浅部含水层THC耦合作用下无机胶体运移堵塞造成地下水源热泵回灌困难的机理研究

Geothermal systems are applied in order to use the heat source for cooling, heating or also to produce energy. When injecting water into an aquifer, clogging occurs, which affect the movement, attachment(also deposition, retention, colmatage) and detachment(also shear, unclogging, decolmatage) of inert suspended particles in recharge water. The consequence is a diminution of porosity, block of the flow pathways. The decrease of aquifer's permeability due to chemical, physical or biological processes，thus makes the system ineffective, expensive and complicated in maintenance. This study we look at the influence of temperature\ hydraulic\ chemical variations of groundwater on the colloid clogging effect in porous aquifers, and focuse on colloid clogging problem in shallow sand aquifer in geothermal heat pump system in Wuhan area in which the typical stratum is floodplain aquifer. Laboratory study is used to understand clogging processes. Upscale sand-column experiment and sand-box experiment will be conducted to analysis the colloid dispersion, transport and precipitate progress in different temperature\ hydro-chemical conditions and different sand structures, which resembles conditions in porous media neighboring hydraulic recharge well. Then we will analysis the colloid clogging effects on the permeability evolution of aquifer stratum during long-term artificial recharge and establish the colloid aggregation and deposition effect model based on the T-H-C (Thermo- Hydraulic- Chemical) coupling framework. Several different operational systems in the Wuhan area are investigated and used as field observations in numerical modeling and validation.

由于各种堵塞造成地下水回灌困难，地源热泵技术对地下水乃至生态环境可能造成严重负面影响。本项目以地下水源热泵回灌系统中无机胶体运移絮凝堵塞机理作为重点，以浅部砂性土多孔介质含水层为研究背景，依托武汉地区二元地层典型热泵工程开展研究。通过不同规模砂柱和砂箱模拟控制试验，再现温度-水流-化学单因素和耦合作用下胶体动水运移-絮凝-沉积过程及其对含水层渗透性变化的影响，分析造成地层损害的水化学和水动力控制条件，确定不同水流速度下的粘粒絮凝临界浓度，建立回灌井周边水动力砂层迁移胶体絮凝阻塞模型；在研究渗流/温度场演化规律的基础上，分析不同的介质孔隙度、渗透率、弥散度的空间变化，建立含水层受到胶体絮凝堵塞影响的渗流场演化模型；研究含胶体生成和阻塞的全耦合THC数学模型，开发计算程序，基于依托工程进行现场条件下回灌堵塞的多场耦合模拟和地层絮凝损害预测和验证。研究成果将为解决地下水回灌困难问题提供理论指导。

由于各种堵塞造成地下水回灌困难，地源热泵技术对地下水乃至生态环境可能造成严重负面影响。本项目以地下水源热泵回灌系统中无机胶体运移絮凝堵塞机理作为重点，以浅部砂性土多孔介质含水层为研究背景，依托武汉地区二元地层典型热泵工程开展研究。通过对含水层渗透率非均质性空间分布参数的试验与建模，分析含水层多孔结构特性对胶体颗粒运移过程影响，建立水力条件对颗粒运移-脱落-淤积过程的理论模型，开展了温度-渗流耦合作用下胶体颗粒生长-絮凝-切割的模拟，基于已开发的地下水源热泵系统饱和-非饱和含水层固液气三相的THM耦合程序，完成考虑颗粒迁移-堵塞效应的多场耦合模拟和地层絮凝损害预测和验证。