A Computational Study of Packoff Using a Combined Drill Bit Stabilizer Particle Tracking Simulation

Abstract The primary cause of packoff in wells is improper hole cleaning resulting from aggregated cuttings and particles from the bottom hole. Drill-bit geometry and rotation plays an important role in dictating returning flow paths of drilling mud and thus transportation of debris particles from the bottom hole. This paper presents an early attempt to investigate the integrated effect of mud flow through drill bit and stabilizer slots on well packoff using computational fluid dynamic (CFD) -based particle simulations. A commercially available three-dimensional (3D) flow solver was used to simulate turbulent flow for both stationary and rotating drill bits and two competing stabilizer designs with different flow by area. The motion of debris was tracked using a discrete phase model in a Lagrangian framework. A set of parametric studies was performed to investigate the effect of stabilizer location, particle size, rate of penetration (ROP), etc. on the hydraulic performance of the integrated assembly in terms of cuttings-transport ratio [the ratio of average particle velocity to average annulus velocity (Ct)], particle concentration, velocity profiles, etc. for a range of flow rates. Results from the combined drill-bit stabilizer simulations were reported and design bottlenecks were identified for a legacy stabilizer model. New insights were gained for design modifications to address packoff. Simulation results show that the particles follow the flow path created by the slanted blades of the drill bit initially and then begin a swirling motion before passing through the stabilizer slots. The new design has a larger flow by area, and it straightens the rotating flow and hence offers faster evacuation of cuttings. The flow profile becomes more uniformly distributed and prevents any clustering of particles, thereby significantly reducing non-productive time (NPT) and improving tripability of the bottomhole assembly (BHA) in oil fields. This study provides insight into stabilizer design concepts and the stabilizer’s location as it is combined with a drill bit. The integrated simulation approach adopted here enables operators to predict the motion of formation cuttings using a simpler particle model in a larger system and helps prevent drillstring packoff.