Experimental and model study on the weakening of gas hydrate-bearing sand considering dissociation

Abstract

Hydrate decomposition changes the mechanical behavior of reservoirs, which threatens the safety of mining wells. Therefore, this study determines the weakening behavior of gas hydrate-bearing sands by performing triaxial shear tests considering decomposition based on drilling data from the Shenhu Sea. The results indicate that gas hydrate-bearing sands, both before and after hydrate decomposition, show a strain hardening trend, and the strength and cohesion increase with hydrate saturation. The dilatancy of the nondissociated specimen increases with hydrate saturation, while that of the dissociated specimen decreases. Moreover, hydrate decomposition causes the strength, cohesion and dilatancy of the specimen to decrease, exhibiting significant weakening behavior. Furthermore, a statistical damage constitutive model is proposed by considering that the microunit strength obeys the Drucker‒Prager criterion and Weibull distribution, and the model well describes the deformation and damage of gas hydrate-bearing sands due to decomposition.