Page 493 - Air and Gas Drilling Manual

10-18 Air and Gas Drilling Manual
2
KE
bh
1 1 2 mixbh V bh 2
KE 0 530 3 38
.
.
bh
2
ft lb
.
KE bh 303 3
ft
The volumetric flow rates of incompressible fluid (water and surfactant) and
compressible gas (air) were determined by trial and error to give a bottomhole kinetic
3
energy per unit volume of approximately 3.0 ft-lb/ft . These volumetic flow rates
have been determined with the non-friction method. Although this method is
invalid for 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.
10.4.2 Major and Minor Losses and Injection Pressure
The governing equations for the second methodology, presented in Chapter 6,
requires trial and error solutions and can be applicable to deep wells with
complicated borehole geometry. As major and minor friction losses are added to
allow the analytic solutions to simulate more closely the actual drilling situation,
the volumetric flow rates of incompressible fluid and compressed gas must be
increased to compensate for the added friction in the system.
Illustrative Examples 10.2 describes the full implementation of the basic
planning steps Nos. 1 to 8 in Section 10.1.
Illustrative Example 10.2 In this illustrative example the given data in
Illustrative Example 10.1 is used for a solution using the friction solution method
given in Chapter 6 (Equations 6-87 to 6-106). Using the general data and results
obtained in Illustrative Examples 10.1, determine the approximate volumetric flow
rates of the incompressible fluid and the compressed air required while drilling at
10,000 ft. Determine the foam bottomhole annulus pressure and the incompressible
fluid and compressed gas 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
7,000 ft to 10,000 ft and determine the derated power available from the prime
mover.
General Data
It is required that the foam quality at the top of the annulus (upstream of the
back pressure valve) be approximately 0.98. This foam quality requirement defines
the relationship of the volumetric flow rate of the incompressible fluid to the
volumetric flow rate of the compressible gas. Thus, the defined foam quality dictates
that only one of the components (either, the flow rate of the incompressible fluid or the
flow rate of the compressible gas) be sought by trial and error technique. The other
component is automatically known via the defined foam quality value. In this