Study On The Rheological And Fracturing Properties Of Viscoelastic Gemini Surfactant

Gemini surfactant is a new type of surface active substance with good prospect,which is composed of two hydrophilic head groups and two hydrocarbon chains covalently connected by a spacer.The special structure of gemini surfactant makes it different from all other traditional surfactants.Aqueous solutions of gemini surfactant can form a dimensional network structure with a high viscosity at low concentration,so fracturing fluid prepared from gemini surfactants possesses good rheological properties,strong self-assembly ability and excellent sand suspension capacity,etc.In order to deeply understand their characteristics,a number of experimental studies have been carried out.In this paper,the following research works were carried out for two gemini surfactants:(1)The surface properties and aggregation behavior of gemini surfactants in aqueous solutions.The properties of gemini surfactants in aqueous solution were studied by the automatic tension meter,fluorescence spectroscopy(pyrene was used as probe)and conductivity meter,including the critical micelle concentration(CMC),aggregation number and surface tension.Surface tension of the product was determined,and the influences of temperature,sodium chloride and short-chain alcohols on the surface activities were studied.The increase of temperature had little effect on the CMC.The sodium chloride had a significant effect on the CMC of gemini micelles,that is,the CMC decreased with the addition of chloride.The type and content of alcohols had an effect on the CMC of surfactant micelles.The more carbon numbers the alcohol(ethanol,n-propyl alcohol and n-Butyl alcohol)had,the more active the aqueous surfactant would be.(2)The rheology of aqueous gemini surfactants.The rheology of aqueous gemini surfactants was studied in this pape.The results showed that gemini surfactants had higher viscosity at lower concentration,therefore,the higher concentration of gemini surfactants solution,the higher viscosity and modulus.When the temperature was higher than 78?,the viscosity was very low.The solution acted out the behavior of Newtonian fluid for the micelles morphology changed to spherical micelles.The viscoelastic characteristics of fluid were analyzed through the steady and dynamic shear experiments.The results showed that the storage modulus was higher than the loss modulus during the whole dynamic shear frequency,which did not conform to Maxwell equation.So the aqueous solutions tended to be a kind of hydrogel.The gemini solutions had the characteristics of shear thinning and shear resistance.(3)The effect of counter ions on the rheology of aqueous gemini surfactants and the determination of the VES formulation.The effect of different kinds of counter ions on the rheology of aqueous gemini surfactants was studied,such as inorganic salt,organic salt,anionic surfactant and polymer.The research showed that NaCl and NaSal could make contribution to the increasing of viscosity.The best 8 formulas of fracturing fluids were found by altering dosage of surfactant and salt with controlling variables method.Through measuring the viscoelastic of them,the best formula was finally confirmed.Systematical evaluations of the best formula were investigated,including basic liquid characteristic,rheological characteristic,anti-swelling effect,gel break characteristic,filtration property and clean-up property.The evaluations showed that the VES formula had a high resistance to heat,salt and shear.Therefore,the test result indicated that the water-based fracturing fluid formulation system can meet the requirements of low damage fracturing fluid.