FINITE ELEMENT ANALYSIS OF MICRO-SEEPAGE IN HYDRATE-BEARING QUARTZ SANDS BASED ON DIGITAL CORES

In this study, the distribution characteristics of gas, water and hydrate in hydrate-bearing quartz sands under different saturation are acquired by X-ray computed tomography (CT). The change of liquid phase permeability is calculated using the finite element method. The flow of fluid in the pores is simulated and the three-dimensional velocity distribution of the pore fluid under the assumed boundary conditions is obtained. The results show that the liquid phase permeability in quartz sand increases gradually with the decrease of hydrate saturation. When the hydrate saturation decreases from 56% to 39%, the liquid phase permeability value of quartz sand increases to the maximum. At the end of hydrate decomposition, the permeability does not increase rapidly with the increase in effective porosity. The CT scan image shows that some methane bubbles are trapped in quartz sand pores and throat. Due to the Jamin effect, the flow of liquid is hindered to a certain extent, which leads to the decrease of liquid phase permeability growth rate. In this study, a calculation method of liquid phase permeability and liquid velocity based on the real pore characteristics of the hydrate-bearing quartz sand is established, which can provide a reference for the study of the evolution mechanism of micro seepage in the process of hydrate exploitation.