Research On Temperature-resistant Foam Flooding In Low-permeability Reservoirs

With the development of some oilfields in China entering the middle and late stages,the large-pore oil in the reservoir had been driven out,so it is urgent to adopt a new way to improve oil recovery.As a new oil displacement method,foam flooding is based on compound multi-element flooding,and using foaming agents to form a stable foam system to achieve profile control and enhanced recovery,which can significantly improve the oil recovery of low-permeability reservoirs.This topic was derived from the needs of the North China Oilfield project.Aimed at the characteristics of high temperature(120.6?),high pressure(31.1 MPa)and low permeability(14.6 m D)in Xiliu Block 10 of the target oil reservoir,the foaming and foam stabilization performance of ordinary foaming agents in this kind of reservoir environment dropped sharply,which resulted in the serious limitation of the application of foam flooding.The design provided an efficient foam flooding formula system suitable for high temperature,high pressure and low permeability conditions,and molecular dynamics simulation method was used to explore the formation,stability and oil displacement mechanism of the foam system.Through research,it was found that the current commonly used foaming agent such as alkyl sulfonate and alkyl benzene sulfonate had a poor foaming performance under high temperature conditions and could not meet the requirements of the project.The experimentally synthesized tetradecyl naphthalene sulfonate could meet the requirements of the project's foaming ratio,foam half-life and liquid-swelling half-life,and it could be used as an alternative foaming agent;through comparison,it was found that polyacrylamide and xanthan gum had poor high-temperature foam stability,and they were not suitable for target reservoir conditions.Welan gum had good foam stabilization performance at room temperature and high temperature,and finally the best foam flooding formula system was a combination of 0.3%tetradecyl naphthalene sulfonate and 0.03%welan gum.The results of comprehensive performance evaluation experiment on the foam system showed that the interfacial tension test value of the composite foam system before and after aging was less than 0.1 m N/m.The various foam performance values such as the salinity test,adsorption resistance test,oil resistance test,temperature resistance test and corrosion test all met the project requirements.The resistance factor experiment showed that the mixed injection method had a better effect than the slug injection.When the gas-liquid ratio was3:1,the pressure difference was the largest,and the maximum resistance factor was 32.11.Displacement experiment showed that the single-pipe flooding experiment improved the recovery by 15.46%;and in the double-pipe flooding experiment,the low-permeability core improved oil recovery by 23.46%,and the high-permeability core improved the recovery rate by 20.27%.The total enhanced oil recovery was 21.80%.In addition,this project also studied the distribution of the molecular structure of foaming agent and foaming stabilizer on the surface of foam liquid film through molecular dynamics simulation,and the characteristic functional groups of foaming agent and foam stabilizer interacted with hydrogen bonding in brine and coordinated with Na~+in the system.It revealed the foam formation,stabilization and oil displacement mechanism of the foam flooding system.