Hydraulic Design of Shale Drill Bit Using an Integrated Numerical and Experimental Approach

Abstract

Abstract Hydraulic design of drill bits for shales is challenging due to the sticky nature of the drilled formation which may cause balling. An integrated numerical and experimental approach was used to tackle this challenge. Computational Fluid Dynamics (CFD) along with a new particle tracking method was used to hydraulically design a fixed cutter drill bit for shales. Following CFD simulations, experimental tests in Pressurized Drilling Lab (PDL) were performed to validate the CFD results. Spherical particles with diameters ranging from 0.1 mm to 10 mm were injected from cutters surface and their average velocities were calculated when leaving the drill bit using discrete particle modeling (DPM) technique. The ratio of average particle velocity to average annulus fluid velocity at a plane with one bit diameter from bottomhole, referred to as the bit Cuttings Transport Ratio (Ct), was then evaluated to study the hydraulic performance of drill bits under different conditions. Effect of nozzle orientation on drill bit hydraulic was modeled in CFD and then validated in the lab using special adjustable oriented nozzles. Furthermore, effects of nozzle count and blade height as well as flow guide on drill bit hydraulics performance were studied both numerically and experimentally. Baseline bits with different nozzle orientations were tested in PDL. Rate of Penetration (ROP) increased up to 17% compared to the baseline bit using improved nozzle orientations. Also, it was found that higher nozzle count is helpful for drill bit cleaning improving the drill bit performance. Drill bits with different blade heights were built and tested in PDL and it was found that there is an optimum blade height which can improve the bit drilling performance. Also, the effect of flow guide on drill bit hydraulics was modeled using CFD and particle tracking method and then it was tested in PDL. Both CFD and PDL results indicated drill bit hydraulics improvement when flow guide was added to drill bit. ROP for the bit with flow guide increased 10% and 20% in high and low hydraulic conditions, respectively. The final shale bit was designed using improved nozzle orientations, proper blade height as well as flow guide. While the final bit balling tendency decreased, the ROP increased about 35% compared to baseline bit in PDL tests indicating the significance of drill bit hydraulics in its drilling performance.