Presentation: Potential Impact of Groundbased Gravity Gradiometer for Subsurface Reservoir Monotoring

Event: EGU General Assembly, Vienna (Austria) 2019
Presentation by Anne-Karin Cooke, Cédric Champollion, Pierre Vermeulen, Nicolas Le Moigne and Sébastien Merlet

Abstract

Ground-based gravity measurements can provide accurate constrains on the water storage dynamics of subsurface reservoirs. At the scale of the measurements time-lapse gravity experiments allow to monitor the water mass balance taking into account both the saturated and the unsaturated zone.

One major characteristic of the gravity measurement is the integration of all water masses across scales: gravity variations can be the effect of continentalscale soil humidity or aquifer (such as seen by GRACE measurements) and of local effects (such as the umbrellaeffect of a building or reservoir heterogeneities). The vertical gravity gradient is similar to gravity while showing a higher sensibility to local masses. The interest of the gradient for subsurface features such as caves is well known.

The objective of the presentation is the specific potential of gravity vertical gradient monitoring for water reservoir studies. The study is first based on existing measurements of gravity gradients time series (with a relative spring gravimeter): can significant hydro-logical signals be detected? Then based on numerical simulations, the potential of future ground-based for reservoir monitoring is investigated.

The capability of the gravity gradient method to detect heterogeneities (contrary to theclassical gravity) is evident: for example the classical Bouguer plate approximation often used to convert gravityinto equivalent water height (even in heterogeneous area such as karst) has no effect on the gravity gradient, hence new models need to be applied that combine gravity and gravity gradient measurements.


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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


ESR4_Molron_v02_iah_belge_chapter_version_website


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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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