Study On Seepage Characteristics Of Methane Hydrate Sediments Under Complex Conditions

Natural gas hydrate is widely distributed in the South China Sea and continental permafrost in China.It has many advantages,such as huge reserves,clean and environmental protection,and has the potential to replace traditional fossil energy.It will play an important role in China’s carbon peak carbon dioxide emissions and neutralization strategy in the future.At present,China has carried out mining tests for many times and achieved great success,but at present,many indicators such as gas production,gas production efficiency and engineering safety can not meet the requirements of mature large-scale production.The low permeability caused by the special geological conditions of hydrate reservoir is the main factor restricting the mining process.Establishing a reasonable and reliable permeability model and exploring its variation law is of great significance to promote the large-scale mining process.The sediments containing hydrate in the South China Sea are mainly silty clay,mixed with sandy soil particles.Silt accounts for more than 40%.Its permeability is seriously affected by the swelling and water sensitivity of soil particles and the particle size distribution data of soil samples.In the exploitation of hydrate,the decomposition of natural gas hydrate and the change of pore space caused by the change of geological stress also make the output of natural gas very unstable in commercial exploitation.Therefore,taking silty clay as the main experimental sample,this paper focuses on the effects of grading conditions,pore pressure,effective stress and other parameters on the permeability of silt sediments.The main work is as follows:1.In order to explore the variation law of gas phase permeability of silty sediments containing methane hydrate under complex conditions,the experimental platform of steadystate gas phase seepage of high-pressure hydrate is designed and built independently.Under the condition of meeting the temperature and pressure of natural gas hydrate synthesis,montmorillonite was used as sediment to study the variation law and trend of permeability with pore pressure in silty sediments with different initial water saturation.2.Under the condition of meeting the temperature and pressure of natural gas hydrate synthesis,montmorillonite is used as sediment to study the influence of different saturation on permeability change under the condition of hydrate decomposition,and to explore the role of effective stress in the above process.3.Mix quartz sand in different quality montmorillonite to make sediment matrix with different gradation.The permeability of different sediments with same hydrate saturation is tested,and the influence of sediment gradation on permeability change is studied.