川东地区东岳庙段沉积环境演化及其页岩油气富集主控因素分析

川东地区下侏罗统自流井组东岳庙段富有机质泥页岩发育,且在局部地区已获工业页岩油气流,但尚未实现规模开发,其页岩油气富集机理研究滞后于生产实践。本文在野外调查和测试分析的基础上,对其沉积环境演化及页岩油气地质条件进行分析,并探讨其页岩油气富集主控因素,以期为实现东岳庙段页岩油气突破提供有益借鉴。结果显示：川东地区东岳庙段发育一个完整的水进水退沉积旋回,富有机质泥页岩主要发育于中部半深湖相,厚约15~30m,TOC平均为1.79%,以II型有机质为主,热演化程度较高,达凝析油—湿气阶段。以黏土矿物粒间孔和有机质孔为主,脆性矿物含量中等,脆性指数平均为62.1%。平均孔隙度为8.85%,而渗透率极低,均值仅0.239mD,呈现出“高孔低渗”特征,层内油气以侧向运移为主。其页岩油气的富集主要受富有机质泥页岩分布、热演化程度和裂缝发育条件的控制。推论垂向富有机质泥页岩连续发育的现今油气低势区是川东地区东岳庙段潜在的页岩油气高产区。

The evolution of sedimentary environments of Dongyuemiao Member and key factors for enrichment of shale oil and gas, northeastern Sichuan Basin

The organic-rich mud shale develops in Dongyuemiao Member of the Lower Jurassic Ziliujing Formation in eastern Sichuan Basin. Although a few of industrial shale oil and gas flow has been obtained, the large-scale production of shale oil and gas hasn''t started yet, and the understanding of the enrichment mechanism of shale oil and gas in the region is not enough. Based on the field investigation and test analysis, this paper analyzes the evolution of sedimentary environments of the Dongyuemiao Member and discusses the main control factors for enrichment of shale oil and gas, in order to provide scientific suggestions for the breakthrough of shale oil and gas in the region. The results show that:(1) The Dongyuemiao Member had experienced a whole retrogradation-progradation cycle, and the organic-rich shale, which is in the semi-deep lake facies, is located at the middle of the Dongyuemiao Member; (2) The thickness of organic-rich shale in the Dongyuemiao Member is from 15 m to 30 m and its average TOC is 1.79%, and the kerogen is mainly in II type; (3) The thermal evolution degree of the Dongyuemiao Member is high, reaching condensate-moisture stage; (4) The pores are mainly composed by the soil mineral intergranular pores and organic pores, and the content of brittle minerals is moderate and the average brittleness index is 62.1% and the average porosity is 8.85%; (5)The permeability is extremely low, with an average of 0.239 mD. It is concluded that the Dongyuemiao Member belongs to the "high porosity and low permeability". The hydrocarbon in the Dongyuemiao Member is mainly migrated along the bed plane in lateral directions. The enrichment of the shale gas and oil in Dongyuemiao Member is closely related to the distribution of organic-rich shale, the thermal evolution of the shale, and the distribution of fractures. The prolific zones for shale gas and oil in Dongyuemiao Member are characterized with thick organic-rich shale and low hydrocarbon accumulation potential.