(746h) Numerical Simulation of Hydrates in Porous Media for Clathrate Based Applications

Maninder Khurana, Praveen Linga*

Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore 117 585, Singapore

Key words: Clathrate hydrate, Numerical Simulation, Porous media, Phase stability

Abstract

Today, Hydrate based applications in porous media are not solely restricted to dissociation of natural gas hydrates for methane production. Hydrate applications have extended to novel applications such as hydrate based gas separation using packed bed, Simultaneous CO₂/CH₄ exchange for CO₂ capture and methane production and more. Numerical simulations have been widely used for studying the phenomenon of hydrate formation and dissociation in porous media. The most widely adopted porous media simulators developed till-date have been mostly reservoir simulators targeted towards methane production or CO₂/CH₄ exchange. Most prominent simulators like Tough+, MH-21 Hydrate Reservoir Simulator, STOMP-HYDT can simulate formation/dissociation of methane hydrates in a variety of porous media. They account for the thermodynamic equilibrium by means of regressed polynomial expressions. The presence of salts/inhibitors is generally accounted by means of shift in equilibrium curve. The simulators have options of either choosing equilibrium based or kinetic based simulation. In equilibrium based models, the local conditions are always assumed to be at the phase equilibria while kinetic models follow some form of linear driving force model.

In all of the simulators, structure I hydrates are a priori assumed while using the regressed polynomial expressions for phase equilibria and for the driving force in the kinetic model. This represents a clear lack in the simulators for the case where hydrates are not restricted to only sI structure. The current simulators cannot accurately capture systems with multiple hydrate phases co-existing. Predicting the presence of different phases, however, is a challenge that requires further phase stability calculations not undertaken by the current generation of simulators.

In current study, we develop a comprehensive simulator inclusive of phase stability and equilibrium predictions coupled with detailed multiphase flow simulation including heat transfer. Simultaneous computation of stability and phase equilibria calculations are first performed by solving coupled non-linear algebraic equations for both stability and isothermal-isobaric flash calculations based on the original study of Gupta et al.¹. The thermodynamic computations are then coupled with an in-house Multi-phase flow simulator in porous media including hydrates. Two-phase flow and molecular diffusions are considered for mass transfer, and heat of formation or dissociation of hydrates are included in the governing equations. The equations are discretized with finite volume difference method to convert to coupled ODEs and are integrated using MATLAB’s ODE solver. The intrinsic kinetics of hydrate formation or dissociation is considered using the Kim–Bishnoi model. Finally, the simulation results of the developed simulator are compared with the existing simulators for validation.

Topic: Gas Hydrates Science and Engineering

*Corresponding author, email: Praveen.Linga@nus.edu.sg

References

1. Gupta AK, Bishnoi PR, Kalogerakis N. A method for the simultaneous phase equilibria and stability calculations for multiphase reacting and non-reacting systems. Fluid Phase Equilib. 1991;63(1-2):65-89.