As one of the innovative technologies, the solid fluidization mining method was proposed in the exploitation of natural gas hydrates. During the production test of fluidization, the high-pressure water jet was used to break the ore bodies of hydrates into fine particles. In this study, bulk ice samples were prepared as an analog of blocky hydrate. Experimental studies were conducted to optimize the jet parameters combination for ice breaking. Moreover, the effects of jet parameters and impact time on erosion diameter, erosion depth, and erosion volume were identified. The results indicate that the erosion volume and erosion depth increase with the pumping rate. As the standoff distance increases, the crushing effect gradually decreases owing to the high energy loss. At the same pumping rate, increasing the nozzle diameter will result in poorer erosion performance. Besides, the erosion depth and erosion volume show a linear increasing trend with the impact time. As for the erosion diameter, it is insensitive to all studied factors except the nozzle diameter. Among the studied parameter range, the optimized combination of jet parameters for the erosion performance has a nozzle diameter of 1 mm, a standoff distance of 1mm and a pumping rate of 90 L/h.

1. INTRODUCTION

Natural gas hydrate (NGH) has long been considered as a possible energy resource for the future.(Timothy S. Collette, 2002; Makogon, 2010) Many countries, including the United States, Japan, Korean, China, and India, have launched ambitious national projects to the further development of gas hydrates.(Yun et al., 2006; Liu et al., 2019) However, great challenges have been encountered in the safe, efficient, and environmentally friendly exploitation of NGH resources. Recently, an innovative exploitation method, the solid fluidization mining method, was proposed by Zhou.(Wang et al., 2017; Zhou et al., 2018) Furthermore, it has been successfully applied to the trial production of NGH in the Shenhu sea area of the South China Sea in 2017.(Zhou et al., 2017) As an important part of the solid fluidization method, the high-pressure water jet was used to cut and crush the hydrate bearing sediments (HBS) into fine particles which are subsequently transported upward along the drilling fluid to the offshore platform.(Wang et al., 2017; Chen et al., 2019) Therefore, it becomes meaningful to conduct experimental studies to optimize the jet parameters for the breaking of hydrate.

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