超临界CO2对深部页岩力学和渗流特性的影响研究

水力压裂开采页岩气的广泛使用所带来的耗水量大和环境污染问题已日渐突出。超临界CO2以其独特的物理特性为强化页岩气开采和页岩气藏地质封存提供了新思路。申请者在前期研究中发现，CO2或其水溶液会改变页岩的力学特性，进而影响页岩气开采效果和地质封存安全性等。但目前关于CO2对页岩影响的研究还处于低温、低压、短时的室内模拟水平。为此，针对我国页岩气埋藏较深的特点，本课题首次对经过高温(100℃)、高压(60MPa)的超临界CO2及其水溶液长时间(1年)浸泡后的页岩进行力学和渗流试验，系统研究超临界CO2及其水溶液作用后页岩力学和渗流特性的变化规律，并通过微观测试获取页岩浸泡前后微观结构等的变化规律，揭示页岩力学和渗流特性的变化机理。结合力学特性、渗流特性和微观试验结果，建立页岩在应力-渗流-化学耦合作用下的损伤本构模型，为超临界CO2强化页岩气高效开发和页岩气藏地质封存提供技术支持。

The widely use of hydraulic fracture for shale gas recovery has brought the problems of large water consumption and environmental pollution to the forefront. Because of the special physical properties, supercritical carbon dioxide can be used to enhance shale gas exploitation and CCS (Carbon Capture and Storage) in shale reservoirs. The applicant’s previous research showed that CO2 or its water-based fluids could affect the shale’s mechanical properties, which would influence fracturing efficiency and the safety of CCS. However, previous studies have only investigated the effect of supercritical CO2 on shale in low levels of temperature, pressure and short duration for fluids-rock interactions. Therefore, based on the characteristics of shale reservoir in China, laboratory tests are firstly applied for shale samples saturated in supercritical CO2 and its water-based fluids with high temperature (100℃), high pressure (60MPa) and long soaking time (1 year) in this research to analyze the mechanical and seepage characteristics of shales. The microstructure variations of shales after imbibition are also tested to reveal the mechanics of shale’s mechanical and permeability changes. Combined with the mechanical and seepage characteristics and microscale results, the damage constitutive models based on the coupled mechanical-hydro-chemical effects can be created to support the supercritical CO2 enhanced shale gas exploitation and the storage of supercritical CO2 in shale reservoirs.