Two very different undergrounds
Around Djelfa, on the High Plateaus, hydrogeological studies describe a syncline whose upper aquifer, in Mio-Plio-Quaternary deposits, is reported to be some hundreds of metres thick on average and is the one most used by wells and boreholes for drinking water and irrigation across the steppe. Below it lie older sandstone and limestone formations of the Albian and Barremian, also water-bearing, reached by deeper boreholes. Water levels and yields vary along the syncline, and the shallow aquifer depends on the rain that falls on the surrounding ranges.
Around Ghardaïa, in the northern Sahara, the picture is the one of the whole Saharan basin: the Continental Intercalaire, a vast sandstone aquifer of Albo-Barremian age, overlain by the Complexe Terminal. Boreholes into the Continental Intercalaire in this region are deep, in some cases beyond a thousand metres, and are completed with successive cemented casing strings and screens; the water comes up warm because of the depth. Shallower wells in the valley floor and the Complexe Terminal serve many local needs but with more variable quality.
The practical lesson is that the same word, well, covers a shallow water-table well of a few tens of metres and a deep artesian borehole, and that the local hydrogeological data, where available from the water authorities or from the studies of nearby boreholes, is the starting point of any project.
Rotary or down-the-hole hammer
Two drilling methods cover most water wells. Mud rotary drilling turns a bit on hollow rods while a drilling fluid is pumped down the rods and back up the annulus, carrying the cuttings and supporting the hole; it suits soft and unconsolidated formations and allows large diameters. Down-the-hole (DTH) hammer drilling uses compressed air to drive a piston that strikes the bit at the bottom of the hole; it is fast in hard rock such as limestone and sandstone and lifts the cuttings with the air. Many rigs can do both, and a well may be started with one and finished with the other as the formations change. The choice is made from the expected geology, the target depth and diameter, and the water available for mud.
From the borehole to a working well
The usual sequence; each step is sized to the aquifer and the intended use.
Siting and design
Review of existing boreholes, geology and the authorization file; choice of target depth, diameters and method.
Drilling
Rotary or DTH drilling in one or more diameters, with a log of formations and water strikes.
Casing and screen
A casing string protects the hole and a screen is set against the water-bearing zone; a gravel pack around the screen filters fine sand.
Cementing
The annulus above the screen is sealed to keep surface water and unwanted layers out, and the wellhead is protected.
Development
Air-lifting, surging or pumping clears the drilling fluid and fines until the water runs clean.
Pumping test
A step or constant-rate test measures the yield and the drawdown, which fixes the pump size and the sustainable flow.
Equipment
Pump, riser, cable, wellhead and the connection to the storage; water quality is analysed before use.
The authorization procedure in brief
Drilling a water well in Algeria requires an authorization for the use of water resources. Since the 2021 reform, applications are examined through a single window that brings together the national hydraulic resources agency (ANRH), the national agency for integrated water management (AGIRE) and representatives of the environment, agriculture and irrigation sectors; the file is then sent to the wilaya, and the authorization is granted by order of the wali. The regulation sets a target of one month for processing a complete file. The works must in general be carried out within eighteen months of notification, a period that the regulation allows to be extended on justified grounds.
The file typically describes the applicant, the land, the intended use and volumes, and the characteristics of the planned well. The practical advice is simple: file early, keep the authorization on site, and have the well drilled by a company that records depths, formations and test results for the final report.
What to expect from a well in each region
General tendencies reported in regional studies; a specific site can differ.
| Aspect | High Plateaus (Djelfa syncline) | Northern Sahara (Ghardaïa area) |
|---|---|---|
| Main aquifers | Mio-Plio-Quaternary; Albian and Barremian sandstones below | Complexe Terminal; Continental Intercalaire at depth |
| Typical depths | From tens of metres to a few hundred metres | From tens of metres to several hundred; over a thousand for the deep aquifer |
| Formations | Alluvium, clays, sandstones, limestones | Sands, sandstones, limestones, clays |
| Water | Generally cooler, quality varies with the layer | Warm at depth; mineralization varies |
| Method | Rotary in soft ground, DTH in rock | Rotary with mud for deep wells; DTH possible in hard layers |
| Recharge | Rain on the surrounding ranges | Very slow; essentially a stored resource |
Water quality and temperature
Water from the deep Saharan aquifer is often warm and may carry a mineral load that calls for cooling or treatment before certain uses; water from shallow aquifers can be affected by what happens at the surface. For a construction site this matters for concrete, where sulphates and chlorides are limited by the specification, and for the camp, where drinking water must be analysed. A laboratory analysis after development, before the pump is installed, is standard practice.
Frequently asked questions
Do you need a permit to drill a water well in Algeria?
Yes. A water well in Algeria requires an authorization for the use of water resources, granted by order of the wali after the file has been examined through the single window created in 2021 that involves the ANRH and AGIRE agencies, with a one-month target for processing a complete application.
How deep are water wells around Djelfa and Ghardaïa?
It varies strongly with the aquifer targeted: wells into the shallow aquifers can be a few tens to a few hundred metres deep, while boreholes into the Continental Intercalaire of the Saharan basin around Ghardaïa are reported to exceed a thousand metres in some cases. Local borehole data and the intended use decide the design.
What is the difference between rotary and DTH drilling?
Rotary drilling cuts the rock with a rotating bit and lifts the cuttings with a circulating fluid, which suits soft and loose formations, while a down-the-hole (DTH) hammer breaks hard rock with air-driven percussion at the bottom of the hole and is faster in limestone and sandstone. Many wells combine both as the formations change.
How long does it take to drill a water well?
A shallow well can be drilled and completed in days, while a deep borehole with several casing strings takes weeks; the authorization procedure, which should be started as early as possible, is often the longest part of the calendar.
Can a well supply a construction site?
Yes. A well drilled on or near the site, with storage in a basin or tanks, is a common way to supply compaction water, concrete and the camp in the interior of Algeria, where no network is available; the water is analysed before use in concrete or for drinking.
How ETAHG can help
SARL ETAHG owns a truck-mounted water well drilling rig with its accessories, recently acquired new, and drills wells for construction sites, agriculture, industry and communities, with its registered office in Bounoura, wilaya of Ghardaïa, and its equipment depot in Djelfa. Depth capacity, method and schedule are discussed per project. See water well drilling for the service and project mobilization for how a well fits into a site start-up.