Post-Neogene Structural Evolution: An Important Geological Stage in the Formation of Gas Reservoirs in China

摘要

Tectonic movements since the Neogene have heen the major developmental and evolutional stages of the latest global crustal deformation and erogenic movements. China is located in a triangular area bounded by the Indian landmass, the West Siberian landmass and the Pacific Plate, characterized by relatively active tectonic movements since the Neogene, and in this region, natural gas would have been very easy to dissipate, or difficult to preserve. Therefore, the characteristics of post-Neogene tectonic movements offer important geological factors in researching the formation and preservation of gas reservoirs in China. Summarizing the reservoiring history of gas fields in China, although there are some differences between various basins, they are all affected by the tectonic movements since the Neogene. These movements have certainly caused destruction to the reservoiring and distribution of natural gas in China, which has resulted in a certain dissipation of natural gas in some basins. As a whole, however, they have mainly promoted the reservoiring and accumulation of natural gas: (1) a series of China-type foreland basins have been formed between basins and ridges in western China, which provide favorable conditions for the formation of large and medium gas fields, as well as controlling the finalization of gas reservoirs in the basins; (2) rows and belts of anticlines have been formed in the Sichuan Basin in central China, which have been the major stages of the formation and finalization of gas reservoirs in that basin; the integral and quick rising and lifting, and a further west-dipping in the Ordos Basin have resulted in a further accumulation of natural gas in gas fields from Jingbian to Uxin; (3) in eastern China, the Bohai movement in the late Pliocene has provided favorable geological conditions for lately-formed gas reservoirs in the Bohai Sea area mainly composed of the Bozhong depression; and it also resulted in secondary hydrocarbon generation and formation of secondary gas reservoirs in other basins, as well as the formation of many carbon dioxide gas fields of inorganic origin; (4) in the offshore area, it promoted not only the formation of gas reservoirs of organic origin, but also the formation of inorganic origin non-hydrocarbon gas reservoirs, as well as the organic and inorganic natural gas of mixed origin, which resulted in the relatively complicated characteristics of gas reservoirs in the area. In short, tectonic movements activated since the Neogene resulted in a reservoiring model mainly characterized by late and superlate hydrocarbon generation and accumulation. These events provide an important geological stage that should not be neglected when studying the formation of gas reservoirs in China.