A Drilling Fluid Gelling Agent Synthesized with Pentaerythritol as Branching Agent

When using gelling agents to increase the gel strengths of water base drilling fluids, it was found that the increase of gel strengths was generally smaller than the increase of viscosity. A low viscosity high gel strength additive PAAVP has been developed to deal with this problem. PAAVP was prepared by the copolymerization of acrylamide (AM), 2-acrylamide-2-methylpropane sulfonic acid (AMPS) and 4-vinyl-1-(3-sulfopropyl) pyridinium salt (4-VPPS) using pentaerythritol as branching agent and cerium ammonium nitrate as initiator. The effects of copolymerization conditions on the viscosity and gel strengths of PAAVP was studied. Introduction of pentaerythritol into the copolymerization system reduced its apparent viscosity and increased its ratio of yield point to plastic viscosity (YP/PV). The optimum concentration of pentaerythritol was determined to be 2.5%-3.0% (mass) of the monomers for the copolymerization. 4-VPPS is beneficial to the thermal stability and salt resistance of the final product, and its concentration in the copolymerization system was 6%-10% (mass) of the monomers. The concentration of the initiator was 0.0275%-0.03% (mass) of the monomers. 1% water solution of the PAAVP produced in accordance with the recommended mass ratio of reactants had apparent viscosity of 27 mPa·s and YP/PV value of 1.45 Pa/mPa·s. The solution, after hot rolling at 150℃, still had 74% of its original apparent viscosity and 54% of its original YP/PV value, showing better thermal stability than xanthan gum. PAAVP dissolved in 5% NaCl solution had 91% of its original apparent viscosity and 85% of its original YP/PV value, demonstrating potential for future application.