High-performance Brine-based Drilling Fluid System for Extended-reach Horizontal Wells

To address the technical bottlenecks of difficult hole cleaning, high friction and torque, and poor wellbore stability in water-based drilling fluids during extended-reach well drilling, a high-performance brine-based drilling fluid system was developed. Based on a potassium chloride-formate composite brine, the system incorporated the self-developed star-shaped polyamine inhibitor HIB and nano-composite friction reducer SLIP, and optimized flow-pattern regulation and multi-stage plugging technologies, achieving synergistic improvements in inhibition, lubrication, cuttings-carrying capacity, and stability performance. Comprehensive comparisons with conventional KCl polymer systems, commercial polyamine systems, and lubricants showed that HIB exhibited significantly better inhibition than conventional polyamine inhibitors via an “adsorption–coating–hydrophobicity” mechanism, with a cuttings rolling recovery rate of 93.6% and a 16 h linear swelling rate of 1.0%. SLIP outperformed existing lubricants through a “microsphere rolling–adsorption film-forming” mechanism, with an extreme-pressure lubrication coefficient of 0.064 and an anti-wear load-bearing capacity of 10 kg. Laboratory evaluations showed that, after high-temperature aging at 150 ℃, the system maintained a yield point/plastic viscosity ratio of ≥0.5, an API filtration loss of <4 mL, a sand-bed pressure-bearing capacity of >7 MPa, strong contamination resistance, and a core permeability recovery value of >86.3%. Field applications in 12 extended-reach wells in several offshore blocks in China demonstrated that tripping friction was reduced by more than 30% and the rate of complex incidents decreased by 65%, providing a reliable technical option for the safe and efficient drilling of extended-reach wells.