Simulation of Depressurization for Gas Production From Gas Hydrate Reservoirs

Abstract

IntroductionToday, increasingly more stringent environmental considerations require that clean sources of energy be found. It is therefore anticipated that the demand for natural gas will continue to increase significantly. Some studies indicate that the amount of methane trapped in gas hydrates in natural settings is 100 times that of conventional gas reserves (1,2) . Therefore, gas hydrates are being considered as a potential source for natural gas production. However, it is not clear what percentage of this huge resource is recoverable, and the technologies for recovering natural gas from hydrates are still under development. Sloan (3) has presented an extensive review of some suggested methods, including depressurization, thermal stimulation, and inhibitor injection. The least energy intensive process is thought to be the depressurization method, since in this method the heat of decomposition is provided by the surrounding formation. AbstractGas hydrates as a significant resource of natural gas have attracted considerable attention in recent years. However, the severe environmental conditions of gas hydrate reservoirs and the solid form of hydrates require extensive technological development before commercial gas production becomes possible. Numerical studies often give useful information for predicting the potential and technical viability of a recovery process.This paper presents a 2D cylindrical simulator for gas production from hydrate reservoirs. The model includes the equations for gas-water two-phase flow, conductive and convective heat transfer, and intrinsic kinetics of hydrate decomposition. The simulator is used to model a hydrate reservoir where the hydrate-bearing layer overlies a free gas zone, such as those discovered in the arctic. A well is drilled and completed in the free gas zone. Pressure reduction in the free gas zone leads to the decomposition of the overlying hydrate and subsequent production of the generated gas.In this paper, we study the impact of the overlying hydrate in improving the production performance of the underlying gas reservoir and investigate the effect of various parameters on gas production behaviour. The rate of gas generated and produced, pressure, temperature, and saturation distributions are studied to investigate the sensitivity of results on individual input parameters. The results suggest that the development of gas reservoirs with overlying hydrates can lead to significant production rates and that the top hydrates have a large impact on increasing the reserve and improving the productivity of the underlying gas reservoir.Modelling of gas production from hydrate reservoirs involves solving the coupled equations of mass and energy balances. A review of analytical and numerical models given by Hong et al. (4) suggests that two approaches with respect to conditions at the decomposition zone have been taken: equilibrium and non-equilibrium. In models using the equilibrium approach, the three-phase hydrate-gas-water interface is at a thermodynamic equilibrium. The ...

Toward Production From Gas Hydrates: Current Status, Assessment of Resources, and Simulation-Based Evaluation of Technology and Potential

“…Their predictions of long-term production based on the kinetic and the equilibrium reaction models practically coincided, and indicated that mass and heat transfer are the dominant (and practically the only) limitation. These results are in agreement with earlier studies (Pawar et al, 2005;Hong and Pooladi-Darvish, 2005), and are exceptionally important because they remove the possibility of a potentially significant obstacle (i.e., kinetic limitation) in the quest for gas production from natural hydrate deposits. A related computational benefit is the reduction of the size of the matrix equations (the equilibrium model requires one less degree of freedom, and, thus, one less equation per cell), resulting in faster executions.…”

“…(a) The TOUGH+HYDRATE code (Moridis et al, 2005a), (Hong and Pooladi-Darvish, 2005) There are a few other simulators of hydrate behavior in porous media (Sun and Mohanty, 2005;Pawar et al, 2005), but these are not widely used. Codes (a) and (b) were calibrated against the data from the thermal dissociation test at the Mallik site (a process that provided an initial basis in the validation effort) and showed good agreement with observations, but exhibited significant deviations when predicting long-term production performance.…”

Numerical Simulation of Methane Production from Hydrates Induced by Different Depressurizing Approaches

“…These information are all described in the above mathematical equations, which constitute a system of four coupled partial differential equations which are non-linearity and cannot be solved analytically (exactly). Several numerical examples have been tested to solve these equations [10,14,15,19,[31][32][33][34][35]. In this work, the fully implicit simultaneous solution method combined with Newton's iterative method is used to solve this model.…”

Evaluation of the Gas Production Potential of Marine Hydrate Deposits in the Ulleung Basin of the Korean East Sea

“…This interest is further fueled by dwindling conventional hydrocarbon supplies, the rapidly expanding global demand for (and the corresponding rises in the cost of) energy, and the environmental desirability of CH 4 as a "clean" fuel. The emerging importance of hydrates as a potential gas resource was the impetus behind the proliferation of recent studies evaluating the technical and economic feasibility of gas production from hydrate deposits [5][6][7][8][9][10][11] , and provided the motivation for this study.…”