Studies on combination of methane gas extraction techniques applicable to gas hydrate reservoirs of Indian continental margins

Gas hydrate is a promising alternate energy to cater to our future fuel requirement. Exploration and extraction for gas hydrate is a nascent science in international scenario and varies with reference to the different site conditions. Methane hydrate is solid clathrate compound that can trap small hydrocarbon natural gas within polyhedral cages formed from hydrogen-bonded water molecules at low temperature and high pressure conditions. Natural occurrence of methane hydrates are reported from permafrost regions and deep ocean marine settings. In India gas hydrates were found to be available in Krishna-Godhavari (KG) basin, Mahanadi basin and Andaman Basin. Occurrence of gas hydrates varies with reference to the different settings with a maximum of thickness of 120 m in fractured clays in KG basin at a water depth of 1000 m and 40m below seafloor. Gas hydrate extraction techniques can be classified under the categories of thermal stimulation, depressurization and inhibitor injection. Each methodology has its own advantage and disadvantages. Phase changes are the key requirement to understand reservoir behavior when applying the gas hydrate extraction technique. This article deals with heat transfer mechanism by thermal stimulation in combination with de-pressurization concept for methane gas extraction. By using thermal stimulation technique, it is possible to confine the energy delivery into the gas hydrate bearing reservoir to dissociate the reservoir for methane production. Since the overburden materials are unconsolidated montmorillonite type clays with high water content and swelling nature, stability of the reservoir in sustainable way is the challenge. By considering the reservoir settings, simulations were performed using MATLAB and TOUGH + HYDRATE software with the results from laboratory studies. Results indicate that it is possible to raise the temperature of gas hydrate bearing sediments to the extent required for dissociation. Experiments were performed using the bentonite clay prepared with matching water content and having similar thermal conductivity to the gas hydrate reservoir associated sediment conditions. It is also observed that the heating the low thermal conductivity sediments bearing reservoir had limitations which could be overcome by combining with the depressurization to pump out the dissociated water in the reservoir. This will work as depressurization concept for further enhancing the dissociation of surrounding reservoir. The energy balance results show that the energy supplied and produced could be better than the ratio of 1: 4. An approach on sustainable extraction and the practical challenges in realizing a field scale system with reference to Indian gas-hydrate reservoir settings are dealt.