泥页岩粘土矿物表面电化学反应及岩体膨胀数值模拟研究

The shale expansion while contacted with water is one of the characteristics of the shale which is different from other rocks，and the main reason of oil drilling downhole accidents. According to statistics,70% of the downhole accident is associated with the shale. Moreover,the wellbore collapse of shale while the formation produces wate is the technical bottleneck of gas drilling. The microscopic mechanism of shale expansion while contacted with water is the electrochemical reaction occurred between the clay mineral surface and water solution,the distance between the crystal paticles increased,and the shale volume expanded. The project studies the problems which include the migration law of the shale pore fluid、the surface electrochemical reaction of the clay mineral 、the relationship between the shale volume expansion and surface electrochemical reaction and etc. By the experimental study, such as the pressure permeation experiment、mineral composition testing、crystal layer testing、Zeta potential testing、hydration stress and strain testing, combined with the seepage mechanism、the clay mineralogy、the colloid chemistry and etc, the theoretical calculation models for the pore fluid seepage、the surface electrochemical reaction and the electric potential distribution of the clay mineral、the stress distribution and the distance change between the clay mineral crystal units are established. With the composition and spatial distribution of shale minerals,and the shale volume expansion is studied with the numerical simulation.

泥页岩遇水体积膨胀是泥页岩区别于其它岩石的特征之一，是诱发石油钻井井下复杂的主要原因，据统计，70%的井下复杂与泥页岩有关，另外，地层出水条件下泥页岩井壁垮塌是气体钻井的技术瓶颈。泥页岩遇水体积膨胀的微观作用机理是泥页岩粘土颗粒晶体表面与水溶液之间发生电化学反应，晶体颗粒之间距离增加，宏观上表现为泥页岩体积膨胀。本项目针对该项技术所涉及的泥页岩孔隙流体渗流运移规律、粘土矿物晶体表面电化学反应及其与泥页岩体积膨胀之间关系等关键问题展开研究，通过压力渗流实验、矿物组分测试、晶层间距测试、Zeta电位测试、水化膨胀应力应变测试等实验研究，利用渗流力学、粘土矿物学、胶体化学等学科知识，建立泥页岩孔隙流体渗流运移、粘土矿物表面电化学反应及电势能分布、粘土矿物晶体之间力学分布及晶体之间距离变化理论计算模型，结合泥页岩矿物组分及空间几何分布，数值模拟泥页岩体积膨胀。

泥页岩水化学反应是泥页岩独有的特征，是造成堤坝溃塌、山体崩塌和井壁垮塌的主要原因。开展泥页岩水化学反应的微观作用机理研究，形成系统的理论与实验评价方法，是避免或有效降低工程复杂事故的重要保障。目前，针对泥页岩水化学反应的相关研究，主要借助室内实验方法定量评价泥页岩水化学反应的宏观表现，还没有一套基于泥页岩水化学反应微观作用机理的系统的理论评价方法。本项目系统研究了泥页岩井壁岩石与井筒之间流体渗流运移规律，并形成了理论计算模型及实验配套设备；其次，深入研究了泥页岩粘土矿物晶体表面电化学反应及粘土表面水化、渗透水化势能控制模型，建立了粘土水化效应与泥页岩岩体膨胀、岩体力学参数劣化等之间关系定量评价模型及配套实验验证方法；最后，考虑井壁岩石渗流效应、粘土水化膨胀及岩石力学参数劣化等因素，建立了泥页岩物理化学耦合作用井壁稳定性评价方法。