Integration of Geochemical Processes and Fracture Flow for Design of Standing Column Wells

在加拿大，30%的能源和53%的电力用于建筑物供暖或制冷。2004至2008年间，地热热泵与地下热交换器的使用在加拿大经历了近150%的增长。尽管它产生了显著的能源节约(高达60%)，但由于地下热交换器的高初始投资成本，建筑设计师采用这种绿色技术并不是一件容易的事情。 立柱井(SCW)是一种直接使用地下水的深层热交换器(最高可达500米)。尽管超临界水系统的建设成本可以比闭环系统低49%至78%，但超临界水系统在加拿大没有得到使用，主要是因为缺乏针对破裂含水层的有效设计工具，对与地下水的地球化学条件相关的风险(堵塞、结垢、溶解、藻类生长)存在误解，以及难以评估这些系统的维护成本。 裂隙渗流和地球化学过程的数值模拟在水文地质中有着广泛的应用。这项研究计划的新奇之处在于它应用于加拿大环境中的地球交换和能源节约。在拟议的研究计划范围内，我们打算开发和实验验证数值模型，以显著增加我们对SCW系统的最佳结构和操作的了解，并反过来指导未来的设计指南。为达致这项长远目标，当局计划进行六项计划： A-在热-水文地质SCW模型中集成地球化学反应-开发一个三维数值模型，模拟立柱井中发生的热、水力、水文地质和地球化学耦合过程。 B-实验验证A热-水文地质数值模型--通过现场实验验证A和C项目范围内开发的数值模型和分析解。 C-将超临界水之间的空间相互作用与光谱方法相结合--在光谱框架内，对超临界水系统中井之间发生的热力和水力相互作用进行综合，以预测到达热泵的地下水温度。 评估压裂流对节能的影响并制定指南-评估裂缝网络对进水温度的影响以及在SCW运行期间产生的节能，并建议设计指南。 E-比较SCW系统和常规系统的生命周期--根据加拿大的经济、气候和地质背景进行生命周期财务分析，并提出设计指南。 F-减轻地球化学条件对超临界水系统运行的影响--评估水文地球化学条件对直接利用地下水的超临界水系统运行的影响，并确定和比较潜在的缓解措施。 综合和研究超临界水运行期间发生的一些地球化学过程，应有助于制订缓解措施和实用的设计准则，并有助于降低超临界水系统的维护费用。在项目C范围内开发的模型将整合到GeoAnalyser中，这是一个基于网络的应用程序，由加拿大地质交换联盟资助，旨在帮助世界各地的设计者设计地理交换系统。此外，在项目D、E和F范围内制定的指导方针将被纳入加拿大CGC的“商业系统设计人员培训”课程。然而，拟议的研究计划最重要的影响将是形成一批训练有素的水文地质学家，专门从事开放式地质交换系统的设计和操作。

In Canada, 30% of energy and 53% of electricity is used to heat or cool buildings. The use of geothermal heat pumps coupled with ground heat exchangers has experienced a growth of almost 150% in Canada between 2004 and 2008. Despite the significant energy savings it generates (up to 60%), the adoption of this green technology by building designers is no easy matter due to the high initial investment cost of ground heat exchangers. Standing column wells (SCW) are deep heat exchangers (up to 500 m) that use directly ground water. Although the construction costs of SCW systems can be 49% to 78% lower than closed-loop systems, SCWs are not used in Canada mainly due to an absence of validated design tools for fractured aquifers, a misunderstanding of the risks associated to the geochemical conditions of the groundwater (clogging, scaling, dissolution, algae growth) and a difficulty to assess the maintenance costs of these systems. Numerical simulation of fracture flow and of geochemical processes is widely used in hydrogeology. The novelty of this research program resides in its application to geoexchange and energy savings in a Canadian environment. Within the scope of the proposed research program, we intend to develop and validate experimentally numerical models to significantly increase our knowledge of the optimal construction and operation of SCW systems and, in turn, orient future design guidelines. To address this long-term objective, six projects are planned: A - INTEGRATE THE GEOCHEMICAL REACTIONS IN A THERMO-HYDROGEOLOGICAL SCW MODEL - Develop a three-dimensional numerical model that simulates the coupled thermal, hydraulic, hydrogeological and geochemical processes occurring in a standing column well. B - VALIDATE EXPERIMENTALLY A THERMO-HYDROGEOLOGICAL NUMERICAL MODEL - Validate, through in situ experimentations, the numerical model and the analytical solutions developed within the scope of projects A and C. C - INTEGRATE THE SPATIAL INTERACTIONS BETWEEN SCWs WITH A SPECTRAL APPROACH - Integrate, in a spectral framework, the thermal and hydraulic interactions occurring between the wells of a SCW system to predict the groundwater temperature arriving at a heat pump. D - EVALUATE THE IMPACT OF FRACTURE FLOW ON ENERGY SAVINGS AND DEVELOP GUIDELINES - Evaluate the impact of the fracture network on the entering water temperature and energy savings generated during the operation of a SCW, and suggest design guidelines. E - COMPARE THE LIFE-CYCLE OF SCW AND CONVENTIONAL SYSTEMS - Perform life-cycle financial analyses based on the economic, climatic and geological context prevailing in Canada and suggest design guidelines. F - MITIGATE THE IMPACT OF GEOCHEMICAL CONDITIONS ON THE OPERATION OF SCWs - Evaluate the impact of the hydrogeochemical conditions on the operation of SCW systems which use groundwater directly and identify and compare potential mitigation measures. The integration and study of some of the geochemical processes occurring during the operation of a SCW should lead to the development of mitigation measures and practical design guidelines and contribute to reduce the maintenance costs of SCW systems. The model developed in the scope of project C will be integrated to GeoAnalyser, a web-based application financed by the Canadian Geoexchange Coalition and intended to help designers worldwide to design geoexchange systems. Additionally, the guidelines developed in the scope of projects D, E and F will be integrated to the course “Training for Commercial System Designers” given by CGC in Canada. However, the most significant impact of the proposed research program will be the formation of highly trained hydrogeologists specialized in the design and operation of open geoexchange systems.