Grafted Starch Foam Stabilizer ESt-g-NAA for High-Temperature Resistant CGA Drilling Fluid via Inverse Emulsion Polymerization

Colloidal gas aphron (CGA) drilling fluid is an environmentally friendly near-balanced drilling technology that has been successfully applied to depleted oil/gas reservoirs. To overcome the limitations of its application in high-temperature drilling, acrylamide (AM), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), and N -vinylpyrrolidone (NVP) are grafted onto starch via inverse emulsion polymerization, and a foam stabilizer ESt-g-NAA with a temperature resistance of ≥150 °C is synthesized. The Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance ( 1 H-NMR) analysis suggest that all monomers are grafted onto starch efficiently. ESt-g-NAA has good solubility and thermal stability, as well as an excellent ability to stabilize foams at high temperatures. Based on microscopic observation, stable aphrons are generated successfully in the CGA drilling fluid prepared by ESt-g-NAA and surfactant after 150 °C aged. Results show that ESt-g-NAA based CGA drilling fluid aged at appointed temperatures (120–180 °C) is a high-performance drilling fluid with shear-thinning behavior, extremely high values of low shear rate viscosity (LSRV), and well-building capabilities.