Gas Production from Methane Hydrates in a Dual Wellbore System

In a previous study using a single wellbore production system, it was demonstrated that a combination of depressurization and wellbore heating is more efficient than depressurization alone, where the endothermic dissociation process rapidly consumes the specific heat of the formation, leading to a sharp decrease in the dissociation rate. This study extends the work on gas production and explores the feasibility of a novel dual wellbore production scheme, where heating and depressurization are conducted on separate wellbores. The drawback with combining heating and depressurization on a single wellbore is that the produced fluids are flowing in an opposite direction to the heat from the wellbore, and this forced convection may slow the dissociation process. Gas production tests are carried out using the dual wellbore system with different combinations of pressure and temperature at the depressurization and heating wellbores, respectively. The ensuing experimental results showed that both increased depressurization and heating can lead to optimized gas production. A production scheme with a higher depressurization compared to a lower depressurization at the same wellbore heating is generally more energy-efficient, while a higher wellbore temperature at the same depressurization resulted in more gas produced but no improvement in efficiency. Although a dual wellbore scheme has been an established practice in the petroleum industry, this is likely to be the first employed in the hydrate gas production tests.