Characterization of preferential flow paths between boreholes in fractured rock using a nanoscale zero-valent iron tracer test

Chuang, Po-Yu; Chia, Yeeping; Liou, Ya-Hsuan; Teng, Mao-Hua; Liu, Ching-Yi; Lee, Tsai-Ping

Characterization of preferential flow paths between boreholes in fractured rock using a nanoscale zero-valent iron tracer test | Caractérisation des chemins d’écoulement préférentiel entre deux forages en zone fracture à l’aide d’un essai de traçage avec un traceur nanométrique de fer zéro valent Caracterización de trayectorias preferenciales flujo entre perforaciones en una roca fracturada utilizando una prueba con trazador de hierro cerovalente a escala nanométrica 采用纳米级零价铁示踪实验描述断裂岩中钻孔之间的优先流通道 Uso de nano partículas de ferro zero valente como traçador para a caracterização de caminhos preferencias de fluxo da água subterrânea entre poços instalados em aquíferos fraturados

2016

Recent advances in borehole geophysical techniques have improved characterization of cross-hole fracture flow. The direct detection of preferential flow paths in fractured rock, however, remains to be resolved. In this study, a novel approach using nanoscale zero-valent iron (nZVI or ‘nano-iron’) as a tracer was developed for detecting fracture flow paths directly. Generally, only a few rock fractures are permeable while most are much less permeable. A heat-pulse flowmeter can be used to detect changes in flow velocity for delineating permeable fracture zones in the borehole and providing the design basis for the tracer test. When nano-iron particles are released in an injection well, they can migrate through the connecting permeable fracture and be attracted to a magnet array when arriving in an observation well. Such an attraction of incoming iron nanoparticles by the magnet can provide quantitative information for locating the position of the tracer inlet. A series of field experiments were conducted in two wells in fractured rock at a hydrogeological research station in Taiwan, to test the cross-hole migration of the nano-iron tracer through permeable connected fractures. The fluid conductivity recorded in the observation well confirmed the arrival of the injected nano-iron slurry. All of the iron nanoparticles attracted to the magnet array in the observation well were found at the depth of a permeable fracture zone delineated by the flowmeter. This study has demonstrated that integrating the nano-iron tracer test with flowmeter measurement has the potential to characterize preferential flow paths in fractured rock.

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