This study proposes a concept and presents a workflow to examine potential reasons for low injectivity of sandstone aquifers. Injection related problems are a major challenge for the sustainable utilization of geothermal waters. In order to completely understand and avoid the geothermal reinjection problems, potential problem sources acting on different scales should be taken into consideration. Thus, in the workflow, possible problem sources are considered on regional, reservoir and local scale and categorized into 1) effect of regional hydraulics (potential presence of overpressure and upward flow) 2) inadequate reservoir performance (limited extent, low permeability and performance) and 3) local clogging processes (particle migration, mineral precipitation, microbial activity). Hydraulic conditions are characterized by defining the pressure regime and the direction of vertical driving forces. The reservoir properties are given by determining the grain size and the size of the reservoir layers, as well as the permeability and the transmissivity of the reservoir and the capacity of the injector. Physical, chemical, and biological clogging processes are investigated by specifying the rock properties and determining particle content of the fluid; by analysing the type, probability and amount of the scaling and estimating the potential for corrosion; and by evaluating the possibility of biofilm formation. The concept and the workflow were first tested on a geothermal site (Mezőberény, SE Hungary, installed in 2012) that had to stop operation because of unsuccessful reinjection. The low injectivity of the well is a consequence of several separate problems and their interaction: Reservoir properties are insufficient due to low permeability and transmissivity of the reservoir and the limited vertical and horizontal extension of the sandstone bodies. Precipitation of carbonates, iron and manganese minerals is predicted in hydrogeochemical models and observed in solid phase analysis. Microbial material is produced from the particularly high organic content of the produced thermal water. Injection problems due to hydraulic effects are not expected since the regional pressure regime is slightly subhydrostatic. In summary, reservoir properties determine a low injectivity, which is further decreased to a critical level by the clogging processes. The proposed generalized concept guides a detailed reservoir and geothermal system analysis which is essential for a sustainable geothermal operation.

本研究提出了一个概念并提出了一个工作流程来检查砂岩含水层低注入率的潜在原因。注入相关问题是地热水可持续利用的主要挑战。为了完全理解和避免地热回注问题，应考虑作用于不同尺度的潜在问题源。因此，在工作流程中，在区域、储层和局部尺度上考虑可能的问题来源，并将其归类为 1) 区域水力学的影响（可能存在超压和向上流动） 2) 储层性能不足（范围有限，渗透率和性能低） 3) 局部堵塞过程（颗粒迁移、矿物沉淀、微生物活动）。液压条件的特征在于定义压力状态和垂直驱动力的方向。通过确定储层的粒度和大小，以及储层的渗透率和透射率以及注入器的容量来给出储层特性。通过指定岩石特性和确定流体的颗粒含量来研究物理、化学和生物堵塞过程；通过分析结垢的类型、概率和数量并估计腐蚀的可能性；并通过评估生物膜形成的可能性。该概念和工作流程首先在一个地热站点（匈牙利东南部的 Mezőberény，安装于 2012 年）上进行了测试，该站点因回注失败而不得不停止运行。井的低注入率是几个单独问题及其相互作用的结果：由于储层的渗透率和透射率低以及砂岩体的垂直和水平延伸有限，储层特性不足。碳酸盐、铁和锰矿物的沉淀在水文地球化学模型中预测并在固相分析中观察到。微生物材料是由产生的热水中特别高的有机物含量产生的。由于区域压力状态略低于静水压力，因此预计不会出现由于水力效应引起的注入问题。总之，储层特性决定了低注入量，通过堵塞过程进一步降低到临界水平。