First EAGE Conference on Near Surface in Latin America

Silver was mined around Gomez Palacio, Durango, Mexico in Colonial times. Small mining operations also occurred in historic times (the 1930s) in the La Soledad mineral claim, northwest of Gomez Palacio city. Here, historical accounts call for an unmarked, lost, abandoned mine shaft that stopped operations nearly a century ago. Vein-type and manto-type mineralization of hydrothermal origin and an abandoned mine are reported within the survey area. The present near-surface 2D electrical resistivity imaging survey was done to search for an unmarked, old, and abandoned mineshaft within the La Soledad mineral claim. The survey comprises five resistivity profiles with variable orientations, covering approximately an area of 1 square km. The smooth, robust, and damped least-squares inversion methods were used to invert the resistivity data; however, successful results are not attributed to a single inversion method. The average imaging depth is estimated at approximately 65 m. The results are satisfactory and suggest an abandoned, shallow, and small mine gallery network with two backfilled mine shafts. Low-resistivity anomalies adjacent to the high-resistivity anomalies in all profiles suggest shallow mineralization zones.

We present an overview of an ambitious geophysical program undertaken by Vale to characterize both tailings storage facilities (TSF) properties around existing mine sites as well as an exploration program for iron ore. Historic magnetics data, geological surveying, borehole information and newly-collected RESOLVE® helicopter frequency domain electromagnetics (EM) and magnetic gradient data is being modelled with 3D joint inversion. We outline the survey goals, data collected, and inversion modeling methodology and show some of the emerging results.

In the present energy transition phase, we must decrease the carbon dioxide footprint of indispensable hydrocarbon energies worldwide, and increase the usage of renewable energies, such as geothermal energy. The increasing interest in carbon dioxide storage monitoring and geothermal exploration for a cleaner low-carbon energy future make passive and active electromagnetic (EM) instrumentation essential technologies to support the reduction of greenhouse gas emissions during the energy transition phase. Passive EM methods, such as AMT (audiomagnetotellurics) and MT (magnetotellurics), employ natural energy as incoming plane waves as the source recorded by receivers that measure the magnetic and electric fields. Active EM methods, so-called controlled-source electromagnetic (CSEM) methods, require a high-power transmitter that generates artificial EM fields with prescribed signal characteristics and an array of receivers that measure the magnetic and electric fields. The Long-offset transient electromagnetic (LOTEM), a type of CSEM method and AMT and MT instrumentation, can monitor fluids' injection and propagation patterns in a carbon-storing formation or a geothermal producing field. These methods are also adequate for geothermal exploration.

Post-critical reflections are usually disregarded during stacking, since the post-critical reflections have their phases shifted compared to the pre-critical ones. Stacking is an important step in seismic processing to increase the signal-to-noise ratio, and, for this reason, an approach which is able to correct the phase shift in post-critical wavelets is desirable. Therefore, we propose a two-step inversion procedure based on performing spectral recomposition to recover signal parameters, such as peak frequency and amplitude, in order to estimate the instantaneous phase variation of each wavelet in a reflection event. With this, we can perform the phase correction in each trace to rotate the wavelets that are shifted after post-critical reflections for optimal stacking with pre-critical reflection.

In near-surface seismic surveys, there are several complex structures that increase the challenge to perform a reliable stratigraphic characterization. A geological structure with a layer which presents an abnormally low velocity increases the difficulty during the seismic processing. To overcome this kind of problem, we propose an analysis of the seismic data during the velocity analysis step in order to detect an abnormally low velocity of a layer by using a nonhyperbolic multiparametric travel-time approximation. With this analysis, it is possible to estimate which layer of the formation has an abnormally low velocity and its spatial position.

The potential of Ground-penetrating radar in geological materials has been discussed. The application areas for GPR are diverse. In this work, high-quality radar data acquired in the field are illustrated by selected case histories.

Two case histories show how radar has been used to map fractures and changes of rock type to 15 m range from metamorphic rocks. Another case history demonstrates how radar has also been used to detect and map the fresh bedrock and the groundwater channels in a landslide. The radar results demonstrate the utility of the high-resolution radar method as an aid for paleoseismological investigations and extrapolation of the information. The radar method is becoming economically viable and it is increasingly used in geosciences.

One of the most important aspects to highlight is that the GPR technique offers a rapid, non-invasive-high-resolution method for detecting and mapping geological features in the subsurface for a specific area. This geophysics method is easy to use and it permits to shows, in the field and real-time, the structures present in an area under study. GPR can be used for a variety of applications that previously could not be solved quickly or required expensive prospecting techniques to be considered practical.