The Research On Geological Characteristics Of Chang 4+5 Reservoir In L21 Area,Jiyuan Oilfield,Ordos Basin

The geological characteristics of reservoir is an important part of fine reservoir description,and it is also the core cornerstone of improving production in the later stage of reservoir.Jiyuan oilfield is one of the six structural areas in the Ordos Basin.It is located in Dingbian county and Yanchi County of Ningxia Hui Autonomous Region.It is located in the west of the northern slope of Shaanxi Province.The production layer is mainly Triassic low permeability ultra-low permeability reservoir.Jiyuan oilfield has become the fastest and most stable Oilfield in recent years.Under the guidance of the theory of sedimentology,petroleum geology,reservoir geology and well logging geology,this study uses the regional structural background and sedimentary background for reference to divide the Chang 4+5 layers in L21 area of Jiyuan oilfield,and this paper describes the structural characteristics and sedimentary characteristics,and study the geological characteristics of the target reservoir in the study area with the aid of analysis and test.In a word,through this study,we have a deeper understanding of the geological characteristics of the target layer in L21 area,and at the same time,we have analyzed and described the reservoir characteristics.In this paper,the following knowledge is obtained:(1)Under the control of marker layer,layer 4+5 of L21 is subdivided into 8 sublayers.The reservoir structure in this area is characterized by West dipping monocline,and there are many East-West trending nose like uplifts in this area.(2)Braided delta front subfacies are developed in Chang 4+5 of the study area,and 5-6 rivers are developed from north to south.The underwater distributary channel and distributary bay microfacies are obvious in plane distribution.The hydrodynamic conditions of Chang 4+521 and Chang 4+522 are the strongest,the sand body is the thickest,the plane distribution of reservoir sand body is controlled by sedimentary facies.(3)The gray fine-grained lithic feldspar sandstone is mainly lithology of Chang 4+5 reservoir in L21 area,and the study area also includes some feldspar lithic sandstone and a small amount of lithic sandstone.The content of interstitial material accounts for 11.1% of the whole rock component,and the interstitial materials are mainly hydromica,chlorite and kaolinite;The average face rate of reservoir rock is 3.43%,intergranular pores and feldspar dissolution pores are the main pore types,with high bound water saturation and narrow two-phase seepage area.The displacement type is mainly net displacement,and the displacement efficiency is better,generally higher than 45%.(4)The study area is affected by diagenesis.The deep burial depth of the target layer makes it suffer from compaction.At the same time,the pressure dissolution,cementation,dissolution and metasomatism all have great late transformation on the pores;the diagenesis stage of the target layer is between the early diagenesis stage B and the middle diagenesis stage A.(5)The main distribution range of porosity of Chang 4+5 reservoir in L21 area of Jiyuan oilfield is between 8% and 13%,with an average of 10.3%.The main distribution range of permeability is between 0.2m D and 2m D,with an average of 1.34 m D,which belongs to low porosity and low permeability reservoir.The evaluation results of heterogeneity are moderate and weak,the interlayer development is relatively stable,and the thickness is relatively thin;the lithology of interlayer is mostly mudstone,and the thickness is also small;the relatively high porosity and high permeability area is widely distributed in the center of the main river and the north of the study area,with porosity > 10%,local > 12%,permeability > 0.5m D,local > 1.5m D.(6)Based on the analysis of the controlling factors of oil-bearing property in the study area,it is considered that the lithologic traps are formed by the change of lithologic physical property.The dominant sedimentary facies belt and good reservoir physical property are favorable for the oil-gas reservoir,and the Chang 4+5 reservoir is a typical lithologic reservoir.