The effect of overconsolidation on the mechanical behaviours of hydrate-bearing silty sediments

Abstract

CO2 sequestration via gas hydrate method shows great potential on promoting global carbon cycling and reducing greenhouse effect through injecting CO2 to hydrate reservoirs. However, the overconsolidation state induced by hydrate formation or interconversion of CO2 and CH4 hydrate would affect the stability of silty reservoirs after CO2 sequestration, but currently, few studies have been presented on this topic. To this end, a sequence of overconsolidation and drained shear tests on CO2 hydrate-bearing silty sediments (HBSSs) were carried out in this study to simulate and elucidate the effect of overconsolidation on the mechanical behaviours of CO2 HBSSs. The results reveal that all HBSSs with different hydrate saturations exhibit strain hardening and shear contraction behaviours with or without overconsolidation, while an increase in the overconsolidation ratio (OCR) enhances the deviator stress and alleviates the contraction effect. In addition, a strengthening effect on the stiffness, strength and resistance of deformation of HBSSs is induced by overconsolidation, while this effect becomes more prominent as the hydrate saturation increases. HBSSs with higher OCRs and hydrate saturations generally have lower stress-dilatancy ratios. Moreover, the shear paths of HBSSs with higher OCRs deviate farther from the normal consolidation line of hydrate-free silty sediments. This study is expected to provide theoretical guidance for the CO2 sequestration via gas hydrate in silty reservoirs.