Simulating gas hydrate formation in the southern hydrate ridge, Cascadia Margin

Abstract

The Cascadia Margin in the Pacific Ocean is a widely investigated region for oceanic gas hydrates. In this study, numerical simulation models are developed to simulate the flow of methane gas up fault zones in the Southern Hydrate Ridge of the Cascadia Margin. Three different hydrate formation scenarios, common to hydrate formation mechanisms in similar settings, are simulated. The tested scenarios are based on both field observations and previous numerical simulation assessments in similar subsea hydrate reserves. Results predict that gas hydrates in this region can be formed from gas migration up faults from deeper sources. The hydrate distribution follows the slope of the southern hydrate ridge but can be disjointed at places due to the presence of low salinity fluids, which results in higher hydrate saturations. The dominant mechanisms of gas migration into the region are advection and buoyancy driven. Capillary pressure forces, density differences, and hydraulic pressure differentials define the migration pathways along with high permeability pathways through faults. The timing of gas hydrate formation ranges between 2000 years and 1650 years for the modeling scenarios tested with the likelihood that the formation time is closer to 1650 years due to the likely presence of multiple faults acting as migration pathways for the gas. For the modeling scenarios tested, the gas hydrate mass generated ranges from 6.46 × 105 kg to 6.837 × 105 kg for the unit vertical cross-section used in the simulations. Predicted results of hydrate saturation are calibrated to field measured well log data for validation and verification.