Using light hydrocarbons to identify the depositional environment of source rocks in the Ordos Basin, central China

摘要

The Carboniferous-Permian coal beds in the Ordos Basin of central China are generally considered the source of gas found in upper Paleozoic reservoirs. However, the coal beds consist of both coal and coaly mudstone, each with a different distribution and potential for hydrocarbon generation. The ability to distinguish the gases generated by each type of source rock is critical for further petroleum exploration. In this study we integrated several light hydrocarbon indices (e.g., the Halpern C7OCSD, the K-2) with carbon and hydrogen isotopes and the distribution of sedimentary facies in order to distinguish the coal-generated gases from the mudstone-generated gases. The differences in the light hydrocarbon contents of the coal and the coaly mudstone relate to the depositional environment, where the coal was deposited on a delta plain and the mudstone was deposited along the delta front. This paper presents a method for accurate gas-source correlation and its integration with sedimentary facies and depositional environment, for improved prediction and exploration of petroleum systems.