Predicting gas generation by depressurization of gas hydrates where the sharp-interface assumption is not valid

Natural gas is an important source of clean energy, and therefore methane hydrates may represent a potential energy resource. A number of analytical models have been reported for predicting the gas production from gas hydrates. All of these analytical models assume that decomposition happens at a sharp-interface that divides the medium into two regions; the hydrate zone and the dissociated zone. However, several detailed studies have shown that in the presence of a mobile (gas or water) phase in the hydrate cap, pressure reduction propagates from the interface into the hydrate zone, leading to decomposition of the hydrate throughout the hydrate zone. Under these conditions, the sharp-interface assumption is not valid. The purposes of this work are: (i) to develop a simple model to predict the rate of gas generation by the depressurization method when decomposition occurs deep inside the hydrate zone, and (ii) to compare the results with a corresponding model that invokes the sharp-interface assumption. It is found that the model with the sharp-interface assumption grossly under-predicts hydrate decomposition and gas generation.