Applications of methane hydrate formation and decomposition

There are enormous natural gas reserves that exist in the form of gas hydrate deposits in many regions of the world. These in situ hydrates are relatively immobile and impermeable. In order to produce natural gas from hydrate reservoirs it is necessary to decompose the hydrate structure. In this work, mathematical models have been developed to investigate the feasibility of thermal or depressurization schemes for natural gas production.;A thermal model is developed by coupling the intrinsic kinetics with the heat transfer rates to describe the decomposition of a hydrate block which is being heated at a constant heat flux. The coupling of intrinsic hydrate decomposition kinetics with heat transfer rate is performed for the first time and the significance of kinetics in the global rate of decomposition has been demonstrated. The simulation results indicate that by changing the system pressure we can move from a heat transfer controlled regime to a regime where both heat transfer and intrinsic kinetics have a significant effect on the global rate of decomposition.;A depressurization model without external heat supply is also developed to describe the hydrate decomposition in a porous medium. Similar to the thermal model, the depressurization model is developed by coupling the intrinsic decomposition kinetics with the heat and mass transfer phenomena. The model considers both the hydrate and the free gas regions and tracks the movement of the hydrate interface (two region moving boundary problem). The transient pressure and temperature distributions are calculated in both the decomposed and hydrate zones in order to determine, whether the depressurization scheme is capable of initiating and sustaining hydrate decomposition at a practical rate. The simulation results indicate that the global rate of hydrate decomposition under depressurization scheme is very slow. This slow rate of decomposition is due to the severe resistance imposed by heat transfer in porous media.;Gas hydrates besides being an energy resource can also cause serious problems in the petroleum industry. In particular, hydrates have been known to plug transportation pipelines. In order to aid in the development of new solutions to the hydrate plugging problems, experiments were performed to investigate the influence of surfactants on the kinetics of methane hydrate formation. The results indicate that the presence of surfactants at low concentration (i.e. 4.10 ;In this work, the hydrate plug formation under emulated stagnant pipeline conditions is also presented. A shutdown offshore pipeline condition is emulated in the laboratory to obtain methane hydrate plug formation data. The experiments were conducted at a temperature of 274 K and at pressures of 4, 5 and 7 MPa. Furthermore, a mathematical model which couples intrinsic hydrate formation kinetics with heat and mass transfer phenomena is presented to describe the overall hydrate plug formation process. The "effective" diffusivities of methane gas through hydrate are estimated by matching the model predictions with the experimental data.