Depositional System And Petroleum Geological Significance Of Toutunhe-Qingshuihe Formation In Nananjihaihe Section,Southern Margin Of Junggar Basin

The Middle Jurassic Toutunhe Formation to Lower Cretaceous Qingshuihe Formation in the southern margin of the Junggar Basin is an important target formation for oil and gas exploration.This paper systematically collates the previous research results and regional geological background data,selects the Nan’an Jihai profile in the the Junggar Basin for fine measurement,obtains lithology,stratigraphic sedimentary textures,structure,paleontology,geochemistry and other data,we analyzed systematically the sedimentary environment,sedimentary facies types,depositional system and evolution model of Toutunhe Formation Qingshuihe Formation in the Nan’an Jihai profile.Collect outcrop samples and combine the core cuttings,rock slices,reservoir physical properties,and other data of Well Tian’an 1 near the study area to study and discuss the reservoir characteristics,favorable reservoir distribution,and petroleum geological significance of the Toutunhe Formation to Qingshuihe Formation.The research results show that:(1)The Toutunhe Formation in the Nan’an Jihai profile can be divided into three profiles,the Qigu Formation can be divided into two profiles,the Kalaza Formation as a whole is one profile,and the Qingshuihe Formation can be divided into two profiles.The stratigraphic distribution of the Toutunhe Formation and Qingshuihe Formation in the south of the Junggar Basin is generally characterized by a trend of being thick in the middle and thin in the east and west.The thick conglomerate profile of the Nan’an Jihai profile is the stratum of the Kalaza Formation,and the mudstone layer at the top of the conglomerate profile is the stratigraphic boundary between the Kalaza Formation and the Qingshuihe Formation.(2)Seven types of sedimentary facies,11 subfacies,and 23 microfacies types can be identified from the Toutunhe Formation to Qingshuihe Formation in the Nan’an Jihai profile.The Toutunhe Formation develops shallow water delta facies and Freshwater lake facies;The Qigu Formation develops seasonal meandering river facies and terminal fan facies;The Kalaza Formation develops alluvial fan facies;The Qingshuihe Formation develops fan delta and brackish lake facies.(3)From the end of the Middle Jurassic to the early Cretaceous,the paleoclimate in the study area changed from semi-arid to humid,and then changed arid to humid.the lake level experienced a process of rising,falling,and rising.The Toutunhe and Qingshuihe Formations developed four sedimentary facies models: shallow water delta to freshwater lake,seasonal meandering river to terminal fan,alluvial fan,and fan delta to semi saline lake.The evolution of its sedimentary system can be divided into 10 stages,which are generally the evolution process of river-delta-lake-river-alluvial fan-fan delta-lake.(4)The distributary channels,underwater distributary channels and beach bars of Toutunhe Formation,the braided distributary channels of Kalaza Formation and Qingshuihe Formation are favorable sedimentary facies types.The sandstone in the Kalaza Formation and Qingshuihe Formation have good porosity and permeability conditions,they are the key targets for further exploration.The study provides a good geological basis for further oil and gas exploration.