Numerical modeling on hydrate formation and evaluating the influencing factors of its heterogeneity in core-scale sandy sediment

Abstract

Natural gas hydrate (NGH) has been regarded as a fossil fuel reserve for the future on account of its tremendous potential. The numerical modeling on NGH formation/dissociation mechanism contributes to better understanding its accumulation and distribution feature, and optimizing the development program. This paper aims to develop a new simulator for the NGH formation in the core-scale sandy sediments based on the computational fluids dynamic (CFD) methods. The mathematical model is established based on the kinetic reaction model of hydrate formation, the permeability reduction model by the NGH, model of heat and mass transfer in porous media. The hydrate formation model is programmed by C language, and used as a subroutine for Fluent software which is adopted to solve the governing equations of the multiphase flow. The simulator scheme is verified by comparison with the experiment and numerical simulation in literature. What's more, this study reproduces the same fluctuant tendency of temperature as the experiment during the 1.0 h–2.0 h for the first time. Different reaction surface models of NGH formation/dissociation are evaluated by the developed codes. The effects of the reaction surface of hydrate (RSH) model and the initial fluids distribution on the hydrate formation process are simulated and analyzed. The variation of the RSH in NGH formation/dissociation should be taken into consideration when modeling the hydrate re-formation in the exploitation of NGH. The initial distribution of water and gas has a great impact on the hydrate formation in the sealed reactor. The hydrate distribution is ununiform, even when assuming the water and methane are mixed uniformly in a homogeneous porous media. This study provides new insight for the parametric estimation of the RSH model in the hydrate formation and dissociation modeling.