远源致密砂岩气成藏主控因素及成藏概率定量评价——以四川盆地西南部中侏罗统沙溪庙组气藏为例

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

四川盆地西南部(以下简称川西南部地区)中侏罗统沙溪庙组致密砂岩气藏属于远源次生气藏,不同构造天然气富集差异性大,成藏主控因素不清。为此,基于远源致密砂岩气成藏条件分析,对比了川西南部地区沙溪庙组7个含气构造的成藏差异性,明确了成藏主控因素,在综合考虑控制致密砂岩气成藏差异性的各类地质因素的基础上,建立了远源致密砂岩气成藏概率的定量评价方法,并预测了天府气田简阳区块沙溪庙组天然气储量丰度。研究结果表明:(1)川西南部地区沙溪庙组主要发育构造—岩性气藏,天然气均源自下伏上三叠统须家河组煤系烃源岩,不同含气构造在天然气组分、储层特征、输导保存条件等方面存在明显差异;(2)烃源岩排烃能力奠定了物质基础,断—盖配置决定了天然气富集层系,断—储耦合控制着天然气聚集效率,储层品质决定了天然气富集规模;(3)烃源岩排烃能力指数、源—储距离指数、储层物性指数、储层厚度指数、断—盖耦合类型指数及断—储配置类型指数可作为评价致密砂岩气成藏概率指标,提出的远源致密砂岩气成藏概率指数(HAI)可用于该地区远源致密砂岩气地质储量预测。结论认为,HAI与储量丰度具有很好的正相关关系,并预测了天府气田简阳区块的HAI值为0.53,沙溪庙组气藏的储量丰度为1.32×10^(8)m^(3)/km^(2),提出的天然气成藏定量评价方法准确度较高,为川西南部地区沙溪庙组天然气勘探开发指明了方向。

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,faultcaprock 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,sourcereservoir 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 1.32×10^(8) m^(3)/km^(2).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.