Study On Conglomerate Reservoir Characteristics Of Lower Wuerhe Formation In Mahu 1 Well Area,junggar Basin

Mahu 1 well area is located in the southern slope of Mahu Sag,Junggar Basin.The target layer of Lower Wuerhe Formation of Permian is rich in oil and gas resources,which is an important productivity potential area of Xinjiang oilfield.However,in the current process of oil and gas production,it is found that the production and pressure decline rapidly,and the control factors of reservoir are unclear.Therefore,it is urgent to carry out reservoir research,clarify the lithofacies and pore types of target strata,clarify the types and characteristics of interstitials,point out the control factors of reservoir,and carry out the research of favorable reservoir distribution,so as to provide basis for evaluation and development in time.Lower Wuerhe Formation can be divided into P₂w₁,P₂w₂and P₂w₃from bottom to top.Among them,P₂w₃is the main oil-bearing formation,showing the characteristics of high resistance box-sawtooth,while P₂w₁and P₂w₂are the secondary oil-bearing formation,showing the characteristics of finger-sawtooth with middle and low resistance.Seven rock facies types including medium conglomerate,small conglomerate,fine conglomerate,pebbled coarse sandstone,medium fine sandstone,siltstone and mudstone can be identified by core observation.Oil and gas are mainly distributed in fine conglomerate,small conglomerate and pebbled coarse sandstone.The pore types of reservoir are mainly residual intergranular pores,followed by dissolution pores,and few micro-fractures and structural fractures are developed.In the interstitial material,turbidite cement is developed,and the complex base is mainly clay minerals,which is mainly Aemon mixed layer.In view of the great influence of turbidiolite on oil and gas identification and reservoir space,the logging interpretation model and dissolution pore interpretation model of turbidiolite are established.It is found that turbidiolite has dual effects on reservoir physical properties.In the early diagenetic stage,it will block the primary pores and reduce the physical properties,while in the postdiagenetic stage,with the fluid transformation,it gradually dissolves and produces secondary pores to improve the physical properties.Through the study of intralayer,interlayer and plane heterogeneity,it is found that the lower Wuerhe Formation reservoir mainly contains positive rhythm,inverse rhythm,homogeneous rhythm and complex rhythm.The fine calculation of reservoir permeability heterogeneity parameters and sandstone density,and according to the distribution characteristics of interlayer and sand body,it is concluded that the Lower Wuerhe Formation has strong overall heterogeneity,in which P₂w₃member is weaker than the other two members.Diagenesis of Lower Wuerhe Formation reservoir mainly includes compaction,cementation and dissolution.According to the characteristics of authigenic mineral association in Lower Wuerhe Formation reservoir,the target horizon is determined to be mainly early diagenetic stage B--middle diagenetic stage B.Based on the analysis of oil test and reservoir characteristics,it is concluded that the Lower Wuerhe Formation reservoir is mainly affected by sedimentary environment and diagenesis.By selecting six parameters including porosity,permeability,lithofacies,sedimentary microfacies,main cementation and pore type,the lower Wuerhe Formation reservoir can be divided into three types.Among them,classⅠreservoir has porosity greater than 12%and permeability between 10m D and 100m D.The lithofacies is mainly fine conglomerate and pebbled coarse sandstone,and the sedimentary microfacies is mainly underwater distributary channel and estuarine sand bar.The cementation is dominated by turbidite,and the pore space is dominated by intergranular pores and dissolution pores,which are mainly developed in P₂w₃member.The porosity of ClassⅡreservoirs is between 6～12%,and the permeability is between 1m D and10m D.The lithofacies are mainly fine conglomerate and small conglomerate,the sedimentary microfacies are mainly subaqueous distributary channel,clastic flow and fan channel,the cementation is mainly turbidiolite and zeolite,and the pore space is mainly intergranular pore and dissolution pore,which are mainly developed in P₂w₃member and P₂w₂member.The porosity of ClassⅢreservoir is less than 6%,and the permeability is less than 1m D.The lithofacies are mainly medium conglomerate and medium fine sandstone,the sedimentary microfacies are mainly debris flow and remote sand bar,the cementation is mainly zeolite and argillaceous,and the pore space is mainly intergranular pores,which are mainly developed in P₂w₁member.