Major controlling factors and quantitative probability evaluation of hydrocarbon accumulation in distal tight sandstone gas reservoirs:A case study on the gas reservoir of Middle Jurassic Shaximiao Formation in the southwestern Sichuan Basin
Major controlling factors and quantitative probability evaluation of hydrocarbon accumulation in distal tight sandstone gas reservoirs:A case study on the gas reservoir of Middle Jurassic Shaximiao Formation in the southwestern Sichuan Basin
The tight sandstone reservoir of the Middle Jurassic Shaximiao Formation in the southwestern Sichuan Basin is a distal secondary gas reservoir.There are significant differences in natural gas enrichment among different gas bearing structures,however,the main controlling factors of hydrocarbon accumulation have not been figured out.Therefore,the hydrocarbon accumulation conditions of distal tight sandstone gas reservoirs were firstly analyzed.And then,7 gas bearing structures of the Shaximiao Formation in the southwestern Sichuan Basin were compared in terms of the differences in hydrocarbon accumulation,and the major controlling factors of hydrocarbon accumulation were clarified.Finally,a method for quantitatively evaluating the accumulation probability of distal tight sandstone gas was established by comprehensively considering various geological factors that control the differences in tight sandstone gas accumulation.On this basis,the abundance of natural gas reserves in Shaximiao Formation of Jianyang Block in the Tianfu Gas Field were predicted.And the following research results are obtained.First,the Shaximiao Formation gas reservoir in the southwestern Sichuan Basin is mainly a structural-lithological gas reservoir,with natural gas sourced from the underlying coal measure source rocks of Upper Triassic Xujiahe Formation.Different gas bearing structures are greatly different in natural gas composition,reservoir characteristics,and migration and preservation conditions.Second,the hydrocarbon expulsion ability of source rocks lays the material foundation,fault-caprock configuration determines the natural gas enriched layers,fault-reservoir coupling controls the natural gas accumulation efficiency,and reservoir quality determines the natural gas enrichment scale.Third,hydrocarbon expulsion capacity index of source rock,source-reservoir distance index,reservoir physical property index,reservoir thickness index,fault-cap coupling type index,and fault-reservoir configuration type index can be taken as the evaluation indicators for hydrocarbon accumulation probability of tight sandstone gas reservoir.And the proposed hydrocarbon accumulation probability index(HAI)of distal tight sandstone gas reservoir can be used to predict the geological reserves of distant tight sandstone gas.In conclusion,there is a good positive correlation between HAI and reserve abundance.It is predicted that the HAI value in the Jianyang Block of the Tianfu Gas Field is 0.53,and the reserve abundance of the Shaximiao Formation gas reservoir is 1.32×108 m3/km2.The proposed quantitative evaluation method for natural gas accumulation has a higher accuracy,pointing out the direction for the exploration and development of the Shaximiao Formation natural gas in southwestern Sichuan Basin.
关键词
远源致密砂岩气/成藏主控因素/成藏概率指数/中侏罗统/沙溪庙组/四川盆地西南部/有利勘探区
Key words
Distal tight sandstone gas reservoir/Major controlling factors of hydrocarbon accumulation/Hydrocarbon accumulation probability index/Middle Jurassic/Shaximiao Formation/Southwestern Sichuan Basin/Favorable exploration area
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