The Directional Drilling Process
By definition, directional drilling involves any attempt to intentionally divert the path of the wellbore. This is almost always done to access otherwise difficult to reach deposits, such as under a lake or mountain. Using a tri cone or PDC bit the wellbore first goes straight down to a predefined depth. This functions as the so-called “kick off point” from which the path of the wellbore will divert. At this point the bit will usually be changed to a specially engineered tri cone that can run on an independent motor. The idea behind this is to have a bit that can rotate to drill under its own power, without any rotation required from the drill string. Thus, when the drill is pointed at the desired angle the force needed to progress through the rock formation comes from the rotation of the tri cone or PDC bit and the Weight On Bit provided by the drill string. In addition to the special motorized tri cone, directional drilling also requires special equipment to measure the progress while drilling. A professional directional driller is essential, and they will require exact knowledge about the progress of the drill bit when determining course.
Rotary Steerable System Drilling and Advances in Tri Cone and PDC Bits
A Rotary Steerable System (RSS) is the newest development in directional drilling. It allows for further steering of the bit while the drill sting is still rotating and providing force. This negates the need for a motor powering the drill bit itself, and reduces the potential areas of failure or mishap. Traditionally tri cone bits have been the go to choice for directional drilling because they are more easily steerable, although this capacity has recently expanded to PDC bits as well. Rotary Steerable Systems use detailed data on the position of the bit, collected while drilling, to send commands to the bit from the surface. Generally they will either send carefully controlled variations in the mud column, or variations in the drill string rotation, to send a message to the tool powering the tri cone or PDC bit. This process, while more complicated than conventional directional drilling, offers significant advantages. The rotation of the drill string helps the transport of cuttings or debris to the surface, resulting in less debris and smoother drilling. Additionally, as the steering can be carefully controlled from the surface it allows for more controlled wellbores with smoother surfaces and greater complexity. The tri cone or PDC bit required for RSS drilling are specifically created for that function and can be very expensive as a result. This is not the sort of drilling process undertaken lightly, and your choice of tri cone or PDC bit should only be made after careful consultation with the directional drilling team for your project.
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