Page 33 - Air and Gas Drilling Manual

1-10 Air and Gas Drilling Manual
string. At the surface the cuttings are removed from the drilling mud by the shale
shaker and the drilling mud is returned to the mud tanks (where the slush pump
suction side picks up the drilling mud and recirculates the mud back to the well).
Reverse circulation can also be carried out using air and gas drilling techniques.
Figure 1-8 shows a typical application of reverse circulation using compressed air as
the drilling fluid (or mist, unstable foam) [7]. This example is a 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
innertube. This is a specialized type of reverse circulation and is usually limited to
small single and double drilling rigs with top head rotary drives. Dual tube and
dual drill pipe are available from a number of manufacturers in the United States and
elsewhere in world (see Chapter 3 for drill pipe details).

Figure 1-8: Dual tube (or dual drill pipe) closed reverse circulation operation.