PONENTE: LAURA DEL VAL (PHD STUDENT)
Subtitulo tesis: A multimethodological approach based on Fiber Optics Distributed Temperature Sensing
Fecha/ Hora defensa: Miércoles 3 de Junio a las 4:00pm
Link en Google Meet: https://meet.google.com/jod-wyna-nve
Detailed characterization of coastal aquifers is essential for proper management of coastal groundwater resources, and coastal areas in general. Still, there is a general lack of systematic monitoring and detailed characterization of the seawater intrusion (SWI). This thesis aims to provide new approaches and methodologies for the characterization of coastal aquifers, and in particular for the SWI dynamics.
At a first stage, a new coastal experimental site was constructed in the Riera de Argentona, 40km North from Barcelona. Three relatively new monitoring systems were tested to characterize the SWI in this site: Cross-Hole Electric Resistivity Tomography (CHERT), Time Laps Induction Logging (TLIL) and Fiber Optics Distributed Temperature Sensing (FO-DTS). From these techniques we were interested in further exploring the use of FO-DTS in a coastal setting. First, an active FO-DTS application to measure groundwater fluxes is proposed. This was done by interpreting the temperature curves generated by heating a single FO cable and measuring the temperature evolution in the same cable. Second, the use of FO-DTS passively, thus by measuring natural temperature changes, is proposed to monitor the SWI. Before field testing, the use of temperature as a tracer of the SWI was studied theoretically. To do this, two numerical models were used to explore the coupled behavior of temperature and solutes at the fresh-salt water interface. Based on the results from the modelling exercise and the conceptual framework resulting from it, FO-DTS was tested for continuously monitoring of the SWI during one year and a half. In parallel, an alternative methodology is proposed to remove environmental trends and noise from measured groundwater heads resulting from pumping tests carried out in coastal aquifers.
The set of methods proposed in this thesis expands the tools and the resolution available to characterize the SWI, contributing to improve our knowledge about coastal aquifers.
Ponente: Tybaud Goyetche (Ph D Student)
Jueves 28 de Mayo a las 12:30 h
Tidal response analysis is a unique low-cost aquifer scale test to determine hydraulic diffusivity (D_h=K/Ss =T/S), and thus the connectivity to the sea, using the analysis of the aquifer response to sea level oscillations. Yet, the method is hardly used in management policies mainly because it never behaves according to traditional theory (analytical solution of Jacob (1950) and Ferris (1952)). To illustrate the complexities of tidal response interpretation, we apply the tidal method to a series of well observations located in a Mediterranean coastal aquifer (Argentona experimental site, Barcelona, Spain). From a harmonic analysis over a two-month period, we identify the main tidal constituents and quantify their amplitude and phase shift (delay between the tidal fluctuation and the well response) at the reference open water and the observation wells. Two different effects are considered: (i) the hydraulic effect caused by the hydraulic connection between the differentiated aquifer layers and the sea, and (ii) the mechanical effect generated by the compression of the undersea aquifer portion due to tidal fluctuations and its propagation landward. Our numerical simulations rely on a specific geometry of the aquifer; therefore, it has allowed us to refine the conceptual model of the studied site and calibrate its hydraulic parameters. We find that hydraulic diffusivity estimations derived from the amplitude attenuation are significantly different from those derived from the phase shift by more than one order of magnitude, when the aquifer is assumed to be homogeneous and only the hydraulic effect is considered. A stratified configuration with different aquifer layers and aquitards and including mechanical effects is required to reproduce properly the head response observed in the wells, particularly for the phase shift calculation. Furthermore, after calibrating the main constituents separately we observe that a decrease in the tidal period leads to higher diffusivity estimates, revealing a scale effect. Our numerical results demonstrate that mechanical effects play a drastic role in aquifer response to tidal oscillations, even in shallow thin aquifers, and must be accounted for proper characterization and estimation of hydraulic parameters in coastal aquifers.
SEMINARIO GRUPO DE HIDROLOGÍA SUBTERRÁNaEA
UNIDAD ASOCIADA CSIC-UPC
Geothermal energy in deep volcanic areas
Jueves 14 de Mayo de 2020 a las 12:30h
Sala virtual GOOGLE MEET
Para unirte a la reunión de vídeo, haz clic en este enlace: https://meet.google.com/snb-qdkn-eex
Link al seminario on-line:https://drive.google.com/file/d/11Cjv9uNLroY0Pnm3m6bP81-qTxvaUvXg/view?usp=sharing
Geothermal energy can produce electricity and heat utilizing the high temperature of the Earth interior. The current installed capacity in EU-28 (1 GWe) should increase by 20 fold to cover the 5% of the electricity demand. Such increase is necessary as part of the solution to change the current energy model, which relies in an 85% on hydrocarbons. The adaptation to a carbon-free energy market can be speeded up by using geothermal energy in deep volcanic areas, in which water is in supercritical conditions. While a conventional geothermal well produces 3-5 MWe, a well in supercritical conditions of water can produce 50 MWe. Yet, this technology is not exempt of risks. In particular, we investigate the induced seismicity risk of a doublet reproducing the conditions found at the bottom hole of the IDDP-2 project. We find that, contrary to most fluid injection projects, seismicity will be mainly induced by cooling rather than by pressure changes. The cooled region around the re-injection well progressively increases, causing cooling-induced stress changes that affect fault stability. Simulation results show that the rate of induced seismicity at the fault increases four orders of magnitude between 7 and 10 years of operation. The induced seismicity rate increase depends on the specific properties of each site, but the lifetime of supercritical geothermal projects will be eventually limited by cooling-induced earthquakes. Nonetheless, properly managed volcanic areas have a huge potential to provide low-carbon electricity.
Parisio, F., Vilarrasa, V., Wang, W., Kolditz, O. and Nagel, T., 2019. The risks of long-term re-injection in supercritical geothermal systems. Nature Communications, 10: 4391
SEMINARIO GRUPO DE HIDROLOGIA SUBTERRÁNEA
Mechanisms and upscaling of dispersion in porous media from the pore to the Darcy scale
a cargo de
Jueves 5 de Marzo a las 12:15 h en Departamento de Ingeniería Civil y Ambiental, Modulo D2-Aula CIHS, Planta Baja
We show that finite P éclet transport can be predicted from the Eulerian velocity distribution of the medium, which is a flow property, together with the correlation distance and tortuosity of the sample, which are geometrical properties. The main assumption is that the medium is made of a network of
tubes that all exhibit a Poiseuille velocity profile. This allows for the derivation of the distribution of mean velocities in the domain from the Eulerian velocity distribution. This distribution is the main input to our model since it contains the true statistics that particles experience. It is due to the di ffusion process that forces particles to sample the full velocity profile over a throat. Predictions from the model are validated against direct particle tracking simulation on real digitized samples for a wide range of P éclet regimes.