Shale gas accumulation conditions and resource potential evaluation of the Cambrian in the Lower Yangtze area

The Cambrian in the Lower Yangtze region is a marine sedimentary stratum with an area of 130×10³km². The Lower Cambrian Hetang Formation (Makufushan Formation) comprisesblack carbonaceous mudstones with a thickness of 276 m and an organic carbon content (TOC) rangingfrom 0.25%-23.52%, averaging 4.54%. The organic matter is mainly of type I, showing favorable conditions for shale gas accumulation. The Lower Cambrian stratum has experienced tectonic movements and transformation duringmagmatic activityduring the Caledonian, Hercynian, Indosinian, Yanshanian and Himalayan periods, and some individual sections have become part of metamorphic rocks. Therefore, the thermal evolution degree of carbonaceous mudstones is high in the Hetang Formation in many areas of the Lower Yangtze region. The maximum vitrinite reflectance (R_o) is 6.32%, indicating for an over mature stage. At the same time, due to large overburden and structural influence, the burial depth of the Hetang Formation also varies. The thickness, burial depth, TOC content and Ro of the carbonaceous mudstones in the Hetang Formation were applied to construct ageological survey and potential evaluation of shale gas in the Cambrian in the Lower Yangtze region. There are mainly three exploration targets including the region from the Shangrao area in the Jiangxi Province to the Tonglu area in the Zhejiang Province, the Yangzhou area in the Jiangsu Province and the Quanjiao area in the Anhui Province, with an estimated resource of 28894×10⁹m³.