Natural Gas Hydrate Decomposition Characteristics at the Exploitation Anaphase via Sediment Warming

Abstract

The exploitation anaphase of natural gas hydrate is with irreducible pressure conditions and low hydrate saturation low temperature, when the hydrates may only decompose via sediment warming. Relevant decomposition characteristics and kinetic mechanisms of hydrate exploitation anaphase are still unclear. In this study, six hydrate sediments with a 10−30% saturation at 3 MPa and 272 K were first prepared, and then three exploitation pressures of 4.5, 5.0, and 5.5 MPa were employed to investigate the hydrate decomposition characteristics at the exploitation anaphase via sediment warming to 291 K. The hydrate decomposition in this study can be divided into constant-volume and constant-pressure processes, and the decomposition rate in the constant-pressure process is approximately 4 times that in the constant-volume process. The relationship between the hydrate decomposition amount and the decomposition rate is exponential under different exploitation pressures. In addition, the temperature in the constant-volume process is positively correlated to the dynamic pressure, which satisfies the Clapiron equation. By energy consumption analysis, it is found that for every 1% increase in hydrate decomposition, the total energy consumption increases by 1‰. The results of this study are helpful for the hydrate decomposition prediction and efficiency optimalization at the exploitation anaphase.