Page 26 - Air and Gas Drilling Manual

Chapter 1: Introduction 1-3
deep drilling of boreholes for the recovery of crude oil and natural gas are almost
exclusively carried out in sedimentary rock. Boreholes for the recovery of
geothermal steam and water are constructed in all three rock types. The rotary
drilling method requires the use of a rock cutting or crushing drill bit. Figure 1-1
shows a typical mill tooth tri-cone roller cone bit. This type of drill bit uses more
of a crushing action to advance the bit in the rock (see Chapter 3 for more details).
This type of bit is used primarily in the drilling of sedimentary rock.

Figure 1-1: Mill tooth 7 7/8 inch tri-cone roller cutter bit IADC Code 126 (courtesy of
Reed Rock Bit Company).
To advance the drill bit in rock requires the application of an axial force on the
bit (to push the bit into the rock face), torque on the bit (to rotate the bit against the
resistance of the rock face), and circulating fluid to clear the rock cuttings away from
the bit as the bit generates more cuttings with its advance (see Figure 1-2).

Figure 1-2: The three necessary components for rotary drilling.