The Blocking Properties of Styrene-Styrene Sulfonic Acid Sodium Salt Copolymer as a Nanodispersing Agent in Water-Based Drilling Fluids

Abstract

Nanoplugging materials are used in drilling fluid systems to seal nanopores and cracks in the shale formation, which is a focus for developing shale gas. In this work, nanoparticles of the St-NaSS copolymer were synthesized by emulsion polymerization of styrene and styrene sulfonic acid sodium salt as monomers. The St-NaSS copolymer was characterized by FT-IR, TGA, and light scanning phase analysis. The results show that the grain size of the St-NaSS copolymer nanoparticles ranges from 37 to 50 nm, and the average diameter is about 43.2 nm. The decomposition temperature of the St-NaSS copolymer is 410.7°C, indicating that the material has good temperature resistance. The St-NaSS nanoparticles have little effect on the rheological properties of the water-based drilling fluid. The plugging performance of the St-NaSS nanoparticles was evaluated by the mud cake simulation method. The permeability of the mud cake is 3.32×10-5 μm2 which is close in value to that of the shale. When the drilling fluid contains 0.5 wt.% of St-NaSS nanoparticles, the plugging rate is 88.93%. The plugging rate of the mud cake increases with increase in the concentration of the St-NaSS nanoparticles. When the amount of rho St-NaSS nanoparticles is 1.0% the plugging effect of the drilling fluid is excellent. Therefore, St-NaSS copolymer nanoparticles can be successfully applied as a plugging agent to provide borehole stability in the shale formation.