Page 419 - Air and Gas Drilling Manual

Substituting the values of H, ˙ w , ˙ w , Q m, P g, P bh, T g, and T av into Equation 9-
s
m
9 yields
,826
. 0 426
505
,
(. 0 949 31 .92 ) 10 000 Chapter 9: Aerated Fluid Drilling 9-23
, 1 827
Q
g
554 .41 505 ,826
, 1 827 ln . 0 0659 10 ,000
519 .67 , 1 827
3
.
Q g 11 05 ft /sec
The air volumetric flow rate in field units is
11
q g (. ) (60 )
05
q g 663 acfm
The volumetric flow rate of compressed air determined above is the flow rate to
be injected into the incompressible fluid volumetric flow rate of 191 gal/min. This
gas flow rate has been determined with the non-friction method. Similar solutions
(in magnitude) will be obtained when using the oil and gas production based non-
friction methods [14, 15]. Although this non-friction method is invalid for a deep
boreholes with complicated geometric profiles, the solution does give a lower bound
value for the full friction solution. The full friction solution will be demonstrated in
the next section.
9.4.2 Major and Minor Losses and Injection Pressure
The governing equations for the second methodology, presented in Chapter 6,
requires trial and error solutions and is applicable to deep wells with complicated
borehole geometry. As major and minor friction losses are added to allow the
analytic solution to simulate more closely the actual drilling situation (for a given
incompressible volumetric flow rate), the volumetric flow rate of compressed gas
must be increased to compensate for the added friction in the system.
Illustrative Examples 9.3 describes the full implementation of the basic planning
steps Nos. 9 to 11 in Section 9.1.
Illustrative Example 9.3 In this illustrative example the given data in
Illustrative Example 9.1 is used for a solution using the friction solution method
given in Chapter 6 (Equations 6-74 to 6-86). Using the general data and results
obtained in Illustrative Examples 9.1 and 9.2, determine the approximate volumetric
flow rate of the compressed air required for the incompressible drilling fluid (drilling
mud) volumetric flow rate of 191 gal/min while drilling at 10,000 ft. Also
determine the compressed air injection pressure while drilling at 10,000 ft. Select an
appropriate compressor system from those given in Chapter 4. Determine the
highest compressor power required from the prime mover to drill the interval from