Drilling Technology

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Figure 3-21: Heavy-weight drill pipe standing in rig rack (courtesy of Smith International).

The unique characteristic of this type of drill pipe is that it can be run in compression in the same manner as drill collars. Most heavy-weight drill pipe is fabricated in Range 2 and 3 API lengths. It is also available in custom lengths shorter than Range 2. Heavy-weight drill pipe are available in 3 1/2 inch, 4 inch, 4 1/2 inch, and 5 inch, 5 1/2 inch, and 6 5/8 inch nominal outside diameters. Figure 3-21 shows two typical heavy-weight drill pipe elements standing in a regular drill pipe rack in a drill rig. One unique feature of heavy-weight drill pipe is the wear pad in the center of the element. The wear pad acts as a stabilizer and improves the stiffness of the heavy-weight stand in the drill string and thus reduces the deviation of boreholes.

Table 3-3 gives the dimensional and mechanical properties for Range 2 heavyweight drill pipe (tube body and tool joints).

Figure 3-22 shows a "tapered" drill string with a drill bit at the bottom, drill collars above the drill bit, heavy-weight drill pipe above the drill collars, and standard drill pipe above the heavy-weight drill pipe.

Figure 3-22: Typical tapered drill string using heavy-weight drill pipe (courtesy Smith International).

Heavy-weight drill pipe elements are used in a number of applications in rotary drilling. Since this drill pipe can be used in compression, this drill pipe can be used in place of drill collars in the shallow wells with small single or double rotary drilling rigs. This drill pipe is also used in conventional drill string for vertical drilling operations as transitional stiffness elements between the stiff drill collars and the very limber drill pipe. Their use as transitional stiffness elements reduces the mechanical failures in the bottom drill pipe elements of the drill string. Heavyweight drill pipe is also used in directional drilling operations where drill collars can be replaced by the heavy-weight pipe. Using heavy-weight drill pipe in place of drill collars reduces the rotary torque and drag, and increases directional control.