Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Doctorat → Egypte → Application of Multi-dimensional Electrical Resistivity and Electromagnetic Induction Techniques to Explore the Groundwater Occurrences at El-Salloum Basin, Northwestern Coast, Egypt

Ain Shams University (2017)

Application of Multi-dimensional Electrical Resistivity and Electromagnetic Induction Techniques to Explore the Groundwater Occurrences at El-Salloum Basin, Northwestern Coast, Egypt

Zarif, Fardous Mohamed Abdel Hamid Mohamed

Titre : Application of Multi-dimensional Electrical Resistivity and Electromagnetic Induction Techniques to Explore the Groundwater Occurrences at El-Salloum Basin, Northwestern Coast, Egypt

Auteur : Zarif, Fardous Mohamed Abdel Hamid Mohamed.

Etablissement de soutenance : Ain Shams University

Grade : Doctor of Philosophy (PhD) in Geophysics 2017

Résumé partiel
The application of geophysical methods for the successful exploration of groundwater in sedimentary terrain requires a proper understanding of its hydrogeological characteristic, especially in arid and semi-arid areas in order to increase the possibility of successful drilling of water wells. Additionally, there is an increasing demand for geophysical surveying in areas of limited information regarding existing wells or hydrogeological data. However, new approaches were necessary to adopt geophysical techniques for subsurface investigations and to deal with special problems inherent in shallow geophysical surveying. In this context, increasing overall efficiency of the geophysical data, model quality, and their sensitivity and resolution of near-surface geological investigations comes into account first. The study area (El- Salloum Basin) extends for about 37 km along the Northwestern coast between Buqbuq at the West of Sidi Barrani and El -Salloum City at the western border of Egypt with a southward extension of about 22 km. It lies between longitudes 25.15º & 25.55º E and latitudes 31.35º & 31.50º N. The study area is characterized by very low relief and mild topography. A flat coastal strip 2-4 km wide is found behind the coastal ridges, located about 10 km east of El- Salloum town. The area between the coastal strip and the plateau has a rather pronounced relief and there are several terraces and a few large depressions to the scarp of the plateau. The northern scarp of the tableland (plateau) is dissected by a series of drainage lines (about 83 wadis). Surface water in El -Salloum basin is very limited most of the year due to unstable patterns of seasonal rainfall. The Middle Miocene rocks (Marmarica Formation) represent the oldest exposures in the investigated area with variable thickness, being controlled by the buried structures on which they have been deposited. The Marmarica Formation is exposed at the surface, forming the Diffa plateau and the bedrock of El-Salloum depression. This formation is considered as the watershed area that drains all the streams and rainfall to a common outlet (e.g. outflow of Wadi Arkeet). This succession is overlain by Pliocene and Pleistocene calcareous rocks, with Holocene and recently deposited white sands forming the coastal ridge. Borehole geological information is limited across the basin. Data of only three water wells are available in the study area (Desert Research Center (DRC), Abu Zreba (AZ) and Ogereen (OG) wells). These wells were drilled by the Desert Research Center. The Abu Zreba well is located towards the north of the study area and the depth to water is 17 m in Oolitic limestone. The DRC well is located in the NE portion of the coastal plain. The depth to water is 21 m and the water bearing formation is fractured chalky limestone interbedded with marl. Ogereen well is located in the southwest of the study area. The depth to water is 49 m in sandy limestone interbedded with dolomitic limestone. The area is affected by numerous NE and NW trending faults with well-developed joints and fractures on the scarp boundaries of El Salloum basin (Selim, 1969). The application of three geophysical techniques sensitive to the subsurface electrical conductivity at different scales proved to be an effective approach to groundwater exploration in El-Salloum basin. The present study aims at determining the vertical and horizontal extensions of the lithologic succession, determining the structural elements that affect the area of study (major and minor faults, fracture system…etc.), identifying the potential water bearing layer/layers, identifying the fracture zones which likely play an important role in determining groundwater occurrence and locating the most suitable sites for drilling groundwater productive wells. Depending on the lithologic succession and the depth to the targeted water bearing formation, geoelectrical methods, including 1D Vertical Electrical Sounding (VES) and 2D Electrical Resistivity Imaging (ERI) proved to be useful techniques in locating groundwater in both porous and fissured media because of their sensitivity to the rock conductivity and fluid flow. On the other hand, the VLF-EM method is considered a quick reconnaissance tool best suited for the identification of conductive zones with steep boundaries and can be particularly useful in locating water bearing fractures and other structures that control groundwater flow and characterized by resistivity contrast at the boundaries of fractured zones. Applying such integrated geophysical techniques (1D-VES, 2D-ERI and VLF-EM) is considered as a promising approach for exploring the water bearing fractured zones in the Middle Miocene Limestone (Marmarica Formation) in El Salloum Basin. The objectives of the present study had been achieved by conducting 18 1D-VES distributed all over the area as a grid of, approximately, 5 km spacing between VES locations. The geoelectrical resistivity field data were acquired using the earth resistivity meter SAS 1000 Terrameter. The Schlumberger array with current electrode spacing up to 300 m in the northern part of the basin and up to 1400 m in the southern part was used. The software IX1D (Interpex Ltd., USA), v. 3.39 was used for the quantitative interpretation of the 1D-VES data. It is a software package for Windows 9x which allows for forward and inverse modeling of 1-D Direct Current (DC) resistivity, Induced Polarization (IP), Magnetotelluric (MT) and Transient electromagnetic (TEM) sounding data. The quantitative interpretation was carried out depending on an initial model created from the available geological and hydrogeological information of the study area.

Présentation étendue (EULC)

Page publiée le 16 mars 2019