Presentation: Cold water injections as innovative smart tracer technique in hot fractured aquifers

Event: IAH 2019 Congress – Groundwater management and governance coping with water scarcity, Malaga (Spain)
Presentation by Richard Hoffmann, Wajid Uddin, Pascal Goderniaux, Alain Dassargues, Jean-Christophe Maréchal, Subash Chandra, Virendra Tiwari, Adrien Selles


Abstract

Robust transport simulations for sustainable management of groundwater in fractured rocks, need accurate observation data about fracture and matrix processes. In aquifers with naturally hot groundwaters (i.e., 30 ºC in South India), heat injections can become difficult and cumbersome, considering strong density influences.

Injecting cold water is a much more promising and innovative tracer technique. Injecting cold water reduces the energy stored in the matrix, as heat is released to the colder circulating fluid in the fractures. Thus, cold water injections can produce very informative reference data for managing hot fractured aquifers using groundwater flow and cold plume transport numerical modeling.

Heat and cold water tracer tests have been performed for the first time in Choutuppal nearby Hyderabad in South India. Sub-horizontal fractures have been intersected by 30 wells drilled in a weathered granite aquifer. A saprolite layer of in average 14 m thickness covers the fractured granite system. The natural granite aquifer background temperature varies yearly between 30 ºCand 35 ºC During the experiments, the natural aquifer background temperature was around 30.3 ºC

The most explored well (CH03) is used as injection well for all experiments. There, an inflatable double packer system isolates one sub-horizontal fracture connecting CH03 with a pumping well (CH12) located at a 5.5 m distance. This set-up allows successive 1-hour injections of 1000 L of hot water (ΔT = +20 ºC) and cold water (ΔT = -20 ºC).

The peak arrival times measured in CH12 are 41 minutes for heat and 51 minutes for cold water. The peak temperature difference measured in CH12 for heat is ΔT = +3.3 ºC and for cold water ΔT = -2.9 ºC This is consistent with the fact that density and viscosity decrease with higher temperatures. Remarkably, cold water shows a slightly faster first arrival. It might indicate that storing energy is slightly faster initiated than releasing energy from the matrix.

First interpretations of the observed tailings show that for hot water injection, the subsequent temperature decrease (back to the background T) seems slower than the observed temperature increase after the cold water injection. It seems that cooling the matrix (i.e. reducing the energy level) is slightly more time consuming and difficult than heating the matrix (i.e. storing energy).

More experiments, e.g. repetitions of these experiments focusing stronger on the tailing for imaging matrix processes, complementing cold water tracing experiments (e.g. push-pull) and the possible parallel use of geophysical imaging tools, are ongoing. Nevertheless, the first tracer tests with cold water injections generated reference data that are very informative for further transport modeling (e.g. using Monte Carlo simulations).


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Presentation: “Identification of 3D fracture distribution and fracture connectivity by combined Ground Penetrating Radar Imagery and Tracer Tests at the Äspö Hard Rock Laboratory, Sweden

Event: CBH Studiedag Hydrogeofysica – Journée d’étude Hydrogéophysique, Rochefort (Belgium), May 2019
Presentation by Justine Molron, Niklas Linde, Ludovic Baron, Peter Andersson, Diane Doolaeghe, Tanguy Le Borgne, Johanna Ragvald, Jan-Olof Selroos, Caroline Darcel, Philippe Davy


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Presentation: Fractured aquifer heterogeneity characterization for advanced transport modelling based on multiple single fracture tracer tests

Event: 45th IAH – Korea (International Association of Hydrogeologists), 2018
Presentation by Richard Hoffmann, Pascal Goderniaux, Angélique Poulain, Alain Dassargues


Abstract

Assessing fractured rocks, like a complex double porosity chalk, requires an advanced heterogeneity characterization and preferential pathway quantification. This contributes for reducing the uncertainty of transport predictions for protecting this excellent drinking water suppliers. With flowmeter tests and optical imaging, a horizontal main fracture between two adjacent 7.55 m distant wells is figured out. Injecting jointly 70 h heat and two solute pulses in a dipole configuration shows a strong heat delay and temperature rebound due to matrix reactions. Using dissolved gases jointly with a solute show, that the higher the tracer diffusivity the higher the confronted flow heterogeneity.

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