Deformation behaviors of hydrate-bearing silty sediments during CH4–CO2 replacement

The deep exploitation of silty reservoirs which store large scales of natural gas hydrate using the replacement method is of great significance for meeting the clean energy demand and reducing carbon emissions. Investigating the effects of CH4–CO2 replacement on the strength and deformation properties of hydrate-bearing silty sediments (HBSSs) plays a vital role in assessing the possible risks and conducting corresponding designs of the silty reservoirs during natural gas production. For that reason, this paper designs a series of CH4–CO2 replacement experiments on the HBSSs followed by the shear tests, and the deformation and strength behaviors of this material during the replacement were obtained and analyzed. The results show that HBSSs presents final compression behaviors after CH4–CO2 replacement while the dilation behaviors could appear due to CH4 hydrate dissociation at the initial stage of replacement. The replacement reduces the Elastic modulus but causes less change on the peak strength and deformation behaviors of CH4 HBSSs. This material also shows the relatively similar stress-dilatancy behaviors before and after partial replacement. The key influence of CH4–CO2 replacement on silty reservoirs may be located in the deformation of HBSSs during the replacement and the Elastic modulus reduction after replacement. These results in this study are wished to provide potential theoretical support for predicting the geo-mechanical response of silty reservoirs if hydrate production is applied using the CH4–CO2 replacement method.