NSG2021 27th European Meeting of Environmental and Engineering Geophysics

In 1991–2001 the all coal mines in the Lower Silesian Coal Basin (LSCB) were closed and remediated. In the middle of the 1990s mine restructuring process started at the Upper Silesian Coal Basin (USCB). At that time 65 coal mines were operational. In 2019 22 mines were still active. The main aims of this presentation are to determine the origin of soil gases in the USCB and LSCB and evaluate gas hazard caused by secondary migration of coalbed methane and carbon dioxide from Carboniferous coal-bearing strata to near-surface zone connected with the restitution of groundwater level to the original position (“piston effect”). For evaluating gas hazard surface geochemical survey and determining the origin of soil and coalbed gases, stable isotope analyses and simulation of generation of thermogenic gases by hydrous pyrolysis experiments were performed. Comprehensive geochemical, geological and hydrogeological studies carried out in the zones of closed mines in the USCB and LSCB allowed for detecting the surface range of occurrence of anomalous concentrations of methane and carbon dioxide at the surface, the mechanism of the flow of these formation gases into the near-surface zone and establish to what an extent the local population living in post-mining areas is hazarded.

The paper deals with a direct time domain modelling of impulsively driven GPR dipole antenna above a homogeneous lossy half-space aiming to estimate the energy stored in the near field. The space-time dependent current is obtained by numerically solving the space-time Hallen integral equation and Pocklington equation via different approaches. The obtained results are compared to the results obtained via NEC and Inverse Fast Fourier Transform (IFFT). Provided the current is known one may calculate the charge distribution along the wire by using the one-dimensional version of the continuity equation. Knowing the space-time distribution of current and charge along the dipole antenna, time domain (TD) energy measures involving spatial integrals of squared values of transient current and charge, pertaining to the energy stored in the electric and magnetic field, respectively, of dipole antenna, are evaluated. Furthermore, total power measure defined as time derivative of the total energy measure is computed. Some illustrative computational examples for transient current, TD energy and power measures are given in the paper.

Seismic data contain rich information carried by different types of waves, such as direct arrivals (P- and S-waves), reflections, diffractions and surface-waves. In order to utilize a specific type of wave, one needs to isolate this wanted signal from others. We propose a method to extract and/or remove mainly the dispersive surface-waves based on their geometrical property in the shot-receiver-time domain for seismic data acquired along 2D acquisition profiles. We first assemble all shot gathers into a pseudo 3D data with dimensions of shot locations, receiver locations, and time. The shot-receiver-time domain enables us to process the data along different dimensions, not restricted to the shot domain only. With the assumption of a 1D velocity model, we find that the dispersive surface-waves in a shot gather behave linearly in a time isochrone, which cuts through all shots and receivers. The linear geometrical property of the surface-waves in the time isochrone allows us to extract them efficiently and effectively using for example curvelet-based transforms. By applying the method along the time isochrones for the time samples where surface-waves are present, surface-waves can be extracted from the pseudo 3D data. We exemplify this method using a synthetic data and a field data.

Ground Penetrating Radar (GPR) data with two different antenna frequencies i.e. 250 and 300 MHz were used to characterize the spatial distribution of the mine tailings and also image the ground-water level in the tailing repository area of an abandoned mine site in Yxsjöberg. GPR result, after processing provided high-resolution image of the subsurface down to maximum ca. 3.2 m depth which indicated higher for the instrument with 250 MHz antenna frequency, compared to 0.7 m effective penetration depth indicated by the instrument with 300 MHz antenna. The vertical continuation of the tailings was identified down to ca. 0.7 m in the results from both antennas and ground water table was indicated at ca. 3 m depth using the 250 MHz antenna, consistent with data from the nearby well. Self-potential (SP) data indicated steady results; however, incompatible with the topography variations, which is presumably produced due to 3D topography variations being compared with 2D SP data. The link between SP data and topography variations and thereby, ground water movement can be further studied using a 3D SP measurement to better understand the direction of the ground water movement and also check its correlation with topography variations at the site.

Lost circulation is one of the most common problems in the drilling of oil and gas wells where mud escapes through natural or induced fractures. Lost circulation can have severe consequences from increasing the operational cost to compromising the stability of wells. Recently, polymeric formulations have been introduced for wellbore strengthening purposes where it can serve as Loss Circulation Materials (LCMs) simultaneously. Polymeric LCMs have the potential to be mixed with drilling fluids during the operation without stopping to avoid non-productive time. In this study, the significance of most common conventional mud additives and their impact on the gelation performance of Polyacrylamide (PAM) / Polyethyleneimine (PEI) has been investigated.

