Ice behaviors and heat transfer characteristics during the isothermal production process of methane hydrate reservoirs by depressurization

Abstract

Methane hydrate is a new environmentally friendly alternative energy source in the future. During its conventional production process by depressurization, ice behaviors and heat transfer characteristics are two key factors affecting the hydrate dissociation rate. In this study, different reservoir temperatures (276.2, 277.2 and 278.2 K) and production pressures (2.3, 2.6 and 3.1 MPa) were employed to investigate the methane hydrate production process. Icing, which increases the reservoir temperature and significantly promotes the dissociation of hydrates instantaneously, is generally observed under 2.3 MPa production pressure due to the large temperature decrease by depressurization. Higher initial temperatures decrease both the formation amount and melting duration of ice, and higher production pressures can avoid the formation of ice by decreasing the temperature drop. In addition, both ice melting and hydrate dissociation are isothermal when limited by the external heat supply. During the hundreds of minutes of ice melting process, the area with ice is estimated to shrink gradually. Similarly, the dissociation rate of hydrates is controlled by the heat supply and even becomes constant when the driving force is small enough (high production pressure). The results of this study are significant for the rate control of methane hydrate exploitation.