岩石学方法区分页岩中有机质类型

有机质孔在富有机质泥/页岩中广泛发育，被认为是含气页岩孔隙系统中重要的组成部分。有机质孔不仅在干酪根中发育，在固体沥青内部同样发现了大量的有机质孔，不同类型的有机质内部有机孔的形态和发育程度有所差异。根据有机质的成因，可将其分为沉积有机质和迁移有机质。沉积有机质为原始的有机质及其蚀变产物，这些有机质未发生过迁移，与陆源矿物紧密结合；迁移有机质存在于矿物孔隙中，由外地迁移过来的沥青或石油，随着热成熟度的增加，可演变成固体沥青或焦沥青，其周缘通常可见自生矿物。自生石英对页岩孔隙的影响具有双重作用，一方面充填了孔隙空间，减少了页岩孔隙；另一方面自生石英起到了支撑孔隙的作用，抑制了页岩的压实，为迁移有机质的充填保留了一部分孔隙空间。沉积有机质和迁移有机质中均发育孔隙，迁移有机质充填三维空间相互连通的矿物孔隙，内部形成的有机质孔隙在三维空间上的连通性要比沉积有机质强。五峰组—龙马溪组页岩由下至上呈网络状分布的迁移有机质逐渐减少，相互连通的有机质孔隙网络也相应减少，页岩储层质量逐渐变差。

Petrographic methods to distinguish organic matter type in shale

Pores within organic matter are widely recognized as a significant component of pore systems in gas shale. These pores form not only in kerogen, but also in solid bitumen, with different morphology and development degree. The source of organic matter can be divided into depositional and migrated organic matter. Depositional organic matter is deposited in direct contact with detrital mineral grains and comprises depositional kerogen and its alteration products. Migrated organic matter occurs in mineral pores initiatially as bitumen or oil that filled the cement-lined pores and cement would separate bitumen or oil from mineral grains and may evolve into solid bitumen and pyrobitumen during maturation. Authigenic quartz has a dual role in influencing shale porosity. On one hand, it reduces shale porosity by filling pore space,while on the other hand,it supports pore preservation by inhibiting shale compaction and preserving pore space for migrated organic matter. There are pores both in depositional organic matter and migrated organic matter. Migrated organic matter is present in three-dimensional connected mineral pores, which produces a pore network with higher reservoir quality than a pore network associated with only depositional organic matter. Migrated organic matter decreases from bottom to top in the Wufeng-Longamxi formations, the connected pore network decreases accordingly, and reservoir quality becomes poorer.