メタンハイドレート資源開発における坑井内流動障害に関する数値計算

Abstract

This paper describes a new algorithm implemented on the scheme, which was developed by authors' previous research in the Discrete Element Method with the Coarse Grid Thermal-Fluid Coupling Scheme to represent formation and decomposition of methane hydrate particles for the flow assurance during operation of the production system. The algorithm represents transient bonding process between methane hydrate particles or methane gas bubbles surrounded by methane hydrate shell. This process involves a phase-change between methane hydrate and methane gas/water, which is related to contacting time and the rate. Several simulations were conducted to validate the new algorithms. Also a simulation, which mimics flow of methane hydrate particles or methane gas bubbles surrounded by methane hydrate shell in the vertical duct, was conducted to examine bonding process under subcooling condition. It was verified that the thermal energy between particles and continuous phase are exchanged correctly under a phase-change with bonding process. Also the scheme was able to represent a phase-change from methane hydrate into methane gas/water by changing the phase- change rate and the Pressure-Temperature diagram. Further, it was found that condition of particle agglomeration during flowing in the vertical duct depends on the strength of the bond. As a whole, the improved scheme enables one to examine the flow assurance without blockage by methane hydrate in the production system if parameters are specified correctly in simulations.