Preparation And Application Of Surfactant Used In Imbibition For Fracturing

The imbibition has been proved to be an important production method for tight reservoirs.Adding a suitable surfactant to the fluid into well can change the surface wettability of the Hydrophobic formation rock to a certain extent,so that the fluid into well and the crude oil in micro crack can exchange location in the process,the spontaneous imbibition efficiency of the liquid in the reservoir rock would be enhanced,and the oil recovery would be improved.In this paper,an anionic-nonionic surfactant?ANS?capable of enhancing the absorption of aqueous solution was designed and synthesized,starting with molecular structure and hydrophilic nano-particles were preferred.The material is compounded to obtain an infiltration synergistic surfactant system?ANF?,which further improves the seepage efficiency.The main research contents and understanding are as follows:?1?Maleic anhydride and isomeric alcohol polyether are used to synthesize the esterification intermediate under the action of a catalyst,and then a surfactant capable of enhancing the osmotic action is synthesized by a nucleophilic addition reaction with sodium sulfite.The molecular chain has both the characteristics of anionic and nonionic surfactants.The molecular structure and functional groups of the synthesized products were confirmed by FT-IR and ¹HNMR characterization.The effects of reaction temperature,reaction time,monomer molar ratio and catalyst on reaction conversion rate were investigated.The results showed that the optimal esterification conditions were as follows:the molar addition ratio of maleic anhydride to isomeric alcohol polyether was 1:2,the amount of catalyst used is 1.0%of the total mass of the monomer,and the reaction was carried out at 100°C for 4h;The optimum sulfonation conditions were as follows:the ratio of sodium sulfite to esterification intermediate molar addition was 1.5:1,the catalyst addition amount was 1.0%of the total mass of the monomer,and the reaction was carried out at 90?for 3h.?2?The physicochemical properties,wetting properties,ability to improve oil wet surface wettability,and spontaneous infiltration efficiency in the core were tested for the osmotic synergistic surfactant.When the concentration of the osmotic synergistic surfactant ANS is 0.3%,the wetting time in fresh water and mineralized water?10g/L?is 85s and 150s,respectively,which can meet the requirements of rapid adsorption and stable adsorption.The absolute value of the Zeta potential on the sandstone surface is beyond 35mV.The contact angle between the oil droplets and the oil-wet core sheet can be increased from 28°to130°,which can effectively improve the surface wettability of the oil-wet rock,and the static spontaneous infiltration efficiency can reach about 38%.If the concentration is too large,the interfacial tension is too low,and the capillary force is insufficient,resulting in a substantially constant or even slightly reduced infiltration rate efficiency.Therefore,the optimum use concentration of ANS is preferably 0.3%.?3?The hydrophilic nanomaterial Nano-SiO₂-500S is preferably compounded with ANS in a certain ratio.When the content of the nano-material in the composite system is 1.5%,the contact angle change of the oil-wet core can be increased to about 120°,and the infiltration efficiency of the system is about43%,which is further improved 5%compared the effect of ANS.The compatibility of the osmotic synergistic composite system with the commonly used additives for fracturing fluids was investigated.The results show that the system will have a certain interaction with the clay anti-swelling agent and the fracturing fluid drag reducing agent,but the overall effect is stable and the compatibility is good.At the same time,the system can be dehydrated and dehydrated in a short time after emulsification with crude oil to achieve oil-water separation.?4?The production process of the infiltration and synergistic surfactant system was determined,industrial production was carried out by the scale-up test,and the on-site filling test of 3 wells was carried out.The performance test was carried out by using the on-site raw materials to prepare a sample,which was basically consistent with the results of the indoor experiment,and the performance was stable.At the same time,the oil content in produced liquid of the test well increased and the water content decreased.It shows that the system can effectively improve the efficiency of spontaneous infiltration and has practical application value.