中国南方下古生界海相页岩气成藏的构造-热力作用效应

Tectonic effects perform key roles in the accumulation of shale gas. This study mainly focuses on the evolution of pore structure and fracture network and the mechanism of shale gas accumulation during the deformation and maturation process of shale gas reservoirs. Self-designed high temperature and pressure deformation instrument is planned to be used to get different maturity and different deformed degree shale samples. Fluids injection methods (mercury injection, N2 and CO2 adsorption) would be employed to quantitatively characterize the pore structure in different maturity and different deformed degree shale. X-ray 3D system and other experiments would be utilized to establish the 3D structure of fracture in shale, and then clarify how fractures react under the changes of stress and temperature. 3D macromolecular structure of organic matter in shale would be constructed based on the high-resolution transmission electron microscopy experimentand Fourier transforms infrared spectroscopy experiments, and the evolution of organic structure of shale will also be discussed. On the aspect of shale gas storage, the free gas content and it evolution will be studied based on the evolution of volume of pores and fractures in shale. Monte Carle simulation and methane adsorption isothermal experiments will be employed to clarify the mechanism of adsorbed gas formation based on the 3D organic molecular models. Lower Paleozoic marine shale samples will be also collected and their pores structure and other characteristics will be tested. Through comparing the characteristics of Lower Paleozoic shale and physical simulated shale, the findings from physical simulated shale will be applied to the actualaccumulation processof Lower Paleozoic shale gas, and then the accumulation mechanism of marine shale gas in south China will be well understood.

围绕“页岩气成藏的构造-热力作用效应”这一科学问题，重点探究构造-热力作用下孔裂隙演化规律与页岩气成藏机制。拟利用自行设计的高温高压变形仪获取不同变质变形程度序列样品，通过流体注入法定量表征页岩孔隙结构在变质/变形中演化模式；利用X-ray三维成像系统等构建不同变质变形程度页岩裂隙三维网络，并阐明其对热力、应力的响应机制。基于透射电镜-红外显微镜联用构建页岩原位有机质三维大分子模型，探明有机质结构在变质变形中的演化特征。在此基础之上，利用有机质分子模型，结合等温吸附试验、孔隙结构表征实验，借助蒙特卡洛法模拟，探明吸附气、游离气赋存机理与演化机制；于此同时，采集不同构造背景的南方海相页岩样品并分析其孔裂隙特征、含气性特征等，通过对比物理模拟样品与自然构造-热演化样品，将变形变质实验所获的演化规律应用于实际的页岩气成藏过程之中，进而阐明构造-热力作用下南方海相页岩气成藏机制。

本次研究以下古生界海相页岩为研究对象，围绕“页岩气成藏的构造-热力作用效应”这一科学问题，以野外调查-实验测试-理论分析为思路，基于钻井岩心及野外剖面样品，重点探究构造-热力作用下页岩孔-裂隙演化规律与页岩气成藏机制。研究主要取得如下成果：（1）联合图像分析、流体注入法，多精度—全尺度精细表征了下寒武统过成熟页岩储层孔裂隙发育形貌、类型、成因及结构特征，系统分析了不同尺度孔隙分形非均质性，阐明了过成熟页岩孔隙发育控制因素；（2）阐明了构造—热力影响下，褶皱、断裂及滑脱层控制下页岩变形特征、不同变形强度页岩孔-裂缝特征的差异性演化过程，及其对页岩气运移保存的影响；（3）利用高分辨率透射电镜实验、红外光谱实验、13C 核磁共振等实验，揭示了页岩干酪根大分子结构特征、演化及有机质孔隙对构造-热力作用的响应机制；（4）基于不同系列温度甲烷高压吸附实验，揭示了页岩气赋存相态温压响应及动态转化规律，构建了页岩气原位赋存气量地质模型，结合埋藏-热演化-生烃-构造改造历史，阐明了构造-热作用下多因素耦合下页岩气成藏过程；（5）以滇东北地区五峰-龙马溪组为例，通过裂缝统计、流体包裹体分析及孔隙表征等手段，揭示了断裂作用对页岩储层孔-裂缝结构的宏观-微观改造机制，并提出了逆断层侧向遮挡宽缓向斜翼部、逆冲断层间传播褶皱高位２种页岩气富集保存有利构造样式。研究成果有助于推进四川盆地盆缘、盆外复杂构造区海相页岩气进一步勘探开发。