The seepage characteristics of methane hydrate-bearing clayey sediments under various pressure gradients

As a wide range of clean energy, methane hydrate is mostly formed in low-permeability clayey sediments. And the gas production rate from low-permeability hydrate reservoirs will be greatly influenced by the seepage characteristics. In this study, a series of seepage experiments was performed on methane hydrate-bearing clayey sediments. The results show that water flow in clayey sediments with different hydrate saturations exhibits both Non-Darcy and Darcy flow behaviors. Additionally, the minimum threshold pressure gradient (TPG) is present during water phase flow of hydrate-bearing clayey sediments, which may be not favorable for methane hydrate exploitation. The minimum TPG firstly decreases and then increases with an increase in hydrate saturation, providing theoretical guidance for the pressure gradient used in depressurization process during methane hydrate exploitation to improve gas production rate. The water permeability (Kw) and the permeability coefficient (k’) firstly increase and then decrease with an increase in hydrate saturation. In addition, the water permeability increases gradually with decreases in the minimum TPG for clayey sediments with different hydrate saturations. The relationship between minimum TPG and water permeability is described by the power function as TPGmin=2.81231×10−4×Kw−0.57767. This relationship provides the basic permeability parameters for the numerical simulation of methane hydrate exploitation.