[Objective]The Permian Luhcaoao Formation in the Jimusaer Sag has developed a continental mixed sedimentary system.Insufficient research on the sedimentary microfacies types of mixed fine-grained rocks and the distribution pattern of sweet spots has hindered the development of shale oil in this area.[Methods]Using core,out-crop,logging,and X-ray fluorescence(XRF)element logging data,analytical testing,oil testing,and production are integrated by lithofacies,sedimentary facies coupling analysis,and dynamic static combination.The sedimentary micro-environment,microfacies classification,model,and its controlling factors on deserts were studied.[Results](1)From the core,eight types of sedimentary structures were identified:wave cross bedding,horizontal bedding,syngenetic deformation structure,pyrite,calcite strip,birds-eye structure and nodule,suture structure,biological fossil,and dolomite dissolution hole.The sub-facies are divided into semi-deep to deep lacustrine,mixed shallow la-custrine,and clastic shallow lacustrine.These are further subdivided into six microfacies:semi deep lacustrine mud,dolomitic flat,mixed beach bar,mixed shallow lacustrine mud,shallow lacustrine sand bar,and clastic shallow la-custrine mud.The sedimentary characteristics and mechanism of different microfacies are different.(2)A sedimenta-ry microfacies model of mixed fine-grained rocks in saline lakes has been established.No.1 member of the Lucaogou Formation evolved from deep to semi-deep to shallow lacustrine from bottom to top.Typical reservoir microfacies are developed in different layers,including shallow lacustrine sand bar,mixed beach bar,and dolomitic flat.Among them,dolomitic flat has a more continuous and large-scale sheet shape,and mixed beach bar has potato shape,with highly developed and different scales.The shallow lacustrine sand bar is intermittent and scale limited;vertically,it is located in the superposition of thin reservoir microfacies and thick mudstone.The Lucaogou Formation No.2 mem-ber is dominated by shallow lacustrine facies.The reservoir microfacies are similar to No.1,but the architecture style is different.The development quantity and scale of dolomitic flat and mixed beach bars are greatly reduced,and shal-low lacustrine sand bars were developed,showing large-scale scattered potato shapes and thick layer superposition vertically.The profile shows that the stacking style of microfacies changed at different positions of the plane.(3)The deposition of the target layer is a transition environment from dry and hot brackish water to salt water,with a high level of paleo-productivity.The lower desert section was deposited in an oxygen enriched environment,but the upper section was deposited in an anaerobic sub reduction to reduction environment.(4)Sedimentary microfacies control desert distribution and oilfield development strategies.The mixed beach bar microfacies is a type Ⅰ sweet spot reser-voir with high development degree,weak heterogeneity and the best production effect.Large scale deployment of hori-zontal well platform operation is adopted for development.The dolomitic flat microfacies is a type Ⅲ sweet spot reser-voir,with strong heterogeneity and general development effect.It is a follow-up replacement oil and gas resource.The shallow lacustrine sand bar is a type Ⅱ sweet spot reservoir being,with overall dispersion,poor continuity,strong heterogeneity,and good production effect.[Conclusions]After the detailed study of the spatial distribution of sedimentary microfacies,the horizontal well development is deployed with reference to the parameters of the nuclear magnet-ic resonance curve.
fine-grained rocksmixed shallow lacustrinesedimentary microfaciesshale oilLucaogou FormationJimusar Sag
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