Dynamic analysis of hydrate-bearing seabed sediments considering methane gas production induced by depressurization

Abstract

Understanding the mechanical behavior of hydrate-bearing sediments during earthquakes is important for the safe and long term gas production from methane hydrates. Additionally, long term and widespread gas production may have effects on the mechanical properties of the seabed ground. In the present study we have analyzed the dynamic behavior of hydrate-bearing sediments considering gas production by the depressurization method. Firstly, we simulated gas production process using a chemo-thermo-mechanically coupled method for different levels of depressurizing pressure. Then, we conducted dynamic analyses by using the results of the production analyses as the initial conditions in order to consider the effects of gas production on dynamic behavior of the sediments. We have modeled the hydrate bearing-sediments as a multiphase mixture composed of gas, water, soil, and hydrates. For the constitutive model for soils, we used a cyclic elasto-viscoplastic model for clayey soils with nonlinear kinematic hardening. A predicted earthquake motion at Kumanonada along the Nankai trough was input. From the numerical results, we have found that the production of natural gas may affect the ground motion during strong earthquakes.