Integrated Characterization of Sand Production for Clayey-Silt Hydrate Formations by Coupling Geomechanics and Pressure Gradient-Based Sand Failure Criteria

Abstract In this work, a robust and pragmatic technique is developed to characterize the sediment deformation and sand production for clayey-silt sediments in the absence and presence of hydrate by coupling reservoir simulation and geomechanics. Such an integrated model considers the pressure gradient-based (PGB) sand failure criterion, changes in both porosity and permeability, and the three-dimensional (3D) displacement dynamics (i.e., deformation). Within the modified hydrate reservoir simulator, its geological module including displacement dynamics and changes in porosity and permeability due to deformation is solved with the staggered grid finite difference approach. Subsequently, the proposed model is validated by reproducing the experimentally measured profiles for both hydrate-free and hydrate-bearing sediments under various conditions. Excellent agreements between the measured profiles and simulation data have been achieved. It is found that, for the radial consolidation, the unconsolidated clayey-silt sediment is excessively compressed with a slight increase in external pressure (σex<0.50 MPa), and then the compaction rate slows down. Consistent with the gas and water production, the sediment subsidence is also composed of three stages, i.e., before hydrate dissociation (confining stress dominated), during hydrate dissociation (both confining stress and hydrate cementing effect), and after hydrate dissociation (confining stress dominated). The numerical results show that the sediment subsidence plays a critical role in porosity variation compared with sand creeping (i.e., development of wormholes or fluidization channels), while the permeability increment from the sand creeping substantially exceeds the permeability impairment from sediment subsidence.