As previously mentioned, rotary rigs began to replace cable tool rigs in the late 1890s. The discovery well for the prolific Spindletop Oilfield in Beaumont, TX was drilled to a depth of 1,039.0 ft with an early rotary rig in 1901 (Spindletop discovery date was January 10, 1901).
In a rotary rig, torque (rotation) is applied to the Drill Pipe or Drill String (hollow steel tubing) with a drill bit attached to the end of the Bottom-Hole Assembly (BHA). As the name implies, the bottom-hole assembly is attached to the bottom end of the Drill String, nearest to the formation being drilled. The drill string is the combined length of drill pipe extending from the rotary system on the drilling rig to the bottom-hole assembly at the bottom of the wellbore). The BHA contains all of the equipment required to drill the current section of the wellbore. This equipment may include Drill Collars (heavy steel tubing used to add weight to the drill bit), directional drilling equipment, LWD or MWD tools, etc.
There are several ways to classify rotary drilling rigs. However, in this class, we will classify them by the location on the rig of the Rotary System. The Rotary System is one of the major systems on the drilling rig and is where the torque is applied. We will discuss two types of rigs with two different rotary systems: a conventional rotary table rig and a top-drive rotary rig.
The following pages will discuss two types of rotary rigs.
- 8.4.2.1: Conventional Rotary Rig or Rotary Table Rig or Kelly Drive Rig
- 8.4.2.2: Top-Drive Rig