四川盆地西部二叠系火山岩气藏成藏条件分析

为了明确四川盆地川西地区二叠系火山碎屑岩气藏的天然气成藏条件,对该区火山碎屑岩气藏储层、气源、成藏组合及圈闭等成藏特征进行了分析。研究结果表明,川西简阳地区火山碎屑岩气藏的成藏有利条件包括:①永探1井以喷溢相火山碎屑熔岩为主,叠合后期蚀变和溶蚀作用,发育以脱玻化溶蚀微孔为主要储集空间的孔隙型储层;②天然气地球化学指标分析对比结果表明,永探1井火山岩气藏天然气来源以下寒武统筇竹寺组为主,简阳地区德阳—安岳裂陷内发育巨厚的寒武系优质烃源岩,为气藏形成提供了充足的气源;③火山碎屑岩储层与寒武系烃源岩组成"下生上储"的近源高效源储组合,烃源断层有效沟通源岩和储层,上覆发育有上二叠统龙潭组泥岩直接盖层和三叠系膏岩区域盖层,生、储、盖组合良好;④成都—简阳地区发育构造—岩性(地层)复合圈闭,初步证实有利含气区面积达1 300 km2,展现出极大的天然气勘探潜力。结论认为,川西地区火山碎屑岩气藏与川西南地区周公山玄武岩气藏在成藏条件方面存在着较大的差异,预测中江—三台地区火山碎屑岩分布面积超过4 000 km~2,其与简阳地区具有相似的火山岩气藏形成条件,是下一步集中突破的有利勘探区带。

Hydrocarbon accumulation conditions of Permian volcanic gas reservoirs in the western Sichuan Basin

In order to figure out the hydrocarbon accumulation conditions of Permian volcaniclastic gas reservoirs in the western Sichuan Basin, we analyzed the hydrocarbon accumulation characteristics of volcaniclastic gas reservoirs in this area in terms of reservoir, gas source, play and trap. It is indicated that the favorable conditions for the hydrocarbon accumulation of volcaniclastic gas reservoirs in the Jianyang area in the western Sichuan Basin are as follows. First, in the Well Yongtan 1, vocaniclastic lava of effusive facies is dominant, and superimposed with late alteration and dissolution, pore-type reservoirs with devitrified dissolution micropores as the main reservoir space are developed. Second, geochemical analysis and comparison on natural gas reveal that the gas of the volcanic gas reservoirs in the Well Yongtan 1 is mainly derived from the Qiongzhusi Formation of Lower Cambrian. Cambrian quality source rocks of great thickness are developed in Deyang–Anyue rift in the Jianyang area and they provide sufficient gas sources for the formation of gas reservoirs. Third, volcaniclastic reservoirs and Cambrian source rocks constitute a proximal high-efficiency source–reservoir assemblage with reservoir in the upper part and source rock in the lower part, hydrocarbon source faults communicate source rocks with reservoirs effectively, and the direct caprock of Longtan Formation mudstone of Upper Permian and the regional caprock of Triassic gypsum rock are developed. Thus, a good assemblage of source, reservoir and caprock is formed. Fourth, tectonic–lithologic (stratigraphic) composite traps are developed in Chengdu–Jianyang area and their favorable gas bearing area is preliminarily confirmed to be 1 300 km2, presenting a great exploration potential of natural gas. In conclusion, the volcaniclastic gas reservoirs in western Sichuan Basin are much different from Zhougongshan basalt gas reservoir in southwestern Sichuan Basin in terms of hydrocarbon accumulation conditions. It is predicted that the distribution area of vocaniclastic rocks in the Zhongjiang–Santai area is over 4 000 km2, and their hydrocarbon accumulation conditions of volcanic gas reservoirs are similar to those in the Jianyang area, so this is a favorable area for exploration breakthrough in the next stage.