Study On Nitrogen Foam Flooding System With Low Interfacial Tension For High-Temperature And High-Salinity Reservoirs

Foam system has good profile control performance.It can plug the high permeability layer effectively through the Jamin effect.But the common foam systems focus on foaming ability and overlook the effect on interfacial tension between oil and water.So it has poor ability to reduce the interfacial tension.And the application of the enhanced foam technique is controlled in high temperature and salinity reservoir.So it is important to prepare a novel low interfacial tension?LIFT?nitrogen foam with high temperature-resistance and salt-tolerance.It has excellent properties to reduce the interfacial tension and good foaming ability in high temperature and salinity environment.The LIFT nitrogen foam was successfully prepared by an amphoteric surfactant and sodium formate through the modified Ross-Miles experiment.It has high foaming ability and can reduce interfacial tension well in high temperature and salinity environment?90°C?18.3×10⁴ mg/L?.And the reservoir adaptability of the LIFT foam has been studied through the high temperature and high pressure testing equipment,the aging experiment and the physical simulation experiment.In addition,the interfacial rheological properties of the LIFT foam system have been studied through the dynamic interface rheometry.In the end,the foam displacement mechanisms for enhanced oil recovery have been studied through the foam displacement in flat-panel sand model and etched-glass micro-models.The results show that the LIFT foam system which is consist of 0.2 wt%⁰.25 wt%HTS-1 and 0.2 wt%⁰.25 wt%sodium formate has the best performance.The foam volume can reach 221 mL and the foam half-life can reach 71 min in high temperature and salinity environment?90°C?18.3×10⁴ mg/L and 5 MPa?.And it can reduce the interfacial tension to0.27 mN/m.The LIFT foam system has good thermal stability and the foaming ability decreases slightly with aging.When permeability less than 3.5?m²,the residual resistance factor of LIFT foam system can reach more than 20.In high temperature and pressure environment,the velocity of gas diffusion and liquid evaporation increase with the increase of temperature.And the interface modulus decreases with the increase of temperature.So the elasticity of the foam film declines and results in a worse foam stability.The foam comprehensive value is down 18%with every increase of 10°C.The drainage speed of liquid film decreases with the increase of pressure.And the interface modulus increases with the increase of pressure.Within certain range,the change of the foam comprehensive value accords with the formula y=3880.8e^0.224x.So the elasticity of the foam film intensifies and results in a better foam stability.The LIFT foam can enhance oil recovery to 26.3%.Comparing with the common foam,the LIFT foam can plug the high permeability layer,emulsify and carry oil better.So it can enhance oil recovery better.