Synthesis of Poly(styrene-vinyl sodium sulfonate-butyl acrylate-ethyl methacrylate) and Its Blocking Mechanism as a Nanometer Material in Water-Based Drilling Fluid

Abstract

Nano-blocking technology has become a key to overcoming a prominent bottleneck in shale gas development. In this paper, poly(ST-VS-B-E) was synthesized by Michael addition reaction using styrene, vinyl sodium sulfonate, ethyl methacrylate, and butyl acrylate. Poly(ST-VS-B-E) was characterized by infrared spectroscopy analysis, laser scattering analysis, and thermogravimetric analysis. The rheological properties of drilling fluid with poly(ST-VS-B-E) were studied by testing the drilling fluid’s properties. The results showed that the median particle size of poly(ST-VS-B-E) was 79.15 nm and it resisted a 359.25 °C high temperature. The yield point of the water-based drilling fluid with 2.5 wt% poly(ST-VS-B-E) added was 27 Pa, and the fluid loss was 3.1 mL, with good drilling fluid performance. Further test results from simulated mud cake filtration and the simulated core penetration showed that when the mass concentration of poly(ST-VS-B-E) was 2.5 wt%, the blocking rates were 66.67% and 93.33%, respectively, and the blocking performance increased gradually with the addition of poly(ST-VS-B-E). Poly(ST-VS-B-E) can be squeezed into the nano-pores of a shale formation under the action of pressure difference, so as to block the formation and prevent the entry of water-based drilling fluid filtrate. Poly(ST-VS-B-E) can serve as a potential nano-blocking material in water-based drilling fluids.