Simulation Study On Hydraulic Circulation Characteristics And Influence Range Of Groundwater Circulating Well

As an in-situ remediation method,circulating well technology has been used abroad for groundwater remediation due to its advantages of being able to be combined with various remediation technologies and high remediation efficiency.The research on circulating well technology in China was still in its infancy.The circulation well uses underground water flow as a carrier to transport repair reagents or capture pollutants,and the repair effect is directly related to the hydraulic circulation effect.Quantifying the water flow characteristics and influence range of the circulation well,clarifying its influence by different factors,is of great significance for deepening the understanding of the hydraulic regulation theory of the circulation well,promoting the promotion and application of the circulation well technology,and even improving the repair effect.However,the mechanism by which the hydraulic circulation characteristics of circulating wells are influenced by different factors wass not fully understood at present,which restricts the characterization of the range of circulation influence.Therefore,strengthening the research on the circulation characteristics and impact range under the hydraulic drive of circulating wells,improving the hydraulic regulation theory of circulating wells,was of great significance for the application and promotion of circulating well technology in China.This study used COMSOL Multiphysics software as the technical platform to construct a numerical simulation system for circulation and solute transport under hydraulic drive in a circulating well.The hydraulic circulation characteristics and solute transport status under the operation of the circulating well were simulated,and systematic research was conducted from the evaluation of the impact range of the circulating well based on water head difference,the determination of the impact range of the circulating well based on solute transport,and the study of the impact range of the circulating well under special circumstances.The water head change caused by the operation of the circulating well was used as an indicator to evaluate the horizontal impact range of the circulating well.The tracer mass concentration injected from the injection port of the circulating well was used as an indicator to evaluate the horizontal and vertical impact range of the circulating well.Analyzed the effects of operating parameters,aquifer properties,and process parameters of the circulating well on the impact range of the circulating well,and constructed an evaluation method for the impact range.The main achievements were as follows:1)The influence range of the circulating well determined by the change in water head was positively correlated with the horizontal permeability coefficient（Kh）of the aquifer,the pumping and injection flow rate（Q）,and the operating time T of the circulating well,while negatively correlated with the vertical permeability coefficient（Kv）.Select three indicators:horizontal permeability coefficient,vertical permeability coefficient,and pumping water injection flow rate to construct the prediction equation for the influence range determined by the head changes of 0.001 m,0.01 m,and 0.1 m:T^0.4040.471Kh^0.3330.444[-（0.649～1.158）ln Kv+（1.594～6.511）].The prediction equation for the influence range determined by the change of 0.5 m water head is constructed using four indicators:horizontal permeability coefficient,vertical permeability coefficient,pumping and injection flow rate,and circulating well operating time:T^0.5050.508Kh^0.0630.071[-（0.389～0.496）ln Kv+（0.756～0.757）ln Q+（2.863～3.101）].The overall error between the estimated value of the formula and the corresponding simulated value is less than 20%.（2）As the operating time increases,the recirculation flow in the circulating well flow field reaches a further range.When the ratio of horizontal permeability coefficient to vertical permeability coefficient is less than 1,the water flow driven by the circulating well is mainly vertical flow,and when the ratio is greater than 1,the water flow is mainly horizontal flow.The change in the distance between the lower screen section and the waterproof bottom plate will change the position of the recirculation flow.An increase in the spacing between the upper and lower sieve sections can increase the vertical range of the recirculation flow.（3）The range of solute horizontal transport is positively correlated with the operating time T of the circulating well and the pumping and injection flow rate Q of the circulating well,while negatively correlated with the vertical permeability coefficient Kv of the aquifer and the length of the upper sieve section Lu.Select the above four factors to construct a prediction equation for solute horizontal transport range:T^0.672Q^0.307Kv^-0.124（-0.097Lu+2.864）.The vertical transport range of solute is positively correlated with the operating time T of the circulating well and the vertical permeability coefficient Kv,while negatively correlated with the horizontal permeability coefficient Kh and the length Ll of the lower sieve section.Use these four factors to construct a prediction equation for the vertical transport range of solutes:Kh^-0.172Kv^0.264(0.354T^-0.55Ll+6.167).Comparing the predicted value of the formula with the corresponding simulated value,it was found that the overall error was less than 27.3%.（4）The accumulation of operating time and the increase of flow rate will both increase the range of solute transport;The increase in the ratio of horizontal permeability coefficient to vertical permeability coefficient will lead to an increase in the horizontal transport range of solutes and a decrease in the vertical transport range;An increase in porosity will reduce the range of solute transport;With the increase of the length of the upper sieve section,the vertical distribution range of solute increases,and the solute concentration distribution at the upper and lower ends becomes concentrated.（5）Compared with the double screen section circulating well,the water head change caused by the height of the two suction ports in the three screen section circulating well is relatively small;Low permeability aquifers will hinder the transport of solutes,but have no significant impact on the range of influence of circulating wells determined by water head changes;Under the operation of dual circulation wells,most of the area between the two circulation wells forms circulating flow.The research in this paper provided a theoretical basis for characterizing the flow field morphology,solute transport,and the spatiotemporal variation of the influence range under hydraulic drive in circulating wells.To provide reference for the on-site layout of the circulating well and the optimization design of the circulating well structure.