四川盆地永探1井二叠系火山碎屑熔岩储层特征

Characteristics of Permian volcaniclastic lava reservoirs in Yongtan 1 well, Sichuan Basin

四川盆地大面积分布二叠系火山岩,但是针对该领域开展的研究工作比较局限。近期永探1井钻遇厚层火山岩孔隙型储层,并获得高产工业气流,表明四川盆地火山岩具备形成大中型气田的可能性。为深化该领域地质认识,给下步勘探部署提供依据,结合永探1井岩心、岩屑、测井和地震资料,研究了该区火山岩储层发育特征。研究结果表明:①成都-简阳地区二叠系火山岩以喷溢相火山碎屑熔岩和溢流相玄武岩为主,纵向发育3个喷发旋回;②永探1井储集岩包括火山碎屑熔岩和玄武岩2大类,其中火山碎屑熔岩发育厚层孔隙型储层,平均孔隙度超过10%,厚度超100 m,是储层主要贡献者;③火山碎屑熔岩储集空间以脱玻化溶蚀微孔、残余气孔为主,裂缝发育程度较低,而玄武岩岩性致密,孔隙不发育,储集空间以裂缝为主;④喷溢相火山碎屑熔岩地震反射总体表现为丘状、杂乱反射,在简阳-三台地区分布面积达6 000 km^2,勘探潜力巨大。结论认为,简阳-三台地区二叠系火山岩储层物性条件总体较好,厚度较大,以孔隙型和裂缝-孔隙型为主,是有利勘探区带。

There are massive Permian volcanic rocks developed in Sichuan Basin, but their researches are very few. Recently, during drilling Yongtan 1 well, thick and porous volcanic reservoirs were found and high-yield gas flow was obtained, indicating that the volcanic rocks have an ability of forming a large-sized gasfield. In order to deepen geological understandings and provide the basis for next exploration deployment, the development characteristics of volcanic reservoirs were studied on the basis of core, cuttings, well-logging, and seismic data of Yongtan 1 well. Results show that(1) the Permian volcanic rocks in Chengdu-Jianyang area mainly constitute volcaniclastic lava of effusive facies and the overflow facies basalt, and three eruption cycles are vertically developed;(2) these reservoirs are mainly composed of volcaniclastic lava and basalt. With average porosity and thickness over 10% and 100 m, respectively, thick porous reservoirs are developed in volcaniclastic lava, which is the main contributor to reservoirs;(3) in volcaniclastic lava, its reservoir space is mainly acted by dissolved micropores and residual pores, and fracture development is lower. While in tight basalt, pores are not developed and fractures are just the dominant reservoir space;and(4) the volcaniclastic lava of effusive facies presents the mounded and chaotic seismic reflection overall, and is distributed in Jianyang-Santai area covering an area of 6000 km^2, so its exploration potential is immense. In conclusion, the Permian volcanic reservoirs in Jianyang-Santai area are featured by better physical properties and greater thickness, and their types mainly include porous and fractured-porous ones, so they are the favorable exploration zones.