Microfacies And Reservoir Geological Characteristics Of Chang 4+5 Oil Layer Sedimentary In Sancha-Tongchuan Area

The Sancha Tongchuan region lies southwest of Ordos Basin,with abundant oil and gas resources.Its Chang 4+5 oil layer formation has been an important exploration field and a backup reservoir replacement layer series in recent years.The sedimentary microfacies characteristics and reservoir geological characteristics were studied using various analysis methods such as core observation,casting thin sections,porosity and permeability measurement,and mercury intrusion analysis,using core,logging,logging,and analytical laboratory data.The results indicate that the Chang 4+5 oil layer formation in the Sancha Tongchuan area is a set of lacustrine delta deposits,mainly developing delta front subfacies,and can be subdivided into underwater distributary channels,inter distributary bays,and underwater natural embankments.The subaqueous distribution channel micro-facies is the best one to develop the oil field.Among them,the oil reservoir is composed of Lithic Argillaceous Sandstone and Feldspathic Sandstones,with Intergrain Porosity and Feldspathic Fluid Porosity.The mean porosity was 11.6% and the mean permeability was 0.7 to 1.0 × 10 ～ 3 μm 2,belonging to a low porosity low permeability reservoir.The main destructive diagenesis is compaction and cementation,and the constructive diagenesis is chlorite film cementation and dissolution.Chang4+5 reservoir is divided into Class I,Class II and Class III reservoir.The area of Class I+II reservoir accounts for more than 50% of the total reservoir area,and the distribution area of Class III reservoir is relatively wide and mostly distributed in strips.Based on the research results of sedimentary microfacies,sand body distribution,and reservoir characteristics,the reservoir formation characteristics of the Chang 4+5 oil reservoir in the Sancha Tongchuan area were studied through the observation of the occurrence,phase state,color,uniform temperature testing,and description of core fractures of hydrocarbon bearing fluid inclusions under the microscope.It is believed that the Chang 4+5 oil reservoir in the Sancha Tongchuan area mainly formed in the middle and late Early Cretaceous(105Ma±),and was mainly filled with hydrocarbon generating organic matter from the Chang 7 oil layer formation.Oil passed through the early Chang 7 The three-dimensional network transport system based on sand body fractures and microfractures in the Chang 6 oil layer group migrates upwards into the Chang 4+5 reservoir,resulting in the formation of Chang 4+5lithologic oil reservoirs and structural lithologic oil reservoirs.The paper summarizes the reservoir formation patterns of two types of oil reservoirs,the Chang 4+5 oil layer group.