The extraction of drinking water is one of the HDDW’s key applications. Whilst drinking water is available in large quantities in the Netherlands, those who live in more arid parts of the world have to resort to other methods of water extraction. One widely used method of seawater filtration and seawater extraction in places like the Middle East and Australia is desalination of seawater.
Desalination of seawater process
During the desalination process, desalination plants extract water from the sea, from which the mineral salts are later removed. Up until now the seawater extraction took place by means of so-called open-water intakes. However, a number of problems are associated with this seawater intake method, namely:
- intake of undesirable and coarse material
- major impact on the aquatic environment
- variable quality of water
- large investments for pre-treatment of the seawater
Seawater intake methods and HDDW advantages
HDDW as a seawater intake method offers an alternative to open-water intakes by drilling under the seabed. HDDW involves installing a sustainable and regenerable filter, surrounded by the seabed as a natural filter-screen. Not only does this eliminate the inflow of undesirable and coarse contaminants, but because of the low flow velocity, the effects on the aquatic environment are minimised. By drilling from a single point, it is possible to install several HDDWs in the form of a fan.
Seawater desalination process
An alternative to open-water intakes has already been applied in vertical beach wells which are dug under the beach and not under the seabed. Furthermore, many vertical wells are needed to meet the frequently high extraction demand of the seawater desalination plants. Given the high capacity of an HDDW, this demand can invariably be satisfied with just a few HDDWs.
A hybrid form between vertical beach wells with a low capacity and HDDW with a high capacity is a slant well. A slant well is drilled in a straight line under an angle until the desired depth. Due to the drilled angle of the slant well it is possible to install a longer filter in the aquifer thus increasing the capacity in comparison to vertical wells. During the construction of the slant well an artificial engineered gravel pack is applied around the wells filter-section to get the optimal water quality.