Synthesis and Performance of a Polymeric Thickening Agent for Weighted Fracturing Fluids

Weighted fracturing fluid is one of the effective methods to deal with high formation pressure encountered during fracturing operation. In mixing weighted fracturing fluids, normal guar gum will leave high concentrations of residues in the fracturing fluids, causing high formation damage. The VES type fracturing fluid has low temperature stability, therefore is unable to be used in high temperature environment. To resolve these problems, a supramolecular polymer BC40 has been synthesized with AM/CnDMAAC/NVP through water solution polymerization. By evaluating the intrinsic viscosity and solubility of the synthesizing products, and through orthogonal experiment and single-factor method, the optimum synthesis condition was obtained, as follows:the total concentration of the monomers of 30%, concentration of the initiator of 0.12%, temperature for the polymerization of 35℃, time for exhausting oxygen by introducing nitrogen of 1 h, and reaction time of 5 h. In a water solution weighted with sodium formate, BC40 performed very well as a viscosifier. Fracturing fluids of different densities mixed at 120℃ and 170 s^-1, had apparent viscosity of more than 30 mPa·s after being sheared for 2 h, showing good high temperature shearing performance. The gel structure formed in these weighted fracturing fluids can all get broken after treatment with gel breaking agent at 95℃. The fracturing fluids, after gel breaking, had low surface tension and low residue contents, and therefore had low damage to the formations fractured.