PrintA conventional rotary rig or rotary table rig or kelly drive rig is a drilling rig where the rotation of the drill string and bit is applied from a rotary table on the rig floor. The conventional rotary rig was the most common rig used during the past century (1900s) and is the drilling rig that you are probably most familiar with from old movies and documentaries. A schematic of a conventional rotary drilling rig is shown in the schematic diagram in Figure 8.03.
| Diagram | Index |
|---|---|
 |
|
| Source: D.T.E. Drilling Components of a Land-Based Rotary Drilling Platform | |
As identified in this figure, the Derrick or Mast (Item 14) is the tall steel structure with its base on the rig floor. On the rig floor the Kelly (Item 19), the Kelly Bushing (not shown), and the Turn Table or Rotary Table (Item 20) are also identified in this figure. These are the components of the Rotary System that provides the torque to the drill string on a conventional rotary rig. A photograph of an actual kelly, kelly bushing, and turn table / rotary table is provided in Figure 8.04(A) while a schematic diagram of the entire assembly is shown in Figure 8.04(B) .
The kelly is a hollow square or hexagonal piece of pipe through which the drill pipe can be passed. This is the pipe marked (I) in Figure 8.04. The kelly is matched to a similarly shaped bushing (square or hexagonal), the kelly bushing, marked (II) in Figure 8.04 which is raised above the rig floor. You can think of the kelly as a hollow square or hexagonal bolt and the kelly bushing as a matching square or hexagonal wrench that turns the bolt. The kelly bushing is set into the master bushing, marked (III) in the photo, with four large metal pins, which in turn sits in the rotary table, marked (IV) in the photo. The rotary table provides the torque required to rotate the master bushing, kelly bushing, kelly drill pipe, and drill bit. The slight rotational blur in the photo implies that the rotary table and kelly were rotating when the photo was taken.
Also shown in Figure 8.04(A) is the Mousehole, marked as (V) in the photo, along with a Joint of Drill Pipe (painted yellow in the lower left-hand corner). The mousehole is the temporary storage location for the next Joint of Drill Pipe to be added to the Drill String. A joint of drill pipe is a 30-foot piece of pipe that is the basic element of the Drill String. Oil and gas companies purchase drill pipe from the steel companies by the joint. Typically, two (a Double) or three (a Triple) joints of drill pipe are connected to form a 60-foot or 90-foot Stands of drill pipe that are racked and stored on the side of the derrick as shown as Item 16 in Figure 8.03 and in the photo in Figure 8.05. Note that the Mousehole is not the same as the Rat Hole (Item 21) in Figure 8.03. On the rig floor, the rat hole is a hole on the rig floor with a large diameter piece of casing extending above the rig floor that is used to temporarily store the kelly when it is disconnected.
Source (Part B): Drilling Formulas: What is Kelly Rig?
