富伊利石页岩气地层水化失稳机理及化学物理耦合控制方法研究

The industrial development of shale gas has been realized at home and abroad based on the medium and long horizontal wells. The oil-based drilling fluids can basically meet the requirement of shale gas drilling, but the environmental acceptability is poor and the cost is high. Water-based drilling fluids that can replace oil-based drilling fluids have high application potential in the future. Due to the failure to solve hydration and the instability of wellbore in shale formation with high content of illite, wellbore collapse is serious in the process of drilling long horizontal wells in shale formation using water-based drilling fluids. This technical problem restricts the application of water-based drilling fluids in shale gas drilling in China. Therefore, this project is focusing on the mechanism and control methods of hydration instability in shale formation. By studying the influence mechanism of shale fabric characteristics, wettability, salinity in water and surface tension on the hydration process, the effects of hydration on shale microstructure and compressive strength, and mechanism of hydration instability will be revealed. On this basis, this project will develop high-efficiency hydration inhibitors and strong plugging agents for shale gas formations, and build chemical-physical coupling method to control shale hydration, which provides the theoretical basis for the development of new water-based drilling fluids for horizontal wells in shale gas formation.

国内外以中长段水平井为基础，实现了页岩气的工业开发，油基钻井液基本能够满足页岩气钻井的需要，但环境可接受性差、成本高，可替代油基钻井液的水基钻井液是未来的发展趋势。由于未能解决富伊利石页岩地层的水化问题，水基钻井液钻页岩气长水平井过程中井壁坍塌非常严重，已成为制约我国水基钻井液推广应用的技术难题。为此，项目拟围绕页岩地层水化失稳机理与控制方法的科学问题，通过研究页岩组构特征、润湿性、水矿化度及表面张力等因素对水化过程的影响机制，阐明水化对页岩微观结构、抗压强度的作用规律，揭示页岩气地层水化失稳机理；在此基础上，研制适用于页岩气地层的高效水化抑制剂和强封堵剂，建立基于化学物理耦合的页岩水化失稳控制方法，为页岩气水平井新型水基钻井液研发提供理论依据。

由于未能解决富伊利石页岩水化问题，水基钻井液钻页岩气长水平井过程中，井壁坍塌问题严重，已成为制约页岩气安全、高效开发的重大技术难题。本项目围绕页岩地层水化失稳机理与控制方法的科学问题，通过研究页岩组构特征、吸附水的物化特征等，揭示了长宁、威远地区页岩气地层以伊利石为主要组分，表面水化是引起页岩水化的主要原因。页岩中与水的羟基数量少，但水化作用力强，当页岩地层中的伊利石与钻井液接触时，它与水以快速水化结合，并且游离羟基和自缔合羟基形成牢固的氢键。同时，页岩层间孔隙、微裂缝发育，毛管力加剧水侵入页岩，致使页岩原始裂缝拓宽、延伸；页岩中可溶盐组分溶解，页岩抗压强度降低，页岩井壁应力分布改变；井壁裂缝间摩擦系数减小，裂缝间易发生滑动，造成页岩井壁水化失稳。在此基础上，研制了高效页岩水化抑制剂和内刚外柔封堵剂，并以这两种处理剂为核心，优选了降滤失剂、润滑剂等，构建了一套页岩气强抑制强封堵水基钻井液。该钻井液在120℃下高温高压滤失量为7.2ml，页岩回收率达90.2%。本课题所得研究成果将为我国页岩气安全高效开发提供理论与技术支撑。