A Plug Removal Technique with Rotary Water Jet: Equipment Design, Simulation Study and Experiments

Abstract The reinjection of cooled thermal waters back into sandstone geothermal reservoirs is restricted by two factors, one is the plug near the well, and the other is the plug of the sand-control screens. Plug removal technique with rotary water jet is proposed to relieve the plug in the vicinity of the well. This paper presents a series of studies about plug removal technique with rotary jet flow, including equipment design, simulation study and experiments. Firstly, the composition and function of the plug removal equipment with rotary water jet were presented. The equipment is mainly composed of spray gun, filter, rotary jet nozzle and guide head, etc. Secondly, the flow field characteristics of the rotary jet in the wellbore were simulated and the flushing effects of distribution of nozzles of the jet plug removal tool under construction conditions were studied. Finally, several experiments were performed with actually plugged sand-control screens removed from a well to verify the feasibility of this technique. And the plug removal result of vertical water jet was compared with rotary water jet. This study indicates that the equipment designed is proved to have high success ratio and remarkable effectiveness. The main principle of the technique is to use a rotary nozzle to generate a high-pressure water jet to directly flush the wellbore, and to remove the plug through high-frequency oscillating hydraulic waves and cavitation noise. Thereby, the plug of the screen and the formation can be removed, and the formation permeability can be improved. The study results show that the plug removal technique with rotary water jet is effective to remove the plugs in screen and the vicinity of the well. And jet pressure is an important factor that affects the plug removal and cleaning efficiency. In conclusion, the presented technique can solve the problem that plug often occurs during the reinjection of cooled thermal waters back into sandstone geothermal reservoirs and have a great effectiveness in field application. It has a great prospect in the increase of geothermal water production and reinjection.