川西地区二叠系火山碎屑岩规模储层发育主控因素与天然气勘探潜力

Main controlling factors and natural gas exploration potential of Permian scale volcanoclastic reservoirs in the western Sichuan Basin

自2018年YT1井首次在四川盆地西部发现孔隙型火山碎屑岩储层以来,2019年TF2井又在川西地区钻揭79 m厚的孔隙型火山碎屑岩储层,取得了该盆地火山岩碎屑岩气藏勘探的重大突破和勘探新进展。为了进一步明确川西地区二叠系火山岩气藏的勘探前景,综合运用地质、地球物理和地球化学等技术方法,基于二叠系火山碎屑岩岩石学和岩相学分析成果,根据最新的物性等资料,对该区火山碎屑岩储层特征及其主控因素等进行了系统研究;进而结合油气成藏要素的匹配关系,探讨了该区天然气勘探的潜力。研究结果表明:①四川盆地二叠系火山岩形成于板块内部地幔柱活动,川西地区主要发育爆发相火山碎屑岩储层,储集空间以弥散状脱玻化溶蚀微孔为主,孔喉分选较好;②火山机构和喷发旋回是控制规模储层发育的主要因素——火山活动早期能量强,形成厚层爆发相储层,是最有利于储层发育的相带,距离火山作用中心越近,爆发相厚度越大、旋回越完整;③二叠系火山碎屑岩气藏下伏发育裂陷槽控下寒武统筇竹寺组优质烃源岩,油气沿高角度断裂运移至优质爆发相储层中,上覆上二叠统龙潭组提供了优质盖层,为天然气大规模运聚提供了有利的成藏组合。结论认为,川西地区二叠系火山碎屑岩具备发育大规模优质储层的地质条件,并且该区油气成藏组合条件良好,天然气资源丰度大,展现出巨大的天然气勘探开发潜力,是四川盆地天然气增储上产的重要领域之一。

Great breakthroughs and new progresses have been realized in the exploration of volcanoclastic gas reservoirs in the Sichuan Basin since a porous volcanoclastic reservoir was discovered in Well YT1 in the western Sichuan Basin in 2018 followed by another one of 79 m in thickness discovered in Well TF2.In order to clarify the exploration prospect of the Permian volcanic gas reservoir in the western Sichuan Basin,this paper systematically studies the characteristics and main controlling factors of volcanoclastic reservoir in this area by using geological,geophysical and geochemical technologies and methods comprehensively,based on the petrological and petrographical analysis results on the Permian volcanoclastic rock,combined with the latest physical property data.Then,the natural gas exploration potential in this area is discussed based on the match relationships between hydrocarbon accumulation factors.And the following research results were obtained.First,Permian volcanic rocks in the Sichuan Basin are the products of intraplate mantle plume activity.In the western Sichuan Basin mainly develops an eruptive volcanoclastic reservoir,whose reservoir space is dominated by diffuse devitrified dissolved micropores with better pore throat sorting.Second,volcanic edifice and eruptive cycle are the main factors controlling the development of scale reservoir.In the early stage of volcanic activity,the energy is strong and a thick eruptive reservoir is formed,which is the most favorable facies belt for reservoir development.The closer it is to the center of the volcanism,the thicker the eruptive facies is and the more complete the cycle is.Third,the Permian volcanoclastic gas reservoir is underlain by high-quality source rocks of Lower Cambrian Qiongzhusi Formation under the control of fault trough whose oil and gas migrates into the high-quality eruptive reservoir along high angle faults,and its overlying Permian Longtan Formation provides high-quality cap rocks.Thus,the favorable play for largescale natural gas migration and accumulation is formed.In conclusion,the Permian volcanoclastic rocks in the western Sichuan Basin have the geological conditions for the development of scale high-quality reservoir.In addition,the conditions of hydrocarbon play in this area are good,natural gas resource abundance is large and natural gas exploration and development potential is great.Therefore,it is one of the important fields for the reserves and production increase of natural gas in the Sichuan Basin.