川西地区中三叠统雷口坡组天然气勘探潜力

四川盆地西部地区中三叠世雷口坡期蒸发膏盐湖盆主要分布在邛崃-成都-德阳一带，发育多套碳酸盐岩、石膏、硬石膏岩及盐岩的沉积旋回，油气勘探实践证实，蒸发岩沉积旋回与油气的生聚成藏关系密切。为分析该盆地雷口坡组的天然气勘探潜力，从气源分析、蒸发岩盆地生烃机理、盆地模拟研究3个方面，论证了川西地区雷口坡组局限-蒸发台地深水澙湖相沉积的富藻碳酸盐岩具有成为大中型气田主力烃源岩的有利条件，估算雷口坡组天然气的资源量介于9 839×10⁸～1.201×10¹² m³。结合储层条件、成藏条件等的分析成果，认为雷口坡组发育台缘滩和台内滩裂缝-孔隙型储层，其顶部发育碳酸盐岩风化壳岩溶型优质储层；风化壳岩溶型储层的发育与雷口坡组在“暴露”“深埋”两大阶段中发生的后生成岩作用有关。结论认为：该区雷口坡组具有形成大中型气田的资源条件，在川西坳陷中央的新场构造带，龙门山前鸭子河隐伏构造带及成都、梓潼凹陷周缘斜坡区，雷口坡组天然气成藏条件优越，勘探潜力巨大。

Gas potential of the Middle Triassic Leikoupo Fm in the western Sichuan Basin

An evaporite lake basin was developed in an area along Qionglai Chengdu Deyang in the western Sichuan Basin during the Middle Triassic Leikoupo period, when multiple sedimentary cycles of carbonates, gypsum, anhydrite and halite were deposited. Petroleum exploration practices reveal that the evaporite cycles are closely related with the generation, migration and accumulation of hydrocarbons. In order to estimate the gas potential of the Leikoupo Fm in the study area, we analyzed the gas source, gas generation mechanism of the evaporite basin and basin modeling. It is believed that the alga rich carbonates of the Leikoupo Fm deposited on a restricted evaporite platform in a deep lagoon of the western Sichuan Basin have the favorable conditions to become the major source rocks of moderate and large gas fields, and the gas resource volume of the Leikoupo Fm is estimated to be 0.983 1.201 TCM. Fractured porous reservoirs of platform margin shoal facies and intra platform shoal facies occur in the Leikoupo Fm. Karstified carbonate reservoirs of weathering crust type are developed at the top of this formation due to epidiagenesis during the “exposure” and “deep burial” stages of this formation. It is concluded that the Leikoupo Fm in the study area has the conditions for the formation of moderate to large gas fields and the potential target areas include the Xinchang structural zone in central of western Sichuan Depression, Yazihe hidden structural zone at the piedmont of Longmenshan as well as the peripheral slope zones of Chengdu and Zitong sags.