关键词: 下寒武统, 页岩气, 主控因素, 滞留烃, 热演化程度, 生储耦合, 保存条件, 中国南方

Abstract: The shale gas resources are abundant of the Lower Cambrian in southern China, which is expected to be a major replacement fi eld for increasing reserves and production. However, geological conditions of the Lower Cambrian are more complex than those of Silurian shale gas. By taking the Lower Cambrian Hetang Formation in the southern Anhui of lower Yangtze area as study object, the geological characteristics and main controlling factors of shale gas accumulation of the Lower Cambrian are studied based on well drilling, logging, core sample, outcrop and lab test data. The results show that the effective hydrocarbon source conditions, reservoir conditions and preservation conditions are the basis for shale gas accumulation, and the proper dynamic coupling and space-time confi guration of the three are the key to shale gas enrichment. (1) The remained hydrocarbon is material basis for shale gas accumulation, and the degree of thermal evolution is the main factor affecting hydrocarbon expulsion effi ciency; (2) The degree of thermal evolution and preservation conditions jointly control the shale gas enrichment. The best window for the coupling of gas generation and reservoir occurs when R_o ranges from 1.8%-3.2%, and high pressure to overpressure formation is conducive to the maintenance of pores; (3) The preservation conditions are the key factors for the formation of shale gas reservoir. The tight roof and fl oor conditions and lateral reverse faults are favorable for the formation of “sealing box”, and the burial history of “late hydrocarbon generation and late tectonic uplift” is conducive to continuous hydrocarbon generation and slow down gas escape. The main target of shale gas exploration of the Lower Cambrian is structural stable areas with weak reformation and moderate thermal evolution.