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

Abstract

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.

Field Scale Mobility and Transport Manipulation of Carbon-Supported Nanoscale Zerovalent Iron in Fractured Media

“…27 Most of these studies attributed nZVI limited migration mostly to deposition due to filtration of large aggregates and/or attractive interactions with the porous medium. 17,27,28,31 Straining was also reported to play a role, though with larger microscale ZVI. 29 On the laboratory scale, straining was demonstrated to play a significant role in nZVI retention, particularly for finer grain size sand.…”

“…Groundwater IS, when reported, was in the range of 0.002 to 0.60 mS/ cm. 17,27,31 In laboratory settings, several authors have illustrated that, under high IS conditions, macromolecule stabilizers' electrosteric repulsion outweigh double layer electrostatic attraction. 18,22,24 In the present study, the effectiveness of high stabilizer concentrations in mitigating double layer attractive forces under high IS conditions is demonstrated on a field scale.…”

Review: Hydrogeology of weathered crystalline/hard-rock aquifers—guidelines for the operational survey and management of their groundwater resources

“…The role of weathering in creation of the fractured layer is also directly or indirectly confirmed by the data sets of most of the authors working on HRA. See for instance Davies et al (2014) and the countries cited previously, as well as Chilton and Smith-Carington (1984), Chilton and Foster (1995), Howard (1999, 2000), Chirindja et al (2017), Dickson et al (2018), Muchingami et al (2019) and Vassolo et al (2019) for Africa; Chambel (2014) for Portugal; Comte et al (2012) for Ireland; Tan et al (2017) for Denmark; Riber et al (2017) for Sweden; Francés et al (2014) for Spain; Krasny (1996) for Central Europe; Baiocchi et al (2014Baiocchi et al ( , 2016 for the Mediterranean Europe; Chou et al (2014) and Chuang et al (2016) for Taiwan; David et al (2014) for Australia; Riber et al (2017), Jahns (1943, Hart (2016), Sanford (2017), Meyzonnat et al (2018) and Setlur et al (2019) for North America, etc. Even if several authors have not attributed the fractures to weathering processes, some others keep an ambiguity on this genetic relationship, while others do not challenge or discuss this issue at all, at least for the uppermost crust (0-2 km; Achtziger-Zupancic et al 2017;Ingebritsen and Gleeson 2017).…”

Preferential Paths of Air-water Two-phase Flow in Porous Structures with Special Consideration of Channel Thickness Effects

“…Chuang et al . 22 characterize the preferential flow paths between boreholes in fractured rock using a nanoscale zero-valent iron tracer test, concluding that further detailed investigations on the preferential paths in real porous structures are required. Liu et al .…”