Effect of groundwater flow in vertical and horizontal fractures on borehole heat exchanger temperatures
2015 (English)In: Bulletin of Engineering Geology and the Environment, ISSN 1435-9529, E-ISSN 1435-9537, Vol. 74, no 2, 479-491 p.Article in journal (Refereed) Published
Vertical closed loop systems, also known as borehole heat exchangers (BHEs), are a popular way of extracting the ground source heat energy. Primary factors affecting the performance of BHEs are the thermal and hydrogeological properties of the subsurface. Groundwater flow is known to potentially influence heat transport and system performance. The effect of groundwater movement is more commonly studied under homogeneous conditions. However, in heterogeneous fractured rocks, BHEs are more common than horizontal or open loops due to lack of sufficient soil layers and productive aquifers. The finite-element modelling shows that fractures can play an important role in BHE functioning. Especially, vertical open fractures (≥1 mm) near the borehole (≤10 m) can have a considerable impact. Although increase in fracture aperture continuously affects the subsurface and BHE temperatures, the increase in its effect progressively lessens. Depending on the distance and aperture, one major fracture influencing the BHE operation performance can be identified; yet a larger number of fractures may govern heat transport (thermal plume outline) and thermal recovery. Individually, horizontal fractures may have less influence than vertical fractures. However, as the density of horizontal fractures increases, their impact can be major, exceeding that of fracture aperture. In particular, we propose that measurements of rock thermal properties be combined with fracture mapping, to better analyse the thermal response testing results and integrate the configuration of fractures in design and layout of the BHE(s). This is particularly valid for (vertical) fractures not intersecting with the borehole.
Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2015. Vol. 74, no 2, 479-491 p.
Crystalline rock, FEFLOW, Fractured rock, Groundwater flow, Heat transport, Thermal response test
Energy Systems Geology Oceanography, Hydrology, Water Resources Geosciences, Multidisciplinary Geophysics
IdentifiersURN: urn:nbn:se:kth:diva-151297DOI: 10.1007/s10064-014-0626-4ISI: 000358381900014ScopusID: 2-s2.0-84957727997OAI: oai:DiVA.org:kth-151297DiVA: diva2:747547
QC 201508272014-09-172014-09-172015-08-27Bibliographically approved