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90 Part I Liquid Drilling Systems

The total flow area of nozzles should be determined by

ρ
r ffiffiffiffiffiffiffiffi
A T = 0:00912q max (4.15)
C d Δp b
After the critical depth is reached, the flow rate is decreased with a
subsequent increase in depth to maintain Δp d = p p if the maximum bit
m + 1
hydraulic power criterion is used or Δp d = 2p p if the maximum jet impact
m + 2
force criterion is used. The flow rate at the depth of interest should be
set to be

r ffiffiffiffiffiffiffiffi
q = m Δp d (4.16)
c

where
Δp d = p p (4.17)
m + 1

for the maximum bit hydraulic power criterion, and

Δp d = 2p p (4.18)
m + 2
for the maximum jet impact force criterion. The total nozzle area should
be determined to be

ρ
0:00912q r ffiffiffiffiffiffiffiffi
A T = (4.19)
C d Δp b
where

Δp b = m p p (4.20)
m + 1

according to the hydraulic horsepower criterion, and

Δp b = m p p (4.21)
m + 2

according to the maximum jet impact force criterion.