Page 268 - Air and gas Drilling Field Guide 3rd Edition

10.5 Nonfriction and Friction Illustrative Examples 259

Pressure (psia)
0 200 400 600 800 1000
0 0
Back Injection
Pressure
−500
−2000

−1000
−4000 Inside Drill String
Depth (ft) −1500 Depth (m)

−6000 Annulus
−2000
Bit
−8000
−2500

−10000 −3000
0 500 1000 1500
2
Pressure (N/cm abs)

FIGURE 10-3. Illustrative Example 10.2 pressures versus depth.

illustrative example in Chapter 8 and lower than the aerated drilling illustrative
example in Chapter 9.
In foam drilling, use of a surfactant with the water and air allows the develop-
ment of a foam structure in the annulus, which in turn provides resistance to the
flow of the foam from the bottom of the annulus. This resistance is demonstrated
2
by the high bottom hole pressure of 1315 psia (907 N/cm abs). In this friction
solution the foam quality upstream of the back pressure value is 0.98 (the same
as in the nonfriction solution), but the bottom hole foam quality in this friction
solution is 0.81 (the nonfriction annulus bottom hole quality is 0.93). This lower
bottom hole annulus foam quality reflects the friction resistance to foam flow in
the annulus. It should be noted that the nonfriction solution approximates the
bottom hole pressure and foam quality under nonflowing or static conditions.
This means that the difference between the friction bottom hole pressure,
2
1315 psia (907 N/cm abs), and the nonfiction bottom hole pressure, 386 psia
2
2
(266 N/cm abs), is 929 psi (641 N/cm ) of friction pressure created by the flow
of the foam structure in the annulus.
Figure 10-4 shows the injection pressure and bottom hole pressure as drilling
takes place from the casing shoe at 7000 ft (2134 m) to the final depth of
10,000 ft (3048 m). Assuming that this example is more typical of a performance