Synthesis and Properties of a Gel Agent with a High Salt Resistance for Use in Weak-Gel-Type Water-Based Drilling Fluid

Insufficient salt resistance is one of the main problems of current weak gel water-based drilling fluid systems. The key to overcoming this problem lies in the development of a core treatment agent with high salt resistance—gelling agent. This study employs free-radical polymerization to synthesize a weak gel water-based drilling fluid gel former (WGA) using the monomers acrylamide (AM), 2-acrylamide-2-methylacrylamide (AMPS), and 2-acrylamidoalkylsulfonic acid. Fourier transform infrared spectroscopy, thermogravimetric analysis, the one-point method, shale rolling recovery rate and linear expansion studies, and environmental scanning electron microscopy are used to characterize the WGA and evaluate its performance. The molecular weight of WGA is 3.51 × 10 6 , the structure meets the design requirements, and the viscosity-increasing effect is remarkable: The apparent viscosity of 5% WGA aqueous solution is 110 000 mPa·s (0.3 rpm), the shear rate increases, and the viscosity decreases rapidly, showing a unique rheological properties. Enhanced salt tolerance: When NaCl is saturated, the apparent viscosity (0.3 rpm) of 2% WGA solution can still reach 10 412 mPa·s. Compared with the solution without NaCl, the rolling recovery of shale is reduced by 15.6%, and the linear expansion rate is increased by 4.5%. The aqueous solution of WGA has a 3D network structure, and its concentration increases, the hydrophobic force between molecular chains increases, and the network structure becomes denser, which makes it able to strongly inhibit the dispersion and swelling of clay minerals. This research lays the foundation for the development of a weak gel water-based drilling fluid system with strong salt resistance.