Study On The Mechanism And Main Controlling Factors Of Nano Surfactant Imbibition Displacement In Tight Reservoir

Among different types of wettability changing surfactants,the adsorption loss of liquid nanofluids in the process of migration in porous media is small,which can effectively change the wettability of rocks.At the same time,it can maintain a certain oilwater interfacial tension to drive the infiltration,and nano-surfactants are widely used in tight oil production.However,nano-surfactant is affected by temperature,pressure,salinity and other factors in the reservoir.Therefore,it is necessary to study the effect of nano-surfactant on oil displacement under different factors,and finally determine the main control factors affecting nano-surfactant oil displacement.In this paper,the tight oil reservoir of the Permian Lucaogou Formation in Jimusar Sag,Xinjiang,is taken as the main research object,and three different types of nano surfactant are synthesized under indoor experimental conditions through microemulsion method: Nano surface active agents A(anionic nano surface active agent-sodium ethoxylated alkyl sulfate),B(cationic nano surface active agent-dodecyl dimethyl tertiary amine),and C(anionic non ionic nano surface active agent-a mixture of polyoxyethylene ether and sodium alkenesulfonate).Through testing experiments such as nano particle diameter,interfacial tension,wetting modification effect,and static/dynamic adsorption performance,the interaction mechanism between nano surfactant and tight oil reservoir is revealed,and a systematic evaluation method for the interaction mechanism between nano surfactant and tight oil reservoir is established;Through microfluidic chip device and nuclear magnetic resonance imbibition experiment,the micro imbibition and displacement mechanism of nano surfactant in tight oil reservoirs was revealed;Using a spontaneous imbibition experimental device to change internal and external factors,determine the rules of nanosurfactant imbibition and displacement under the influence of various factors,and analyze the main controlling factors that affect its effectiveness.The main research results are:(1)Three kinds of nano-surfactants are synthesized in the laboratory,with the particle size of nano-scale and good injectivity,which can effectively reduce the rock wettability,maintain a certain oil-water interfacial tension,and promote the infiltration and displacement of oil;(2)The larger the mesh number of rock powder,the larger the specific area and the higher the adsorption capacity.Oil-wet cores often have large adsorption rates of nanosurfactants.In the same case,the higher the concentration of injected nano-surfactant,the higher the adsorption capacity,and the lower the concentration,the more difficult it is to enter the deeper pore throat of the core.Under the same core wettability(water wetting)and injected nano-surfactant concentration,the adsorption amount of nano-surfactant decreases with the increase of rock permeability;(3)The wettability of two adjacent pores changes faster,so water is absorbed in them.Then,although water absorption also occurs in the central prominent pores,the rate of water absorption is smaller than that of the adjacent two pores;This leads to the side flow around the pore and residual oil in it.Infiltration resistance has little effect on capillary force,and the dominant role for infiltration is still small pores.;(4)Anionic nano-surfactant A is 6.02% higher than cationic nano-surfactant B,and anionic non-ionic nano-surfactant C is 10.10% higher than cationic B.When the concentration range of nano-surfactant is 2000mg/L-5000mg/L,with the increase of nano-surfactant concentration,its wetting modification effect will increase,and the final oil recovery degree will increase.However,excessive nano-surfactant can not further change the surface wettability of the solid phase,and the lower oil-water interfacial tension has the opposite effect on the percolation displacement;(5)The temperature is increased from 25℃ to 50℃,and the final recovery rate is increased by 3.91%;The temperature is increased from 50 o C to 75℃,and the final recovery rate is increased by 3.77%.The oil displacement efficiency of short core is higher than that of long core.The oil displacement efficiency of nano-surfactant C in formation water is 27.01%,and that of nano-surfactant C in deionized water is 24.31%.Nano-surfactant in saline solution has better oil displacement efficiency.The pore size of the high permeability core is larger,and the nano surfactant solution is easier to enter the pore and interact with the tight reservoir,and the spontaneous imbibition displacement effect is better.(6)According to the improvement rate of the final recovery degree under various factors,reservoir permeability,type of nano surfactant,and core type are the main controlling factors for the oil displacement effect of nano surfactant.Nanosurfactant concentration,temperature,and pressure are secondary factors.