Coarse Grid Numerical Simulation of Reaction Kinectics Model in the Gas Hydrate Reservoirs

AMIR SHAHBAZI*, MEHRAN POOLADI-DARVISH*,**, HASSAN HASSANZADEH***, *UNIVERSITY OF CALGARY, **FEKETE ASSOCIATES INC., R&D DIRECTORATE

Copyright 2008, International Conference of Gas Hydrates (ICGH 2008).

Proceedings of the 6th International Conference on Gas Hydrates (ICGH 2008), Vancouver, British Columbia, CANADA, July 6-10, 2008.

A number of simulation studies of hydrate decomposition in porous media have shown hydrate decomposition zone could be narrow, especially when permeability at initial hydrate saturation is low. Field scale simulation of gas production from hydrate reservoirs with (fine) grid blocks that allow accurate modeling of the decomposition region becomes impractical. This paper proposes a methodology for the use of coarse grid blocks for the simulation of hydrate decomposition without loss of accuracy. This study focuses on the modeling of an energy self sustaining gas production process from hydrate reservoir known as depressurization technique. In this process the pressure reduction diffuses within the hydrate layer resulting in the decomposition of hydrate structures and gas generation. A 1-D mathematical model is introduced which incorporates energy balance, fluid flow and kinetics of hydrate decomposition. Numerical results are shown to demonstrate the lack of accuracy of this solution when coarse grid blocks are used. This study uses Taylor series and determines additional terms and a correction parameter (a), which when are incorporated in the coarse-grid model improves its accuracy. It is shown that a single value of correction parameter (a) is sufficient to improve the accuracy of all variables (pressure, temperature and hydrate saturation), and for all times. A relation is obtained between the correction parameter and the coarse-grid size. The success of methodology in improving the accuracy of modeling with coarse grid cells and matching the results of a solution with a highly refined grid has been demonstrated for two systems with various properties.