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Characteristics and Exploration Potential of Natural Gas Accumulations in Carboniferous Pinchout Belts in East Sichuan

Li Wei1,Zhang Zhijie1,Wang Yang2,Zhang Chaojun1   

  1. 1 PetroChihnas Research Institute of Petroleum Exploration and Development; 2 PetroChina Southwest Oil and Gas Field Company
  • Online:2015-03-15 Published:2015-05-21

Abstract: Carboniferous pinchout belts developed in a large area in the eastern part of Sichuan Basin. The reservoirs of these pinchout belts are strongly heterogeneous, leading to a complex natural gas accumulation law. It is concluded that the stratigraphic pinchout belts of Carboniferous Huanglong Formation in East Sichuan are controlled by a series of factors, such as strata, lithologic characters, structural and fault, with development of lithologic-structural compound gas reservoirs, structural-lithologic-stratigraphic compound gas reservoirs and lithologic gas reservoirs. In the strongly folded areas, natural gas is accumulated mainly in a lithologic-structural compound pattern because these gas reservoirs are influenced by structural characteristics. In the wide and gentle slope areas, natural gas is accumulated mainly in a lithologic-stratigraphic compound pattern. It is also assumed that the lithologic gas reservoirs of stratigraphic pinchout belts are not only small-scale and numerous but also abnormally high and ultra abnormally high in pressure, showing the characteristic of strong regional lithologic closure. Development of compact belts of reservoirs creates the favorable conditions for large-area lithologic closure of the structural enclosing slope zones. It is concluded that four favorable exploration areas exist in East Sichuan – the Guangan-Chongqing Carboniferous southwestern pinchout belt, the Mingyuexia-Peilingbei Carboniferous southern pinchout belt, the Carboniferous pinchout belt east of Liangping palaeo-uplift, and the Kaixian-Macaoba Carboniferous northeastern pinchout belt. These belts are not only the favorable development areas of Carboniferous lithologic-stratigraphic compound traps in East Sichuan but also the important new types of Carboniferous natural gas exploration in the future.