Page 22 - Air and gas Drilling Field Guide 3rd Edition

2.1 Rotary Drilling 13

FIGURE 2-3. Typical self-propelled single drilling rig (courtesy of George E. Failing Company).

either a dedicated prime mover on the rig deck or a power take-off system that
allows utilization of the truck motor as the prime mover for the drilling rig equip-
ment (when the truck is stationary). Small drilling rigs can provide axial force to
push the drill bit into the rock face through the drill string (via a chain or cable actu-
ated pull-down system, or a hydraulic pull-down system). A pull-down system trans-
fers a portion of the weight of the rig to the top of the drill string and then to the drill
bit. The torque and rotation at the top of the drill string are also often provided by a
hydraulic top-head drive (similar to power swivel systems used on larger drilling
rigs), which is moved up and down the mast (on a track) by the chain, cable, or
hydraulic drive pull-down system. However, some of these rigs retain the traditional
rotary table. Many of these small single drilling rigs are capable of drilling with their

masts at angles as high as 45 to the vertical. The prime mover for these rigs is usu-
ally fueled by either propane or diesel.
The schematic layout in Figure 2-4 shows a typical self-propelled double dril-
ling rig. This example rig is fitted with a mud pump for circulating drilling
mud. A vehicle motor is used to propel the rig over the road.
The same motor is used in a power take-off mode to provide power to the
rotary table, draw works, and mud pump. For this rig, this power take-off motor
operates a hydraulic pump that provides fluid to hydraulic motors to operate the