Research On Non-ionic And Amphoteric Surfactants Used In Fracturing Fluids

With the development and utilization of oil and gas resources,there are more and more low permeable oil fields in our country.Clean fracturing liquid has the lower filtration,lower residue and the more rapid flowback than polymer fracturing fluid,so it can meet the requirements of the oil field.In order to achieve better fracturing effect,new clean fracturing fluid which was different from the traditional fracturing fluid were prepared based on the point of interaction between the surfactant cross linking in aqueous solution.The property of clean fracturing fluid were researched and it has practical significance for the production of oil field.Through the screening of raw materials,oleic acid and N,N-dimethyl-1,3-propylene amine were used to synthesis the nonionic surfactant oleic acid amide propyldimethyl amine by condensation reaction.The optimum synthesis conditions were determined:molar ratio of material was 1:1.1,reaction temperature was 170℃,reaction time was 8h.Epichlorohydrin and sodium bisulfate synthesized white powder 3-chloro-2-hydroxy propyl sulfonic acid sodium under the condition of 85 ℃,material quantity was 1:1,4h.The nonionic surfactant which was synthesized and 3-chloro-2-hydroxy propyl sulfonic acid sodium were used to synthesize amphoteric surfactant oleic acid amide sulfo hydroxyl propyl betaine.The suitable synthesis condition was:molar ratio of material was 1:1.1,reaction temperature was 85℃,reaction time was 8h.Using infrared analyzer and nuclear magnetic resonance instrument to test and analysis the structure of synthetic product,amide and sulfonic acid were determined in the target product.The critical surface tension value of nonionic surfactant was 30.5mN/m,critical micelle concentration was 7.4 × 10-6mol/L;The critical surface tension value of amphoteric surfactant was 30.0mN/m,critical micelle concentration was 6.1 × 10-5mol/L.Cloud point of nonionic surfactant was 5℃,Krafft point of amphoteric surfactant was below zero,so they had better solubility.Different kinds of additives were selected to test the viscosity of the aqueous solution under different experimental conditions.The results were as follows:under the condition of 25℃,pH= 9,2.5wt%nonionic surfactant+ 0.4wt%additive SDS,then the solution formed gel system;the mass concentration of amphoteric surfactant was 2%,the mass concentration of citric acid was 0.6%,pH value was 6,the solution can form gel system.There were lots of micelles which size were 500~800nm in two kinds of gel system by laser light scattering aggregate.Worm-like micelles and reticular structure of two kinds of gel system can be seen in the microscopic image by environmental scanning electron microscope.Rheology of the fracturing fluid was texted by HAAKE RS600 rheometer.In the condition of 25 ℃ and 170s-1 in the shear rate test,the concentration of nonionic surfactant was 2.5%,the concentration of additive SDS was 0.4%,pH value was 9,the largest apparent viscosity of nonionic surfactant fracturing fluid was 220mPa s.The concentration of amphoteric surfactant was 2%,the concentration of citric acid was 0.6%,pH value was 6,the largest apparent viscosity of amphoteric surfactant fracturing fluid was 187mPa·s.Two system have good shear stability and conform to the power law equation.Flow activation energy of nonionic surfactant and amphoteric surfactant were 94.33kJ/mol and 83.25kJ/mol,the temperature sensitivity was small.With the scope of 0.1 HZ～50HZ,nonionic surfactant and amphoteric surfactant fracturing fluid showed good viscoelastic,rheological properties accord with Maxwell model.With the condition of the mass concentration of nonionic surfactant and additive SDS were 2.5%and 0.4%,the heat-resistant temperature of the fracturing fluid system was 76 °C;the mass concentration of amphoteric surfactant and citric acid were 2%and 0.6%,the heat-resistant temperature of the fracturing fluid system was 70 ℃.Two systems had better carrier than guanidine gum fracturing fluid.With kerosene as the breaker,25 ℃,the viscosity of nonionic surfactant gel breaking liquid was 2.4mPa·s after 1h;the viscosity of amphoteric surfactant gel breaking liquid was 3.2mPa·s after 1h.The gel breaking performance of two systems all met the regulation of SY/T6376-2008 "fracturing fluid general technical conditions",gel breaking liquid residue was zero and no damage to the formation.Core permeability damage rate of gel breaking liquid of nonionic surfactant fracturing fluid and amphoteric surfactant fracturing fluid were 15%and 12%,so two kinds of the surfactant fracturing fluid all met the regulation and application requirements to a certain extent.