Jet breaking tools for natural gas hydrate exploitation and their support technologies

Abstract

Marine natural gas hydrate (NGH) reservoirs in China are characterized by shallow burial depth and weak cementing. In view of these characteristics, it is in an urgent need to develop a series of technologies and support tools to ensure safe, economical, green and efficient NGH exploitation. In this paper, a new technical idea of NGH jet breaking and fluidization exploitation without changing the temperature and pressure conditions of NGH reservoirs was proposed, and the support nozzle tools for NGH jet breaking was designed, experimentally tested and optimized. Then, the relationships between the jet breaking parameters of nozzles (e.g. working pressure drop, flow rate, and lifting and lowering velocity and frequency) and the borehole diameters and breaking rates of broken NGH were investigated based on laboratory tests, and the field construction engineering charts of NGH jet breaking and fluidization exploitation were established. Finally, this method was practically verified at Well Liwan 3 in the South China Sea. And following research results were obtained. First, the NGH jet breaking and fluidization exploitation technology can increase the production efficiency of NGH exploitation, protect the safety of reservoir bottom and reduce the energy consumption of NGH exploitation. Second, by using the nozzle tools of NGH jet breaking, the generated borehole diameters are regular, broken particles can flow back well, and the lowering velocity of jet breaking without pilot holes is less than 7.1 m/h. Third, the engineering charts of NGH jet breaking and fluidization exploitation interpret the influential laws of jet breaking behaviors and construction parameters on the borehole diameters and breaking rates of NGH so as to provide a reference for the selection of NGH production test technology parameters. And fourth, the successful implementation of the NGH jet breaking and fluidization technology in the production tests of Well Liwan 3 verifies the feasibility of NGH jet breaking and fluidization exploitation process, and exhibits its promising application prospects in NGH future commercial exploitation.