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Reservoir Characteristic and Controlling Factors on Physical Properties of Lower Jurassic Tight Sandstone in the Qiudong Sub-Sag, Turpan-Harmi Basin
详细信息   
摘要
The Lower Jurassic of the Qiudong sub-sag in the Turpan Harmi basin is mainly a set of coal-bearing clastic rocks dominated by feldspathic lithic sandstones.The southern margin of the sub-sag is a braided river delta sand body,and the northern is a fan delta sand body.Both the delta plain and front sandstone have great thickness,good connectivity,and large composite area.They are mainly located in the Qiuling,Qiudong,Wenjisang,Kekeya and Shanle.Based on the analyses of conventional thin sections,casting thin sections,core physical properties,grain sizes and mercury injection data of the Lower Jurassic reservoir,it is concluded that the Lower Jurassic rocks are relatively coarse,mainly belonging to medium-coarse sandstone or sandy conglomerate.The pore types are mainly intragranular dissolved pores,residual intergranular pores and micro-fractures.The pore combination is fracture-residual intergranular pore-intragranular dissolved pore.The content of montmorillonite(S%) is less than 25% and it is during the late diagenesis A1 Stage with strong compaction,strong particles plastic deformation,relative weak dissolution and weak cementation.The average porosity and permeability are 6.0% and 0.30×10-3μm2,respectively,and the maximum connectivity throat radius is less than 1.5μm,so the reservoir was considered as a micro-throat tight reservoir.The main controlling factors on the reservoir development were sedimentary microfacies,diagenesis and tectonic process.The distribution of reservoir sandstones was controlled by sedimentary microfacies.The compaction reduced pores and dissolution increased part of the pores.The micro-fractures resulting from the tectonic process improved reservoir permeability.Areas east to the Dongshen 2 well-Ji 1 well were favorable distribution region for the J1s reservoir in the southern margin of Qiudong Sag.Aktash,Kekeya and Zhao 4 well areas were more favorable area for J1b in the northern margin of Qiudong Sag.

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