Styrene butadiene resin/nano-SiO2 composite as a water-and-oil-dispersible plugging agent for oil-based drilling fluid

In this paper, styrene butadiene resin/nano-SiO2 (SBR/SiO2) composite was synthesized by the continuous emulsion polymerization method, which was used as a plugging agent for oil-based drilling fluid (OBDF) to enhance plugging efficiency in shale formations. The characterization of SBR/SiO2 was measured by Fourier transform infrared spectroscopy, thermal stability and scanning electron microscopy. The results implied that the structure of SBR/SiO2 was consistent with design. The dispersion of SBR/SiO2 in water and mineral oil were studied by particle size distribution and rheological analysis. The results indicated that SBR/SiO2 can be dispersed in water and mineral oil simultaneously, while most normal OBDF plugging agents can only be dispersed in water or mineral oil. Since OBDF is a water-in-oil emulsion, when the plugging agents can be dispersed in two continuous phases, the plugging efficiency can be maximized. And it's the first time to explain plugging ability from dispersion perspective and produce the plugging agent for OBDF which can be dispersed in two phases. Then the plugging ability was evaluated by filtration volume, porosity physical adsorption instrument (BET), and pressure transmission test. The results showed that SBR/SiO2 can enter into the nanopores of shale formations and significantly reduce fluid invasion, thereby improving wellbore stability. Finally, the dispersion and plugging mechanism of SBR/SiO2 were analyzed. This study might provide an avenue to solve the wellbore instability and reservoir damage owing to OBDF during the drilling process by adding the plugging agent which can form a dense filter cake and reduce fluid loss in shale formations.