Experimental Study On The Influence Of Freezing Wall On Groundwater Temperature Field And Flow Field During Oil Shale In-situ Mining

The industrial development prospect of oil shale in-situ mining is broad,but it will also have a great impact on the groundwater environment.Therefore,to study the changes of groundwater temperature field and flow field during the freezing process of freezing wall in ICP in-situ mining technology,to explore its characteristics and mechanism of action,and on this basis,a reasonable and feasible design plan for freezing wall was put forward.It could provide a theoretical basis for economically and effectively preventing the impact of in-situ oil shale mining on groundwater environment.In this paper,on the basis of ascertaining the basic background of freezing wall technology in oil shale in-situ mining and understanding the principles of oil shale in-situ mining technology,a comprehensive simulation experiment platform for freezing wall refrigeration system and hydrogeology was established.The experiment and numerical simulation of oil shale in-situ frozen wall technology were analyzed,and the influence laws and mechanisms of different influencing factors on the temperature field and flow field were analyzed.Based on this,a reasonable and feasible design plan for the frozen wall was proposed,and the results were obtained as follows:?1?It could be seen from the experiment that the freezing wall formed when the medium was coarse sand was the thickest and the temperature droped the fastest,followed by medium sand and finally fine sand.Under the same medium condition,the flow rate with large hydraulic gradient was fast,the thickness of the frozen wall expanded slowly,and the frozen wall was thin.The common points of the flow fields formed under different hydraulic slopes and medium conditions were that the water level line upstream of the freezing well was concave toward the axis of the freezing well arrangement,and the water level line downstream of the freezing wall was also concave toward the axis of the freezing well arrangement.After that,the velocity of the water flow was uniform and the direction was single.The freezing range was different under different hydraulic gradients.The larger the freezing wall range,the greater the change in water flow direction.?2?The experimental model was generalized,the groundwater flow field model under the influence of the in-situ oil shale mining frozen wall was established,and the Fluent software was used to solve it.The experimental schemes under different conditions were simulated separately,and the results were the same as the experimental results.The influencing factors of freezing wall formation were analyzed,and the influence of different media,initial soil temperature,groundwater flow rate,water convection heat transfer coefficient and freezing well temperature on groundwater temperature field and flow field were simulated.It could be seen that the greater the thermal conductivity of the medium,the greater the latent heat of phase change,the lower the temperature of the soil,the lower the flow rate of groundwater,the larger the natural convection heat transfer coefficient of water,and the lower the temperature of the freezing well,the greater the downstream freezing range and the area where the velocity is 0 m/s.?3?Applying the results of the experimental size numerical model to the size of the test site,the hydrogeological conditions was generalized,and a model was established for solving.The measurement method of the non-interference zone and its area was proposed,and the effects of the number of freezing wells,the spacing of the freezing wells,the shape of the freezing wall,the temperature of the freezing well,and the groundwater flow rate on the area of the non-interference zone were analyzed through numerical simulation.According to the simulation results,the greater the number of freezing wells,the greater the spacing of freezing wells,the larger the groundwater flow rate in suitable scale,and the larger the area of non-interference zone.The area of the non-interference zone where the freezing wells were arranged in a linear shape was the largest.When the area of the non-interference zone was the largest,the temperature of the freezing well was 230.15K.?4?According to the simulation results of different combinations of main influencing factors,the optimal layout plan of the freezing wall was obtained to maximize the area of the non-interference area.It could be seen that the optimal value combination was that the number of freezing wells was 11 wells,the arrangement shape was linear,the spacing of freezing wells was 2.4m,the temperature of freezing wells was 230.15K,and the flow rate of groundwater was 3×10^-6m/s,so the area of non-interference area was 240.57m².This thesis has important academic significance and application value to study the influence law and mechanism of freezing wall on groundwater temperature field and flow field during in-situ oil shale mining.The research has important guiding significance for the actual production work,and has certain value for the prevention and treatment of environmental problems such as oil shale pollution of groundwater.The research results and numerical simulation technology can be extended to scientific research and production in other similar areas.