This work helps in better understanding the process of using polymeric formulations in drilling activities. It provides insights to integrate gelling systems that are conventionally used for water shut-off during the drilling operation to replace the conventional loss circulation materials to provide a higher success rate.

Since early days definition and targeting of ore bodies at Malmberget have been done with success by geophysical methods by way of ground gravimetric and geomagnetic exploration methods. Recent reworking of pre 1980s surface gravity and vertical component magnetic field measurements showed a coincident but prominent north-south oriented anomaly within the eastern limits of the exploration permit. Because the area is largely free from infrastructural development, aside from the nearby railway track running parallel to the anomaly for some length, it was considered a good site to test the passive seismic method. Collected data was processed using body-wave seismic intereferometry followed by the conventional reflection seismic procedures. The obtained seismic sections show that the anomaly identified by gravity and magnetic surveys is detected at a depth of 450 to 550m and that the causative reflector plunges approximately 40 degrees to the north. Seismic data were dependably processed to a depth of 2.5 km opening the possibility to derive important structural information.

Traditional geoelectric array configurations, such as e.g. the Wenner-Schlumberger or the Dipole-dipole, may be very effective in one-dimensional or robust two-dimensional investigations, but they are not sufficiently sensitive to SESEP inhomogeneities, which have a Small Effect on the Surface Electrical Potential distribution due to their small size and/or large depth or small resistivity contrast to the host. Their characterization is possible by applying quasi null arrays, which provide very small signals above a homogeneous half-space. Such arrays produced very good results in numerical investigations. In this paper their field applicability is demonstrated which has been heavily questioned. The quasi field analogue modelling experiments validated all of the numerical modelγling results. Many or all of the γ11n arrays could detect prisms and vertical sheets located at depths larger than those detectable by traditional geoelectric configurations. The horizontal resolution of the γ11n arrays, too, proved to be better than that of the traditional arrays.

On the basis of this quasi field analogue study, γ11n arrays are expected to be well applicable to indicate SESEP targets (e.g., caves, mines, tunnels, tubes, cables, dykes, fractures), or to follow small variations in the subsurface conditions (monitoring of e.g. dams or waste deposits).

Treatment wetlands are engineered systems for small communities that have been designed to take advantage of the same processes that occur in natural wetlands, the main problem affecting treatment wetlands is the development of clogging wich leads to the exclusion of some subparts of the filter, becoming ineffective for the treatment critically reducing the lifetime of the plant. Time-domain induced polarization is used to image clogging distribution of a gravel filter from a horizontal subsurface flow treatment wetland. Experimental data performed on the laboratory demonstrates the linear relationship between the normalized chargeability and the amount of clogging in the gravel filter because of the substantial increase of the cation exchange capacity caused by clogging coating these grains. Therefore, we were able to convert the normalized chargeability tomograms obtained with the field data into a 3D distribution of the percent clogging. This method allows to identify the zones were the clogging has accumulated through the filter and therefore predict preferential flow paths and dead flow zones. This is an important task to plan preventive measures and anticipate the filter obstruction that may decreases the effectiveness of the wastewater treatment system.

This study contributes to an ongoing project of geothermal heating/cooling system design for an office building in Quebec City, Canada.

In this study, a heat tracing experiment using time-lapse cross-borehole ERT was performed. The time-lapse ERT inversion was conducted in order to image the spatiotemporal resistivity changes due to the heat injection.

The inverted models were compared qualitatively to the pumping/injection rate log and temperature logs at different depths in the monitoring well. These comparisons demonstrate that the inversion results show the same trend as the temperature logs, notably they both clearly show the injection and the recovery phase of the experiment.

Our results indicate that cross-borehole ERT could be used as an additional monitoring tool for heat injection tests.

The mining operations of Ouels, also named Castel-Minier, close to the village of Aulus-les-Bains in the Pyrenees, was mainly effective between the 13th and 16th centuries. It was the most important mine in the French Kingdom during the 14th century, and was operated for silver, cupper and lead. Today, it is a site for archaeological studies and the archaeologists are specially interested in the cavities left by the exploitation. It is with the aim of retrieving the voids left in a remote area that geophysical facilities are requested, following the discovery of a 20th century plan attesting to the existence of a shaft and a vein in this area.

Two geophysical methods have been implemented: Electrical Resistivity Tomography (ERT) and microgravimetry. The first has been used on two parallel profiles spaced 15 m apart, and allowed the detection of a very high resistive body that could fit a cavity at less than a depth of 5 meters. On the other side, microgravimetry revealed two anomalies. It seems to confirm the one seen by ERT, while a second anomaly may attest to a deeper cavity hypothetically lying at 15 to 20 m depth. These hypotheses are compatible with the archaeological expectations.