Organic Geochemical Features of the Upper Paleozoic Coal-Bearing Deposits in Ordos Basin, North-Central China

The exploration of hydrocarbon resources plays a critical role in fulfilling the world’s increasing demand for energy. In this regard, the distribution and source rock characteristics of coal measure stratum in the whole basin are important and must be studied. However, systematic research has not been conducted yet. In this study, organic geochemical data, drilling data, and fieldwork were used to examine the source rock distribution of the Upper Paleozoic stratum. The results revealed that Upper Paleozoic coal-bearing rock series are mostly present in the Benxi, Taiyuan, and Shanxi formations, and mudstones and coals are formed frequently in tidal flat deposits. The layers of the coal and mudstone are primarily thick on the western sides, eastern sides, and northern sides, thin in the middle region, and gradually thinner from north to south. The source rocks are mostly enriched in the east and west of the basin. The results of the Rock-Eval pyrolysis analysis indicated that the overwhelming majority of the coal comprises excellent source rocks, all limestones are poor source rocks, and most mudstones are good–excellent source rocks. The kerogen type of most of the rock samples is type Ⅲ, suggesting typical “gas source” kerogen. Humus is derived from terrestrial organism and aquatic algae remnants, indicating a diversified parent material input. These results evidence that studied source rocks are at the postmature-dry gas stage.