STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

856 Drilling and Well Completions
Equations 4-108 and 4-109 become
a=
(l.0)Q + 34.52(60)(0.7292)'
53.3Q
b=
1.136 x lo-"'
0.03835
The bottomhole temperature tbh(OF)
is approximately (see Table 4-109)
kh = 37.60 + O.Ol(l0,OOO)
Thus,
= 137.6 F
Equation 4-123 becomes
2.003 x 10-3Q2 = {[(1694.7)' + b(547.6)2] e2a(10.000)/547.6 - b(547.6)2}0.5
where a and b are functions of the unknown Q and are given above.
The above equation must be solved by iteration for values of Q. The value
of Q that satisfies the above equation is
Q = 2,110 actual cfm
This is the upper value of the minimum air volumetric flowrates for the interval
to be drilled (i.e., 8,500 to 10,000 ft).
Surface Compressor and Booster Requirements
Once the governing minimum air volumetric flowrate has been found for an
interval to be drilled, the compressors of fixed volumetric flowrate can be
selected. An additional compressor is usually on site as a stand-by to have
additional air available in case of unexpected downhole problems and to have
a compressor available in the event one of the operational compressors needs
to be shut down for maintenance.
The number of fixed volumetric flowrate compressors is selected such that
the necessary minimum air volumetric flowrate is exceeded. The air volumetric
flowrate that the compressors produce is shown as the real air volumetric
flowrate. This real air volumetric flowrate, Q (actual cfm) is used to calculate
the bottomhole pressure. Bottomhole pressure, P, (lb/ft2 abs) is determined by
P, = [(P: + bT;" )ezahnav - bTf]0'5 (4-128)
where Q is used to find the new values of a and b.