Study On Gas Phase Characteristics And Oil Displacement Law Of Light Oil Reservoir In X Block

At present,the proven reserves of low permeability oil fields account for an increasing proportion of proven oil and gas resources.However,low permeability oilfield has the characteristics of low permeability,low porosity,high temperature,high pressure and difficult exploitation,which is not conducive to development.X block belongs to low permeability reservoir,which has the problems of poor water injection development effect and low recovery efficiency.Gas flooding is an effective way to develop low permeability reservoirs.Hydrocarbon gas is an easily available gas source for oil fields and does not pollute the formation.However,there are relatively few studies on the development of hydrocarbon gas injection in the process of gas drive development at home and abroad.Therefore,based on the geological and reservoir conditions of low permeability reservoirs in X block,this paper carried out indoor experimental research on the influence of hydrocarbon gas injection on the PVT phase state of formation fluid,the minimum miscible pressure of hydrocarbon gas crude oil system,and the oil displacement of long core injection of hydrocarbon gas.The variation law of formation fluid phase state characteristics and gas injection development law of low permeability reservoirs in X block are clarified,which provides theoretical basis for the compilation of development plan.The results show that（1）The injection of hydrocarbon gas can improve the physical properties of crude oil.After the formation crude oil dissolves the hydrocarbon gas,the physical properties before and after dissolution are compared and analyzed.It is concluded that the saturation pressure increases by 80.6%after dissolving 50mol%gas,the gas-oil ratio increases by 145.4%,the volume coefficient increases by 83.2%,the density of crude oil decreases by 19.0%,the viscosity decreases by 45.6%,and the shrinkage rate decreases by63.7%.（2）In the process of multiple contact experiments,it is found that the mass transfer of C₁,C₆,CO₂ and other components in crude oil and hydrocarbon gases can effectively improve the viscosity and density of crude oil,which is conducive to improving oil recovery.（3）The minimum miscible pressure of hydrocarbon gas determined by slim tube experiment is 48.08MPa,and the empirical formula method predicts that it is 48.75MPa,43.21MPa and46.37MPa,respectively.Compared with the results of slim tube experiment,the error range of minimum miscible pressure predicted is 1.38%-10.14%.（4）In the long core displacement experiment,the recovery rate of continuous hydrocarbon gas injection is 40.98%,which is higher than that in the depletion experiment.The recovery rate in the depletion experiment is positively correlated with the depletion pressure.The greater the depletion pressure,the higher the recovery rate.（5）The optimal displacement scheme of hydrocarbon gas injection in low permeability reservoir of X block is determined:the injection rate is 0.5m L/min,the injection gas and water slug are 0.1PV respectively,the gas-water ratio is 1:1,and the final recovery rate of core can reach 72.59%.In this paper,the research on gas injection characteristics and oil displacement law of low permeability reservoir in X block is of great significance for the formulation of low permeability reservoir development plan and the evaluation of development effect.