Study Of Sequence Stratigraphy And Sedimentary Facies Of Xishanyao Formation In Yongjin Area, Junggar Basin

The Yongjin area is located in the Zhong 3 block of the Junggar Basin.The area is structurally located on the abdomen of the Junggar Basin and on the south wing of Chemo Ancient upliftand.The Xishanyao Formation is currently the main oil-bearing stratum in this area and has developed several sets of stratigraphic-lithological oil and gas reservoirs.Currently,the 8 wells have been drilled to obtain industrial production in the Yong 1 Well,Yong 2 Well and Yong 3 Well Jurassic Xishanyao Formation.The other wells also have good oil and gas displays.Among them,Yong 1 well tested 72.07m~3/d of oil and 5562m~3/d of gas in the 5873m-5888m section,demonstrating that the Xishanyao Formation has good exploration and development potential.However,due to the influence of the Chemo Ancient upliftand campaign in this area,the Xishanyao Formation was exposed to different degrees of exposure and erosion.It is difficult to distinguish stratums and there is insufficient understanding of stratum distribution.At the same time,the predecessors'description of the typical sedimentary facies symbol of the Xishanyao Formation in the study area is not yet elaboration.The study of the sedimentary system in the sequence framework is relatively weak,leading to the insufficient understanding of the depositional environment,the history of sedimentary development and the distribution of sedimentary patterns in the area.It has become a key issue that restricts exploration and development of reservoirs in the area.This paper makes a comprehensive analysis of well logging,well logging,geochemical analysis,core observation and thin section analysis of Jurassic Xishanyao Formation in Yongjin area.Guided by discipline theory such as sequence stratigraphy,sedimentology and reservoir geology.By identifying the boundary interfaces such as the bottom interface of the consolidated sand body,the lithologic lithofacies transition surface and the lake flood surface.Defining the division of the Xishanyao Formation stratigraphy.On this basis,the Xishanyao Formation is divided into two three-level sequences:SQ1 and SQ2 from bottom to top.Among them,The SQ1 sequence is divided into the TST and the HST in the study area;The SQ2 sequence is only identified in the Yong 6 well and Yong 7 well areas as a complete LST,TST and HST.Other wells only divide the water into the system domain(TST)and High System Domain(HST).Through the study of the comparative characteristics of single well and well sequence stratigraphy of the Xishanyao Formation,the objective stratigraphic isochronal stratigraphic framework was established.On the basis of sequence isochronal stratigraphic framework,according to the Xishanyao Formation rock color,sedimentary structure characteristics,paleontology,sedimentary structure,logging phase,geochemistry,etc.established sedimentary facies partitioning program.The Xishanyao Formation is considered to be a set of alluvial(interwoven river plain subphase)and delta(delta front and pre-delta subfacies)sediments.The delta front is the dominant subfacies of the Xishanyao Formation.The microfacies mainly include branch channels,lake mud,peat bogs,Burst fan,underwater diversion channel,estuary dam,far sand dam,diversion bay,front delta mud,sand debris flow,sand slide,etc.Based on the analysis of the single well phase and well relative ratio and the evolution law of the plane sedimentary facies of the Xishanyao Formation,the sedimentary evolution model of the target stratum was established.At the same time,based on the characteristics of the plane distribution of sand bodies,the development of micro-phase properties and the distribution characteristics of oil reservoirs.Based on the characteristics of the distribution of sedimentary facies.Evaluation and prediction of favorable reservoirs in the Xishanyao Formation in the study area.Using the TST period of the SQ1 and SQ2 sequence as the mapping unit,the distribution map of favorable reservoirs in the Xishanyao Formation in the Yongjin area was compiled.It was considered that during the SQ1 sequence TST period,the more favorable reservoir areas were distributed in the Yong 8 and Yong 2 well areas.The sand body spreads along the branch channel.During the SQ2 sequence TST,the most favorable reservoir areas are distributed in Yong 2,Yong 1,Yong 3 and Yong 6 well areas.The more favorable reservoirs are mainly distributed in the Yong 7 well area and the sand dams and litter sand deposition areas at the front of underwater distributary channels and estuary dams.