Creep of Sediment Containing Synthetic Methane Hydrate

The time-dependent behavior of methane hydrate sediments is of great significance in the long-term mechanical stability of methane hydrate reservoirs and also in the evaluation of gas productivity from methane hydrate reservoirs. However, almost no information is available concerning the time-dependent behavior of methane hydrate sediments. In this study, firstly, drained triaxial compression creep tests were conducted for synthetic methane hydrate mixed with Toyoura sand under the conditions of a confining pressure of 9 MPa, pore water pressure of 8 MPa and temperature of 278 K. Secondly, experimental data on creep strain and strain rate were analyzed. Finally, the results obtained in creep tests were discussed and compared with the strain-rate dependence of strength in constant-strain-rate tests. The findings can be summarized as follows.(1) Creep strain monotonically increased with elapsed time. Strain rate decreased gradually at first, then took the minimum value and finally began to increase.(2) At the beginning of creep test, strain rate was inversely proportional to the m-th power of elapsed time. Just before failure of the specimen, strain rate was inversely proportional to the m-th power of residual time.(3) The lower the creep stress level, the longer the creep life.(4) Creep behavior was closely related to the strain-rate dependence of strength in constant-strain-rate tests.