Difference Of Microscopic Characteristics Of Tight Sandstone Reservoirs And Its Influence On Movable Fluid In Longdong Area,Ordos Basin

With the development of tight reservoir development technology,great achievements have been made in recent years.With the progress of exploration and development,some problems have gradually begun to be exposed,such as high water saturation in the early stage of well production or low liquid production during the process of exploitation,resulting in the inability of large-scale popularization and application of some mature development technologies.Therefore,it is of great significance for the development of oil and gas fields to study the distribution characteristics and differences of micro pores and throats in tight sandstone reservoirs and to explore their impact on reservoir movable fluid.Taking two layers in three regions of Longdong area as the research object,this paper compares and analyzes the microscopic characteristics and differences of tight sandstone reservoirs by using experimental techniques such as cast thin section,scanning electron microscope,X-ray diffraction,conventional mercury injection,constant velocity mercury injection,nuclear magnetic resonance and oil-water phase permeability,and discusses the factors affecting the movable fluid capacity of reservoirs.The response relationship of different pore throat characteristics in production is established when combined with production practice.The understanding of this study is as follows:1.Affected by multiple sources,the contents of feldspar and igneous rock debris in Huaqing Chang 6 reservoir are higher than those in Banqiao-Heshui Chang 6 reservoir,and the contents of quartz and metamorphic rock debris in Maling Chang 8 reservoir are slightly higher than those in Banqiao-Heshui Chang 8 reservoir.The content of carbonate rock in Huaqing Chang 6 reservoir is higher than that in other areas.2.The physical property of Chang 6 reservoir in Huaqing area is slightly better than that in Banqiao-Heshui area.The physical properties of Chang 8 reservoir in Maling area are better than those in Banqiao-Heshui area,but the physical properties are poor as a whole.The influence of carbonate cement on Chang 6 reservoir is greater than that on Chang 8 reservoir,and the influence on porosity is greater than that on permeability.When the content of carbonate rock exceeds 5%,the influence on reservoir porosity and permeability will increase significantly.When the content increases,the rate of porosity and permeability decrease will increase significantly.3.The high mica content of Huaqing Chang 6 reservoir is the main reason for the decrease of reservoir porosity,while the development of a large amount of illite,ankerite and ferrocalcite in the late stage is an important reason for reservoir densification.The higher limestone and dolomite debris in Banqiao-Heshui Chang 6 reservoir provide the material basis for the occurrence of dissolution,but the strong late cementation makes the reservoir worse as a whole.The development of authigenic illite,ankerite and ferrocalcite formed in the middle and late stage of Banqiao-Heshui Chang 8 reservoir is an important reason for reservoir densification.In Maling Chang 8 reservoir,the content change of clastic particles has an obvious influence on the pore size of the reservoir.4.Intergranular pore is the main reservoir space in the study area.The pore distribution curve of Huaqing Chang 6 reservoir is bimodal,and the void space in this reservoir are mostly small pores.The pore distribution characteristics of Banqiao-Heshui Chang 6 reservoir are bimodal distribution,and the reservoir pore type is small pore fine pore.The pore distribution characteristics of Banqiao-Heshui Chang 8 reservoir are multi-peak distribution,dissolution pores and residual intergranular pores play predominant role in this area.The average pore radius distribution curve of Maling Chang 8 reservoir shows a single peak shape,but it drags longer towards the direction of large pores,and the whole pore-throat spaces are dominated by pores,fine pores and small pores.5.Vertically,the pore throat development of Chang 8 reservoir in the study area is better than that of Chang 6 reservoir.The pore throat radius obtained by nuclear magnetic resonance shows that in the reservoir of the study area,the pore throat radius which between 0.1 μm～1μm is the main pore throat type in the reservoir in the study area.6.The fluid flow capacity of reservoir is the result of the joint action of many factors.The factors affecting the fluid flow capacity of reservoir are also different in different regions.The throat radius is the main factor restricting the fluid flow capacity of Huaqing Chang 6reservoir.Average pore radius,clay mineral content and average throat radius are the main factors affecting the fluid capacity of Banqiao-Heshui Chang 6 reservoir.Total pore volume,total throat volume,average pore radius and average throat radius are the main factors affecting the fluid flow capacity of Banqiao-Heshui Chang 8 reservoir in the study area.The main throat radius and average throat size are the main factors affecting the fluid flow capacity of Maling Chang 8 reservoir.In general,the size of throat is one of the key factors affecting the seepage capacity of tight sandstone reservoir in the study area.