Geomechanical property evolution of hydrate-bearing sediments under dynamic loads: Nonlinear behaviors of modulus and damping ratio

Abstract

Understanding dynamic mechanical properties of hydrate reservoirs is essential for ensuring safety and economic hydrate production. The modulus, damping ratio, and Poisson's ratio are critical parameters in interpreting seismic surveys and well logging data and the stability prediction of hydrate reservoirs during production or under earthquake conditions. In this paper, the shear and Young's moduli and damping ratios were evaluated by conducting resonant column tests on the synthetic hydrate-bearing specimens with respect to hydrate saturation, stress state, strain range, void ratio, pore pressure, and stress history. Regardless of the test conditions, a distinct increase in the damping ratio with an increase in the modulus of hydrate-bearing specimens could be used to identify the hydrate occurrence. The stress and hydrate improve the modulus of hydrate-bearing specimens; however, the exponent enhancement of stress on the modulus of hydrate-bearing specimens is suppressed by high hydrate saturation. In addition, a rapid nonlinear decrease in the normalized modulus of hydrate-bearing specimens with high hydrate saturation occurred under identical strain increments, and the corresponding damping ratio also increased rapidly. Along with the modulus data of other synthetic and natural hydrate-bearing specimens determined using various methods, a definite exponential relationship between Eh = E0 ∗ en∗Sh and different parameter settings was established to satisfy various application conditions. In contrast, the Poisson's ratio of hydrate-bearing sediments should be determined with caution because of its relationship with specimen deformation or damage.