André Revil

The self-potential method : theory and applications in environmental geosciences

Foreword Preface 1. Fundamentals of the self-potential method 2. Development of a fundamental theory 3. Laboratory investigations 4. Forward and inverse modeling 5. Applications to geohazards 6. Application to water resources 7. Application to hydrothermal systems 8. Seismoelectric coupling Appendix A: a simple model of the Stern layer Appendix B: the u-p formulation of poroelasticity References Index.

Three‐Dimensional Electrical Resistivity Tomography of the Solfatara Crater (Italy): Implication for the Multiphase Flow Structure of the Shallow Hydrothermal System

The Solfatara volcano is the main degassing area of the Campi Flegrei caldera, characterized by 60 years of unrest. Assessing such renewal activity is a challenging task because hydrothermal interactions with magmatic gases remain poorly understood. In this study, we decipher the complex structure of the shallow Solfatara hydrothermal system by performing the first 3-D, high-resolution, Electrical Resistivity Tomography (ERT) of the volcano. The 3-D resistivity model was obtained from the inversion of 43,432 resistance measurements performed on an area of 0.68 km2. The proposed interpretation of the multiphase hydrothermal structures is based on the resistivity model, a high-resolution infrared surface temperature image, and 1,136 soil CO2 flux measurements. In addition, we realized 27 soil Cation Exchange Capacity (CEC) and pH measurements demonstrating a negligible contribution of surface conductivity to the shallow bulk electrical conductivity. Hence, we show that the resistivity changes are mainly controlled by fluid content and temperature. The high-resolution tomograms identify for the first time the structure of the gas-dominated reservoir at 50 m depth that feeds the Bocca Grande fumarole through a ~10-m-thick channel. In addition, the resistivity model reveals a channel-like conductive structure where the liquid produced by steam condensation around the main fumaroles flows down to the Fangaia area within a buried fault. The model delineates the emplacement of the main geological structures: Mt Olibano, Solfatara crypto-dome, and tephra deposits. It also reveals the anatomy of the hydrothermal system, especially two liquid-dominated plumes, the Fangaia mud pool and the Pisciarelli fumarole, respectively.

Design and Implementation of Geophysical Monitoring and Remote Sensing during a Full-Scale Embankment Internal Erosion Test

This paper describes the conception and deployment of a multi-geophysics and remote sensing approach to monitoring internal erosion in a test embankment that was loaded and brought to failure in Booneschans, Netherlands in fall 2013. IJkdijk is a full-scale field testing embankment constructed to facilitate sensor validation testing for monitoring embankment loading and failure conditions. The embankment was constructed of a single zone high plasticity clay embankment with sand foundation. The test embankment was subjected to reservoir loads simulating tidal and storm surge conditions known to induce internal erosion in actual embankments. Geophysical monitoring of subsurface conditions was pursued using self-potential and passive seismic methods. Concurrent terrestrial lidar remote sensing methods was implemented to track millimeter scale deformation. Each of these monitoring approaches was implemented successfully and yielded useful spatial and temporal information throughout the seven days of testing, from initial reservoir loading to completion of the test.

Variations of petrophysical properties and spectral induced polarization in response to drainage and imbibition: a study on a correlated random tube network

We implement a procedure to simulate the drainage and imbibition in random, 2-D, square networks. We compute the resistivity index, the relative permeability and the characteristic lengths of a correlated network at various saturation states, under the assumption that the surface conductivity can be neglected. These parameters exhibit a hysteretic behaviour. Then, we calculate the spectral induced polarization (SIP) response of the medium, under the assumption that the electrical impedance of each tube follows a local Warburg conductivity model, with identical DC conductivity and chargeability for all the tubes. We evidence that the shape of the SIP spectra depends on the saturation state. The analysis of the evolution of the macroscopic Cole–Cole parameters of the spectra in function of the saturation also behaves hysteretically, except for the Cole–Cole exponent. We also observe a power-law relationship between the macroscopic DC conductivity and time constant and the relative permeability. We also show that the frequency peak of the phase spectra is directly related to the characteristic length and to the relative permeability, underlining the potential interest of SIP measurements for the estimation of the permeability of unsaturated media.

Self-potential: A Non-intrusive Ground Water Flow Sensor

ABSTRACT The flow of the ground water in an aquifer or during pumping test generates an electrical current (called the streaming current), which is of advective nature. The resulting electrical field (streaming potential field, one of the components of the self-potential field) can be remotely measured at the ground surface or in boreholes. We first discuss the underlying physics of this electrokinetic effect and the role of the electrical double layer coating the surface of the grains. We show how the drag of the excess of electrical charge of the pore water by the flow is equivalent to a source current density. Then, we discuss the metrological aspects, the type of voltmeter and electrodes required to carry out good measurements in field conditions. Two applications are discussed in steady-state conditions. The first is dedicated to the flow of water in shallow aquifers. In this case, the streaming current and the conduction current are nearly balanced and, inside the aquifer, the electrical equipotenti...

Hydrothermal system of the Papandayan Volcano from temperature, self-potential (SP) and geochemical measurements

Papandayan volcano in West Java, Indonesia, is characterized by intense hydrothermal activities manifested by numerous fumaroles at three craters or kawah, i.e. Mas, Manuk and Baru. The latter was created after November 2002 phreatic eruption. Since 2011, numerous volcano-tectonic B events are encountered and the volcano was set on alert status on several occasions. The purpose of the present study is to delineate the structure of the summital hydrothermal system from Self-Potential (SP), soil temperature and gas concentrations in the soil (CO2, SO2 and H2S) data. This combination of geophysical and geochemical methods allows identification of the weak permeable zones serving as preferential pathways for hydrothermal circulation and potential candidates to future landslides or flank collapses. This study is an on-going collaborative research project and we plan to conduct electrical resistivity tomography (ERT) and also Induced-Polarization (IP) surveys. Additional data would allow the 3D imaging of the s...