Deviating the Wellbore by Positive Displacement Motor (Directional Drilling)

A positive displacement motor (PDM) is one of the most popular tool for drilling a directional well. It works by boring downwards and pumping mud through the motor itself. As shown in figure 1, the bottom section of the motor has an adjustable bend housing.

Figure 1 – Positive Displacement Motor (Courtesy of Schlumberger)

Before the motor is run into the hole, a set-up process needs to be carried out

  1. The bend will be adjusted according to the directional performance that the motor needs to achieve. This bend is only very slight, usually being under 2°.
  1. The motor is hooked up to navigational tools, which are then calibrated, in order for the driller to see where the bend is pointing when drilling. These tools are known as measurement while drilling, or MWD, and are described in detail later in this document.
  1. The other parts of the system will be adjusted to account for the required directional performance- the severity of this will depend on the drill design.

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