Temperature-Responsive Nano-SiO₂ Composite for Improving Shale Stability in Oil-Based Drilling Fluids

Abstract

The development of nanomicrometer pores and microfractures in shale gas formation leads to frequent wellbore instability during shale gas drilling, which seriously restricts the safe and rapid drilling of shale gas. In this work, N-isopropylacrylamide (NIPAM), N-hydroxyethyl acrylamide (HEAA), styrene (St), and nano-SiO 2 were used as raw materials to prepare the temperature-responsive nanocomposite named NHS/SiO 2 . NHS/SiO 2 was highly sensitive and exhibited reversible temperature sensitivity, with a lower critical solution temperature (LCST) of 82 °C. The amphiphilicity of NHS/ SiO 2 positively affected the stability of oil-based drilling fluids (OBDFs). The effects of NHS/SiO 2 on the plugging property of shale were tested by experiments on fluid loss, pressure transfer rate, shale specific surface area, shale pore volume, and shale strength. NHS/SiO 2 significantly plugged shale pores at 130 °C, with a specific surface area reduction rate of shale from 22.19% to 65.95% and pore volume reduction rate of shale from 30.73% to 68.51%. NHS/SiO 2 exhibited obvious oil adsorption in white oil and the water-in-oil emulsions after reaching the LCST. The maximum oil adsorption rate of NHS/SiO 2 in the water-in-oil emulsion was about 23.41 g/g. Finally, the mechanism of NHS/SiO 2 to improve the shale stability in OBDFs was further proposed. At high temperatures, NHS/SiO 2 increased its elastic deformation ability by adsorbing oil for a long time, thus improving the plugging efficiency.