天环坳陷页岩气井井壁失稳机理及防塌钻井液技术研究与应用

Research and Application of Wellbore Instability Mechanism and Anti-sloughing Drilling Fluid Technology for Shale Gas Wells in Tianhuan Depression

针对天环坳陷构造区块泥页岩地层井壁失稳问题,通过复杂地层矿物组成、微观构造、理化性质以及三轴应力实验综合分析,提出了“封堵+润滑”的双效协同井壁防塌对策。泥页岩微裂缝、微孔隙发育,地层岩样易水化膨胀以及岩心表面亲水性较差是造成井壁失稳最主要的原因。通过加强地层封堵能力和降低水平段摩阻,可达到稳定井壁的目的。所构建的高效防塌钻井液体系抗NaCl能力为10%,抗CaCl_(2)能力为1.0%,抗劣土能力为10%,回收率为99.6%,对80~100目砂床侵入深度为8.4 mm,较现场水基钻井液渗透性封堵性能有明显提升,能够封住200μm和400μm模拟裂缝,承压能力达到5 MPa,抑制水化分散能力和裂缝性封堵能力优良。在现场应用过程中,水平段的平均井径扩大率低于6%,平均钻速达到4.7 m/h,钻井液体系的静滤失量控制在5 mL以下,在润滑防塌、井眼净化及储层保护方面都起到了很好的效果。研究结果表明,该防塌钻井液体系有效解决了天环坳陷构造区块钻井过程中出现的井壁失稳问题,节约了钻井成本,具有较好的推广前景。

To address the problem of well wall instability in the mud shale formation in the Tianhuan Depression Tectonic Block,a dual-effective collaborative well wall collapse prevention countermeasure of"blocking+lubrication"was proposed through a comprehensive analysis of the mineral composition,microstructure,physical and chemical properties of the complex formation and triaxial stress experiments.The development of microfractures and microporosity in the mud shale,the easy hydration and swelling of the formation rock samples and the poor hydrophilicity of the core surface are the main causes of well wall instability.By strengthening the plugging ability of the formation and reducing the friction of the horizontal section,the purpose of stabilizing the wellbore can be achieved.The constructed high-efficiency anti sloughing drilling fluid system has a NaCl resistance of 10%,a CaCl_(2) resistance of 1.0%,a poor soil resistance of 10%,and a recovery rate of 99.6%.The invasion depth of 80~100 mesh sand bed is 8.4 mm,which is significantly improved compared with the permeability and plugging performance of on-site water-based drilling fluid,and can seal 200μm and 400μm simulate the fracture,the pressure bearing capacity reaches 5 MPa,and the ability to inhibit hydration dis-persion and crack sealing is excellent.In the process of field application,the average well diameter expansion rate in the horizontal section is less than 6%,the average drilling speed reaches 4.7 m/h,and the API filtration is controlled below 5 mL,which has played a good role in lubrication and anti sloughing,borehole purification and reservoir protection.The research results show that the anti sloughing drilling fluid system effectively solves the problem of wellbore instability during drilling in the structural block of Tianhuan Depression,saves drilling costs,and has a good promotion prospect.