Page 656 - Air and Gas Drilling Manual

12-20 Air and Gas Drilling Manual
Comparing the above two directional drilling situations, it is clear that the
higher minimum volumetric flow rate is the appropriate selection (i.e., 1,630 acfm).
This is true for two important reasons. First, even though the sliding situation
gives a lower minimum volumetric flow rate, cuttings will accumulate in the low
side of the borehole and there is no mechanism for getting them up into the flow
stream since there is no rotation of the drill string (the lower flow rate is a false
minimum). Second, the 1,630 acfm value ensures that all critical cross-sections in
3
the annulus have a kinetic energy per unit volume of 3.0 ft-lb/ft or greater.
12.5 Injection Pressure and Selection of Compressor Equipment
Air and gas technology directional wells for the oil and natural gas recovery
operations are often drilled using inert atmospheric air as the drilling fluid. Thus,
when selecting the type and number of compressor units for a directional drilling
operation, the number and capacity of the accompanying membrane units must also
be determined.
Illustrative Example 12.3 For the planned directional drilling operation given
in Illustrative Example 12.2 above, determine the number of semi-trailer mounted,
Dresser Clark Model CFB-4, four stage, reciprocating piston compressor units (see
Figure 4-25) required to drill the 3,000 ft of directional openhole shown in Figure
12-8. The compressor units are rated at 1,200 acfm each. Also, determine the
number of skid mounted membrane filter units rated at 1,500 acfm each that will be
needed to supply the drilling operation with inert atmospheric air. It is required that
the inert atmospheric air have only 5 percent oxygen content.
As determined in Illustrative Example 12.2 above, the minimum volumetric
flow rate while drilling at the end of the 3,000 ft directional borehole is
approximately 1,630 acfm. Figure 12-5 shows that the membrane filter units are
about 50 percent efficient when producing inert atmospheric air with 5 percent
oxygen content. Therefore, four compressor units and four membrane units will be
required to provide the compressed inert atmospheric air. The approximate
volumetric flow rate to the drill string during the directional drilling operation will
be 2,400 acfm. The factor of safety in volumetric flow rate will be
,
FS = 2 400
,
1 630
FS = 147
.
Illustrative Example 12.4 For the planned directional drilling operation given
in Illustrative Examples 12.2 and 12.3 above, determine the bottomhole annulus
pressure drill string injection pressure while drilling at the end of the 3,000 ft
directional borehole. Also, determine the total fuel consumption rate for the
compressors when drilling at the end of the 3,000 ft directional borehole.
This solution is very similar to that given in Illustrative Example 11.2 except
the drilling rate for this directional drilling operation is anticipated to be 30 ft/hr (as
opposed to 60 ft/hr in Illustrative Example 11.2). The PDM downhole motor is the
same and the required power and drill bit speed outputs are the same (i.e., 25