Basin structure and water quality of the Oligocene aquifer in the Sebkhet El Behira basin (central Tunisia)

Figures & data

Figure 1. Location map of the studied area showing geological outcrops, field cross-sections, seismic lines and correlation wells.

Figure 2. Seismic section (L2) calibrated to the PP1 petroleum well showing Oligocene faulted horizon extension and thickness variations according the basin structuring in subsiding synclines and resistant anticlines.

Table 1. Characterization of the Oligocene aquifers (well positions are given in Fig. 1).

Well no.	Total depth (m)	Depth to water level (m)	Salinity (g/L)	Aquifer thickness (m)	Flow rate (L/s)
1	256	68.6	0.7	40.5	8
2	160	62	1.4	95
3	140			50
4	280	72.15	1.72	70	20
5	300			240 (reservoir thickness)
6	350	74.7	1.07	42	7.8

Figure 3. N–S Oligocene lithostratigraphic and aquifer correlation of hydraulic deep wells along western flank of Cherahil and Siouf anticlines.

Figure 4. Lithostratigraphic column of Oligocene Fortuna Formation reservoir levels in the north of Cherahil anticline (position shown on Fig. 1).

Figure 5. Lithostratigraphic column of Oligocene Fortuna Formation reservoir levels in the south of Cherahil anticline (Kodia Lhamra).

Figure 6. Seismic line (L6) interpretation showing Oligocene and Mio-Plio-Quaternary horizon structure and subsurface to surface faults, subsiding syncline and high anticline basin relationship of Sebkhet El Majdoul (position shown on Fig. 1).

Figure 7. Seismic line (L7) interpretation showing Oligocene and Mio-Plio-Quaternary horizon structuring and subsurface to surface faults, subsiding syncline and high anticline basin relationship of Sebkhet El Majdoul (position shown on Fig. 1).

Figure 8. Isochrone map of the top Oligocene horizon in two-way time in milliseconds (with respect to DP = 400 m a.s.l.).

Figure 9. Depth map of the top Oligocene horizon (in m) (with respect to the topography).

Table 2. Comparison of hydrological and seismic data.

Well no.	Hydrogeological data (m)		Seismic data (m)
	Aquifer depth	Aquifer thickness	Reservoir depth	Reservoir thickness
1	120	40.5	100–200	120–140
2		95	100–200	100–120
3	60	50	0–100	120
4	230	70	200–300	240
5	60	240*	0–100	260
6	80	42	100	260

* Reservoir thickness

Figure 10. Isopach map of Fortuna Formation (in m).

Figure 11. Three-dimensional representation of top Oligocene reservoir showing the presence of three sub-basins (1, 2 and 3).

Figure 12. Piezometric map of the Mio-Plio-Quaternary aquifers in Sebkhet El Behira–Garaat El Majdoul showing underflow pathways and highlighted water lines (modified from Mansouri 1980).

Figure 13. Digital elevation model and piezometric map of the Mio-Plio-Quaternary aquifers in Sebkhet El Behira–Garaat El Majdoul.

Table 3. Chemical composition of the Oligocene aquifer.

Sample	pH	Ce (ms/cm)	Cl^− (mg/L)	HCO3^− (mg/L)	SO4^2− (mg/L)	Na^+ (mg/L)	Ca^2+ (mg/L)	Mg^2+ (mg/L)	K^+ (mg/L)	Balance
1	8	1.03	142	274.5	227.62	202	99.5	3.15	2.54	3%
2	8.1	2.21	230	366	272.92	217	134.4	22.4	3.94	0%
3	8.4	1.33	121	335.5	275.69	209	79.3	15	11.04	0%
5	8	1.35	153	366	233.3	192	90.1	20.9	7.61	–1%
TN09.14			600	120	300	175	300	150

Mansouri, R., 1980. Contribution à l’étude hydrogéologique de la plaine de Sebkhet El Behira (Sud Ouest de Kairouan). Thèse Troisième Cycle. Université de Bordeaux, France, 107 p.

 Google Scholar