Use of modified polystyrene micro-nano spheres to improve the inhibition and plugging performance of water-based drilling fluids

Abstract

Wellbore instability is a challenging issue in drilling engineering, especially in shale formations. The objective of this paper is to achieve wellbore stability by changing the hydrophobicity of the shale surface and plugging the micro-nano pores through the synthesis of modified polystyrene micro-nano spheres (MPS). The MPS was characterized through Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), particle size distribution, and transmission electron microscopy (TEM). The inhibition and plugging performance of MPS were evaluated through linear expansion, shale recovery, and plugging of polytetrafluoroethylene (PTFE) microporous membrane. To study the inhibition and plugging mechanisms of MPS, contact angle, pore size distribution, and SEM analysis were performed. The results showed that MPS was spherical with a particle size distribution of 91–712 nm and had good thermal stability. The MPS had excellent compatibility with drilling fluids and better inhibition than KCl, polyamines, and SiO2. When using PTFE microporous filter membrane as a filtration medium, the API filtration loss volume of 3 wt% MPS aqueous solution was only 42 mL, while that of the solution without MPS was 260 mL. The pore size of the PTFE microporous membrane was decreased after plugging. The MPS adsorbed on the shale surface to form a hydrophobic layer, which could weaken the hydrophilicity of shale. The contact angle of shale slices treated with 2 wt% MPS was 108.2°. Furthermore, SEM observations indicated that MPS can improve the quality of mud cakes and plug the small pores. MPS has potential applications in improving wellbore stability.