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Product development at the WOT: Drilling with compressed air

Saturday, February 22nd, 2020 Comments Off on Product development at the WOT: Drilling with compressed air

(An update on this system using a motorised drill can be found here)

The WOT has years of experience with manual well drilling with the Baptist- and EMAS method. Both methods require tools that can easily be manufactured in a workshop with readily available materials. De drilling sets can be made in a simple workshop with an angle grinder and a stick welder. Because of this, the methods can be used in remote areas. The baptist method, developed by Terry Waller, uses the principle of an inertia pump. The drilling set essentially consists of a drilling pipe with a one-directional valve which is moved up and down in the well. If the downward acceleration is higher than the gravitational acceleration, the drilling fluid (which contains the sediment) will be accelerated up the drilling pipe. Because of this, water with sediment can be transported to the surface where it enters a basin. The sediment will settle and clean water flows back into the well via a small duct.

The EMAS method is developed by Wolfgang Buchner. Here the water flows in the other direction; via the drilling pipe water is pumped down with a manual pump. Then the water flows upwards through the annulus taking sediment with it. The dirty water enters a basin and the sediment sinks. The clean water can be pumped into the well again.

The higher the speed of the drilling fluid, the more particles can be taken along. An advantage of the Baptist method is the fact that the drilling fluid is brought up through the drilling pipe. Because the drilling pipe has a relatively small cross-section compared to the annulus, high fluid speeds can be achieved with a small amount of volume displacement. The EMAS method uses the annulus to transport the sediment up. This means that if the diameter of the well increases more volume should be moved to achieve the desired velocity, or the diameter of the pipe should be increased, but this increases the weight which is undesirable. Therefore, the diameter of wells made with the EMAS method is limited.

There are many ways to automate the drilling methods to a certain extend. Manual drilling can be a labour intensive job which requires increasingly more effort at increasing depths. Jetting drilling sets are for example available or another option is to replace the manual pump for EMAS drilling with an automated pump. Also, attempts have been made at automating the up and down movement of the drilling rod.





Since 2019 the WOT has been working on another method, which uses compressed air to pump around the drilling fluid. The method uses an airconditioning compressor (Power: 400 W, V ≈ 40 Lpm Atm, Pmax > 20 bar). The hose from the compressor enters the drilling pipe 40 cm above the drill. The air that is injected decreases the average density of the mixture in the drilling pipe. Because of this, it will ‘float’ on the liquid in the well. As a result, the fluid with sediment exits the drilling pipe at the top. It enters a basin where the particles sink and clean water flows back into the well.

Setup for airlift-drilling (at the background behind the PVC-tube a bucket with the compressor is visible)
The compressor, cooled in water

This method has a few great advantages:

  • The water flows back through the drilling pipe. Because of this, a bigger well diameter can be realised with a relatively small drilling pipe diameter because the flow will stay high (light material).
  • The flow down through the annulus is low, reducing the erosion on the walls of the well
  • A relatively small flow is required to meet the required speed for particle transport. Little work for pumping and thus low electricity costs.
  • No mechanical components (valves, pumps) get into contact with the drilling fluid. So there is no time loss or maintenance needed.
  • Used refrigerator/arco pumps are readily available.
  • Small fuel generators are readily available.

The method is tested 6 times at different places in the Netherlands. Drilling times are measured. The well diameter is about 150 mm in all cases. Factors governing the speed of drilling are mostly the person drilling and the ground type. The average drilling speed (excluding brakes) was 3.8 meters per hour.

Furthermore, the speed is dependent on the used drill. It was developed further during the drilling attempts. The most successful design, which worked on multiple locations, is shaped like shown in the picture below. The latest version is made of wear-resistant steel (RAEX 400), because of which resharpening is needed less often. Plans have aroused to try the drilling method in harder ground types. Soon the technical drawings of the most recent design will be shared with relevant organisations and will be placed on this website. Also is being looked into further automation of the drilling process. This way we hope to contribute to increasing the accessibility of clean drinking- and irrigation water.