A Method for Producing Natural Gas from Gas Hydrate Deposits

Constantin Cranganu
Brooklyn College of the City University of New York, Brooklyn, NY

Gas hydrates are increasingly considered a potential energy resource. Various methods of exploiting gas hydrates (thermal stimulation, depressurization, inhibitor injection, etc.) have been proposed so far, but each of them has some drawbacks. To overcome some of these drawbacks, we propose a new method for producing methane from gas hydrates. The method uses in situ thermal stimulation by introducing a specially designed hydrate heating apparatus into a horizontal borehole drilled in gas hydrate deposits (GHD). Instead of using water or other hot fluid injected from the surface or another location away from the GHD, an air/gas fuel mixture is introduced into a combustion vessel from the surface via a fuel injection tubing string directly in the GHD. Burning the fuel mixture results in producing the heat necessary to dissociate hydrates in the GHD themselves. The freed natural gas is then conveyed to the surface via a casing that is lining the wellbore. This method has the advantage of permitting the dissociated gas to be produced through the same wellbore through which the air/gas fuel mixture is injected, thereby avoiding the need of using two wells (injection and exploitation). An estimated energy gain efficiency of the proposed method shows that only about 1.5 to 2.5% of gas produced will have to be burned to decompose hydrates. Previous estimates of other thermal decomposition methods, for example steam injection, show that about 8-10% of gas produced will have to be burned just to decompose hydrates.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005