| Fracturing technology is an important method to produce oil and gas well production, the fracturing fluid should transport proppant, delivery pressure, create the new fissure in formation. The fracturing fluid plays a critical role on fracturing operation.Viscoelastic surfactant fracturing fluid is a new type of fracture system.The viscoelastic system, which based on the viscoelastic surfactant as the main agent and other additives. Although the viscoelastic surfactant fracturing fluid a new type of hydraulic fracturing fluid, it has become an important fracturing technology,due to its good capacity of viscoelasticity and shear resistance, automatic gel breaking, little formation damage, less residue content, simple and rapid when the viscoelastic surfactant fracturing fluid is prepared in filed application.To further study the theory of viscoelastic surfactant fracturing fluid, three kinds of cationic surfactants are designed and synthetized, including tetradecyl dimethyl hydroxypropyl ammonium bromide(C14-2-1-1), cetyl dimethyl hydroxypropyl ammonium bromide(C16-2-1-1), octadecyl dimethyl hydroxypropyl ammonium bromide(C18-2-1-1),by long chain alkyl bromine generation and N,N-dimethyl propyl alcohol amine as main reagent Synthesis conditions are optimized respectively through orthogonalization experiments characterrized synthetic product by IR and1H-MNR spectrum, and surface activity are studied.Explore the possibility that the cationic surfactant used as a fracturing fluid and selecte sodium salicylate as additives through the experiment. Through testing the viscosity of the combined systems, it is found that the optimum formulation is2.5%cetyl dimethyl hydroxypropyl ammonium bromide as host agent and1%soldium salicylate as auxiliary,and viscosity of formula system is up to489mPa·sThrough evaluating its performance of high temperature resistance, shear resistance, viscoelasticity,gel breaking and sand carrying, damage rate to core matrix, residue content and the compatibility of the formation water, the results show that:Formula of fracturing fluid has good viscoelastic,and rheological parameter’n’is0.23062,’K’is19.49.It has good heat resistance shear resistance at170s-1,and viscosity is40mPa·s when temperature is90℃,and system viscosity can still achieve30mPa·s after shearing one hour at170s-1. It has good performances of sand-carrying, the free settling velocity of ceramsite in the formula of fracturing fluid is0.0516cm/min. Automatically gel breaking after meeting kerosene, good compatibility with formation water performance, lower residue content, the damage rate to core substrate is only4.19%. |
