Genetic types and source characteristics of hydrocarbon gases adsorbed by Mesozoic-Paleozoic marine strata in well CSDP-2, Laoshan uplift, South Yellow Sea Basin

Based on the analysis of molecular and carbon and hydrogen isotopic composition of adsorbed hydrocarbon gases within different period's strata in well CSDP-2 of Laoshan uplift in the South Yellow Sea Basin, the genetic types and source characteristics of adsorbed hydrocarbon gases were discussed.Different period's strata exhibit different contents of adsorbed hydrocarbon gas and the main enrichment horizons are the Fentou Formation, Gufeng Formation, Chuanshan Formation, Qixia Formation and Huanglong Formation in turn.Adsorbed hydrocarbon gas enriched in strata is controlled by many factors, including lithology, organic contents and hydrocarbon gas migration etc.Gufeng Formation mainly shows source rock characteristics, while Fentou Formation, Chuanshan Formation, Qixia Formation and Huanglong Formation mainly show reservoir characteristics.The hydrocarbon gases adsorbed in the strata of each period are mainly thermogenic types, among which the Gufeng Formation, Fentou Formation and Qixia Formation are partially deviated from the thermogenic areas due to the mixing of the same type with different source gases or the same gas in different periods.The source organic matter type of adsorbed hydrocarbon gases belongs to type Ⅱ kerogen (marine source rock), in which some horizons have type Ⅲ kerogen (terrestrial source rock) mixed.The thermal maturity (R_o) of adsorbed hydrocarbon gas is between 0.6% and 1.6%, which is in the range of maturity to over-maturity.The results provide geochemical basis for the exploration of Mesozoic-Paleozoic oil and gas in Laoshan uplift, South Yellow Sea Basin.