| Gas injection and water injection are conventional techniques in the development of ultra-low permeability reservoirs,and low viscosity gas and water have serious channeling problems under the influence of cracks.Foam and emulsion can effectively solve the problem of gas channeling and water channeling,along with the imbibition phenomenon between cracks and matrices.Surfactant plays an important role in foaming,emulsification and imbibition,but it is easy to inactivate the surfactant under high temperature and high salt conditions in the reservoir.Based on the above problems and considerations,the surfactant enhanced gas flooding and enhanced water flooding methods adapted to the development of ultra-low permeability fractured reservoirs are studied in order to further improve the effects of gas flooding and water flooding,so as to significantly improve the oil recovery in ultra-low permeability fractured reservoirs.Taking the synthesis of temperature and salt resistant surfactants as the research premise,the design of the new method for emulsion performance evaluation and the dynamic/static imbibition experimental device as the auxiliary and improvement of the synergy method research,the methods of performance evaluation experiment of injected surfactant system,core seepage experiment,core oil displacement experiment,capillary infiltration experiment and core imbibition experiment were applied,combined with the effect of mine field test,from four aspects:synthesis and performance test of functional temperature and salt resistant surfactant,the surfactant-assisted CO2 expansion and volume method,surfactant in situ emulsification and flooding method,the surfactant seepage and oil displacement mechanism and experimental method improvement,it was studied and demonstrated.The main conclusions and understandings are as follows:（1）The low interfacial tension surfactant DHT,foaming agent FH and emulsifier GOP-10 with good surface chemical properties,temperature and salt resistance and anti-adsorption properties were synthetisiert.The water-soluble and hydrophilic balance of surfactant molecules is regulated by characteristic functional groups such as sulfonic acid group,ethoxy group and dihydrocarbon chain,so that the surfactant maintains good interface characteristics under high temperature and high salt conditions.The applicable salinity and temperature of DHT reach 56000mg/L and 120℃,and the applicable salinity and temperature of FH and GOP-10 both reach 42000mg/L and 90℃.After three static or dynamic adsorption,the low interfacial tension properties,foam properties and emulsification properties of DHT,FH and GP-10 were not significantly reduced,and the adsorption resistance was good.（2）An injection method of CO2 gas flooding assisted by surfactants and subsurface foam formation by drip injection of foaming agent was proposed,and the CO2 foam seepage pressure plate under the injection method was established,and the process parameter selection method of the mine site was determined.Three low-tension foam systems with strong,medium and weak foam properties were divided and screened,and the FCI values were between 4000～5000,2000～4000 and less than 2000,respectively.With the increase of oil saturation,the stable seepage pressure of foam decreases,and when the oil saturation is 53%,the stable seepage pressure of foam in the medium-strength foam system is only 0.9MPa;under oil-containing conditions,the stable seepage pressure of medium and low strength foam system foam is about 1.6 times that of single gas injection.The continuous drip injection volume of 15-17PV is the basic requirement for the foam profile to reach the extreme value,which can increase the inspiration volume of the hypopermeable tube by 1 time.As a whole,it shows good injectivity and suction profile adjustment.（3）A new method for quantitatively evaluating the degree of emulsion emulsification and emulsification stability of emulsion-emulsion comprehensive index method-is proposed.Through the test and comparison of the three emulsion performance evaluation methods,the results show that the emulsion comprehensive index method can effectively and quantitatively evaluate the emulsification stability of emulsion.There was little difference between the comprehensive index of emulsion under crude oil and simulated oil,and there was a significant positive correlation between surfactant concentration and the comprehensive index of emulsion.With the increase of injection concentration and PV number,the flooding effect of surfactant solution is enhanced,and when the concentration is 0.3%and the PV number is 0.3 injected,the recovery range is increased by about 8%.The polymer solution with stronger sealing performance and in-situ emulsification of surfactant can effectively plug cracks with a permeability of 150×10-3μm2,promote the utilization degree of crude oil in the matrix,and increase the recovery rate by 8%-11%.（4）A method of converting the height of the self-absorbing hygroscopic phase is proposed to determine the capillary water wettability.The addition of surfactant and the reduction of pipe diameter can promote the spontaneous infiltration of strong water-wet isometric capillaries,and have little effect on weak water-wet isometric capillaries.Although surfactants have a better effect on the wettability of weak wet capillaries than strong wet capillaries,the initial wet strength of capillaries plays a more important role in the spontaneous infiltration process.A device is designed to enables simultaneous dynamic and static imbibition experiments by adjusting the speed of the motor.The static imbibition recovery rate of the device was 1.55%higher than that of the imbibition bottle,and the dynamic imbibition recovery rate was 3%-6%lower than that of the displacement dynamic imbibition method.Dynamic imbibition experiments were conducted to simulate the flow velocity of fractures with different crack widths.The results show that imbibition is more likely to occur near fractures with a crack width of 50-100μm. |
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