Study On Gel Breaking Method And Reusing Of Clear Fracturing Fluid In Shallow Oil And Gas Reservoirs

Under the formation conditions of shallow oil and gas reservoirs, clear fracturing fluid cann’t be broken quickly and thoroughly due to inadequate contact with crude oil and formation water, which is not conducive to fracturing fluid flow back and would do harm to formation. Therefore, an internal gel breaker should be added in fracturing fluid of shallow oil and gas reservoirs. However, clear fracturing fluid would breaks in advance when breaker was added directly into clear fracturing fluid, and fracturing fluid cann’t carry sand effectively. Aiming at the problem, it is important to design a sustained-release microencapsulated gel breaker. At the same time, there is a study carried out on reusing feasibility of flow-back fluid, to reduce the costs of clear fracturing fluid, and provide technical support for large-scale application of clear fracturing fluid.Based on MES as the main material, the effects of various components under different concentrations on micelle formation and morphological transformation were investigated by analyzing viscosity-temperature curve Regarding viscosity as standard, the anionic clear fracturing fluid formula is: 4.0%MES+4.0%NaCl+0.6%BS-12. Under the condition of 50℃, adding breakers to clear fracturing fluid directly, the results showed that hexanol, formation water, kerosene and methyl all can make clear fracturing fluid break, and the kerosene does better. So the kerosene was chosen as the internal gel breaker for clear fracturing fluid.Using complex coacervation, by single factor experiments method, the optimal preparation conditions for microencapsulated gel breaker of clear fracturing fluid were as follows: gelatin/gum arabic ratio1:1, wall material concentration 4.0%; core/wall ratio 2:1; emulsifier(Span80+Tween80, HLB=14.0) concentration 3.0% of core; coacervation pH3.0~4.7, stirring speed 700 rpm, temperature 50℃,time 20min; curing 60 min with formaldehyde; drying temperature 65℃. Under these conditions, the surface of microencapsulated gel breaker was spherical, the yield was 71.9%, the encapsulation efficiency was 61.8%, and the release rate would reach 100% when the pressure was 30 MPa. The results of performance evaluation shows that the viscosity remaining of fracturing fluid is 26% after continuously sheared for 2.5h at 60℃ with microencapsulated gel breaker concentration 4.0%. The microencapsulated gel breaker shows good sustained-release and temperature resistance, and can be used with high concentration. In addition, the microencapsulated gel breaker could release integrally by the combined action of temperature and pressure.Using column chromatography, kerosene was removed from the gel breaking fluid. Based on the dealt waste fluid, regarding viscosity as the standard, the addition concentration of each component of clear fracturing fluid: 0.8%MES+0.5%NaCl+0.2%BS-12. The reusing clear fracturing fluid remains 50mPa·s at 75 ℃and has good heat resistance and shear tolerance, proppant suspension, gel breaking properties and compatibility, average damage rate is about 9.63%. The reusing clear fracturing fluid system has nearly the same properties with the original clear fracturing fluid system, realizing the reusing of clear fracturing fluid, thereby reducing the cost of clean fracturing fluid.