The Research On Micro-geological Characteristics And Remaining Oil Distribution Of Chang 8₁ Reservoir In Maling Oilfield

The low permeability resources are very rich in Ordos Basin,and it has important theoretical and practical significance for the study of the microscopic characteristics of the?special?low permeability reservoirs and the distribution of remaining oil.In this paper,the Chang 8₁ reservoir of Maling Oilfield is taken as the research object.The target layer of the study area belongs to the typical extra-low-ultra-low permeability reservoir.The distribution of oil and water is complicated.In the production process,the production declines rapidly and moisture content of the oil well rises rapidly.Through the comparison and division of the stratum,the characteristics of sedimentary microfacies and sand body distribution are studied,and using casting sheet,scanning electron microscope,X-ray diffraction,physical property testing,high pressure mercury intrusion,constant velocity mercury intrusion,nuclear magnetic resonance and oil-water phase infiltration experiments are used.The microscopic pore throat characteristics and seepage characteristics of the stratum were studied in detailed.Based on the cluster analysis,reservoirs was divided into the flow unit,and the microscopic remaining oil distribution characteristics of the reservoir were studied in depth.The results show that the thickness of the target stratum is stable in the study area,belonging to the braided river delta front subfacies,and the underwater distributary channel sand body is developed.The lithology is mainly lithic feldspar sandstone and feldspar lithic sandstone,clay minerals and carbonate cements are more developed,and the overall physical properties of the study area are poor.The total facial porosity of the reservoir is 2.94%.The mixed pores composed of intergranular pores and feldspar dissolved pores are mainly developed,and the pore structure of the reservoir is divided into four types.The reservoirs of II and III pore structures are more distributed in the study area.The pore radius of all samples is concentrated between 100?m and 190?m,and the average throat radius is between0.289?m and 1.250?m.Size and distribution characteristics of throat,pore throat sorting and connectivity have important control effects on reservoir properties.The dynamic fluid content of different samples is quite different,and the average movable fluid saturation is 44.75%.The characteristics of microscopic pore throat structure have an important influence on the movable fluid content.The oil and water relative permeability curves are divided into four types.The storage and seepage capacity corresponding to the seepage curve are weakened in turn;the reservoirs are divided into four types of flow units:E,G,M,and P by cluster analysis.The physical properties and oil-bearing properties are deteriorated in turn,and the productivity is reduced in turn.The E and G-type flow unit is the main area of remaining oil enrichment;according to the micro-water flooding displacement pattern,the reservoir is divided into four types:uniform displacement,network displacement,finger-network displacement,and finger displacement.Among them,the uniform displacement type of sample has the best oil displacement effect,it mainly distributed in E-type flow units,and the microscopic remaining oil type is mainly composed of stuck and surrounding remaining oil.The microscopic remaining oil distribution is affected by reservoir physical properties,pore throat development characteristics and wettability.