Impact of gravity on hydrate saturation in gas‐rich environments

• Published in: Water resources research 2016-02, Vol.52 (2), p.1265-1285
• Main Authors: You, Kehua, DiCarlo, David, Flemings, Peter B.
• Format: Article
• Language: English
• Subjects: Buoyancy; Flow rates; fractional flow; Gas flow; Gravity effects; hydrate saturation; hydrocarbon migration; Hydrostatic pressure; Laboratories; method of characteristics; Saturation; Solidification; Water pressure
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1002/2015WR017975

We extend a one‐dimensional analytical solution by including buoyancy‐driven flow to explore the impact of gravity on hydrate formation from gas injection into brine‐saturated sediments within the hydrate stability zone. This solution includes the fully coupled gas and liquid phase flow and the associated advective transport in a homogeneous system. We obtain the saturations assuming Darcy flow under combined pressure and gravity gradients; capillary forces are neglected. At a high gas supply rate, the overpressure gradient (gradient of water pressure deviation from the hydrostatic pressure) dominates the gas flow, and the hydrate saturation is independent of the flow rate and flow direction. At a low gas supply rate, the buoyancy (the drive for gas flow induced by the density difference between gas and liquid) dominates the gas flow, and the hydrate saturation depends on the flow rate and flow direction. Hydrate saturation is highest for upward flow, and lowest for downward flow. Hydrate saturation decreases with flow rate for upward flow, and increases with flow rate for downward flow. In all cases, hydrate saturation is constant behind the hydrate solidification front. Gas saturation is homogeneous and close to the residual value for upward flow at a low rate; gas flows at the rate it is supplied. Gas saturation is much greater than the residual value, and decreases from the gas inlet to the hydrate solidification front for downward flow at a very low rate. The effect of gravity is usually negligible in laboratory experiments, yet is significant in natural hydrate systems. Key Points: We extend an analytical model for hydrate formation by including gravity Hydrate saturation depends on flow rate and direction at low gas supply rate Gravity effect is negligible in laboratory experiments and significant in fields