Effect of synthetic water-soluble polymers on the properties of the heavy water-based drilling fluid at high pressure-high temperature (HPHT) conditions

Nowadays, by rising age of oil wells, the utilization of high pressure-high temperature (HPHT) additives in deep well drilling is unavoidable. In this study, a terpolymer of acrylamide/2-acrylamido-2-methyl propane sulfonic acid/N-vinyl caprolactam and a tetrapolymer of acrylamide/2-acrylamido-2-methyl propane sulfonic acid/3-allyl Oxy-2-hydroxy-1- propane sulfonic acid/acrylic acid were synthesized by solution polymerization and characterized by Fourier transform-infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA) and hydrogen nuclear magnetic resonance (1HNMR) techniques. The effect of crosslinking agent, transfer agent and comonomer contents of the synthesized polymers on the fluid loss and the rheological properties of the heavy drilling fluid containing these synthesized products were studied. The stability and performance of the tetrapolymer were better in the heavy drilling fluid at high temperature and high salt concentration. The fluid losses of the prepared heavy drilling fluid by tetrapolymer were 1.9 and 2.1 cc/30 min in NaCl saturated water and formation water of Iran reservoirs at 150 °C, respectively.