Study On Quantitative Characterizing Method Of Tight Oil Reservoir In Yanchang Formation Of Ordos Basin

With the deepening of exploration and development,unconventional oil and gas reservoirs have been paid more attention.As an important part of unconventional oil and gas,tight reservoir has become a hot research field in the world because of its abundant resources.The study of diagenesis and micro pore structure characteristics of tight reservoir is the key of reservoir evaluation.Then it is very important to quantify the diagenesis and micro pore structure characteristics.In this study,the Chang 7 tight oil reservoir in the area of Haojiajian of Jiyuan oilfield in Ordos Basin is taken as the research object.With the complexity of the origin of the tight oil,due to the sedimentation and diagenesis relatively have a great influence on the densification degree of reservoir,the characteristics of tight oil reservoirs in different blocks are also different.The heterogeneity of tight oil reservoir is comparatively strong,and the influence of micro pore throat structure on physical property is relatively complex,then it is relatively difficult to obtain porosity,permeability and oil saturation.Aiming at Chang 7 tight oil reservoir in the area of Haojiajian,in this master dissertation,the effects of compaction,cementation and denudation for reservoir physical property are investigated,the influence of diagenetic evolution for reservoir physical properties is analyzed quantitatively.Secondly,the micro pore throat structure was studied by using the data of scanning electron microscope,casting slice and high pressure mercury injection,and the pore types,pore throat size and its combination,pore structure were evaluated quantitatively.Finally,on the basis of lithology identification,calculation of mineral composition is carried out,then,the fine evaluation of physical property and oiliness of reservoir are carried out.Base on the research the results are as follows:(1)Diagenesis has a great influence on the tight reservoir in the area,and the compaction and cementation are stronger.The quantitative analysis results show that the average pore size of original reservoir is 33.6%,the compaction ratio is 71%,and the cementation rate is 45%.Under the condition of strong compaction and cementation,the original pore has disappeared and the average value is 1%,the secondary dissolution porosity is 13.8%.(2)In the study area,the fine sandstone,siltstone and mudstone are mainly developed,and the application effect of interval acoustic transit time and natural gamma is better.For fine sandstone,the value of interval acoustic transit time<230?s/m,the value of natural gamma<95API;for siltstone,the value of interval acoustic transit time between 230?s/m to 270?s/m,the value of natural gamma between 95 API to 135API;for mudstone,the value of interval acoustic transit time>270?s/m,the value of natural gamma>135API.(3)The throat type in reservoir sand body is mainly composed of the sheet throat and the bent sheet throat,followed by sieve-tube throat,a small amount of necking throat,while the pore shrinkage and dotted throat are less.In the study area,the type of pore combination in Chang 7 reservoir mainly are dissolved pore-intergranular pore,intergranular pore,dissolution pore,and the contents of them were 53.87%,21.58% and 18.6%,respectively.(4)With the increase of the number and radius of the big throat,the correlation between pore throat radius and permeability is increased,and the change of pore throat radius is the key to improve reservoir quality.In the case of the same permeability,the pore throat radius of good reservoir is obviously larger than that of poor reservoir.With the increase of reservoir property of sandstone,the pore throat radius increases rapidly.(5)Based on modeling of porosity and permeability,the oiliness of tight reservoir is evaluated by modifying the electrical parameters of Archie formula.According to the chart of the rock electric parameter,the values of a,b,m and n in the study area were 1.305,1.1648,1.655,and 2.1018,respectively.According to the well test and production test data that the lower limit of electrical and physical properties of effective reservoir in study area are as follows: AC>213?s/m,DEN<2.65g/cm3,RLLD>20?·m,?>6.5%,PERM>0.03 mD.