Simulation of a High-velocity Jet to Predict Its Influence on Crack Initiation and Propagation in Jet-assisted Drilling

An effective method to significantly increase the rate of penetration (ROP) in hard formations is the application of ultra-high pressure jet-assisted drilling. To obtain a better understanding of the impact of the high-velocity jet on the hole bottom, the velocity, pressure and shear stress distributions are evaluated both analytically and numerically. These distributions are of great interest, since they particularly influence the fracture initiation and propagation of the rock to be drilled. The analytical approach is based on the mechanics of a turbulent impinging jet. This is mainly done to better comprehend the interaction of the governing parameters downhole and to find an optimum configuration for such a jet-assisted drilling system. The computational fluid dynamics (CFD) simulation is conducted by an open source software for turbulent, steady-state, incompressible and isothermal flow. Nozzle diameter, impingement height and exit velocity are varied in several simulation runs. Moreover, the shear stress distribution at the bottom is determined in the CFD simulation, which will contribute to a better understanding of the crack initiation downhole. The contribution of this work is the evaluation of an optimum configuration to obtain the maximum impact of the high-velocity jet.