Hydrodynamic Mechanism and Reliability Testing of a Novel Rotary Self-Priming Equivalent Circulating Density Reduction Tool

Summary

As oil and gas exploration and development continue to extend into deepwater and ultradeepwater environments, the coexistence of high-pressure, high-temperature (HPHT) conditions and a narrow mud-weight window reduces the allowable bottomhole pressure margin and increases the likelihood of drilling complications, such as kicks and losses. Conventional managed pressure drilling (MPD) with constant bottomhole pressure is often costly, constrained by limited subsea backpressure capacity, and unable to deliver source-level annular pressure reduction. To address these limitations, we present a novel rotary self-priming downhole tool for equivalent circulating density (ECD) reduction. The proposed tool harvests the hydraulic energy of circulating drilling fluid through a turbine and converts it into mechanical power to drive rotating components, thereby generating a self-priming suction effect that enables a localized and controllable pressure drop, ultimately reducing ECD. An integrated tool/wellbore-coupled flow model was developed in ANSYS Fluent to quantitatively characterize the pressure-drop response to drilling fluid density, installation depth, and flow rate. The simulations show that increasing the fluid density from 1.2 g/cm3 to 1.8 g/cm3 slightly enhances the pressure drop, reaching a maximum of 2.1 MPa. The installation depth has a negligible effect, with the pressure drop remaining stable at 1.9–2.0 MPa. When the flow rate increases from 1,500 L/min to 2,500 L/min, the pressure drop increases by only 0.07 MPa, indicating a weak flow rate sensitivity within the tested range. Field trials demonstrate stable operation over 1.5–2.5 m3/min, achieving a maximum pressure drop of 1.9 MPa with an approximately 10% deviation from the numerical predictions. These results confirm that the proposed tool can effectively reduce ECD and expand the operational pressure window, providing an economical and efficient downhole annular pressure-reduction solution for safe deepwater drilling.