Page 28 - Air and gas Drilling Field Guide 3rd Edition

2.2 Circulation Systems 19

CONTINUOUS
SAMPLE
DISCHARGE
AIR OR
MIST TOP HEAD
ROTARY DRIVE

OUTER PIPE
INNER PIPE

FIGURE 2-8. Dual tube (or dual drill pipe) closed reverse circulation operation.

dual tube (or dual drill pipe) closed reverse circulation system. The closed system
is characterized by an annulus space bounded by the inside of the outer tube and
the outside of the inner tube. This is a specialized type of reverse circulation and
is usually limited to small single and double drilling rigs with top-head rotary
drives (see Chapter 4 for drill pipe details).
Reverse circulation drilling operations require specially fabricated drill bits.
Figure 2-9 shows a schematic of the interior flow channel of a tricone rotary drill