Numerical Modelling of Methane Hydrate Dissociation in Sandy Porous Media by Depressurization with a Parametric Study

Yin, Zhenyuan (National University of Singapore, Lloyds Register Global Technology Centre) | Moridis, George (Lawrence Berkeley National Laboratory, Texas A&M University) | Tan, Hoon Kiang (Lloyds Register Global Technology Centre) | Linga, Praveen (National University of Singapore)

OnePetro 

Abstract

Due to its increasing abundance, cleaner and lower emissions upon combustion, natural gas (NG) has been considered as the best transition fuel away from coal and oil to a carbon-constrained world. Methane gas is the major component in NG accounting for 70-90%, and is also the major constituent found in natural gas hydrates (NGHs). The amount of CH4 preserved in NGHs is vast and estimated to be 20,000 trillion cubic meter (TCM) worldwide. This outweighs the proved NG reserve on earth, which is 865.4 TCM, and doubles the combined reserve of all fossil fuels. Thus, NGHs have been considered as a potential future energy source. Extensive geological surveys and drilling programs have been carried out during the past two decades at various countries (Canada, USA, Japan, S. Korea, India, China, etc.) to identify the location of these NGH reservoirs, to quantify the amount of gas deposited and to recover hydrate cores to analyze their thermophysical and geomechanical properties. Extensive research have also been carried out in laboratories to synthesis gas hydrate mimicking marine and permafrost conditions, and to study their fundamental behavior of formation and dissociation. In this study, we numerically analyzed an experiment of methane hydrate bearing sediment (P = 6.2 MPa) with hydrate saturation SH = 40% dissociation process induced by depressurization (P = 4 MPa) in a 1.0 L reactor with the production of water and gas. The simulation-predicted cumulative gas production shows an excellent agreement with the experimental measurement. In addition, from the evolution of phase saturation over time, it is revealed that hydrate dissociates from outer boundary to inner core. In addition, methane gas migrates to the reactor outer boundary first and accumulates to the upper section of the reactor mainly due to buoyance effect, while water drains down to the bottom of the reactor due to gravity. The parametric study on the fulids and thermal transport parameters (absolute permeability, k and HBS composite thermal conductivity, kθ) and the kinetic parameter () concluded that the gas production process is predominated controlled by thermal and kinetic reaction paramters, while flow paramters does not play a significant role in the current smallscale reactor.