Experimental research on the erosion characteristics of organ-pipe cavitating jet for hydrate-bearing sediments

Abstract

Cavitating jet is regarded as a promising breaking rate improvement technology in both the marine natural gas hydrate (NGH) fluidization exploitation method and the integrated radial jet drilling and completion method. Experimental studies on the influences of standoff distance, erosion time, inlet flow rate and hydrate saturation on hydrate-bearing sediments (HBS) breakage by organ-pipe cavitating jet (OPCJ) were conducted. The methane HBS synthesized in laboratory were employed as the experimental samples. The breaking effect were evaluated by four quantifiable indicators: erosion pit volume and maximum depth, and jet specific energy and specific cutting energy. Results show that under the same inlet flow rate, the standoff distance and erosion time have significant influences on the erosion pit shape. For the erosion pit volume and depth, the optimal standoff distances are respectively 4 mm and 5 mm (the diameter of nozzle is 1 mm), in which condition the OPCJ efficiencies of erosion and penetration on HBS are greatly improved. The ultimate erosion depth is 215 mm at an inlet flow rate of 0.085 L/s. The critical breaking velocities of OPCJ and conical jet (CJ) on HBS with hydrate saturation of 50% are respectively estimated to be 17.8 m/s and 24.2 m/s. Increasing hydrate saturation significantly decreases the erosion efficiency of OPCJ on HBS. The inlet flow rate is the most significant factor for the erosion pit volume and depth. This study provides a reference on the potential field applications for the NGH fluidization exploitation method and the integrated radial jet drilling and completion method.