Jetting - general

From Akvopedia
Jump to: navigation, search
English Français Español भारत മലയാളം தமிழ் 한국어 中國 Indonesia Japanese
Jetting icon.png

Jetting is based on water circulation and water pressure. As opposed to sludging, water is pumped down the drill pipe and the ‘slurry’ (water and cuttings) is transported up the borehole between the drill pipe and the borehole wall. A motor pump is used to achieve an adequate water flow. The drill pipe may simply have an open end, or a drill bit can be added. Partial or full rotation of the drill pipe can be used. Thickeners (additives) can be added to the water in order to prevent hole collapse and reduce loss of working water (drill fluid).

Jetting is practiced in a wide range of varieties. The most simple consists of driving a plastic pipe down with water pressure from a motor pump (no drill bit and no rotation, with the water flow jetting the sand up). The depth is limited (no drill bit and extendable pipes). Other systems make use of extendable plastic or galvanized pipes and a drill bit and are rotated during drilling. With these systems greater depth can be reached.

Suitable conditions

Manually rotated jetting
Typical drill bit

Suitable for weakly cohesive sands and silts. Manual jetting is generally used up to depths of 35 meters.

Advantages Disadvantages
- Very quick in fine and medium sand formations.
- Generally limited to sandy soils. Soft clay will be penetrated only very slowly and coarse gravel and other highly permeable materials (cracks in the formation) cause loss of working water and cannot be drilled. The borehole stays open by water pressure. To prevent collapsing fluid-drilled boreholes must be kept full of water during the entire drilling and well installation process.

- A large amount of working water needs to be available on the drilling location (several 200 liter drums/hour). The drilling and well installation needs to be done on the same day. Leaving the borehole open during the night has a high risk of collapsing.
- The use of large quantities of water, the use of drilling fluids to greater depths and a motor pump make the equipment cost relatively high.

Construction, operations and maintenance

Jetting. Credit: WEDC.

All drilling equipment, except the motor pump and some valves, is locally produced.

Field experiences

Jetting is mainly used in Niger, Chad, Madagascar, Nigeria, Senegal, Burkina Faso, Uganda, Kenya, Soudan, Benin, Sri Lanka and western countries.

Manuals, videos and links

  • Lifewater Resources on hydrogeology, well construction, all drilling techniques, hand pumps and more. Lifewater Canada, update 2004.
  • Manuals on Percussion drilling, well construction, manufacturing tools. Cliff Missen, Wellspring Africa, draft 4.
  • Lots of articles on Jetting. Rural Water Supply Network.
  • PAT-Drill - Engine powered drilling equipment and small machines.
  • Lone Star Bit - Engine powered drilling equipment and small machines.
  • Deep Rock - Engine powered drilling equipment and small machines.
  • Drillingfab. - Engine powered drilling equipment and small machines.