Silica-Based Microsphere Structure and Its Multifunctional Efficacy in High-Temperature and High-Salinity Drilling Fluids

With the continuous increase in horizontal displacement during unconventional oil and gas drilling, drilling operations are commonly plagued by high frictional resistance, severe pipe sticking issues and difficulties in directional drilling. Conventional single-component water-based drilling fluid lubricants fail to satisfy multifunctional demands, including high-temperature resistance, salt tolerance and long-term lubrication. In this work, a novel microsphere lubricant, RB-Si, with high-temperature and high-salinity resistance was developed by combining the merits of solid and liquid lubricants. The product was synthesized using myristic acid and triethanolamine as raw materials via co-reaction with boric acid and nano-silica. Laboratory tests reveal that after aging at 180 °C, the lubrication coefficient reduction rates of based mud, saturated salinity-based mud and a high-density (2.0 g/cm3) drilling fluid gel system containing 1.0 wt% RB-Si reached 90.1%, 83.3% and 62.8%, respectively. Meanwhile, RB-Si can effectively plug the micropores in the filter cake, reduce fluid loss, inhibit shale hydration and swelling, and exhibit excellent compatibility with drilling fluids. RB-Si rapidly adsorbs onto the surfaces of metallic drill strings and formation rocks to construct a durable and high-strength lubricating film, accompanied by the rolling friction of the incorporated microspheres, thereby reducing frictional drag between the drill string/casing and the drill string/borehole wall. This lubricant effectively mitigates high frictional resistance under prolonged friction conditions, and is expected to provide technical support for long-horizontal-well drilling.