Geomechanical Response of Known Permafrost Hydrate Deposits to Depressurization and Thermal Loading

Authors: Jonny Rutqvist (speaker), George J. Moridis, and Timothy Collett

Venue: 6th International Conference on Gas Hydrates 2008, Vancouver, British Columbia, July 9-12, 2008. (http://www.icgh.org [external site]).

Abstract: Simulation of the system behavior of hydrate-bearing geologic media involves solving fully coupled mass and heat balance equations. The models need to simulate equilibrium or kinetic processes of hydrate formation and dissociation. TOUGH+HYDRATE is a widely used code for gas hydrate simulations. The code can model non-isothermal gas release, phase changes and flow of fluids and heat. It accounts for up to four mass components and four possible phases. Because hydrate simulations require intensive computational effort, many studies that involve serial processors are limited by problems of complexity and scale. With the growing availability of multi-core CPUs, Linux clusters, and super-computers, the use of parallel processing methods is a distinct advantage. This study develops a domain decomposition approach for large-scale gas hydrate simulations using parallel computation. The approach partitions the simulation domain into small sub-domains. The full simulation domain is simulated integrally by using multiple processes. Each process will be in charge of one portion of the simulation domain for updating thermophysical properties, assembling mass and energy balance equations, solving linear equation systems, and performing other local computations. The linear equation systems are solved in parallel by multiple processes with a parallel linear solver. The multiple processes are run in parallel on shared- or distributed memory multiple-CPU computers. A hybrid approach, running multiple processes in each CPU and using multiple CPUs, may achieve additional speedup. During calculations, communication between processes is needed to update sub-domain boundary parameters. An efficient inter-process communication scheme has been developed. The new approach was implemented into the TOUGH+HYDRATE code and demonstrates excellent speedup and very good scalability. For many large-scale problems, this method can obtain linear or super-linear speedup. This paper will show applications of the new approach to simulate three dimensional field-scale models for gas production from gas-hydrate deposits.

Related NETL Project:
This presentation is related to the NETL project G308-01, “Numerical Studies for the Characterization of Recoverable Resources from Methane Hydrate Deposits.” The objective of this project is to develop a reservoir model that simulates the behavior of hydrate-bearing geologic systems and evaluates appropriate hydrate production strategies for both permafrost and marine environments, including thermal stimulation, depressurization and dissociation induced and/or enhanced by inhibitors (such as brines and alcohols). This research will enhance natural gas hydrate research and development activities by bringing new numerical simulation capabilities and laboratory measurements to bear on the difficult problems of characterization and gas recovery of methane hydrate deposits.

Project Contacts
NETL – Richard Baker (richard.baker@netl.doe.gov or 304-285-2714)
LBNL – George Moridis (GJMoridis@lbl.gov or 510 486-6709)