The interface evolution during methane hydrate dissociation within quartz sands and its implications to the permeability prediction based on NMR data

摘要

Nuclear magnetic resonance (NMR) is an effective method used for measuring and predicting the properties of methane hydrate (MH)-bearing sediments. In this work we present the results of MH-related interface evolution during the MH dissociation process obtained by X-ray computed tomography (CT) imaging technique. Some implications of interface evolution for the NMR-based property predictions are analysed based on the experimental measurements. The results show that the areas of MH surface and MH-brine interface decrease slowly in the early stage of dissociation, but turns to decrease rapidly in the later stage. A conceptual model for determining the NMR transverse surface relaxivity (rho 2) in the hydrate-bearing sediment is proposed by considering these changes of MH-related interface. Predictions based on this model show that the NMR transverse surface relaxivity and effective permeability are both influenced by the influencing weight and surface area proportions of the MH-brine surface and sand-brine surface.