The Geomechanical Behavior of Hydrate Reservoirs: Implications for Drilling and Production

Abstract We performed uniaxial compression tests on specimens from a sandy silt reservoir with a hydrate saturation greater than 80% and on specimens of the same reservoir without hydrate present. During loading, the hydrate-bearing reservoir samples are stiffer than equivalent samples without hydrate. When we hold the stress, the hydrate-bearing specimens continue to compress and the lateral stress increases to equal the vertical stress within one day. We interpret that this visco-plastic behavior will impacts reservoir compression and the evolution of stresses during production. We also suggest that burial of a hydrate reservoir may result in in-situ stresses that are isotropic and equal to the overburden stress. We integrate these observations with a conceptual geomechanical model to describe the evolution of stress state and compaction in a reservoir that undergoes production by pressure drawdown. In our example, a 5 MPa depressurization is causes gas hydrate dissociation. This decrease in pore pressure increases the effective stresses which causes significant compaction, decrease in reservoir permeability, and perturbs stresses near the wellbore. The viscoplastic behavior of hydrate-bearing sediments will impact in situ stresses and gas production from hydrate reservoirs.