Numerical Simulation of Methane Hydrate in Sandstone Cores K. Nazridoust, G. Ahmadi and D.H. Smith Department of Mechanical and Aeronautical Engineering Clarkson University, Potsdam, NY National Energy Technology Laboratory U.S. Department of Energy, Morgantown, WV

 Ice-like Crystalline Substances Made Up of Two or More Components  Host Component (Water) - Forms an Expanded Framework with Void Spaces  Guest Component (Methane, Ethane, Propane, Butane, Carbon Dioxide, Hydrogen Sulfide) - Fill the Void Spaces  Van der Waals Forces Hold the Lattice Together Gas Hydrates

 A 1 m 3 block of hydrate at normal temperature and pressure will release ~ 164 m 3 of methane  Methane hydrate energy content of ~ MJ/m 3  Methane gas – 42.0 MJ/m 3  Liquefied natural gas 16, MJ/m 3 Energy Content

Objectives  To Provide A Fundamental Understanding of Species Flow During Hydrate Dissociation  To Assess the Reservoir Conditions During Hydrate Dissociation  To Develop a Module for Simulation of Gas Hydrates Dissociation to be Incorporated in FLUENT™ Code  Potential Energy Resources  Potential Role in Climate Change  Issues During Oil and Gas Production  CO 2 Sequestration Importance of Gas Hydrates

Three-Phase Flow in Methane Hydrate Core, Depressurization

Hydrate Core

Continuity: Saturation: Darcy’s Law: Hydrate Dissociation - (Kim-Bishnoi, 1986) Kinetic Model: Intrinsic Diss. Constant = 124 kmol/Pa/s/m 2, and Activation Energy ∆E = J/kmol Governing Equations

Energy Equation Effective Thermal Conductivity Masuda, et al. (1999), c = 56,599 J/mol, d = J/mol.K. Hydrate Dissociation Heat Sink Governing Equations

Equilibrium Pressure Makagon (1997), A = K-1, B = K-2, C = Ambient Temperature Outlet Press.

Initial Conditions Core Temperature (K) Initial Pressure (MPa)3.75 Initial Hydrate Saturation0.443 Initial Water Saturation0.351 Initial Gas Saturation0.206 Initial Porosity0.182 Initial Absolute Permeability (mD)97.98 Boundary and Ambient Conditions Ambient Temp. (K)Outlet Valve Pressure (MPa) Case Case Case Case Case

Hydrate Core cm 15 cm 22.5 cm cm

Simulation T amb. =275.15K

Simulation T amb. =275.15K

Temperature: Comparison with Data Ambient Temp. (K) Outlet Valve Pressure (MPa) Case

- Case (2) Cumulative Gen./Diss.: Comparison with Data Ambient Temp. (K)Outlet Valve Pressure (MPa) Case

Five-spot Technique Four wells to form a square where steam or water is pumped in Gas is pushed out through the 5th well in the middle of the square Aquifer Zone

Simulation

 Depressurization method under favorable conditions is a feasible method for producing natural gas from hydrate.  Gas generation rate is sensitive to physical and thermal conditions of the core sample, the heat supply from the environment, and the outlet valve pressure.  Porosity and relative permeability are important factors affecting the hydrate dissociation and gas generation processes.  For the core studied the temperature near the dissociation front decreases due to hydrate dissociation and then increases by thermal convection.  Increasing the surrounding temperature increases the rate of gas and water production due to faster rate of hydrate dissociation.  Decreasing the outlet valve pressure increases the rate of hydrate dissociation and therefore the rate of gas and water production increases. Conclusions