Enhanced Gas Production from Hydrate Reservoirs with Underlying Water Layer

The recovery of natural gas from a marine hydrate reservoir is a complicated geological process, involving heat and mass transfer inside hydrate-bearing sediments as well between the overburden and underlying layers. Yet, most attention has been paid merely to the evolution of the hydrate reservoir itself. The idea has been proposed to consider as a whole the hydrate layer together with the overburden and underlying layers. In this work, the enhanced gas production behavior from the hydrate reservoir with an underlying water layer was specifically studied. It is found that the initial pressure propagation from the hydrate layer to the free water layer was very difficult; this thereby dominated the early stage of hydrate dissociation. The following dissociation of hydrate was majorly controlled by the heat supply from the sensible heat of the water layer and the resulting temperature distribution. A stepwise depressurization could significantly help enable a stable production rate, and the accumulative water yield depended strongly on the overall pressure drop, regardless of the process of depressurizing. Injecting heat was limited by the low efficiency of horizontal heat transfer resulting from the long distance and low thermal conductivity. The results are helpful in terms of providing guidance to field tests where there is commonly an underlying water layer and water production is frequently encountered.