Flow Field Characteristics of Swirling Abrasive Jet Nozzle for Geothermal Radial Jet Drilling

Abstract

Radial jet drilling (RJD) technology is a viable alternative to drill multiple horizontal laterals outward from the main vertical wellbore, which is more efficient exceed conventional hydraulic stimulation technology in geothermal resource exploitation. Swirling abrasive waterjet (SAWJ), generates by twisted tapes inside the nozzle, is one key technique of RJD to form the laterals efficiently. In this paper, SAWJ flow field is investigated by numerical simulation, with twisted tapes of angle from 0°to 720°, length from 30 mm to 90 mm and other geometry parameters. The K-Epsilon model and Euler multiphase model were used. Introduced the swirl number S to denote the swirling intensity inside and outside the nozzle. The velocity and dynamic pressure distribution of 30% volume concentration abrasive phase and water phase are discussed. Numerical simulation suggests that there is no potential core (velocity is constant in the center) appeared in the jet area. On the sections normal to jet axis, tangential velocity component profiles are of M-shaped distribution and radial N-shaped, where impact energy concentrates into an annular shape. With larger angle of the twisted tapes, the swirling flow generates by twisted tape is of greater tangential velocity and swirling intensity. After, the swirl decays along the jet axis. Swirling makes the distribution area of abrasive increase, each abrasive particle is accelerated to three-dimensional velocity. On the impact surface, abrasive particles' dynamic pressure is larger than that of water, makes it possible to drill holes in geothermal reservoir efficiently. The investigation on SAWJ is of great significance for exploiting aquifer and hot dry rock (HDR) geothermal reservoir.