Experimental Study On Reducing The Minimum Miscible Pressure Of Carbon Dioxide-Crude Oil

CO₂miscible flooding is one of the important methods to improve oil recovery in low permeability reservoirs.Minimum miscible pressure(MMP)is a key parameter to realize CO₂miscible flooding.In most oilfields in China,the minimum miscible pressure is generally higher than formation pressure.When CO₂and crude oil are miscible,formation rupture is easily caused,and CO₂miscible flooding cannot be realized.If the minimum miscible pressure of CO₂and crude oil can be effectively reduced,such reservoirs can be flooded with CO₂miscible,which will have a significant breakthrough in the application of CO₂in enhanced oil recovery.In order to explore and solve the problem of high miscibility pressure between CO₂and crude oil,this paper takes the crude oil of Y oilfield as the research object,compares the minimum miscibility pressure of CO₂and crude oil in this block by using thin tube experiment method and core displacement method,and studies the main factors affecting the minimum miscibility pressure of CO₂/crude oil in the target block.Based on the existing CO₂oil displacement mechanism,a series of experiments were carried out by adding alcohol,alkane and surfactant to CO₂/crude oil system.Test the interfacial tension of CO₂/crude oil system after adding different regulators,analyze its variation law,and analyze its mechanism of reducing the minimum miscible pressure.The experimental results show that compared with the thin tube model,the simulated core used in core displacement method is more consistent with the actual porous medium structure,and the minimum miscible pressure measured is 22.34MPa.The experimental results show that compared with the thin tube model,the simulated core used in core displacement method is more consistent with the actual porous medium structure.The minimum miscible pressure measured in this paper is 22.34MPa under the condition of bound water.The results showed that Ethylene glycol butyl ether(EGBE)significantly reduced the minimum miscible pressure of CO₂/crude oil among different regulators,and the optimal injection slug size was 0.5wt%.The measured minimum miscible pressure of CO₂/crude oil before and after addition was 22.34mpa and 17.52mpa,respectively,with a decrease of 21.56%.Under the experimental conditions higher than the minimum miscible pressure,the final recovery of gas flooding,water to gas flooding and water to gas alternate injection are 74.24%,75.53%and 78.11%,respectively.Water/CO₂alternate injection has a better recovery effect.With water/CO₂injection,the final recovery was significantly improved by adding 0.5wt%and 0.7wt%EGBE slug,and the corresponding total recovery was increased by 14.03%and 15.56%,respectively,and the oil exchange rate was increased by 7.05%and 7.77%,respectively.Therefore,at the experimental conditions above the minimum miscible pressure,considering the dosage of chemical agent and the increase of recovery rate,adding 0.5wt%EGBE was the best addition to reduce the minimum miscible pressure,and oil recovery was significantly improved.