Ground Penetrating Radar prospection at the charterhouse of Bourgfontaine

International audienc

Theoretical analysis of long offset time-lapse frequency domain controlled source electromagnetic signals using the method of moments: Application to the monitoring of a land oil reservoir

International audienceWe present a sensitivity study applied to water front monitoring of an onshore oil reservoir, using a remote controlled source electromagnetic method (CSEM) with electric dipoles and a borehole‐to‐surface configuration. We have developed an optimized and parallelized code based on the method of moments, in order to study the influence of several static or time‐varying background uncertainties on the time‐lapse CSEM signal (also called 4‐D CSEM). Analysis of the relative and absolute variations in phase or quadrature of the time‐lapse signal induced by the fluid substitution process, inside the reservoir, has shown that the vertical electric dipole allows the shape of the water front to be monitored, while remaining less sensitive (compared to a horizontal electric source dipole) to the total volume of substituted fluid. We have examined the influence of missed anomalies (1‐D/3‐D), with more or less conductive properties, near to the ground surface or the reservoir, and with or without time‐varying properties. In most cases, the 4‐D signal behaves like a reliable filter, canceling almost all response anomalies. However, it can also lead to strong, local perturbations of the time‐lapse signal. We have also shown that in the presence of steel cased boreholes at the source location, or with outlying steel cased boreholes, the recording of exploitable data does not present insurmountable difficulties at low frequencies (∼1 Hz), and for a dense array of surface receivers. These positive results with CSEM monitoring suggest that minimal, coarse‐time 3‐D explorations should be used to ensure reliable interpretation of the monitored data

Glacier ice in rock glaciers: a case study in the Vanoise Massif, Northern French Alps

International audienceWe investigated the Sachette rock glacier, Vanoise Massif, Northern French Alps, using former equilibrium line altitude reconstruction from glacial deposits, aerial photograph analysis, and ground-penetrating radar (GPR). The rock glacier is a young (probably 0.15–0.16 m ns−1) and reflectors having a dipping-syncline structure, typical of true glaciers. Consequently, the rock glacier structure is described as being constituted of a glacial massive ice core embedded into diamictons. Our study of the Sachette rock glacier highlights possible significance of rock glaciers and interactions between glacier and permafrost in alpine environments

Ground Penetrating Radar prospection at the charterhouse of Bourgfontaine

International audienc

Full Waveform Inversion of Seismic Data for 2D Shallow Structures Imagery−Limitations and Perspectives

International audienc

Full Waveform Inversion of Seismic Data for 2D Shallow Structures Imagery−Limitations and Perspectives

International audienc

Comparison between DC ERT and Moving Multi-Depth Electrostatic Arrays in an Urban Context

International audienceA series of experiments was undertaken in the province Scania in southern Sweden with the aim to acquire a better knowledge about the electrical resistivity of the soil surrounding heating and water distribution pipes, in order to assess the risk of corrosion. Electrical Resistivity Tomography (ERT) and moving multi-depth electrostatic arrays have been applied to determine the resistivity distribution in an urban context along selected pipes. Implimentation of the ERT was done by drilling holes, in the mostly paved surfaces, and inserting electrodes with a gel to decrease electrode contact resistance. The moving multi-depth electrostatic arrays was implimented in a “sliding” carpet dragged along the lines. Direct comparison between ERT and “sliding” carpet results show a good coherence. This confirms the high interest of the second solution for in-town measurements due to its easy implementation. The interpretation of the data proved to be complicated and was not simply explained as a pipe embedded in a homogeneous layer, which show that a careful attention must be paid to other external information about the underground work history. One practical application might be the mean resistivity values of the medium surrounding the pipe(s), to be used as a tool by the pipe owner

Geophysical characterization of near-surface formations in the La Villa River catchment (Los Santos, Panama)

International audienc