Optimal driving force for the dissociation of CH4 hydrates in hydrate-bearing sediments using depressurization

Abstract

In this study, three kinds of driving forces for the dissociation of CH4 hydrates were experimentally investigated to determine which was optimal for a consistent control of the depressurization process. A specially designed one-dimensional (1-D) reactor was used to examine the production behavior of CH4 from the hydrate-bearing sediment using depressurization at different temperatures. The saturation of CH4 hydrate based on the mass balance in the 1-D reactor was cross-checked with the saturation value obtained by powder X-ray diffraction. Under a constant pressure-based driving force (ΔP = 0.4 MPa), the dissociation rate of CH4 hydrate was slower at a higher temperature, whereas under a constant temperature-based driving force (ΔT = 1.0 K), an almost similar dissociation rate was observed at different temperatures. However, the dissociation behavior of CH4 hydrate with a constant modified chemical potential-based driving force (Δμ) demonstrated a remarkable consistency over the entire temperature range. Furthermore, it was found that the Δμ immediately reflected an abrupt temperature drop and subsequent recovery during depressurization. The experimental results clearly indicate that the Δμ can be adopted as a universal parameter to control the depressurization process consistently and will be useful for optimizing the production process of natural gas hydrates using depressurization.