Undrained creep behavior of CO2 hydrate-bearing sand and its constitutive modeling considering the cementing effect of hydrates

Abstract

A technique for carbon dioxide (CO2) capture and storage using CO2 hydrates where CO2 is stored as solid hydrates in the seabed ground, is attracting attention. Shallow sediments may be the most suitable seabed ground for CO2 hydrate storage because these unconsolidated soil sediments satisfy the limitation for the low-temperature condition. Hence, the deformation properties and long-term stability of gas hydrate-bearing sediments during and after gas storage must be investigated. In this study, a series of undrained triaxial creep tests were conducted on artificially made CO2 hydrate-bearing sand specimens to study the fundamental time dependent property of hydrate-bearing sediment. We extended an elasto-viscoplastic constitutive model by introducing a cohesion component and its degradation on surfaces and applied the proposed model to creep tests on gas hydrate-bearing sand.Three findings were obtained from the experiments and modelling. First, CO2 hydrate-bearing sand specimens showed accelerated creep behavior, which was characterized by the creep stress ratio level, regardless of the hydrate saturation. Second, creep accelerated under undrained conditions before the stress reached the critical state line obtained from the monotonic loading tests, and the stress ratio at the occurrence of acceleration creep was higher for specimens with a higher hydrate saturation. Third, the elasto-viscoplastic constitutive model which considered the cementing effect of hydrates was able to well reproduce the undrained creep behavior of hydrate-bearing sand with different hydrate saturations under relatively high creep stress levels.