Discovery of overpressure gas reservoirs in the complex structural area of the Lower Yangtze and its key elements of hydrocarbon enrichment

The complexity of the structure in the Lower Yangtze area makes it very difficult and risky to explore for oil and gas in this area.How to make a breakthrough in oil and gas exploration has been the focus of attention in recent years.In 2019, two sets of abnormal high-pressure natural gas layers were firstly discovered in the Triassic Zhouchongcun Formation in Wuwei depression of the Lower Yangtze.The pressure coefficient reached 1.9, which was the highest one in East China.This new discovery made a significant breakthrough in the oil and gas exploration and proved the good resource prospect in the lower Yangtze.The new discovery of the overpressure gas reservoir reveals four key control factors for natural gas enrichment in Wuwei depression, namely deep stable basement, intracontinental in-situ block, favorable facies zones of black shale, multiple layers of anhydrite, and favorable source rock and good capping conditions, which provide stable tectonic setting, good structural preservation, favorable source rock and good capping conditions for oil and gas.The above geological factors are also conducive to the Permian shale gas enrichment in Wuwei depression.Accordingly, a new idea of conjoint exploration of Triassic conventional natural gas and Permian shale gas in one well is put forward.Finally, the configuration of the above four key elements in the Lower Yangtze region suggests that Wangjiang depression shares similar geological conditions with Wuwei depression, which making it a next priority for oil and gas exploration.