四川盆地吴家坪组相控孔隙型储层勘探新发现及油气勘探意义

New exploration discovery of facies controlled porous reservoir in the Wujiaping Formation of the Sichuan Basin and its significance to oil and gas exploration

近期,LX1井在四川盆地上二叠统吴家坪组钻遇滩相优质孔隙型储层,且油气显示良好,与前期"吴家坪组只发育裂缝型储层,天然气勘探潜力较小"的认识不一致。为了进一步弄清吴家坪组天然气勘探潜力,拓展盆地油气勘探新层系、新领域,在区域地质背景分析的基础上,通过钻井—地震标定,落实了四川盆地北部(以下简称川北地区)沉积相展布,利用岩石薄片、测井等资料系统分析了吴家坪组的储层特征,并结合勘探、研究新进展指出了该层系的勘探方向。研究结果表明:(1)四川盆地开江—梁平海槽西侧吴家坪期发育大型台缘带,面积为3600 km2,台缘带内发育高能台缘滩相沉积;(2)受台缘滩相控制,吴家坪组发育滩相孔隙型储层,储层岩性为亮晶生屑石灰岩、云质石灰岩、灰质白云岩、颗粒白云岩和粉—细晶白云岩,储集空间主要为生物铸膜孔、粒间溶孔、晶间溶孔,孔隙度介于3.3%~4.8%;(3)川北地区二叠系茅口组孤峰段、吴家坪组和大隆组发育的烃源岩直接与吴家坪组台缘滩相储层接触,形成下生上储、旁生侧储的最佳源储组合,海槽西侧吴家坪组台缘带紧邻烃源岩生烃中心,具备优越的天然气成藏条件。结论认为,四川盆地吴家坪组发育台缘滩相孔隙型储层,具油气成藏条件优越,是二叠系天然气勘探的又一重要层系,该认识对拓展四川盆地天然气勘探新领域具有重要的意义。

Recently,Well LX1 encounters quality porous reservoir of beach facies in the Upper Permian Wujiaping Formation in the Sichuan Basin,where hydrocarbon shows are good.In the early stage,however,it was considered that there is only fractured reservoirs in the Wujiaping Formation and natural gas exploration potential is limited.In order to further clarify the natural gas exploration potential of Wujiaping Formation and expand new oil and gas exploration strata and fields in the Sichuan Basin,this paper confirms the distribution of sedimentary facies in the northern Sichuan Basin by means of well-seismic calibration,based on regional geological background analysis.Then,the reservoir characteristics of Wujiaping Formation are analyzed systematically based on thin section,logging and other data.Finally,combined with new exploration and research progresses,the exploration direction of Wujiaping Formation is pointed out.And the following research results are obtained.First,a large platform margin belt is developed in the Wujiaping Formation on the west side of Kaijiang-Liangping trough in the Sichuan Basin,and its area is 3600 km2.And within the platform margin belt develops a high-energy platform margin beach facies deposit.Second,under the control of platform margin beach facies,porous reservoir of beach facies is developed in the Wujiaping Formation.The reservoir lithology is bioclastic sparite,dolomitic limestone,limy dolomite,granular dolomite and powder-fine crystalline dolomite,and the reservoir space is mainly biological moldic pore,intergranular solution pore and intercrystalline solution pore,with porosity ranging from 3.3%to 4.8%.Third,in the northern Sichuan Basin,the source rocks developed in the Maokou Formation Gufeng Member,Wujiaping Formation and Dalong Formation of Permian directly contact with the platform margin beach facies reservoir of Wujiaping Formation to form the optimal source rock-reservoir assemblages of lower source rock-upper reservoir and side source rock-side reservoir.The platform margin belt of Wujiaping Formation on the west side of the trough is close to the hydrocarbon generation center of source rocks,so it is superior in natural gas accumulation conditions.In conclusion,porous reservoir of platform margin beach facies is developed in the Wujiaping Formation of the Sichuan basin,which has good hydrocarbon accumulation conditions,so it is another important series of strata of Permian natural gas exploration.This cognition is of great significance to expand new natural gas exploration fields in the Sichuan Basin.