳定性。首先，通过实验，对微生物（巴氏芽孢杆菌，下同）在无固相钻井液体系中的适应性进行研究，优选出适应微生物生长的无固相钻井液及材料的最佳加量，并对微生物在其中的生长动力学进行了研究，进而构建了微生物无固相钻井液体系。在此基础上，通过正交实验，系统研究了微生物无固相钻井液体系固壁效果，结果表明：钙源（氯化钙）浓度越高、初始菌种浓度越大、作用时间越长，其固壁效果越好。然后，利用XRD、SEM以及CT等测试技术，对经过微生物无固相钻井液处理后的碎石土颗粒所形成的岩心进行微观分析。结果表明，岩心中生成了碳酸钙晶体，其粒径处于5-25um范围内，分布于孔隙及其周围的颗粒表面。碳酸钙晶体的生成，导致岩心沿其纵轴方向上的面孔隙率波动较大，两端差异更明显。最后，构建微生物无固相钻井液体系加固钻孔孔壁过程的数值模型，并采用有限元软件COMSOL Multiphysics 对这一过程进行数值模拟分析，结果表明这一过程中生成的碳酸钙分布不均匀，岩心上部生成的碳酸钙要多余下部，两侧多余中间，且在某些点发生明显地聚集。综合微观分析和数值模拟结果，揭示了微生物无固相钻井液固壁作用机理。