Abstract
Since huge amounts of CH4 are bound in natural gas hydrates occurring at active and passive continental margins and in permafrost regions, the production of natural gas from hydrate-bearing sediments has become of more and more interest. Three different methods to destabilize hydrates and release the CH4 gas are discussed in principle: thermal stimulation, depressurization and chemical stimulation. This study focusses on the thermal stimulation using a counter-current heat-exchange reactor for the in situ combustion of CH4. The principle of in situ combustion as a method for thermal stimulation of hydrate bearing sediments has been introduced and discussed earlier [1,2]. In this study we present the first results of several tests performed in a pilot plant scale using a counter-current heat-exchange reactor. The heat of the flameless, catalytic oxidation of CH4 was used for the decomposition of hydrates in sand within a LArge Reservoir Simulator (LARS). Different catalysts were tested, varying from diverse elements of the platinum group to a universal metal catalyst. The results show differences regarding the conversion rate of CH4 to CO2. The promising results of the latest reactor test, for which LARS was filled with sand and ca. 80% of the pore space was saturated with CH4 hydrate, are also presented in this study. The data analysis showed that about 15% of the CH4 gas released from hydrates would have to be used for the successful dissociation of all hydrates in the sediment using thermal stimulation via in situ combustion.
Highlights
Clathrate hydrates are ice-like solids composed of a three-dimensional network of hydrogen-bonded water molecules that confines gas molecules in well-defined cavities of different sizes
The striking advantage of using thermal stimulation via in situ combustion for the gas production from natural gas hydrates is the position of the heat source: the reactor is located within the hydrate-bearing sediments, the heat is generated where it is needed without any losses of energy during transportation
The production test was performed in the LArge Reservoir Simulator (LARS), which has been described in detail elsewhere [2]
Summary
Clathrate hydrates are ice-like solids composed of a three-dimensional network of hydrogen-bonded water molecules that confines gas molecules in well-defined cavities of different sizes. We will focus on the thermal stimulation method, which was already tested successfully in a field test in the framework of the Mallik Scientific Drilling Project in the Northwest Territories in the Canadian Arctic during the winter of 2001/2002 During this gas production test a hot fluid was pumped through about 600 m of permafrost into depths of 900–1100 m where the hydrate-bearing sediment occurred. An alternative method to thermal stimulation via hot fluid circulation may be in situ combustion of CH4 in a counter-current heat-exchange reactor. The striking advantage of using thermal stimulation via in situ combustion for the gas production from natural gas hydrates is the position of the heat source: the reactor is located within the hydrate-bearing sediments, the heat is generated where it is needed without any losses of energy during transportation. Recent results from production tests in a pilot plant scale are presented and discussed
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