Experimental research on the mechanical properties of methane hydrate-bearing sediments during hydrate dissociation

This paper describes studies of the effect of hydrate dissociation on the safety and stability of methane hydrate-bearing sediments. Methane hydrates within the sediments were dissociating under the conditions of a confining pressure of 0.5 MPa, 1 MPa, 2 MPa and a temperature of -5 degrees C. After 6 h, 24 h, or 48 h, a series of triaxial compression tests on methane hydrate-bearing sediments were performed. The tests of ice-clay and sediments without hydrate dissociation were performed for comparison. Focusing on the mechanical properties of the sediments, the experimental results indicated that the shear strength of the ice-clay mixtures was lower than that of the methane hydrate-bearing sediments. The strength of the sediments was reduced by hydrate dissociation, and the strength tended to decrease further at the lower confining pressures. The secant modulus E-s of the sediments dropped by 42.6% in the case of the dissociation time of the hydrate of 48 h at the confining pressure of 1 MPa; however, the decline of the initial yield modulus E-0 was only 9.34%. The slower hydrate dissociation rate contributed to reducing the failure strength at a declining pace. Based on the Mohr-Coulomb strength theory, it was concluded that the decrease in strength was mainly affected by the cohesive reduction. Moreover, the mathematical expression of the M-C criterion related to the hydrate dissociation time was proposed. This research could be valuable for the safety and stability of hydrate deposits in a permafrost region. (C) 2013 Elsevier Ltd. All rights reserved.