Distribution feature of micro-pore and throat and evaluation of movable oil in extra-low permeability reservoir：A case study in Yingcheng Formation, Shiwu Oil Field

Based on the laboratory analyses of porosity and permeability as well as the measurement of capillary pressure by mercury injection,the features of micro-pore and throat in extra-low permeability reservoirs have been studied.The micro-pore and throat radius is small,and the distribution of pore and throat is characterized by strong heterogeneity,resulting in the low permeability of reservoir and the high saturation degrees of irreducible water and oil.Movable oil in micro-pore and throat is defined using border formation theory.The threshold for movable oil has been found,by means of which movable and unmovable oils by water drive can be distinguished in extra-low permeability reservoir.The eva-luation of Yingcheng Formation in the Shiwu Oil Field has been carried out using the above-mentioned method,and the result is in accordance with that of nuclear—magnet resonance.