Abstract—This paper describes a one-dimensional numerical model for natural gas production from the dissociation of methane hydrate in hydrate-capped gas reservoir under depressurization and thermal stimulation. Some of the hydrate reservoirs discovered are overlying a free-gas layer, known as hydrate-capped gas reservoirs. These reservoirs are thought to be easiest and probably the first type of hydrate reservoirs to be produced. The mathematical equations that can be described this type of reservoir include mass balance, heat balance and kinetics of hydrate decomposition. These non-linear partial differential equations are solved using finite-difference fully implicit scheme. In the model, the effect of convection and conduction heat transfer, variation change of formation porosity, the effect of using different equations of state such as PR and ER and steam or hot water injection are considered. In addition distributions of pressure, temperature, saturation of gas, hydrate and water in the reservoir are evaluated. It is shown that the gas production rate is a sensitive function of well pressure. Keywords—Hydrate reservoir, numerical modeling, depressurization, thermal stimulation, gas generation. NOMENCLATURE Adec = specific surface area per unit bulk volume, m -1 AHS = specific area of hydrate particles, m -1 E = activation energy, J/mol fe = fugacity of gas at T and pe, kPa fg = fugacity of gas at T and pg, kPa l g . = generation rate of phase l per unit volume, kg/m3s h l = specific enthalpy of phase l, J/kg K = absolute permeability, md K c = thermal conductivity, w/m·K K 0 d = intrinsic decomposition rate constant, kmol/m2kPa·s k d = decomposition rate constant, kmol/m2kPa·s k rl = relative permeability to phase l M c = molar mass of component c, kg/kmol NH = hydrate number (= 5.75) P l = pressure of phase l, kPa P c = capillary pressure between gas and water, kPa P e = H-V-Lw equilibrium pressure, kPa q ml = mass production rate of phase l per unit volume, kg/m3s H Q . = heat of hydrate decomposition per unit volume, J/m3s F. Esmaeilzadeh (phone: +987112343833; fax: +987116287294; e-mail: esmaeil@shirazu.ac.ir), M. E. Zeighami (e-mail: mo_zeighami@yahoo.com), and J. Fathi are with Chemical and Petrochemical Engineering Department, Shiraz University, Shiraz, Iran. in Q . = direct heat input per unit volume, J/m3s R = gas constant (= 8.314 J/mol·K) S wr = irreducible water saturation S gr = residual gas saturation S l = saturation of phase l l S = normalized saturation of phase l t = time, s T = temperature, K v l = velocity of phase l, m/s U l = specific internal energy of phase l, J/kg = porosity l = viscosity of phase l, Pa·s l = density of phase l, kg/m3 SUBSCRIPT g = gas w = water H = hydrate R = rock i = initial condition I. INTRODUCTION AS hydrates are ice-like crystalline materials and non- stochiometric compounds that contain water and gases with small molecules such as CH 4 and which can occur at temperatures above the freezing point of water. Gas hydrates are treated as a potential energy resource for the future because a large amount of methane gas is trapped in hydrates reservoirs. One volume of hydrate could release 150 to 180 volumes of gas at standard conditions. The high concentration of methane gas puts the energy content of hydrate-bearing formations on a par with bitumen and heavy-oil reservoirs, and much higher than the energy content of other unconventional sources of gas, such as coal bed [1]. According to [2], the world resources of carbon trapped in hydrates have been estimated to be twice the amount of carbon in known fossil fuel deposits. There fore, developing methods for their production behavior are attracting considerable attention. The technologies for recovering methane from hydrates are very challenging and are still under development. The three most practical methods are: (1) depressurization, in which the pressure of an adjacent gas phase is lowered to cause decomposition. (2) thermal stimulation, in which an external source of energy is used, and (3) inhibitor injection, in which F. Esmaeilzadeh, M. E. Zeighami, and J. Fathi 1-D Modeling of Hydrate Decomposition in Porous Media G PROCEEDINGS OF WORLD ACADEMY OF SCIENCE, ENGINEERING AND TECHNOLOGY VOLUME 31 JULY 2008 ISSN 1307-6884 PWASET VOLUME 31 JULY 2008 ISSN 1307-6884 648 © 2008 WASET.ORG World Academy of Science, Engineering and Technology International Journal of Chemical and Molecular Engineering Vol:2, No:5, 2008 49 International Scholarly and Scientific Research & Innovation 2(5) 2008 ISNI:0000000091950263 Open Science Index, Chemical and Molecular Engineering Vol:2, No:5, 2008 publications.waset.org/3808/pdf