Study On The Comprehensive Reservoir Evaluation And Controlling Factors Of Chang 6 Oil Set,Yanchang Formation In Gutun Area,Ganguyi Oilfield

Chang 6 reservoir of Gutun area in Ganguyi oilfield has typical characteristics of low porosity and low permeability and strong heterogeneity,which has caused many problems in oilfield development,such as low oil production and poor water injection effect and so on.Therefore,it is urgent to study the reservoir characteristics and its main controlling factors in this area,analyse and predict the distribution area of high quality reservoir,to provide reference for further oil and gas exploration and development.Guided by reservoir geology,comprehensively apply the data of core observation&description,casting thin section,X-ray diffraction,scanning electron microscope,constant-pressure mercury injection,constant-speed mercury injection.On the basis of deep understanding of stratigraphic development characteristics,structural characteristics,sedimentary microfacies and distribution characteristics of sand bodies in the study area,the petrology,physical property,micro pore structure and diagenetic evolution stage of Chang 6 reservoir are mainly studied.The main controlling factors of Chang 6 reservoir are summarized from three aspects:sedimentation,diagenesis and structural fractures,on which the comprehensive evaluation criteria and schemes of Chang 6 reservoir are put forward.Study suggests that Chang 6 reservoir in Gutun area is stably developed and gently structured,the main reservoir body is delta front underwater distributary channel sand body.Fine-grained feldspar sandstone with low composition maturity and medium structure maturity is the main reservoir sandstone,which has intergranular pore and solution pore as the main pore type,and average porosity of 8.21%,average permeability of 0.52×10^-3?m².Generally Chang 6 reservoir has poor physical property and type?micro-pore structure of low displacement pressure and small pore throat,the permeability of reservoir is mainly controlled by the average throat radius.Diagenesis types of reservoir Chang 6 in Gutun area are compaction,cementation,metasomatism,dissolution and fracture.By reducing the primary porosity the compaction compacts the reservoir,through the enlargement of carbonate,zeolite,quartz and feldspar the cementation blocks up pore space,under the action of organic acid the dissolution of clinopalite,feldspar and other minerals occurred in the middle diagenesis stage,during which the intergranular and intragranular dissolved pores are formed to improve reservoir physical properties.Under the influence of two stages of tectonic movement,4 groups of macroscopical natural fractures were developed in the direction of EW,NE,EW and NNW,while providing access to oil and gas migration and accumulation,it also led to the phenomenon of water flooding in some oil wells where artificial fracturing and water injection were implemented.The main controlling factors of Chang 6 reservoir in Gutun area are sedimentary,diagenesis and structural fractures,based on this and combined with micro-pore structure and dynamic production data to establish the comprehensive evaluation criteria for reservoirs,according to which Chang 6 reservoir can be divided into 3 types of high quality reservoir,general reservoir and poor reservoir.Predict of the distribution of various reservoirs in the study area and provide guidance to the further construction and development of oilfields.