MAPPING DEEP GROUNDWATER RESOURCES, ARABIAN PENINSULA
CASE STORY
The project was initiated and coordinated by Guideline Geo’s distributor in the region and the purpose was to show the ability of the TEM (Transient ElectroMagnetic) method to map depth, quantity and quality of the groundwater resources.
A remote and dry survey area, located 1000 m above sea level and with no springs or other indication of groundwater resources what-so-ever, was chosen for the evaluation of the ABEM WalkTEM instruments.
Knowledge of the geology and hydrogeology in the survey area is sparse and only information from general geological mapping is available in the area. This information combined with local inspection of the geology during the field campaign works as a baseline in evaluation of the geophysical results.
SOLUTION
The fieldwork was conducted by a representative from Guideline Geo AB assisted by our local partner in the region, Mr. Najeeb Rashid Abdullah Al-Mugheiry representing Infinite Geological Solutions LLC accompanied by a field crew of four persons.
The equipment used for the survey comprised an ABEM WalkTEM Tx/Rx, a TX60 transmitter, RC5 and RC200 antennas and 40×40 m as well as 100×100 m transmitter loops. Transmitted current in Low Moment was 2 Amps and in High Moment 55 Amps.
The data were processed and inverted in Aarhus SPIA TEM software from Aarhus Geosoftware and visualized in sections and horizontal sliced maps in Aarhus Workbench, also from Aarhus Geosoftware.
RESULTS
The geophysical result from the survey is visualized in the section below. The vertical bars indicate the TEM soundings along the section line.
Low resistivity layers (resistivity < 40-50 ohmm) reflect clay- or silt-rich layers. In this interval, decreasing resistivity reflects increasing content of clay/silt. High resistivity layers represent layers of sand, gravel, sandstone or limestone. The layer of very high resistivity seen from approx. 800 meters until 500 meters above sea level is interpreted as layers of sandstone or limestone above the groundwater table.
The drop in resistivity from >300 ohmm to 100 ohmm at approximately 500 meters above sea level is interpreted as the regional groundwatertable located within a layer of sandstone or limestone.
Geophysical results
Based on the geophysical results, a preliminary interpretation of the limestone bedrock interface is produced:
Geological results
ACKNOWLEDGEMENT
Guideline Geo AB wishes to express our gratitude to Mr. Najeeb Rashid Abdullah Al-Mugheiry from Infinite Geological Solutions LLC based in Muscat, Oman for local liaison and valuable assistance when collecting the data.
