Horizontal Directional Drilling – How does it work?

Step 1: Pilot drilling

The pilot drilling is the most important phase of Horizontal Directional Drilling (HDD). This phase determines the final route of the pipeline. During this pilot drilling, you need a drill head with a jet at the end of the flushing pipe. On this drill head, you can find a “steering plate”.  The drill head will move in different directions by rotating the steering plate. By turning the steering plate in a certain direction, the drill head will follow.

The figure on the right illustrates how the control plate (diagonally flat on the chuck) guides the chuck upwards.

By turning the rods 90 ° left or right (or 180 °), the drill head can be steered “unlimited”. This way, obstacles can be avoided. The position of the drill head is displayed on a “clock”.

By rotating the rods continuously, the drill head will simply go straight and not change direction.

In the pilot drilling, it is important that a sufficient amount of bentonite is present to obtain a borehole and ease the execution of the next steps.

B = Drilling fluid S = Soil R = Return fluid (= B + S)

The figure shows how the jet at the front of the drill head loosens the sand and uses the drilling fluid to guide the sand out of the borehole.

Step 2: Clearing the borehole
After the pilot drilling, the borehole is enlarged with the use of a “reamer” so the pipe can be placed

At the final clearing stage, the tube is attached to the reamer by means of a “swivel” and pulled into the borehole. The purpose of the swivel is to keep the tube straight, so it will not rotate.

When clearing, it is important to respect the calculated clearing time. This is based on the amount of soil to be transported and the bentonite pump capacity. Sand accumulations can occur when the reaming process goes too fast since the speed of the rinse mixture becomes lower than the speed required to transport the sand. The drilling fluid that can be used is Quik gel or Wyoming bentonite. This form of bentonite has proven its worth over many years. It is a type of bentonite that is easily mixable with water, resulting in a smooth drilling fluid, which comes into its own in various types of soil.

The drilling fluid has 5 different functions:

  1. Transport of loosened surface
  2. Keeping the loosened surface “in mixture”
  3. Maintain the stability of the borehole by laying a film
  4. Lubrication
  5. Cooling down the components

Step 3: Placing the pipe
During the final stage of reaming, the tube is attached to the reamer via a swivel and thus drawn into the borehole.

To get as little friction as possible, the pipe is temporarily placed on supports (rolls). The distance between the rolls depends on the type of material (PE, Steel, …), the diameter and the thickness of the pipe.

horizontal directional drilling explanation

Bofram is specialized in Bentonite pump units for horizontal directional drilling

The units developed and built by Bofram are 100% remote-controlled and provide the process with a controlled amount of bentonite mixture during the controlled drilling. The liters, working pressure, and engine speed can be read on the remote control.

The total package is a super-advanced tool for HDD activities.
Advantages: fuel savings, time savings, easy error detection.

If you have any questions or comments regarding this article, please feel free to contact us. We are happy to help you.

Advice or questions about directional drilling?

Call for an appointment +31 (0)486-459045 or mail to info@bofram.nl