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页岩储层孔隙发育特征是页岩储层评价的重要内容,也是开展页岩油气赋存机理研究的基础。提出了通过“基质类型—孔隙产状—孔隙成因”划分孔隙类型的方案。利用氩离子抛光和场发射扫描电镜技术观察孔隙发育情况,根据基质类型和孔隙产状,识别了4类孔隙:粒间孔、粒内孔、有机质孔和微裂缝,并根据孔隙成因将粒间孔分为碎屑颗粒间原生孔、黏土矿物片体间孔和颗粒间溶蚀孔,将粒内孔分为长石颗粒内溶蚀孔、黏土矿物片体内孔和黄铁矿晶体间孔。有机质孔主要为有机质颗粒内的微裂缝和有机质内孤立分布的孔径较小的孔隙。微裂缝主要表现为纹层缝或页理缝。综合孔隙图像分析、低温液氮吸附实验结果、孔隙结构参数与矿物组成、有机碳含量和有机质成熟度等参数相关性分析,认为沉积条件、成岩作用和有机质热演化控制了孔隙的形成和保存。半深湖—深湖沉积环境下,富有机质页岩中发育重力流成因的薄层砂质纹层,纹层段碎屑颗粒含量高,有利于形成碎屑颗粒粒间孔、碎屑颗粒粒内孔和顺层微裂缝。早期成岩作用阶段形成黄铁矿,有利于形成黄铁矿晶间孔,但黄铁矿也是压实作用的主要参与者;压实作用造成粒间孔和粒内孔的孔径变小和孔体积降低,碎屑颗粒和黄铁矿与有机质颗粒间呈凹凸接触,有机质孔在压实作用下闭合导致有机质孔不发育;溶蚀作用促进长石粒间溶孔和长石粒内溶孔的形成,一定程度改善储层质量。在成熟度达到一定阶段(RO≈0.75%)后,开始出现有机质孔。有机质孔发育程度差,一方面受成熟度的影响,另一方面可能是压实作用造成的。此外,富有机质泥页岩渗透性较差,烃类被吸附在有机质表面或溶于干酪根内部,造成干酪根体积膨胀也可能是有机质孔不发育的一种原因。
The pore development characteristics of shale reservoirs are an important part of shale reservoir evaluation and the foundation for the study of shale hydrocarbon accumulation mechanism. Proposed by “matrix type - porosity production - pore origin ” scheme of pore type. The pore development was observed by argon ion polishing and field emission scanning electron microscopy. Four types of pores were identified according to the type of matrix and the occurrence of porosity: intergranular pores, intragranular pores, organic pores and microcracks. According to the pore formation, The pores are divided into primary pores between detrital particles, intercrystalline pores of clay minerals and intergranular dissolution pores, and the intragranular pores are divided into dissolution pores of feldspar grains, intercrystalline pores of clay mineral fragments and intergranular pores of pyrite crystals. The organic pores mainly consist of micro-cracks in the organic matter particles and small pores with isolated pores distributed in the organic matter. Microcracks mainly manifested as grain seam or page seam. Based on the analysis of the comprehensive pore images, the experimental results of cryogenic liquid nitrogen adsorption, the correlation between pore structure parameters and mineral composition, organic carbon content and organic matter maturity, it is considered that the deposition conditions, diagenesis and thermal evolution of organic matter control the formation and preservation of pores. Under the condition of semi-deep lacustrine-deep lake sedimentary environment, the thin sandy layer with gravity flow developed in organic-rich shale has a high content of detrital particles, which is favorable for the formation of detrital intergranular pores and detritus particles The inner hole and the layer of micro-cracks. Pyrite formation during the early diagenesis stage favors the formation of intergranular pores of pyrite, but pyrite is also a major contributor to compaction; the compaction results in smaller pore sizes of the intergranular and intragranular pores and pore volume Reduced, debris particles and pyrite and organic particles were in contact with each other, organic matter pores closed under compaction led to the organic matter pore is not developed; dissolution of feldspar intergranular pores and feldspar dissolved particles to promote the formation of pores, To some extent, improve reservoir quality. After the maturity reached a certain stage (RO ≈ 0.75%), began to appear organic pores. Organic matter pore development is poor, on the one hand by the maturity of the impact, on the other hand may be caused by the compaction. In addition, the permeability of organic-rich mud shale is poor. Hydrocarbons are adsorbed on the surface of organic matter or are dissolved in kerogen, resulting in the volume expansion of kerogen, which may also be one of the reasons for the under-development of organic matter.