四川盆地平昌地区侏罗系大安寨段沉积特征及演化模式

Sedimentary characteristics and evolution pattern of Jurassic Da’anzhai Member in Pingchang area,Sichuan Basin

四川盆地侏罗系大安寨段油气资源丰富,是致密油勘探开发的重要层位,目前针对大安寨段的勘探研究工作主要集中在川中地区,对于川东北地区研究较少,制约了该区的致密油勘探进程。利用野外露头、岩心、薄片、测井、录井等资料,对大安寨段沉积特征及沉积演化模式开展研究。结果表明:川东北平昌地区下侏罗统自流井组大安寨段沉积构造相对稳定,发育完整的水进水退旋回,陆源碎屑物供给缺乏,以湖相碳酸盐岩和泥页岩为主,主要发育浅湖亚相和半深湖亚相;受湖平面变化控制,介壳灰岩与暗色泥页岩交互发育,大三亚段和大一亚段以中—厚层介壳灰岩为主,为浅湖介壳滩微相,可作为良好的储层;大二亚段岩性主要为大套暗色泥页岩夹薄层泥质介壳灰岩,为半深湖沉积环境,泥页岩有机质丰度高,可作为良好的烃源岩;平昌地区大三亚段和大一亚段厚层介壳滩是致密油勘探的目标。研究成果可为四川盆地平昌地区侏罗系大安寨段油气勘探提供有力的依据。

Jurassic Da’anzhai Member in Sichuan Basin is rich in oil and gas resources and is an important horizon for tight oil exploration and development.At present,the exploration and research work for Da’anzhai Member is mainly concentrated in central Sichuan Basin,and there is less research for northeast Sichuan Basin,which re‑stricts the tight oil exploration process in this area.Based on the data of field outcrop,cores,thin sections and log‑ging,this paper studies the sedimentary characteristics and sedimentary evolution of Da’anzhai Member.The re‑sults show that the sedimentary structure of Da’anzhai Member of Lower Jurassic Ziliujing Formation in Pingchang area of northeast Sichuan Basin is relatively stable,with complete water inflow and regression cycles and lack of ter‑rigenous clastic material supply.It is characterized by lacustrine carbonate rocks and shale,and mainly develops semi-deep lake and shallow lake sub-facies.Controlled by the change of lake level,shell limestone and dark shale are developed alternately.Da 3 sub-member and Da 1 sub-member are mainly medium thick shell limestone and shell bearing mudstone,which are shallow lake shell beach microfacies and can be good reservoirs.The lithology of Da 2 sub-member is mainly a large set of dark shale with thin argillaceous shell limestone,which is a semi-deep lake sedimentary environment.Shale has high organic matter abundance and can be good source rock.The thick shell shoals in Da 3 sub-member and Da 1 sub-member in Pingchang area are favorite targets for tight oil explora‑tion.The research results provide strong basis for oil and gas exploration of Jurassic Da’anzhai Member in Pingchang area in Sichuan Basin.