Study On Seepage Characteristics Of Deep Fracture Surrounding Rock And Its Influence On Geothermal Field In Typical Coastal Metal Mine

This paper takes the submarine metal mine Sanshan Island Xinli mine site as the engineering background,and applys COMSOL Multiphysics to establish a multi-fracture surrounding rock seepage and heat transfer model.The seepage characteristics of the surrounding rock and its influence on the ground temperature field under the intersection of multiple fractures are studied,which can provide a theoretical basis for the design and construction of deep mining projects in submarine metal mines and the prevention and control of hydrothermal disasters in mines.The main research and conclusions of this paper are as follows:(1)Sanshan Island Xinli mine is partly buried under the sea,covered by seawater,with developed tectonic fractures and strong permeability,and is a tectonic fracture-filled deposit with medium hydrogeological conditions.Influenced by groundwater,the rock temperature at the fracture zone is abnormal and the temperature gradient is large.The high temperature and high humidityd environment of the mine greatly affects the physical and mental health of workers,and there is a risk of sudden water and heat damage.(2)COMSOL Multiphysics was applied to establish a seepage model of multi-fractured perimeter rocks in submarine metal mines,and the seepage characteristics of the model were simulated and studied as follows:(1)The groundwater seepage velocity in the fractures of the perimeter rocks of the seabed metal mine shows a general trend of first decreasing,then smoothly flowing and finally increasing,and the maximum seepage velocity appears at the entrance and exit of the groundwater;the seepage velocity will change abruptly near the intersection point of the fractures,and the fractures containing non-flowing groundwater have less influence on the abrupt change value,while the fractures containing flowing groundwater have significant influence on the abrupt change value of the seepage velocity.The abrupt change of velocity and the maximum flow rate of multiple fracture intersection are the key points of concern for downhole safety control.(2)The larger the fracture angle is,the smaller the seepage velocity at the groundwater entrance and exit,the smaller the flow rate is,the more obvious the sudden change of groundwater seepage velocity at the fracture intersection;when the fracture diameter is in 0.5～2mm,the sudden change of seepage velocity at the fracture intersection is obvious,when the diameter is between 0.1～0.5mm,the sudden change of seepage velocity at the fracture intersection no longer occurs.The permeability of the surrounding rock is positively correlated with the seepage rate at the entrance of fractured groundwater.(3)The temperature field was added on the basis of obtaining the seepage model of multi-fractured rocks in mines to analyze the influence of seepage characteristics of rocks on the ground temperature field of the mine,and the results are as follows:(1)The farther the fracture enclosure is from the roadway,the higher the temperature is.At the same time,the fracture angle is negatively correlated with the average temperature of fracture II exit,and positively correlated with the average temperature of fracture IV exit;when the fracture diameter is at a low level,the cold front surface advances more slowly along the direction of groundwater flow,the larger diameter is,the faster the low temperature area develops,the more obvious the development along the direction of groundwater flow in the fracture,the average temperature of the exit also decreases faster with time.(2)With the increase of seepage velocity at the entrance of fracture II,the area of cooling area in the mine ground temperature field gradually expands.The larger the seepage velocity is,the higher the heat exchange efficiency between the low-temperature groundwater and the high-temperature surrounding rock,and the larger the heat exchange is;as the thermal conductivity of the surrounding rock increases,the right boundary of the cooling area in the ground temperature field gradually moves toward the entrance of the groundwater,and the area of the cooling area in the ground temperature field of the mine gradually decreases.