Investigation on the plugging mechanism of nanocomposite polyacrylate copolymers in water-based drilling fluids: Experiments and applications

The plugging of nanopores and cracks in shale formation has become the critical technology that promotes the development of shale gas. Herein, nanocomposite polyacrylate (Poly-TALC) copolymers were successfully prepared by emulsion polymerization using butyl acrylate and triallyl isocyanurate as the raw material. Poly-TALC was characterized by fourier transform infrared spectroscopy (FTIR), laser light scattering particle size analysis, scanning electron microscope (SEM) and thermogravimetric analysis (TGA). The rheological properties and plugging performance of Poly-TALC were evaluated by a six-speed rotational viscometer, filter cake permeability test, core permeability test and pressure transfer experiment. Results revealed that Poly-TALC exhibited a particle size distribution ranging from 75.27 to 95.29 nm, while maintaining notable stability at 327.75 degrees C. Upon the addition of Poly-TALC to the drilling fluid, both the apparent viscosity and plastic viscosity insignificantly changes. At a Poly-TALC dosage of 1.0%, the filter cake's permeability was 1.2 x 10-5 mu m2 with a plugging rate of 56.9%, while the permeability of the core was 1.2 x 10-6 mu m2 with a plugging rate of 84.0%. The decrease in permeability was not significant beyond a Poly-TALC dosage of 1.0 wt%. Pressure transfer experiments demonstrate that Poly-TALC is able to form a multi-stage dense seal within the rock core, which can effectively prevent formation water from immersing into shale formation and improve shale wellbore stability.