Analysis of Bit-balling Failure and Hydraulic Structure Optimization Design of Annular-grooved PDC Bits

In deep wells, which are complex and difficult to drill, existing polycrystalline diamond compact (PDC) bits suffer from low rock-breaking efficiency and short footage. To resolve these issues, a annular-grooved PDC bit is proposed. A prototype of the bit is developed and a field test is completed. Balling failure of the annular-grooved bit is observed. The bit-balling failure mechanism is analyzed by computer simulation, and the influence of the annular-groove structure on the bit bottom hole flow field is studied. The bit hydraulic structure is optimized from the aspects of nozzle position, junk slot space, and nozzle number. The results reveal that When the height of the rock ridge is 10–15 mm and the width is 7.5–10 mm, the bottom hole flow field of the bit is relatively good, reducing the adverse rock ridge effect on bit hydraulics.And the rock ridge adversely affects the bottom hole flow field by reducing the turbulent kinetic energy of the bottom hole, enabling the formation of cleaning dead angles in the rock ridge area, and causing the velocity distribution of the cutter surface to be uneven.Finally, the 8½" WY516G annular-grooved PDC bit is developed and the field drilling test was completed. No balling was observed on the bit, thereby validating the correctness of the hydraulic structure optimization. The rate of penetration (ROP) of the annular-grooved bit is at a high level in the region. Compared with bits in the same formation in adjacent wells, the ROP increased by 24.3%, which verifies that the annular-grooved PDC bit can reduce rock breaking energy consumption and improve ROP, thereby providing technical guidance for the field application of the annular-grooved bits. The results herein will assist in accelerating the exploration and development of deep difficult-to-drill formations and reduce drilling costs.