微生物钻井液在深厚覆盖层钻探中的应用及固壁护心机理研究

Application and mechanism of microbial drilling fluid for wall stabilization and core protection in deep overburden drilling

摘要:

针对深厚覆盖层钻探中存在的孔壁失稳与岩心采取率低等技术难题，本文以巴氏芽孢杆菌为核心微生物，基于微生物诱导碳酸钙沉淀（MICP）技术，综合考虑微生物生长特性与钻井液流变性能要求，构建了羧甲基纤维素钠（CMC）和生物聚合物（XC）2种适用于绳索取心钻进的微生物钻井液体系，并在我国西部某重大水电勘察工程的深厚覆盖层取心钻探中进行了工程应用试验，完成了258.75 m钻探进尺，同时根据岩心样品表面和内部的X射线衍射与扫描电子显微镜分析结果，探讨了微生物钻井液固壁护心作用机理。研究表明：在CMC加量为0.8%、XC加量为0.3%时，既能保障微生物的良好生长，又能满足钻进过程对钻井液流变性能的要求，确定微生物钻井液配方为0.8% CMC/0.3%XC+巴氏芽孢杆菌（OD₆₀₀=0.8）+0.5%氯化钠+2%尿素+2%胰蛋白胨；2种微生物钻井液均兼具良好的流变性能与生物活性，现场应用中有效维持了孔壁稳定，岩心采取率超过90%，实现了深厚覆盖层长孔段裸孔钻进，显著简化了孔身结构；钻井液中的微生物在岩心表面及孔壁周围诱导生成碳酸钙晶体（球霰石、方解石等），沉积于覆盖层松散颗粒表面及孔隙中，有效胶结松散颗粒，形成致密保护层，从而实现固壁护心。研究为深厚覆盖层取心钻探孔壁失稳、岩心采取率低等技术难题提供了新的解决方案，对提升深厚覆盖层钻探勘察质量具有重要的工程应用价值。

Abstract:

To address technical challenges such as borehole wall instability and low core recovery in deep overburden drilling， this paper constructs two microbial drilling fluid systems suitable for wire-line coring-sodium carboxymethyl cellulose （CMC） and biopolymer （XC）-based systems—using Bacillus pasteurii as the core microorganism， based on microbially induced carbonate precipitation （MICP） technology and by comprehensively balancing microbial growth characteristics with drilling fluid rheological requirements. Engineering application tests were conducted in deep overburden coring for a major hydropower exploration project in western China， achieving a total footage of 258.75 m. Concurrently， the mechanism of wall stabilization and core protection of microbial drilling fluids was investigated through X-ray diffraction （XRD） and scanning electron microscope （SEM） analyses of core sample surfaces and interiors. The results indicate that a CMC dosage of 0.8% and an XC dosage of 0.3% ensure good microbial growth while meeting the rheological requirements for drilling fluid in the drilling process. The optimized formula is determined as： 0.8% CMC/0.3% XC + Bacillus pasteurii （OD₆₀₀=0.8） + 0.5% NaCl + 2% urea + 2% tryptone. Both microbial drilling fluids exhibit excellent rheological properties and biological activity. Field applications demonstrated effective borehole wall stability maintenance， with core recovery rates exceeding 90%， enabling long-section open-hole drilling in deep overburden and significantly simplifying the borehole structure. The microorganisms in the drilling fluid induced calcium carbonate crystal formation （e.g.， vaterite， calcite） on core surfaces and around borehole walls. These crystals deposited on the surfaces of loose overburden particles and within pores， effectively cementing the loose particles to form a dense protective layer， thereby achieving wall stabilization and core protection. This study provides a novel solution for technical problems such as borehole wall instability and low core recovery in deep overburden core drilling， holding significant engineering application value for improving the quality of deep overburden drilling and exploration.