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With the continuous deepening of natural gas exploration, the quality of discovered resources gets worse and exploration targets are getting more and more complicated, so it is necessary to develop and improve natural gas geological theories continuously in order to tap and discover more natural gas resources. Therefore, geological theories on the formation of large gas fields were studied during the 12th Five-Year Plan period and the following progresses were mainly achieved. (1) Gas generation modes were established of oil cracking and highly evolved coal-measure source rocks in different geologic conditions. (2) A model was set up for evaluating quantitatively the hydrocarbon expulsion and detainment of various source rocks with different abundance. (3) Natural gas genesis identification chart was built up with multiple parameters and indexes. (4) Two carbonate rock sedimentation patterns and two tight sandstone sedimentation patterns were established. (5) A new method was developed for evaluating caprock–reservoir displacement pressure difference of immediate caprocks. (6) The hydrocarbon accumulation pattern of large gas fields was established and their main controlling factors and distribution laws were summarized. Then, the natural gas exploration theories were deepened in the following five fields and their application achievements are remarkable. First, the hydrocarbon-accumulation geological theory used for large ancient carbonate gas fields was innovatively understood to promote the discovery and confirmation of the Anyue supergiant gas field in the Sichuan Basin. Second, the hydrocarbon-accumulation geological theory suitable for large tight sandstone gas fields was developed to guide the exploration of tight sandstone gas in the Ordos and Songliao basins. Third, the hydrocarbon-accumulation theory of platform margin reefs was deepened to expand the exploration of platform margin reef gas in the Sichuan Basin. Fourth, the hydrocarbon accumulation mechanism and enrichment theory of large condensate gas reservoirs were deepened to guide the exploration of large condensate gas reservoirs in the Tarim Basin. And fifth, the exploration theory of volcanic gas reservoirs with hydrocarbon-generation fault troughs as basic units was completed to realize the strategic replacement of volcanic gas reservoir exploration. Keywords: 12th Five-Year Plan, China, Large gas field, Geological theory of natural gas, Research progress, Genesis identification, Hydrocarbon accumulation theory, Exploration theory, Exploration achievements |
