| The reservoir of Wenxiyi district in Tuha oilfield is a typical low-viscosity（0.7m Pa·s）,low-permeability(≤100×10-3μm2),high-temperature（84.2℃）reservoir whose heterogeneity is serious.According to the results of foam flooding field test,the conventional foaming agent used in field foam flooding plays a role of mobility control to a certain extent,however it can’t activate the residual oil effectively resulting in a large amount of residual oil and low recovery.In order to further improve the oil recovery over water flood,the ultra-low interfacial tension foam system KX-037 is optimized in this paper.Firstly,the advantages and disadvantages of the ultra-low interfacial tension system KX-037under various factors were investigated compared to the non-ultra-low interfacial tension old system XHY-4 selected in the previous field test in this block.Secondly,experiments on sealing ability,adsorption performance and surface wettability were carried out to reflect the dynamic performance of the ultra-low interfacial tension foam system in porous media.Then,the experiment was conducted to compare and evaluate the strong oil washing ability and flooding effect of the ultra-low interfacial tension system and the old system XHY-4 from the micro and macro perspective.Finally,the optimal injection parameters for the block are optimized by physical model test which have practical significance to carry out foam flooding test and industrial processes in oil fields.Under reservoir conditions,the foam complex index of KX-037 foam system at the effective concentration of 0.1%is 60.86×104m L·s and the equilibrium interfacial tension is 2.26×10-3m N/m.The data proves that its foam performance is good and the interfacial tension reaches ultra-low levels.Compared with the non-ultra-low interfacial tension old system XHY-4,the KX-03 foam system has better temperature and oil resistance,The sealing ability test confirmed that the foam system had stronger sealing ability when the effective concentration 0.1%,gas-liquid ratio 1.0:1.0,injection rate 1.0m/d and other parameters were selected,static adsorption experiments indicated that the maximum static adsorption capacity is 0.65mg/g,and KX-037 has ability to improve the wettability of rock surface,which could change the rock surface from oil wetting to water wetting.Using the improved laser-etched microscopic visualization model,we analyzed the residual oil type,distribution and flooding effect of foam flooding in old system XHY-4 and ultra-low interfacial tension system KX-037.The microscopic experiments show that KX-037 system activates a large amount of columnar and angular residual oil,increasing swept volume from 18.9%of the old system to 25.5%and the oil recovery over water flood have increased from 22.5%of the old system to31.8%.The macroscopic experiments display that the enhanced recovery rate was increased from 7.6%of the old system to 18.7%in the natural core experiment after injecting the foam liquid 0.3PV,which proved that the oil washing ability of KX-037was significantly better than old system.In double-tube core displacement test,the profile control effect of KX-037 system is significant,the duration of profile control is long and the oil-increasing effect of high permeability tube is obvious.The oil recovery over water flood（double tube）from 9.67%to 18.64%.Finally,the optimal injection parameters of KX-037 foam system for the block were determined by physical model experiment:slug size 0.3PV,injection timing98.15%（composite water-cut）.The ultra-low interfacial tension foam system can maintain a good profile control ability and the enhanced recovery rate of double-tube core displacement test increases gradually when the permeability ratio is less than 9.2. |
