Experimental Investigation On EOR By Carbonated Water Injection In Tight Oil Reservoirs

Tight oil reservoirs usually have problems of low pressure level,low sweep efficiency and low oil recovery.This paper proposes a method of carbonated water injection,confirming the effect and feasibility of carbonated water injection?CWI?and active carbonated water injection?CWI adding surfactant,ACWI?for tight oil reservoirs.Providing basis for application of ACWI in tight oil reservoirs,so it has a certain guiding significance to realize reasonable and effective development for tight oil reservoirs.First,three types of surfactants provided by Changqing Oilfiled are selected to determine critical micelle concentration?cmc?and emulsions types of surfactants.Results demanstrate that No.II surfactant has the lowest interfacial intension;cmc is0.02%wt,and the type of emulsion is the upper phase emulsion;it is insensitivity to salinity,achieving the best flooding effect.Core displacement experiments are performed to compare the oil recovery of surfactant injection,CO₂/water-alternating-gas injection?WAG?,CWI and ACWI in tight oil reservoirs.Results demanstrate that CWI recovery is 7%more than that of water flooding,and 3%more than that of the degree of WAG.ACWI achieves the best performance with 10%recovery than that of the water flooding.Core displacement experiments are performed to do CWI sensitivity analysis including slug size of ACW,concentration of CO₂ in ACW.and different kinds of surfactants.The injection strategy is water flooding+ACWI+CO₂/WAG injection in order to evaluate the effect of oil increment.Results demanstrate that the optimum CO₂ concentration of ACW is 0.410mmol/cm³,and in that concentration 0.8PV is the optimal slug size for ACW injection,resulting in 26.76%oil increment during ACW injection and CO₂/WAG injection after water flooding.The ACW with No.II surfactant solution achieves the best performance of oil recovery.The high temperature high pressure device is used to conduct high temperature high pressure imbibition to evaluate the effect of imbibition recovery by pressure and imbibition fluids.Results demanstrate that the imbibition recovery under high pressure is higher than that of atmospheric pressure.The imbibition recovery of CW under high temperature high pressure is 39.20%.The high temperature high pressure ACW imbibition achieves the best performance with a recovery of 46.32%.