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The development of geologic theories and exploration findings of natural gas in China supplement each other. Since the 11th Five-Year Plan in 2006–2010, geologic theories of natural gas in China has achieved notable advancement in many aspects, of which, are mainly reflected in the following seven aspects. Among them, there are two research progresses in the basic geological theory enumerated as follows. (1) The formation mechanisms of three types of natural gas that have been studied broadly including highly evolved coal-based source rocks, crude oil pyrolysis gas, and biogas. The cracked gas mode of coal-based source rocks, whole process hydrocarbon-generating mode of humus-type organic matter, and continuous biogas generation mode have been thoroughly advanced. (2) The theory of genetic identification between crude oil pyrolysis gas and kerogen pyrolysis gas, aggregated crude oil pyrolysis gas and dispersed crude oil pyrolysis gas, organic and inorganic gases, coal-type gas and oil origin gas, has been enriched extensively. There are five theoretical advances in the field of hydrocarbon accumulation in large gas fields: (1) the theory of hydrocarbon accumulation in ancient carbonate rock, “five paleo-structures control accumulation”, has been proposed innovatively; (2) the accumulation theory of tight sandstone gas in craton basins, foreland basins, and rift basins have been well-established; (3) the accumulation mode of “three-micro conveying, near-source enrichment, and sustained preservation” for ultra-deep and weak deformation zones has been established; (4) the accumulation theory of volcanic gas reserves in rift basins with basic elements of hydrocarbon generation troughs has been established and improved; (5) lastly, the accumulation theory of offshore high-temperature, overpressure, and deepwater gas were methodically deepened. The development of geologic theories of natural gas has promoted many new exploration discoveries. The accumulation theory in ancient carbonate reservoirs paved the way for the exploration of Anyue gas field in the Sichuan Basin, the largest single reserve in China. The new understanding of tight sandstone gas accumulation in the foreland thrust belt helped the first gas field discovery in the size 1 × 1012 m3 in an ultra-deep layer in the Kuqa Depression. The accumulation theory of ultra-deep reef reservoirs has guided the exploration of Yuanba gas field, the deepest-buried reef gas field in China. The theory of offshore hydrocarbon accumulation has led to remarkable discoveries in the South China Sea. Some of the said discoveries are the Dongfang 13-2 gas field, the largest gas field in China located in self-supported areas, and the Lingshui 17-2 gas field, which is a hundred billion cubic meters in size and is located in the deepwater exploration field. Keywords: Natural gas, Basic geological theory, Mechanism of gas generation, Accumulation of large gas fields, New exploration findings |
