Construction Of CO₂ Sensitively Clean Fracturing Fluid System And Recycling Mechanism Research

In order to realize the recycle of the fracturing fluid,a CO₂-sensitive clean fracturing fluid system was constructed.The system consists of HETA and lauryl sodium sulfate（SDS）.The recirculation of the fracturing fluid is realized by CO₂.The results showed that the clean fracturing fluid was a pseudoplastic fluid with high consistency coefficient and strong non-Newtonian fluid property,which is a typical power law fluid.The results showed that the system had a good shearing resistance at low shear rate and a shear thickening effect after 170 s^-1,510 s^-1,170 s^-1 shearing respectively for 2 min.It also showed that the viscoelasticity of the system was mainly viscous in the low frequency range,while the elasticity was dominant in the high frequency range.The thixotropy of the system was unconspicuous.The dynamic fracturing coefficient of the system was 6.0×10^-4 m/min^1/2,and it had a good performance of sand-carrying and shear resistance of heat resistant,which could meet the application requirements.The damage of the fracturing fluid system to the core could meet the standard of SY/T 6376-2008 through the filtration damage test.When the capsule was used as the breaker,the gel breaking speed was faster,and the viscosity of the fluid was less than 5 mPa·s,the interfacial tension was 0.85 mN/m,the surface tension was27.1 mN/m.The residue content of the system was found to be 0 mg/L.The re-drainage performance of the clean fracturing fluid was found to be above 70%,and the flowback rate increased with the increase of formation permeability.By means of rheological means,dynamic light scattering and electron microscopy,the mechanism of the cleaning fracturing fluid system’s sensitivity to CO₂ was explored intuitively.At the same time,restudying the carrier performance,the shear resistance of heat-resistant,filtration performance,the static and dynamic filtration damage and flowback filtration performance of the three-cycle system,the three-cycle system was found to maintain good performance compared with the initial system.