Cavitation damage inducing the improvement of jet breaking efficiency during hydrate drilling

Abstract

Natural gas hydrate (NGH) is an environment-friendly energy source with great development potential. Cavitation jet is a promising technology to improve drilling rate for both the solid fluidization method and integrated method of radial jet drilling and completion. This work aims at the improvement of jet breaking efficiency and thereby the NGH production. Firstly, gas hydrate-bearing sediments (GHBS) samples are synthesized in laboratory, and the erosion tests are conducted with the conical jet (CJ) and convergent-divergent cavitation jet (CDCJ). Then, the distribution characteristics of velocity, cavitation and pressure are simulated in CJ and CDCJ flows. Finally, the collapse behaviours of a single cavitation bubble near a hydrate surface are investigated to preliminarily identify the responsible cavitation damage mechanisms. Results indicate that the CDCJ shows stronger reaming effect and performance of hole depth extension. Under the present hydraulic conditions, the CDCJ increases the erosion pit volume by 30% and saves the specific energy by 23%. The cavitation damage along the hydrate wall can be produced by the combination of impulse pressure and thermal damage. This study reveals the effect of cavitation damage on GHBS and presents preliminary insights into the potential application of cavitation jets in NGH production.