Experimental Study On Recovery Characteristics Of Oil Phase In Low-Permeability Medium Under Different Injection Fluids And Recovery Techniques

How to effectively develop low-permeability reservoirs is the main problem in our country’s petroleum development field.As an important means of enhancing oil recovery in low-permeability reservoirs,displacement and huff-n-puff methods have received extensive attention in recent years.In view of the commonly used media in the current displacement and huff-n-puff processes,this paper carried out a comprehensive and in-depth laboratory research on the oil recovery characteristics of CO₂,N₂,water and nano-solution in low-permeability media.The specific experimental research factors included different injection media,different recovery techniques,different permeability of low-permeability media and different system pressures.Based on the different interaction mechanisms between various displacing media and the oil phase,the experimental results are deeply analyzed and discussed.In this paper,three low-permeability Beray outcrop cores with the diameter of2.5cm and the length of 5cm with three different permeability intervals（0.1m D,0.5m D,10m D）were used to simulate the real formation conditions（temperature 50℃,back pressure 15MPa/25MPa）,carried out an experimental study on the effect of supercritical CO₂（ScCO₂）and N₂,water,nano-solution displacement and huff-n-puff oil recovery.The experimental results show that:（1）In cores with all permeability,the displacement recovery rate of supercritical CO₂is the highest,and its maximum value can reach about 90%.The recovery rate of N₂displacement is second,the highest is 52.08%.The total recovery rate of water and nano-solution displacement is not much different,the maximum recovery rate of water displacement is 48.91%,and the maximum recovery rate of nano-solution displacement is 46.37%.The better displacement effect of CO₂can be attributed to the fact that it reached a miscible state with the oil phase under the experimental conditions.（2）The recovery rate of gas injection（ScCO₂and N₂）huff-n-puff increases with the increase of core permeability.Compared with N₂huff-n-puff,supercritical CO₂has higher huff-n-puff recovery efficiency.The supercritical CO₂huff-n-puff recovery rate decreases less with the huff-n-puff rounds,and the lower the core permeability is,the more effective huff-n-puff rounds can be carried out,while the recovery rate of N₂huff-n-puff decreases rapidly with the increase of huff-n-puff rounds,and the number of effective huff-n-puff rounds that can be carried out is less.Compared with the liquid injection huff-n-puff process,the recovery rate of gas injection huff-n-puff is much higher than that of liquid injection huff-n-puff.This research work has important reference significance for in-depth understanding of the enhanced recovery effect and mechanism of supercritical CO₂,N₂,water and nano-solutions in low-permeability reservoirs,and then to guide their reservoir applicability applications.