Nolwenn Lesparre

Muons tomography applied to geosciences and volcanology

Imaging the inner part of large geological targets is an important issue in geosciences with various applications. Different approaches already exist (e.g. gravimetry, electrical tomography) that give access to a wide range of information but with identified limitations or drawbacks (e.g. intrinsic ambiguity of the inverse problem, time consuming deployment of sensors over large distances). Here we present an alternative and complementary tomography method based on the measurement of the cosmic muons flux attenuation through the geological structures. We detail the basics of this muon tomography with a special emphasis on the photo-active detectors.

Direct prediction of aquifer thermal energy storage system efficiency using short-term push-pull tests

Aquifer thermal energy storage (ATES) systems are designed to recover in winter the heat stored in the aquifer during summer. In practice however, spatial heterogeneity or non-favorable hydrogeological conditions reduces the energy efficiency. In many cases, a deterministic approach is used to calibrate the subsurface component of those systems, neglecting the quantification of uncertainty. In this contribution, we propose to use the recently-developed prediction-focused approach to forecast the heat storage capacity of an alluvial aquifer. We compare the ability of two different push/pull tests to make this prediction. We first analyze the performance of the method using synthetic cases and validate the approach using field data. For both, we show that the method is able to forecast the posterior distribution with realistic uncertainty. We also identify the experiment which has the highest information content for the desired prediction. Then we forecast the long-term heat storage capacity of the aquifer and assess its uncertainty. This final result can be used to design properly the heat pump associated with the system.

Spatio-temporal Monitoring of Heat Storage in a Shallow Aquifer Using Electrical Resistivity 4D Imagery and DTS

The design of groundwater heat pumps requires a good understanding of the aquifer and heat flow conditions. Issues of short-circuit or recycling between cold and hot wells have to be carefully considered. Surface geophysical methods allow monitoring subsurface processes without additional perturbations of the medium. Within available methods, the electrical resistivity imagery (ERI) applied in time-lapse (TL) is appropriate. Here, we monitored with ERI and distributed temperature sensors (DTS) a heat plume propagation during an experiment of hot water injection in a shallow aquifer. DTS and TL ERI measurements acquired from two boreholes provide a local estimate of the heat propagation through the medium. TL ERI were also performed from a grid at surface to follow the 3D plume shape formation and evolution through time. The different complementary data validate the potential of surface TL ERI for monitoring in 3D the behavior of shallow heat plumes. ERI highlight the heterogeneity of the aquifer by distinguishing regions with higher or lower hydraulic conductivity. In the higher hydraulic conductivity zone, the heat might be evacuated through water flow, while in the lower hydraulic conductivity area heat storage is achievable. Thus, in that last region the plume temperature decreases progressively with time.