Distribution laws of large gas fields and further exploration orientation and targets in China

With the rapid expansion and extension of natural gas exploration and development, it is more and more difficult to discover large-scale reserves in China. To intensify the research on new natural gas exploration domains, we reviewed the progress and trend of natural gas exploration and analyzed the main areas with large-scale proved gas in place (GIP). Then, based on a statistic analysis of large gas fields in China as well as their hydrocarbon accumulation characteristics, their genetic systems were classified and each system's distribution law was also identified. Some research results were obtained. First, carbonate paleo-uplifts of cratonic basins, tight sandstones of extensive gentle slopes and thrust structures of foreland basins are the main areas with large-scale proved GIP in China. Second, there are five genetic systems for large gas fields, i.e. cratonic rift and paleo-uplift (A), stable slope of low-angle open lake (B), thrust structure of piedmont fault depression (C), faulted uplift and igneous rock of intracontinental pull-apart fault depression (D), and anticline structure of epicontinental strike-slip fault depression (E), and one genetic system (F) for unconventional gas, i.e. adsorption and accumulation in nano-scale space. Third, there is one core genetic system for large conventional gas fields in each geologic cycle. Fourth, two-level accumulation, i.e. no migration inside the source and large-scale transportation termination, exists in each single genetic system, and sequential accumulation is formed under the control of multiple factors in the areas where multiple genetic systems are superimposed. Fifth, the multi-system superimposed area is rich in large gas fields and the multi-stress hinge zone in the central area is the natural gas convergence zone. Finally, the future orientation and targets of natural gas exploration in China were pointed out. First, the system A includes Sinian-Lower Paleozoic in the Sichuan Basin, Cambrian in the Tarim Basin and Cambrian-Ordovician in the Ordos Basin. Second, the system C includes the transform zone of Kuqa thrust structure, the northwestern Sichuan Basin and the southwestern Tarim Basin. Third, the system E includes the basins in the eastern China seas. Fourth, the system F includes organic-rich shales in South China and deep coal beds in the Ordos Basin in central China.