Geochemical characteristics and genesis of deep marine carbonate natural gas in China

The deep and ultra-deep oil and gas has been a prominent exploration direction in the field of petroleum industry in recent years. The deep oil and gas resources are mainly distributed in the carbonate rocks, clastic rocks and igneous rocks, of which the carbonate rock reservoirs account for about 40% of global oil and gas reserves for their superior reservoir properties. Currently, a number of large oil and gas fields have been discovered in the deep marine carbonate rocks in China, especially in the Sichuan and Tarim Basin, thus showing a broad oil and gas exploration potential in the deep marine carbonate rocks. In this paper, the genesis and source of deep natural gas in the Tarim and Sichuan Basin has been systematically studied. The results show that the natural gas in the deep marine carbonate rock reservoirs is not only sourced from the deep-source rocks, but the substantial crack of crude oil in the reservoir under the condition of high burial depth and high geotemperature can provide abundant natural gas sources for the deep reservoir. Accordingly, the contribution of gas from oil cracking should be concerned in evaluation on deep natural gas resources.