Study On Unconventional Reservoir Characteristics In Santanghu Basin And Its Application

As an important oil-producing area of Tuha oilfield,Santanghu Basin is a guarantee for the stable oil production.There are mainly four types of lithologic reservoirs in Santanghu Basin.Low-permeability sandstone reservoir,sedimentary tuff reservoir,mixed shale oil reservoir and weathered crust/inner volcanic reservoir.The complex reservoir conditions also directly lead to the great difference of physical properties of these reservoirs,so it is difficult to choose the dessert area.In this paper,from the perspective of reservoir,the characteristics of microscopic pore structure of four kinds of lithologic reservoirs were characterized qualitatively and quantitatively by conventional core physical property test,high-pressure mercury injection,low ow temperature nitrogen adsorption and desorption technology.On these area,the static experiment of fluid occurrence and the dynamic experiment of water displacement were carried out by nuclear magnetic resonance(NMR)testing and centrifugal technology,and the reservoir fluid occurrence state was analyzed.Finally,the four kinds of lithologic reservoirs are evaluated in different grades,and the dessert areas for subsequent development are optimized.The results of this study can not only provide a theoretical basis for the effective development of four different lithologic reservoirs in Santanghu basin,but also provide a reference for the orderly and effective development of different lithologic reservoirs in other regions through the comparative study of the characteristics of various lithologic reservoirs.The results show that the overall physical properties of the four reservoirs in the study area are poor and the pore structure is complex.The sedimentary tuff reservoir has strong homogeneity and pore throat is well developed.Shale reservoir is the least developed and the porosity is the most subtle,while volcanic rock and low-permeability sandstone reservoir are between the two.With the increase of permeability,the movable flow percentages in the four reservoirs increase in varying degrees,and the development potential becomes better.According to the analysis of movable fluid content,the development potential of tuff reservoir is the best,shale reservoir is the worst,and low permeability sandstone reservoir and volcanic reservoir are between them.The reservoir fluids mainly occur in the submicron and micron pore spaces.For the vast majority of reservoirs,even though there are a lot of nanoscale pores in the reservoir,fluid cannot flow in the reservoir due to the small pore throat.Accordingly,the submicron and micron pore spaces account for a relatively small but have a large percolation potential.In addition,the larger the boundary layer thickness is,the greater the seepage resistance of reservoir fluid is,and the more difficult the reservoir development is.Based on the analysis of pore structure and fluid occurrence state,the sedimentary tuff reservoir is the dessert reservoir in Santanghu basin of Tuha oilfield.