Study On Betaine Viscoelastic Surfactant Self-diverting Acid Technology

Viscoelastic surfactant self-diverting acid diversion acidizing technique is a newlydeveloped reservoir stimulation technique,with the advantage of simple preparation,gelbreaking easily,small formation damage,slow and lower filtration.When the pH value is about2,the viscosity of the system increases with the free Ca2+,Mg2+chelating with viscoelasticsurfactant molecules to make the arrangement of the surfactant molecules changing,then theself-diverting acid turn from the high permeability zone into the low permeability zone.Thesystem loses its viscosity by touching with hydrocarbons,water diluting,and mixing with gelbreaker.the ideal structure of the viscoelastic surfactant is the structure that with longstraight-chain hydrophobic carbon chain without branching structure,having the hydrophilicstructure such as amide bond,,ether bond, and double bonds,the amide group as the couplinggroup of the positive and negative charge centers, the carboxyl anionic groups as the negativecharge center.The oleic acid,3–Dimethylamino propyl ammonia and sodium chloroacetate areused to synthesize the acid amide propyl betaine by amide and quaternary ammonium. Bythe orthogonal experiment, the optimal conditions of the amidation reaction is that170°C,catalyst0.5wt%,and the mass ratio of oleic acid and3-dimethylamino alanyl1:1.1,and thereaction time7hours;The the optimal conditions of the quaternization reaction is that90oC,mass ratio of tertiary and sodium chloroacetate1:1.1,and the reaction time8hours,the pHvalue7~8.In order to better serve the acidizing operation, the rheological analysis of theself-diverting acid is taken,and the effects of the concentration,temperature,pH value,shearand shear history, inorganic ion concentration are measured. Viscoelastic surfactantself-diversion acid is the shear thinning system， which belongs to power law fluid.Therotating dis reactor is used for the reaction kinetics. Under the experimental condition,thekinetics equation is J=3.824×10-6C1.3829,and the reaction is dominated by H+mass transfer coefficient; The effect of temperature on the diffusion coefficient doesn’t follow Arrheniuslaw.The reaction rate increases slowly with the temperature rising,when the temperature isabove70oC,the reaction rate increases rapidly.Based on the Darcy law and some assumption，the diversion criterion is developed.When the self-diverting acid is on the diversion, thelog-log curve between Rpand ko/Φois a line.