海相页岩成岩-成烃过程中孔隙结构的演变——来自热模拟实验的启示

页岩在沉积埋藏过程中，孔隙的形成、演变与成岩-成烃过程是同步的。为了揭示成岩-成烃作用对页岩孔隙结构的影响，以西加拿大盆地上白垩统海相未成熟页岩为研究对象，开展了地质条件约束下页岩从未成熟到过成熟阶段的成岩-成烃热模拟实验，并利用高分辨扫描电镜对热模拟后样品的微观结构进行分析，运用低温液氮吸附-脱附实验和Frenkel-Halsey-Hill （FHH）模型对实验样品的孔隙发育特征和分形维数进行定量分析。结果表明：①成岩-成烃过程中页岩的孔隙结构复杂多变，主要发育介孔和大孔，以楔状或平行板状狭缝型孔隙为主；②页岩中的孔隙比表面积主要为小于15 nm的微孔和介孔所贡献；③有机质丰度并非影响孔隙分形特征的主要因素，孔隙的结构分形维数与平均孔径存在明显的负相关关系，孔径越小孔隙间的连通性越差，孔隙结构越复杂；④不同演化阶段孔隙的分形特征差异明显，成熟阶段的生烃作用导致黏土矿物转化及矿物溶蚀可大大降低孔隙结构及表面的复杂程度，高过成熟阶段有机质孔的大量形成可增大孔隙表面的粗糙程度并使得页岩具有高的孔隙比表面积。

Evolution of pore structure during diagenesis and hydrocarbon generation of marine shale: the inspiration from thermal simulation experiments

During the deposition and burial of shale, pore formation and evolution are synchronized with the diagenesis and hydrocarbon generation processes. To reveal the effect of diagenesis and hydrocarbon generation on the pore structure of shale, taking the Upper Cretaceous marine immature shale in the Western Canada Basin as the research object, this study carries out the thermal simulation experiments on the diagenesis and hydrocarbon generation of shale from immature to over-mature stages under the geological conditions, analyzes the microstructures of samples after thermal simulation using the high-resolution scanning electron microscope, and quantitatively analyzes the pore development characteristics and fractal dimensions of experimental samples using the liquid nitrogen adsorption-desorption experiment and the Frenkel-Halsey-Hill (FHH) model. The results show as follows. (1) During diagenesis and hydrocarbon generation, the pore structures of shale are complex and changeable, mainly developing mesoporous and macroporous, with the shape of wedge or parallel plate. (2) The specific surface area of pore is mainly contributed by micropores and mesopores with the diameter smaller than 15 nm in shale. (3) Organic matter abundance is not the main factor affecting the fractal characteristics of pores. There is a clear negative correlation between the fractal dimension of pore structure and the average pore size, the smaller the pore size, the poor the pore connectivity, and the more complex the pore structure. (4) The fractal characteristics of pores in different evolutionary stages are obviously different.The clay mineral transformation and mineral dissolution caused by hydrocarbon generation in the mature stage can greatly reduce the complexity of pore structure and surface, while the formation of a large number of organic matter pores in the mature stage can increase the roughness of pore surface and make shale have a high pore specific surface area.