| dc.description.abstract | Interest in gas hydrates as an energy resource has grown continuously over the last decades, and it has significantly increased since the beginning of the last decade. Much of the interest has come from countries with limited access to conventional hydrocarbon resources, and/or with a strategic interest in developing alternative hydrocarbon resources. Although the gas-in-place volume estimates of gas locked in gas hydrates remains uncertain, they indicate a vast resource volume. These vast resource volumes, combined with the environmental desirability of gas compared to other hydrocarbon fuels and the growing worldwide energy demand, leads to the conclusion that the potential of gas hydrate as an energy resource is very large. However, gas production from gas hydrate reservoirs do not yet exist on a commercial scale as a consequence of the unique challenges associated with drilling and production from these reservoirs.The goal of this thesis has been to investigate and understand these unique drilling- and production related challenges, with an emphasis on the drilling related challenges, to suggest and evaluate possible methods and technologies that could solve these challenges, and to make recommendations of how these challenges can be overcome using existing methods and technologies. Background information concerning the properties and characteristics of gas hydrates and the classification of different types of gas hydrate reservoirs have been covered to provide a base from which the drilling and production related challenges could be discussed. A Matlab model has also been developed and simulated to investigate the annulus temperature profile during drilling at a specific depth, as keeping a low temperature in the annulus was found to be an important factor in reducing the drilling related challenges.The first of the two main findings in this thesis is that production wells can be drilled safely and effectively in formations containing gas hydrates by using a combination of different existing technologies. This involves drilling with managed pressure drilling in combination with other methods. These methods are: casing while drilling, where technically and economically possible; surface mud cooling, to reduce the temperature in the annulus and prevent dissociation of gas hydrates in the formation and cuttings; drilling with high circulation rate; and insulated equipment, if necessary. The second major finding is that the recommended production strategy for all three classes of gas hydrate reservoirs is depressurization combined with thermal stimulation in the near wellbore area. Thermal stimulation is important to prevent the formation of ice and secondary gas hydrates that has a disadvantageous effect on the near wellbore permeability and, consequentially, the gas production rate and cumulative gas production volume. Suggested further work includes:-Determining experimentally the gas hydrate dissociation rate as a function of P&T that can be used to estimate the free gas volume in the annulus during drilling-Continued investigation into methods and technologies for reducing drilling related challenges in gas hydrate formations, for instance, the potential of surface mud cooling on annulus temperature distribution-Improvements of the Matlab model and program, for instance including the effect of a riser, variable formation temperature, radiation heat transfer, and heat generation due to friction between the drill string and the formation | nb_NO |
