Exploitation Activities Analysis And Potential Hazards Prevention Of Marine Gas Hydrate

Marine gas hydrate(MGH)has large reserves,low pollution and high energy efficiency,and it also has great development potential and broad application prospects.Due to the complexity of hydrate reservoir conditions and the temperature-pressure limitation of the equilibrium zone,there are many problems in the exploitation of marine gas hydrate,and improper exploitation is liable to cause serious geological and environmental hazards.Based on the extensive collection of literatures,this paper comprehensively analyzes theoretical methods and numerical calculations to study the decomposition mechanism of marine gas hydrates,the influence of different exploitation factors under thermo-hydro-mechanical coupling,the stability of production wells and exploitation reservoirs,and potential disaster prevention research.The main research results are as follows:(1)The effect of hydrate saturation on gas production rate has the best value.The higher the temperature,the greater the influence of gas pressure on gas production rate.Temperature has little effect on Darcy velocity but great influence on porosity,and the overall seepage effect does not change significantly.The outlet pressure has a great influence on Darcy velocity.The larger the pressure difference,the greater the effective stress changes,and the permeability is inversely proportional to the production pressure difference.The initial permeability is proportional to seepage effect,which lead to the pore stress decreases while the effective stress increases,and the porosity is less affected by the permeability.(2)The angle of the production branch well increases,resulting in a decrease damage at the joint,and the seepage effect around the borehole is weakened,and also the displacement mainly occurs around the wellbore and gradually decreases;the support force plays a major protective role in production well;the outlet pressure has a great influence on the seepage effect around the production wells.With the increase of pressure,the pressure difference decreases and the damage degree of the wellbore decreases(3)The larger decomposition of hydrate reservoir,the greater the reduction of safety factor.The displacement of stratum and the trend of landslide show different changes with the hydrate reservoir as the boundary line;The influence of buried depth on safety factor decreases first and then rises,which critical depth is 125 m;The plastic strain development and safety factor values influenced by the slope angle are positively correlated with the slope angle and have obvious regionality.(4)Potential hazards in marine hydrate exploitation are classified into marine geological hazards,marine ecological and environmental hazards and marine engineering disasters.The whole lifecycle prevention management can be divided into pre-preparation stage,mid-control stage and post-protection stage.To achieve this goal,we can adopt the "three-step" strategy of realizing economic exploitation from trial production in the short term,maintaining a certain level of economic exploitation in the medium term and forming a global hydrate resource sharing mechanism in the long term.