Study On The Effect And Mechanism Of Surfactant Compound System To Improve Imbibition In Tight Oil Reservoir

Tight oil and gas reservoirs have the characteristics of low reservoir porosity,low permeability,large seepage resistance,rapid production decline.Imbibition uses capillary force as the main driving force for oil-water displacement,which is one of the important mechanisms to improve the recovery rate of tight reservoir.Surfactant can effectively improve the imbibition recovery rate by changing the wettability of rock surface.Therefore,it is of great significance to study the mechanism of surfactant to improve the recovery rate of tight sandstone.In this thesis,using tight sandstone cores from a block in the J oilfield,static spontaneous imbibition experiments is carried out by mass method.The effect and mechanism of surfactant and nano particles on the imbibition recovery rate of tight sandstone core are studied.The type and concentration of surfactant are optimized and compounded to study its influence on the rate of core imbibition recovery.Two kinds of common nanoparticles,nano graphene oxide（GO）and nano SiO₂,are selected to study their dispersion and carried out imbibition experiment.The effect of surfactant added to nano solution on the rate of imbibition recovery was studied.The core scale and reservoir scale models of tight sandstone are established by using numerical simulation software.The effects of huff and puff fluid,injection rate,injection volume,soaking time and huff and puff rounds on oil production by water injection huff and puff are studied.The following conclusions are obtained:The anionic surfactant SDBS with the concentration of 0.1%has the best effect on improving the core imbibition recovery degree in this block.When the anionic surfactant SDBS and non-ionic surfactant Tuwen 80 are compounded in a certain proportion,the imbibition recovery rate is higher than that of a single surfactant.The research shows that the wettability change ability of surfactant is the key factor to promote the imbibition.The study found that nano GO and nano-SiO₂ can improve the imbibition recovery rate of tight cores.0.2%PVP can effectively prevent the aggregation and precipitation of nano GO in solution.Nano GO alone can not improve the imbibition recovery,but the imbibition recovery can be obtained by compounding a small amount（0.05%）of nano GO with 0.1%surfactant,which is about 2.2%higher than that added with only surfactant.Nano-SiO₂ can only change the wettability of the rock surface and does not have the ability to reduce the oil-water interfacial tension.After nano-SiO₂ and surfactant are configured into a composite system,the imbibition recovery rate increases with the increase of SiO₂ nanoparticle concentration.Comparing the imbibition recovery rate of the two nanoparticles,it is found that the combination of nano GO and surfactant has a better effect on changing the wettability and reducing interfacial tension,but the imbibition recovery degree of nano SiO₂ and surfactant is higher.Adding surfactant in the process of water injection huff and puff can achieve better oil recovery effect than formation water.On the premise that other parameters are certain,the injection speed and injection amount are not the bigger the better,the injection rate and injection volume are 200m³/d and 20000m³ respectively.The length of soak time affects whether the imbibition can fully play the role of oil-water replacement.Whether it is core scale or reservoir scale,a longer soaking time will reduce the recovery degree and oil increase rate.For the core scale,the soak time is40min,and for the single well scale,the soak time is 60 days.Six rounds of huff and puff are simulated.It is found that after three rounds,the increase of single round oil production is not obvious,so it is suggested to select three rounds of huff and puff.In this thesis,the experiment and numerical simulation are combined,and the surfactant and nanoparticles are added to the imbibition solution.The research results provide some reference for the imbibition to improve the recovery degree and water injection huff and puff production in this block in the future.