摘要： 四川盆地下侏罗统自流井组大安寨段一直是四川盆地致密油勘探的重要层位之一。针对该层位的研究已逾半个世纪,但岩石类型分类粗略、沉积环境及储集岩类型认识不清等问题是导致该层段致密油勘探未获重大突破的重要原因。鉴于此,笔者等开展了对四川盆地东部重庆北碚和平水库剖面下侏罗统自流井组大安寨段湖相碳酸盐岩岩石类型及沉积环境的研究。研究发现,该剖面大安寨段为湖相碎屑岩与碳酸盐岩的混合沉积,由5大类岩石组成,可细分为14种岩石类型。碳酸盐岩厚度占剖面总厚度的60％以上,以泥晶灰岩为主,介壳灰岩和介屑灰岩次之;在纵向上形成了4个较为典型的向上变浅沉积序列。根据各岩石类型宏观、微观沉积特征及岩石纵向组合形式,进一步分析了各岩石类型的沉积环境,结果表明,北碚地区下侏罗统大安寨段沉积时期为滨、浅湖环境,以低能碳酸盐沉积为主;高能与较低能环境成因的介壳滩并非碳酸盐沉积的主体。湖泊进入碳酸盐沉积阶段和钙质骨壳生物的大量繁育是大安寨期湖相碳酸盐岩形成的主要原因。结晶介屑灰岩和泥晶白云岩可能是川东地区致密油的储集岩类,在今后的勘探中,应提高对滨浅湖环境、易受大气淡水改造的岩石类型的重视程度。

关键词: 四川盆地, 大安寨段, 湖相碳酸盐岩, 岩石类型, 沉积序列, 沉积环境

Abstract: The Da-anzhai Member of Lower Jurassic Ziliujing Formation in Sichuan Basin is one of the important horizons of dense oil exploration,and has been studied over half a century. However, due to rough classification of the rock types and unclear understanding of the sedimentary environments and reservoir types, no major breakthrough has been achieved. For this reason, the study of lacustrine carbonate rock types and their sedimentary environments in the Da-anzhai Member of Heping Reservoir section in Beibei area,Chongqing,eastern Sichuan Basin was carried out. The results indicate that those mixed sediments recorded in the Da-anzhai Member largely comprise of terrigenous clastic rocks and carbonate rocks. And 5major rock categories and 14 rock types accordingly are further classified. Carbonate rocks evidently dominates through the thickness occupying more than 60％,of which micrite ranks the first,followed by the shell limestone and the bioclastic limestone. Each microfacies assemblage ordered vertically,where 4 representive upward-shallowing sequences existed. Sedimentary environments of various rock types are further analyzed according to their macro-micro characteristics and vertical combination forms. The results show that the Da-anzhai Member in Beibei area is shore-shallow lake with weak hydrodynamic condition,mainly featured by low-energy carbonatite,while the shell shoal developed in high- and low-energy environments is not the main part of carbonate sedimentation. The initiation of carbonate sedimentation phase and the massive blooming of calcareous skeleton fauna are the main causes for sedimentation of the Da-anzhai lacustrine carbonates. Crystal line bioclastic limestone and micritic dolomite of shore-shallow lacustrine facies may be the reservoir rock for dense oil in eastern Sichuan Basin. In further exploration, more attentions should be paid to the shore-shallow lacustrine rocks which could be easily dissolved by meteoric water.

Key words: Sichuan Basin, Da-anzhai Member, lacustrine carbonate, rock type, sedimentary sequence, sedimentary environment

中图分类号: 

• P588.24＋6