Simulation On Methane Emission In Depressurization Exploitation Of Marine Hydrate In Sea Area

With the decline of traditional energy sources,research on non-traditional energy sources has gradually increased.A large amount of methane hydrate in the formation is considered an important and clean potential energy source.China has good natural gas hydrate occurrence conditions and resource prospects.Natural gas hydrates have been discovered in the South China Sea and the Qinghai-Tibet Plateau permafrost,and natural gas hydrate resources are abundant.Since 1999,China has conducted several natural gas hydrate surveys in the South China Sea.In 2007,the Guangzhou Marine Geological Survey conducted drilling analysis on the Shenhu area of the South China Sea and obtained natural gas hydrate samples,which made the South China Sea Shenhu sea area become China.Gas hydrate research area.In this paper,the Shenhu sea area in the South China Sea is used as the research area.Based on the physical data,pore water characteristics,petrological characteristics and mineral composition analysis of the actual strata in the area,the hydration during the mining process is carried out when the vertical well is used for depressurization.TOUGH+HYDRATE software is used to simulate the whole decomposition process,and the influence of methane fugitive environment in natural gas hydrate depressurization process is simulated to determine the influence of methane dispersion on the surrounding marine environment during hydrate development.The rate of decomposition of matter is first increased,then decreased,and then gradually increased.The accumulated methane retained in the hydrate layer is less than the accumulated methane production,and a part of the methane gas generated by the decomposition of the hydrate diffuses into the overlying layer,increasing with time.The methane gas entering the overlying layer gradually increases.The pressure of depressurization has a significant effect on the total gas production and the total amount of fugitive gas in the hydrate layer.As the wellbore pressure decreases,the total gas production gradually increases,and the total amount of fugitive gas gradually decreases.The methane dispersion in the hydrate mining process mainly has the following two aspects to the surrounding marine environment.(1)As the simulation time passes,the anaerobic oxidation reaction occurs and the anaerobic oxidation reaction consumes a large amount of sulfate.This causes the interface between sulfate and methane to gradually move toward the bottom of the sea,and the concentration gradient of methane is also larger,and the interface depth is shallower.As the reaction time increases,the fumed methane and the sulfate infiltrated in the top seawater accumulate at the interface.The anaerobic oxidation reaction is the most intense,the more pressure,the greater the methane emission concentration,and the stronger the anaerobic oxidation reaction.It has an impact on the stability of the marine ecological environment.(2)The fugitive gas during the depressurization process has a significant impact on the stability of the seabed slope in the study area.The analysis found that the greater the pressure drop of the mining pressure,the more pressure,and the greater the effective pressure.As the pressure of mining decreases,the safety factor of the model decreases gradually.With the subsequent mining,the effective stress of the whole model increases gradually,and the lower the safety factor,the more likely the landslide will occur.