超临界CO2压裂页岩多物理场耦合机理研究

Supercritical CO2 (SC-CO2) fracturing shale reservoirs not only can efficiently develop shale gas, but also can achieve CO2 storage and reduce environmental stress. At present, SC-CO2 fracturing technology is still in the initial stage, and there is no systematic research on the crack initiation and extension of SC-CO2 fracturing. This project intends to simulate the SC-CO2 fracturing process by indoor triaxial fracturing experiment, combined with CT technology to scan fractured rock samples to obtain fracturing characteristics, based on Simulated Annealing Method and 3D Digital Core Reconstruction Technology to build a 3D Crack Distribution Digital Model to analyze the crack initiation and extension of SC-CO2 fracturing. On the basis of laboratory experiments and based on Discrete Fracture Network, the mathematical model of SC-CO2 fracturing under the coupled effect of binary medium field-stress field-seepage field is established by using seepage theory and stress theory, and using COMSOL finite element numerical solution platform for numerical solution to simulate the fracturing initiation and extension、stress change and fluid migration process and to reveal the multi-field coupling mechanism in shale SC-CO2 fracturing. This study is of great significance to accurately grasp the situation of SC-CO2 fracturing in shale reservoirs and promote the efficient exploitation of shale gas resources in China.

超临界CO2压裂页岩储层，既能高效开发页岩气，又能实现CO2埋存，减少环境压力。目前超临界CO2压裂技术尚处于初级阶段，对于超临界CO2压裂过程中的多物理场综合作用缺乏深入系统的研究。本项目拟采用室内三轴压裂实验模拟超临界CO2致裂过程，结合CT技术扫描压裂岩样获取压裂特征，基于模拟退火法和三维数字岩心重构技术建立三维裂缝分布数字模型，分析超临界CO2压裂裂缝起裂及延展规律；在室内实验基础上，综合运用渗流场和应力场理论，基于离散裂缝网络方法，建立考虑双重介质场—应力场—渗流场多场耦合作用下的超临界CO2压裂数学模型，利用COMSOL有限元数值求解平台进行数值求解，模拟计算压裂萌生与延展、应力变化及流体运移过程，揭示页岩超临界CO2压裂中的多场耦合作用机理。本研究对于准确掌握页岩储层超临界CO2压裂状况，推动我国页岩气资源的高效开采具有重要意义。

超临界CO2压裂页岩储层，既能高效开发页岩气，又能实现CO2埋存，减少环境压力。目前超临界CO2压裂技术尚处于初级阶段，对于超临界CO2压裂过程中的多物理场综合作用缺乏深入系统的研究。本项目采用室内三轴压裂实验系统开展了不同水平地应力差、不同泵注排量下页岩超临界CO2室内压裂实验，研究了水平地应力差和泵注排量对压裂缝形态特征的影响机理；结合CT技术扫描压裂岩样及数字岩心技术提取了页岩超临界CO2压裂裂缝几何参数并量化了裂缝分布特征，分析了超临界CO2压裂裂缝起裂及延展规律，建立了页岩超临界CO2压裂裂缝等效渗流模型；在室内实验基础上，综合运用渗流场和应力场理论，基于离散裂缝网络方法，建立了考虑双重介质场—应力场—渗流场多场耦合作用下的超临界CO2压裂数学模型，精确模拟了页岩超临界CO2压后复杂裂缝网络模型流固耦合特征，揭示了页岩超临界CO2压裂中的多场耦合作用机理。本研究对于准确掌握页岩储层超临界CO2压裂状况，推动我国页岩气资源的高效开采具有重要意义。