posted on 2015-12-17, 04:36authored byKnut A. Birkedal, C. Matt Freeman, George
J. Moridis, Arne Graue
Numerical tools are essential for
the prediction and evaluation
of conventional hydrocarbon reservoir performance. Gas hydrates represent
a vast natural resource with a significant energy potential. The numerical
codes/tools describing processes involved during the dissociation
(induced by several methods) for gas production from hydrates are
powerful, but they need validation by comparison to empirical data
to instill confidence in their predictions. In this study, we successfully
reproduce experimental data of hydrate dissociation using the TOUGH+HYDRATE
(T+H) code. Methane (CH4) hydrate growth and dissociation
in partially water- and gas-saturated Bentheim sandstone were spatially
resolved using Magnetic Resonance Imaging (MRI), which allows the
in situ monitoring of saturation and phase transitions. All the CH4 that had been initially converted to gas hydrate was recovered
during depressurization. The physical system was reproduced numerically,
using both a simplified 2D model and a 3D grid involving complex Voronoi
elements. We modeled dissociation using both the equilibrium and the
kinetic reaction options in T+H, and we used a range of kinetic parameters
for sensitivity analysis and curve fitting. We successfully reproduced
the experimental results, which confirmed the empirical data that
demonstrated that heat transport was the limiting factor during dissociation.
Dissociation was more sensitive to kinetic parameters than anticipated,
which indicates that kinetic limitations may be important in short-term
core studies and a necessity in such simulations. This is the first
time T+H has been used to predict empirical nonmonotonic dissociation
behavior, where hydrate dissociation and reformation occurred as parallel
events.