| Abstract: | The pneumatic fracturing technique is used to enhance the permeability and porosity of tight unconsolidated soils (e.g. clays), thereby improving the effectiveness of remediation treatments. Azimuthal self potential gradient (ASPG) surveys were performed on a compacted, unconsolidated clay block in order to evaluate their potential to delineate contaminant migration pathways in a mechanically-induced fracture network. Azimuthal resistivity (ARS) measurements were also made for comparative purposes. Following similar procedures to those used in the field, compressed kaolinite sediments were pneumatically fractured and the resulting fracture geometry characterized from strike analysis of visible fractures combined with strike data from optical borehole televiewer (BHTV) imaging. We subsequently injected a simulated treatment (electrolyte/dye) into the fractures. Both ASPG and ARS data exhibit anisotropic geoelectric signatures resulting from the fracturing. Self potentials observed during injection of electrolyte are consistent with electrokinetic theory and previous laboratory results on a fracture block model. Visual (polar plot) analysis and linear regression of cross plots show ASPG lobes are correlated with azimuths of high fracture strike density, evidence that the ASPG anisotropy is a proxy measure of hydraulic anisotropy created by the pneumatic fracturing. However, ARS data are uncorrelated with fracture strike maxima and resistivity anisotropy is probably dominated by enhanced surface conduction along azimuths of weak ‘starter paths‘ formed from pulverization of the clay and increases in interfacial surface area. We find the magnitude of electrokinetic SP scales with the applied N2 gas pressure gradient (??PN2) for any particular hydraulically-active fracture set and that the positive lobe of the ASPG anomaly indicates the flow direction within the fracture network. These findings demonstrate the use of ASPG in characterizing the effectiveness of (1) pneumatic fracturing and (2) defining likely flow directions of remedial treatments in unconsolidated sediments and rock. ?? 2008 Elsevier B.V. All rights reserved. |
| Genre: | Article |
| ProdID: | 70032874 |
| Citation Author: | Wishart, D. N.; Slater, L. D.; Schnell, D. L.; Herman, G. C. |
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| Citation End Page: | 144 |
| Citation Issue: | 3-4 |
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| Citation Language: | English |
| Citation Larger Work Title: | Journal of Contaminant Hydrology |
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| Citation Number Of Pages: | 11 |
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| Citation Search Results Text: | Hydraulic anisotropy characterization of pneumatic-fractured sediments using azimuthal self potential gradient; 2009; Article; Journal; Journal of Contaminant Hydrology; Wishart, D. N.; Slater, L. D.; Schnell, D. L.; Herman, G. C. |
| Citation Start Page: | 134 |
| Citation Volume: | 103 |
| Citation Year: | 2009 |
| Type: | citation/reference |
| Text: | Hydraulic anisotropy characterization of pneumatic-fractured sediments using azimuthal self potential gradient; 2009; Article; Journal; Journal of Contaminant Hydrology; Wishart, D. N.; Slater, L. D.; Schnell, D. L.; Herman, G. C. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1016/j.jconhyd.2008.09.023 |
| Date Other: | Thu, 1 Jan 2009 00:00 -0600 |
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