Influence of CO_(2)or flue gas(СО2+N_(2))injection on the change in gas permeability of a subpermafrost hydrate-saturated reservoir:Results of experimental modelingOA

Large volumes of natural gas stored in hydrate form within marine and subpermafrost environments represent a significant resource for potential extraction and use.Various methods for developing hydrate deposits are currently under investigation.A promising strategy for efficient methane production involves the injection of carbon dioxide(CO_(2))or flue gas mixtures(CO_(2)+N_(2)).The introduction of these gases into hydrate-bearing sediments induces methane hydrate dissociation,followed by its partial replacement by CO_(2)hydrate without compromising wellbore integrity.In addition,the CO_(2)-based approach facilitates carbon sequestration within hydrate structures,thereby reducing greenhouse gas emissions.For effective implementation,a detailed understanding of gas permeability behavior in response to CO_(2)or flue gas injection into hydrate-bearing formations is essential.This response was experimentally investigated by injecting CO_(2)and flue gas into sand-clay samples under pressure and temperature conditions representative of subpermafrost gas hydrate reservoirs.The experiments demonstrate that gas permeability decreases markedly during CO_(2)/CH_(4)replacement in the model reservoir,due to the additional formation of CO_(2)hydrate from residual pore water.This reduction may reach several tens of percent,particularly in reservoirs with high residual water content.Consequently,sediments with higher total saturation and lower hydration coefficients exhibit substantially reduced gas permeability following CO_(2)or flue gas injection.Overall,the findings indicate that the extent of permeability reduction during CO_(2)or flue gas injection is strongly governed by the initial reservoir properties and secondary hydrate formation processes.This understanding enables improved prediction and optimization of the CO_(2)/CH_(4)replacement process for the efficient and safe exploitation of gas hydrate resources.