270
K. S. Gemail et al.
the same resistivity curve may produce many interpreted curves (Koefoed 1979).
Depends on the geologic information and the available data of 16 boreholes (Gamma
ray and resistivity logs), a good initial model was suggested during the inversion
process by. During these procedures, some layer parameters were fixed based on the
available layer thicknesses which obtained from the close borehole information as a
ground truth.
In addition to the DC resistivity field survey, sixty water samples were gathered
from the shallow well pumping from Taref aquifer (60–120 m) to cover the whole
area (Fig. 7). Using typical calibrated field equipment, the pH, Temperature (T),
Total Dissolved Solids (TDS) and Electrical Conductivity (EC) were tested in field.
The GPS system of GARMIN GPSMAP 60Cx, was used to verify the geographical
coordinates of each sample points.
4 Results and Discussion
4.1 Aquifer Characterizations
Resistivities of geological materials vary over a wide range, based on mineral composition, degree of saturation, clay content, and TDS (McNeill 1980; Edet and Okereke
2002). The resulting 1D resistivity models were calibrated with the lithologic unites
from the nearby boreholes. Figure 8 shows examples of the correlation between
sounding points 8 and 19 with B-45 and T-9 boreholes, respectively (for location
see Fig. 7). Depending on this calibration, a spectrum of resistivity for the different
lithologic units in the studied area; could be delineated as listed in Table 1.
To illustrate the aquifer geometry and the layer distributions in the area, four
geoelectrical sections were created in N-S and E-W directions based on the interpreted resistivity data and the lithological information from the available boreholes
(Figs. 9 and 10). Four resistivity layers are recognized based on the analysis of the
constructed section. The topmost geoelectric layer consists of thin layer (average
1.5 m) and corresponding to sand, silt and clay with widely ranges of resistivity (17125 .m) from the north to the south where the ferruginous sandstone is exposed
in the southern parts. The second geoelectric layer representing the Mut Formation
that composed mainly of shale and act as cover overlying the Taref aquifer. This
layer has an average thickness of 24 m with resistivity average of 11 .m. The thickness of Mut layer increases significantly towards the north and north-east directions,
while, it thins or locally absent completely towards the south giving rise to the next
geoelectric zone (Taref Formation).
The third geoelectric layer varies in thickness from 76 to 122 m which is widely
distributed in the area and interpreted to coincide with the shallow aquifer of Taref
Formation. The Taref water-bearing layer displays a reasonable resistivity values
ranging from 11 to 337 .m reflecting gradually sands intercalated with thin clay
layers. Along E-W sections (Fig. 9), groundwater was found to be fresh and showed
K. S. Gemail et al.
the same resistivity curve may produce many interpreted curves (Koefoed 1979).
Depends on the geologic information and the available data of 16 boreholes (Gamma
ray and resistivity logs), a good initial model was suggested during the inversion
process by. During these procedures, some layer parameters were fixed based on the
available layer thicknesses which obtained from the close borehole information as a
ground truth.
In addition to the DC resistivity field survey, sixty water samples were gathered
from the shallow well pumping from Taref aquifer (60–120 m) to cover the whole
area (Fig. 7). Using typical calibrated field equipment, the pH, Temperature (T),
Total Dissolved Solids (TDS) and Electrical Conductivity (EC) were tested in field.
The GPS system of GARMIN GPSMAP 60Cx, was used to verify the geographical
coordinates of each sample points.
4 Results and Discussion
4.1 Aquifer Characterizations
Resistivities of geological materials vary over a wide range, based on mineral composition, degree of saturation, clay content, and TDS (McNeill 1980; Edet and Okereke
2002). The resulting 1D resistivity models were calibrated with the lithologic unites
from the nearby boreholes. Figure 8 shows examples of the correlation between
sounding points 8 and 19 with B-45 and T-9 boreholes, respectively (for location
see Fig. 7). Depending on this calibration, a spectrum of resistivity for the different
lithologic units in the studied area; could be delineated as listed in Table 1.
To illustrate the aquifer geometry and the layer distributions in the area, four
geoelectrical sections were created in N-S and E-W directions based on the interpreted resistivity data and the lithological information from the available boreholes
(Figs. 9 and 10). Four resistivity layers are recognized based on the analysis of the
constructed section. The topmost geoelectric layer consists of thin layer (average
1.5 m) and corresponding to sand, silt and clay with widely ranges of resistivity (17125 .m) from the north to the south where the ferruginous sandstone is exposed
in the southern parts. The second geoelectric layer representing the Mut Formation
that composed mainly of shale and act as cover overlying the Taref aquifer. This
layer has an average thickness of 24 m with resistivity average of 11 .m. The thickness of Mut layer increases significantly towards the north and north-east directions,
while, it thins or locally absent completely towards the south giving rise to the next
geoelectric zone (Taref Formation).
The third geoelectric layer varies in thickness from 76 to 122 m which is widely
distributed in the area and interpreted to coincide with the shallow aquifer of Taref
Formation. The Taref water-bearing layer displays a reasonable resistivity values
ranging from 11 to 337 .m reflecting gradually sands intercalated with thin clay
layers. Along E-W sections (Fig. 9), groundwater was found to be fresh and showed