Study on a New Hydraulic Lifting Dual-Gradient Drilling Technology and Equipment

To address the challenges of narrow pressure windows, poor cuttings transport efficiency, and frequent kick–loss coexistence in deepwater and complex formation drilling, a hydraulic lifting dual-gradient drilling technology and equipment was proposed and investigated. The technology employs a power fluid-driven Downhole Annular Pressure Regulation Tool to achieve segmented controllability and dynamic adjustment of wellbore pressure, forming an “increasing-upper and decreasing-lower” dual-gradient pressure system. The Downhole Annular Pressure Regulation Tool integrates a turbine motor and an axial-flow pump, which realize energy conversion and hydraulic lifting, respectively. Numerical simulations show that the optimized axial-flow pump delivers a head of 5.85 m and an efficiency of 88.1% at the design flow rate of 20 L/s, while the turbine motor achieves a maximum efficiency of 85.7% with a torque increase of about 20%, indicating good system compatibility. Laboratory experiments verified the feasibility and stability of the system, with a maximum bottom-hole pressure reduction of 0.258 MPa, through the adjust of the hydraulic lifting parameters, a 46.4% reduction in kick rate, and a 39.7% reduction in loss rate are achieved. The results demonstrate that this technology enables precise wellbore pressure regulation and risk control, providing a new technical route for safe and efficient drilling in deepwater and complex formations.