Just as in the drilling of a drinking water well, horizontal directional drilling requires a great deal of expertise and know-how. Both activities have been performed successfully for many years. Until recently, however, combining them was thought to be impossible. HDDW technology combines both these activities, resulting in a perfect horizontal drinking water well.
Step-by-step plan: The following steps are required for the construction of an HDDW under the seabed:
- Pilot drilling A drilling rig accurately pushes the drilling head through the earth, through the desired aquifer. A hollow pipe behind the drilling head fills the drill hole with drilling fluid to prevent it from collapsing. If drilling takes place under the seabed, the drilling head will re-emerge in the sea. In this case, marine operations are required. Another alternative is for the drilling head to remain under the seabed. This will do away with the need for marine operations.
- Clearing the drill hole To clear the drill hole, a drilling rig pulls a clearing device through the drill hole. Depending on the desired diameter, this process takes place once or several times. Everytime the process is repeated, the diameter of the clearing device increases. The use of drilling fluid keeps the drill hole from collapsing.
- Installation of filter system When the drill hole is large enough, a casing is drawn in. The filter pipe is placed inside this temporary casing. If required, an artificial screen can then be applied. The temporary casing is removed, the required pumps are installed and the filter system is ready.
- Development of the well In order to put the HDDW into use, the well must be developed. This means that the drilling fluid in the system must be removed and the soil composition must be optimised.
Only after development is the HDDW ready for use during the desalination process.