关键词: 准噶尔盆地, 盆1井西凹陷, 石炭系, 风城组, 上乌尔禾组, 天然气, 成藏条件

Abstract: Recently, major gas discoveries have been made in the near-source lower combination of the Carboniferous-Permian in wells SX16 and SX18 in the peripheral West Well Pen 1 Sag in Junggar Basin, showing prospects of a large gas production area. However, there is a lack of systematic study on gas distribution rule and favorable exploration areas of the Carboniferous-Permian gas reservoirs in the study area, which restricts the understanding of gas accumulation law and exploration deployment in the near future. As a result, by using seismic, logging, core, thin section and geochemical experimental data, hydrocarbon accumulation conditions such as source rock, reservoir and transport system have systematically been analyzed, and the hydrocarbon accumulation patterns of three major oil-bearing layer groups in the Carboniferous-Permian have been established. In addition, the further exploration orientation has been proposed. The study results show that: (1) Two sets of highquality source rocks are observed in Fengcheng Formation and Lower Wuerhe Formation, with large thickness of 80-200 m, burial depth of greater than 7000 m, high thermal evolution degree, and R_o of greater than 1.72%, which have reached the stage of large-scale gas generation and have gas source conditions for the formation of large and medium-sized gas fields. (2) Three sets of large-scale reservoirs were developed, providing basis for high-yield gas production. The Carboniferous reservoir is dominated by volcanic rocks, with high-porosity stomatal overflow volcanic rocks and explosive volcanic breccias developed, good physical properties after weathering and fracture transformation,and the maximum porosity of more than 20%; In Fengcheng Formation, the conventional glutenite, unconventional dolomitic tight sandstone, and unconventional dolomitic shale are orderly distributed, with an average porosity of lower than 8% but large distribution area of more than 2600 km²; The sand bodies in the first member of Upper Wuerhe Formation are overlapped and contiguous in the sag area, forming lithologic trap groups. (3) The stereoscopic transport system was formed by matching of deep and large fault system in the Hercynian and unconformity surface, which was conducive to the large-scale gas accumulation in the lower combination. (4) The three major oil-bearing layers showed different hydrocarbon accumulation patterns, among which the Carboniferous was dominated by “upper source rock and lower reservoir, and a large-span connection of source rock and reservoir”, it was coexistence of unconventional and conventional gas in source rock in Fengcheng Formation, and it was a large-scale stratigraphic-lithologic trap type gas reservoir in Upper Wuerhe Formation. It is concluded that the gas accumulation conditions are good in the Carboniferous-Permian in West Well Pen 1 Sag and its peripheral area, showing great potential for gas exploration. The favorable exploration orientations include the Carboniferous structural gas reservoir near source rock area in the nose uplift zone, the conventional glutenite gas reservoir, unconventional tight gas and shale gas in Fengcheng Formation, and the first member of Upper Wuerhe Formation in the sag area.