| Taking the Lucaogou Formation in the south Junggar Basin and the Taerlang Formation in the northwest Tuha Basin as the researching objects,by applying stratigraphy,petrology,sedimentology,reservoir geology and other theories,the main sedimentary facies types and their lithofacies combination characteristics in the mixed sedimentary facies belts were analyzed,the sedimentary modes of the mixed sedimentary facies belts were established,the mixed sedimentary process types and the controlling factors were discussed,what's more,combining the characteristics of source rock and reservoir rock,together with the relationships between them,the favorable lithofacies types were predicted,which can provide basis for the saline lacustrine basin petroleum exploration.Through field geological investigation of 12 outcrop profiles of the Lucaogou Formation in the south Junggar Basin and the Taerlang Formation in the northwest Tuha Basin,Hongyanchi profile,Guodikeng profile,Shuixigou profile,Xidalongkou profile,Taerlanggou profile,and Eweiergou profile,with continuous formation exposed,were picked out for careful measurement,observation and description.On this basis,according to the contact relationship of strata,lithological characteristics and well logs,and by applying wavelet transform method,the drilling and outcrop stratigraphic cycles were divided.Lucaogou Formation can be divided into the first section,the second section and the third section fro m bottom up,and further divided into 5 fourth level cycles.Taerlang Formation can be divided into the first section,the second section,the third section and the fourth section from bottom up,and further divided into 6 fourth level cycles.Through rock thin section identification,X-ray diffraction,scanning electron microscope and other methods,the component types,contents and textures of the rocks in the mixed sedimentary facies belt were carefully analyzed,the definition of mixed sedimentary rock was redefined,at the same time,by applying the “sedimentary structure+texture+component types” naming scheme,the lithofacies types were classified.This paper defined the mixed sedimentary rock as the sedimentary rock composed of terrigeneous clastic particles and authigenic non-diagenesis formed carbonate minerals mixed in the same rock layer,there is no certain minimum content standard for terrigeneous clastic particles and carbonate minerals.In the studying area,most of the siltstone,carbonate rock,shale and a small number of sandstone in the mixed sedimentary facies belt are composed of terrigenous clastic particles,carbonate minerals and clay minerals,belonging to mixed sedimentary rocks,according to the 50% content boundaries of the three co mponents,which can be classified into 3 types,i.e.,(silt)sandstone,carbonate rock and normal mixed sedimentary rock,and further divided into 9 subclasses.On this basis,23 kinds of lithofacies types were identified from the mixed sedimentary rocks in the studying area,and 3 kinds of lithofacies types were identified from the clastic rocks.Through observing and describing core and outcrop,meanwhile,analyzing data such as drilling,well logging,and microelement test,the sedimentary environment,sedimentary facies types and their lithofacies combinations features were carefully studied.The studying areas are typical saline lacustrine basins,generally with semi-salt to salt water environment under dry heat climate.Lucaogou Formation in the south J unggar Basin mainly develops near shore subaqueous fan and(semi)deep lake facies,among which the mixed sedimentary rocks and the mixed sedimentary strata are widely developed in the outer fan of near shore subaqueous fan and the(semi)deep lake facies,together forming the mixed sedimentary facies belt of Lucaogou Formation.Taerlang Formation in the northwest Tuha Basin develops fan delta,turbidite fan and(semi)deep lake facies,among which the mixed sedimentary rocks and the mixed sedimentary strata are widely developed in the fan delta front,turbidite fan and(semi)deep lake facies,together forming the mixed sedimentary facies belt of Taerlang Formation.Lucaogou Formation develops 4 types of lithofacies combinations,while Taerlang formation develops 5 types of lithofacies combinations.According to the lithofacies combination features of different sedimentary facies and their paleogeography backgrounds,two kinds of mixed sedimentary facies sedimentary modes were established.Through macroscopical outcrop observation and microscopical rock thin section identification,mixed sedimentary rocks,mixed sedimentary strata and mixed sedimentary types and features were studied in detail,based on that,the main mixed sedimentary controlling factors were further analyzed.Mixed sedimentary rocks can be divided into fabric mixed sedimentary rock and interbedding mixed sedimentary rock,mixed sedimentary strata mainly include clastic rock-mixed sedimentary rock strata and mixed sedimentary rock strata.Synthesizing the types and characteristics of mixed sedimentary rocks and mixed sedimentary strata,it was considered that the mixed sedimentary facies belt mainly develops abrupt mixed deposition type and gradual mixed deposition type.Hot and dry climate is the prerequisite for Lucaogou Formation and Taerlang Formation to develop mixed sedimentary rocks and strata,tectonic movement leads to different sedimentary facies combinations between Lucaogou Formation and Taerlang Formation,lake level fluctuation and source supply together control the mix types of terrigenous clastics and carbonate minerals.Synthesizing the casting thin section identification,scanning electron microscope analysis,physical properties,high pressure Hg injection test and other methods,the diagenesis types,reservoir space types,pore throat structure and physical properties of the reservoir rocks in the studying area were analyzed,meanwhile,by considering the TOC content and hydrocarbon potential of the source rock and the relatio nship between source rock and reservoir rock,favorable lithofacies types were predicted.Compaction and dissolution are the main diagenesis types,interparticle and intragranular dissolution pores are the main reservoir space types.Lucaogou Formation and Taerlang Formation reservoir physical properties are poor,mainly tight reservoir and extremely low porosity and permeability reservoir.Turbidite fan and(semi)deep lake are favorable lithofacies development area,where the reservoir and source rock share nice spatial relationship.Favorable lithofacies in turbidite fan include sandstone with sandy carbonate particles,micrite with sand,limy siltstone,and micrite with silt,favorable lithofacies in(semi)deep lake include sheet like muddy siltstone,limy(dolomitic)siltstone and limestone or dolomite. |
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