Construction and Performance Evaluation of High-Performance Hydrophobic Anti-Collapse Water-Based Drilling Fluids

Wellbore instability due to shale hydration has been a major technical challenge for drilling with water-based drilling fluids. The hydrophilicity of shale is the essential cause of its hydration. In this paper, high-performance hydrophobic anti-collapse drilling fluids were constructed by using a homemade hydrophobic nano-film-forming inhibitor and a polymer film-forming filter loss reducer as the core treatment agents. By changing the hydrophilicity of shale, shale hydration was inhibited. The rheology, filtration loss, inhibition, plugging, lubrication and hydrophobicity of the constructed hydrophobic anti-collapse drilling fluids were systematically evaluated through several experiments. The experimental results showed that the hydrophobic anti-collapse drilling fluids had good performances. The viscosity of the drilling fluids changed little after aging at 180 ℃. The filtration loss of the drilling fluids was less than 5 mL at ambient temperature and pressure, and less than 20 mL at high temperature and high pressure. The linear swelling rate of the bentonite samples in the drilling fluids was less than 6%. The rolling recovery rate of the rock cuttings after aging at 180 ℃ was more than 90%. Under the effect of hydrophobic nano-film-forming inhibitor in the drilling fluids, the contact angle of shale could be increased to 125°. Shale changed from hydrophilic to hydrophobic. Shale hydration was inhibited by reducing shale-water contact and reaction.