Study On Seepage Characteristics Of Hydrate-bearing Sediments Under Loading

As a clean energy with huge mining potential,natural gas hydrate(NGH),an ice-like compound,widely exists in the permafrost-associated layers and submarine margins.Due to the certain permeability of hydrate reservoir which is a porous medium with,the seepage characteristics impact on the gas and water flow in the exploitation of NGH and further determine the development and economics of mining technology.For this reason,a series of researches on pore percolation characteristics of hydrate deposits have been conducted at home and abroad.It's noted that the depressurization method is suitable for the hydrate reservoir in proper temperature and permeability,and the most remarkable feature is that it is the most economical mining method without continuous excitation.However,up to now,there are few studies on the effect of volume change of soil on pore flow in hydrate-bearing sediments.Therefore,in this study,the effect of pore percolation of hydrate deposits under different loads was focused on and studied systematically.In this paper,we firstly reformed the existing test bed for the seepage of hydrate-bearing sediments,and then studied the pore flow in the hydrate-bearing sediments of the sewer with different loads.Besides,the full coupling control equation of the seepage and deformation of hydrate deposits was systematically studied by using COMSOL software,and the comparison between other published examples with the model in this paper were also conducted.The following conclusions are drawn.1.Due to the compaction of pore space and pore throat,the gas permeability of the hydratebearing clay under high axial stress is less than that under the low effective axial stress.2.The energy transport model of pore medium in the process of hydrate decomposition was established,and the coupling laws of the physical quantities associated with the decomposition of hydrate under different drainage,exhaust and heat transfer conditions at the local position were analyzed.3.Compared with the experimental results of Masuda and the examples in Uchida,the practicability and reliability of the model were confirmed.For depressurization,the model can accurately describe the decomposition of hydrate,the decrease of pressure and the endothermic phenomena caused by gas production.For the thermal decomposition,the model can also accurately give rise to temperature rise,gas saturation and pressure rise.Finally,through comparison and analysis,it was confirmed that the model established in this study could effectively simulate natural gas production and temperature change,which would be of great significance for natural gas mining.