Reaction Kinetic Characteristics and Model of Methane Hydrate Formation in Porous Media

Abstract

Most of the natural gas hydrates on Earth are buried in shallow formations under deep water. Comprehensively understanding the reaction kinetic characteristics of gas hydrate in porous media is very beneficial to the deep exploration of the hydrate accumulation in nature. In this paper, the formation process of CH4 hydrate in porous media was simulated physically, using a reactor that is operating at high pressure and low temperature. The hydrate phase equilibrium and reaction kinetic characteristics at different temperatures, pressures, sand grain sizes, and clay contents were assessed. Based on the determination of relevant hydrate kinetic parameters, a novel mixing-flux hydrate reaction model was proposed, which can be used for numerical simulation of gas hydrate accumulation. The experimental results show that the porous media can make the phase equilibrium of CH4 hydrate shift to the right under the capillary effects on the gas and hydrate phases. Low temperature and high pressure can provide a large driving force for hydrate formation, but large clay content and small sand grain size usually give a negative effect on the CH4 transfer in the porous media. It often leads to a slow hydrate formation rate and hard distinction of pressure drop between hydrate nucleation and growth stages. Based on the experimental results, the hydrate nucleation kinetic parameters were regressed, and the activation energy (E a), as well as the reaction frequency factor (k fo), of hydrate growth were fitted to be 75.45–90.85 kJ/mol and 8.72 × 108–6.02 × 1011 mol/(m2 kPa day), respectively. In the numerical simulation of hydrate accumulation, the hydrate formation process can be described by coupling the low-flux reaction and the high-flux reaction, which consume the CH4 dissolved in water and the free CH4 gas in pores, respectively. This novel mixing-flux hydrate formation model is suitable for the flexible and practical hydrate accumulation simulation, which can consider various gas sources and transfer states in the hydrate reservoir.

Influence of the Particle Size of Porous Media on the Formation of Natural Gas Hydrate: A Review

“…They considered the capillary effect in the gas phase, hydrate phase, and gas phase and hydrate phase, and the results showed that the phase equilibrium curve shifted to the right by 3−8 °C when only the capillary effect on the gas phase was considered (Figure 14B), the phase equilibrium curve shifted to the left by 1−5 °C when only the capillary effect on the hydrate phase was considered (Figure 14A), and the phase equilibrium curve shifted to the right by 1−6 °C when the combined effect of the capillary effect on the two phases was considered (Figure 14C). Zhang et al 60 argued that her data supported Liu and Fleming's 116 views that the presence of porous media can induce more relaxed conditions of hydrate formation.…”

“…As a result, methane gas has difficulty migrating to the bottom of the sand bed, which hinders the conversion of water to hydrate. Kumar et al 59 and Zhang et al 60 conducted similar experiments with silica sand and clay, and the results showed that a higher water conversion rate was only observed in the experiment with larger sand, while a lower water conversion rate was observed in the experiment with smaller sand and high clay content. Adeyemo et al 96 used silica gel to prove this conclusion.…”

“…Previous research − has established that different particle sizes and their ratio in the sand bed will produce different sizes of pores, which will affect the hydrate formation rate. More small particles will block the gap between large particles, which reduces the specific surface area and connectivity of the system, impedes mass transfer, and reduces the formation rate.…”

“…At the same time, a large amount of water in the pores expands the clay, limiting the migration of gas and impeding the formation of the hydrate. Zhang et al 60 also emphasized that an increase in clay content would lead to smaller pores, lower permeability, and a lower hydrate formation rate. Ji et al 61 observed the formation of methane hydrate in small and large pores by using the excess gas method.…”

Performance analysis of an on-site hydrogen facility for fuel cell trains

“…Hoffrichter et al, in [7], developed a narrow FC prototype locomotive, achieving about 10% and 40% for vehicle and FC system efficiency. Zang et al, in [8], experimentally tested a fuel cell/battery/supercapacitor train, consuming almost 1.5 kg of hydrogen for 1-hour drive cycle.…”