Effectiveness of two Tetrapolymers as Viscosifiers and Fluid Loss Reducers

Aim: To synthesize and evaluate the effectiveness of two tetrapolymers as viscosifiers and filtration control agents in water-based drilling fluids for application in moderate saline and geothermal environment.
Study Design: Orthogonal design involving monomer feed ratio, monomer solid content, initiator dosage, reaction temperature and pH was used to establish optimum synthesis conditions.
Methodology: The tetrapolymers, TP1 and TP2, consisting of acrylamide-sodium 2-acrylamido-2-methylpropanesulfonate-sodium acrylate - N, N’-dimethyl acrylamide and acrylamide-sodium 2-acrylamido-2-methylpropanesulfonate-N-Vinyl-2-pyrrolidone-styrene were synthesized by free-radical polymerization. Monomeric compositions of the tetrapolymers were established by Fourier transform infrared spectroscopy. Rheological and filtration control properties were used as indicators to evaluate the effectiveness of the tetrapolymers in aqueous bentonite-based drilling fluids.
Results: TP1 provided superior viscosity build-up efficiency and fluid-loss control (9.0 cm3/30 min - 10.0 cm3/30 min) compared to TP2 fluid losses ranging from 11.5 cm3/30 min to 21.5 cm3/30 min in salt-free bentonite muds at temperatures between 120ºC and 160ºC. Comparatively, TP1 reduced fluid loss to 4.0 cm3/30 min -12.0 cm3/30 min whilst TP2 exerted less filtration control of 12.0 cm3 /30 min -39.5 cm3 /30 min in salt contaminated muds.
Conclusion: Both tetrapolymers were considered suitable drilling mud additives with TP1 demonstrating excellent viscosity build-up efficiency and fluid-loss control at elevated temperatures. TP2, however, exhibited better salt tolerance in aqueous salt medium and bentonite-based muds.