The Experimental Study On CO₂ Flooding For Ultra-low Permeability Reservoir In Chang 8 Oil-baring Formation Of Southern Erdos

Nowadays the development of low-permeability reservoirs especially ultra-low permeability reservoirs is difficult.The conventional water flooding injection is difficult and the result is bad.Due to its peculiar physical property of easily dissolved in crude oil and easily reach miscible,carbon dioxide?CO₂?can greatly change the oil mobility,what's more,CO₂ flooding makes a good use of carbon dioxide gas which is significant for reducing the greenhouse effect and environment protection.Thus CO₂ flooding is currently an effective way to develop the ultra-low permeability reservoirs.This paper studied the CO₂ flooding mechanism with PVT test to compare the oil phase change before and after CO₂ injection based on the ultra-low permeability rocks and formation conditions in Chang 8 oil-baring formation,Southern Erdos.It studied the rules of CO₂ flooding using flooding experiments,where the minimum miscible pressure was acquired with capillary experiment.In addition,it studied the rules of different CO₂ flooding methods and optimized the CO₂ huff-puff coefficient.The results show that CO₂ can greatly reduce the oil density and viscosity,tremendously reduce the threshold injection pressure,increase the volume factor,extract most of the light hydrocarbon in the oil,reduce the surface tension to almost zero,increase the capillary number to infinite,so to reach a miscible condition.After comparing several different CO₂ flooding methods,the results show that the CO₂ miscible flooding gives the highest oil recovery,which also has the lowest flooding differential pressure.The CO₂-water slug flooding has an oil recovery that comes after CO₂ miscible flooding,and its flooding differential pressure is relatively high and gas-oil ratio is relatively small.Water flooding has the lowest oil recovery and highest flooding differential pressure.For all the CO₂ flooding methods,the oil production is still high when the gas-oil ratio is high,which means that a high gas-oil ratio is not an indication of gas breakthrough,it is actually due to the production of oil that CO₂ was dissolved in.When CO₂ flooding was performed after water flooding,the oil recovery was also greatly increased,but the oil production was delayed.For CO₂ huff-puff,the best approach is to select the optimum soaking time and the most economic gas injection volume,and the earlier the gas is injected,the better the effect will be.