Pore Structure Characteristics And Reservoir Evaluation Of Tight Oil In Qingxi Sag Of Jiuquan Basin

The tight oil exploration in Jiuquan basin is at the initial stage.Less research on the characteristics of tight oil reservoir,especially the micro pore structure.Therefore,this paper through the study of the micro pore structure,so as to further evaluate the reservoir.Jiuquan Basin Qingxi Sag is a typical tight reservoir.The lithology of tight reservoiris mainly dominated by carbonate rocks,with some of the clastic rocks in the middle.Different lithologies have different diagenetic mechanisms,which lead to different pore structures.The porosity of carbonate reservoir is tight but developed fracture,so that the carbonate reservoir has similars to rageporosity and permeability.Reservoir porosity and permeability has a positive correlation,the better there servoir porosity,permeability the better.Based on the date analysis of casting lamella and scan electron microscope,the major type of pores of the reservoir were primary pores and the secondary pores.The distribution range of pore diameter is between 0.082?m and 5.969?m.The throat is tube-shaped and schistose,the main size of throat is micro throat,fracture distribution as a throat is very wide.Classify and evaluate the pore and throat characteristics of reservoir,and compare the different level of them,four types of pore structure were obtained: middle and small pore throat type,middle and small pore fine throat type,micro pore fine throat type and nano pore and micro throat type.Through the comparison of the pore structure characteristics and the extraction of the parameters of mercury injection curve,the reservoir can be classified and evaluated.The least of the four types of resrevoir is the type with high permeability and high heterogeneity.The other three kinds of reservoirs have different degrees of development.