Experimental Study On The Formation And Stability Of CO₂ Hydrate Caprocks Research And Effect Evaluation

With the continuous development of society,the demand for energy is also increasing endlessly.With the gradual consumption of traditional fossil energy,natural gas hydrates,as a kind of new energy source with huge energy content and widely existed in the seabed and permafrost,has entered the eyes of researchers in various countries.With the deepening of research,countries such as the United States,Japan,and China have begun trial mining of natural gas hydrate reservoirs in their permafrost regions or sea areas.Among the many mining methods,the most commercial prospects is the depressurization method,but natural hydrate reservoirs do not have a mature caprocks,which reduces mining efficiency during mining and is prone to seafloor methane gas leakage and geological disasters such as tsunami earthquakes.This thesis is based on the method of depressurization mining.The experimental equipment built by the laboratory is used to study the formation and stability of CO₂ hydrate caprock and the one-dimensional simulated depressurization mining and effect evaluation experiment of CH₄ hydrate.Specific research content includes:?1?Study on the formation and stability of CO₂ hydrate caprock.A CO₂ hydrate caprock was formed in a self-built reaction kettle and its stability was investigated.It was found that the CO₂ hydrate caprock formed by adding sodium dodecyl sulfate?SDS?is denser and thicker,has better sealing effect,can withstand higher pressure difference?7475 k Pa?and is stable for a long time?than 24 h?.And low temperature is good for the maintenance of the cover layer is not destroyed.?2?One-dimensional simulated depressurization experiment and effect evaluation experiment of CH₄ hydrate.Explore the effects of hydrate promoter SDS and overlying CO₂ hydrate caprock on the depressurization process.The experiment found that after adding SDS,the gas production was basically unchanged compared with the blank control group,but the water yield was reduced by 16%,which effectively increased the gas-water ratio.When the CO2 hydrate capping layer is used for mining,the gas-water ratio is up to 5935.1?L/L?at the initial stage of mining,and the mining efficiency is extremely high,but the cap layer cannot maintain the entire mining process and is easily destroyed.The SDS added to form the cap layer is also very easy to block the production well and related pipelines,which affects the mining efficiency.