Multiscale Laboratory Verification of Depressurization for Production of Sedimentary Methane Hydrates

Abstract

Summary This study reviews how production of methane from hydrates can be triggered by dissociation of the hydrate structure. Techniques leading to dissociation of hydrates are summarized by pressure depletion, thermal stimulation, and injection of inhibitors. Depressurization is considered to be the most-cost-effective method and is easily implemented in gas reservoirs with overlying hydrate layers. Examples and status of pressure-depletion tests on field scale will be reviewed. In hydrate reservoirs not adjacent to gas zones, the success of pressure depletion is dependent on sufficient permeability to allow for pressure perturbations to reach within the hydrate reservoir and to allow for flow of dissociated gas. This effect has been investigated in this paper by performing controlled pressure depletions on hydrate-filled sandstone cores. Dissociation pressures at given temperatures have been quantified as well as recovery of methane as a function of pressure decrements lower than dissociation pressure. Hydrate dissociation was found to take place over a range of pressure values because of salinity changes in the water phase. A 2D porous silicon-wafer micromodel has been used to gain insight into the mechanisms of hydrate dissociation. Direct visualization of hydrate melting induced by both depressurization and heating is reported from pores replicating authentic sandstone pores. Thermal stimulation led to a more-uniform hydrate melting compared with pressure depletion, and depressurization was most effective when the hydrate was in direct contact with gas bubbles.