Study On Reducing Miscible Pressure Of CO₂ Flooding By Miscible Agent In P Block

CO₂ flooding is one of the important means to improve the oil recovery of reservoirs in tight oil.Influenced by continental sedimentary structure.The physical properties and geological characteristics of crude oil in tight oil reservoir are poor,The minimum miscible pressure of reservoir is generally higher than formation pressure,so it is difficult for CO2 to form miscible with crude oil under formation conditions to realize miscible flooding.Enhanced oil recovery is limited.How to effectively reduce oil miscible pressure and transform immiscible displacement into miscible displacement is of great significance for improving oil recovery in tight oil reservoirs.Aiming at the high miscibility pressure.It is difficult to achieve miscibility under formation pressure.the feasibility study of reducing miscibility pressure in laboratory is carried out.Taking crude oil in block P as the research object,a series of experiments were carried out by adding four types of miscible agents,namely alcohols,ethers,esters and surfactants,to the CO₂/crude oil system.Viscosity method and interfacial tension method were used to screen the miscible agent,and evaluate the effect of miscible agent on reducing crude oil viscosity and interfacial tension.Optimization of slug parameters by CO₂displacement experiment.After optimizing the miscible agent,the performance of miscible agent to reduce miscible pressure and improve crude oil recovery was evaluated.The experimental results show that the best miscible agent 2-Butoxyethanol is selected through viscosity experiment and interfacial tension experiment.After adding 0.5wt%miscible agent,the viscosity reduction of crude oil reaches 10.37%.The miscible pressure measured by interfacial tension experiment decreased to 19.27MPa,with a decrease of 17.65%.The core displacement experiment optimized the slug size of the miscible agent,and the optimal injection slug size was 0.5wt%.The final recovery rate is 83.84%by adding 0.5wt%2-Butoxyethanol.The performance evaluation of the miscible agent showed that the miscible pressure decreased to 22.8MPa and 15.1%after adding 0.5%2-Butoxyethanol.The minimum miscible pressure is26.8MPa,and after adding 2-Butoxyethanol,the oil recovery rate is increased by 1.5%.The miscible pressure is 22.8MPa,and the oil recovery rate is increased by 2.7%.Therefore,in view of the reservoir geological conditions in block P,2-Butoxyethanol can reduce the miscible pressure of CO₂ flooding and improve the oil recovery.