Control of tectonic differentiation on the formation of large oil and gas fields in craton basins: A case study of Sinian-Triassic of the Sichuan Basin

Craton basins are the main sites where marine carbonate oil and gas reservoirs develop in China. However, the previous studies scarcely focused on the controlling effects of tectonic differentiation on the formation of large oil and gas fields in the ancient craton basins. In such circumstances, it is difficult to evaluate and select the favorable zones for exploring carbonate oil and gas. In this paper, based on the research results of the Sinian-Triassic prototype basin and lithofacies paleogeography of the Sichuan Basin, the tectonic differentiation pattern of craton basins and its controls on the accumulation elements and the distribution of hydrocarbons were analyzed with reference to the concept that structures control the sedimentation and distribution of oil and gas. The study reveals the results in three aspects. First, the intra-cratonic graben controls the high-quality source rocks and the hydrocarbon generation center, which forms good source-reservoir assemblage with the high-quality reservoir in the platform margin at the flank, showing excellent near-source accumulation conditions. Second, the three types of paleo-uplifts (i.e. differential denudation, syn-sedimentary, and folding) and the deep-large faults developed in the craton are favorable for the formation and distribution of large-scale carbonate reservoirs. Third, the superimposed areas with tectonic differentiation in multiple periods and multiple types are favorable for forming large oil and gas fields. It is concluded that the marine carbonate rocks show a huge oil and gas exploration potential in the Sichuan Basin. Attention should be paid to the new exploration targets of natural gas, such as the Sinian Dengying Fm. in the platform margin at the east flank of Deyang-Anyue graben, the Lower Cambrian Longwangmiao Fm. on the slope of paleo-uplift in central Sichuan Basin, and the Middle Permian Maokou Fm. in central-west Sichuan Basin, where oil and gas accumulation conditions are favorable.