渝东南地区页岩气富集区差异性分布成因

Causes leading to difference of different wellblocks in southeastern Chongqing in shale gas enrichment

为了揭示我国南方海相页岩分布广泛,但含气性差异巨大的原因,选取渝东南地区五峰组—龙马溪组页岩含气量不同的2个典型井区A井区和B井区进行对比分析,结果表明:含气量高的A井区页岩具有有机碳含量高、成熟度高的特点,而含气量低的B井区页岩具有有机碳含量低、成熟度相对低的特点;A井区页岩具有伊/蒙混层含量低、比表面积大、有机质孔十分发育的特点,而B井区页岩具有伊/蒙混层含量高、比表面积小、有机质孔发育较少、矿物溶蚀孔十分发育的特点;A井区页岩裂缝基本不发育,而B井区页岩裂缝十分发育。因此,A井区生烃条件、储集条件和保存条件均优于B井区,是页岩气富集于A井区而未富集于B井区的原因。预测页岩气地质甜点需综合考虑生烃条件、储集条件和保存条件,三者相匹配是页岩气成藏的关键。

Marine shale widely distributes in southern China,but there is great difference of different areas in shale gas enrichment. In order to reveal the causes,the shale gas content of Wufeng- Longmaxi formation in two typical wellblocks of A and B in southeastern Chongqing is compared and analysed. The results show that: the shale of high gas content in wellblock A is of higher organic matter content and maturity than the shale of low gas content in wellblock B; the shale in wellblock A is characterized by low illite /smectite layer content,large specific surface area and abundant organic matter pores,while the shale in wellblock B is characterized by high illite / smectite layer content,small specific surface area,few organic matter pores and abundant mineral dissolution pores; few fractures are developed in the shale of wellblock A,while a lot of fractures are developed in the shale of wellblock B. Therefore,the reasons why shale gas is more abundant in wellblock A than in wellblock B are that the hydrocarbon generation,reservoir and preservation conditions of wellblock A are better than those of wellblock B. Therefore to predict the sweet points of shale gas should comprehensively consider hydrocarbon generation,reservoir and preservation conditions,and their good matching is the key to the accumulation of shale gas.