Page 207 - Air and Gas Drilling Manual

Chapter 5: Shallow Well Drilling Applications 5-49
TN
˙
=
W
td
, 5 252
where T is the applied torque to the top of the drill string (ft-lb), (5-11)
N is the rotary speed (rpm).
For this example, Equation 5-11 becomes
(, 2 000 ) (60 )
W ˙ =
td
, 5 252
W ˙ td = 22 .9
Assuming an overall mechanical efficiency for the hydraulic top drive system is, ε
m
= 0.8, the actual shaft horsepower needed for the hydraulic pump which operates the
top drive system is estimated to be
W ˙ = 22 .9
td
. 080
W ˙ = 28 .6
td
Thus, the total actual shaft horsepower required by both the compressor and the
˙
hydraulic pump operating the top drive, W , is
t
˙
W = W ˙ as + W td
˙
t
˙
W = 193 .2 + 28 .6
t
˙
W = 221 .8
t
The prime mover power ratio is
.
PR = 221 8 ( 100) = 65 1
.
.
340 8
Figure 4-17 can be used to obtain the approximate diesel fuel consumption rate for
the prime mover at this power level. At this power level the approximate diesel fuel
consumption rate is 0.558 lb/hp-hr. The total weight rate of flow of diesel fuel to
the prime mover is

˙ w = . 0 558 (221 . ) =8 123 .8 lb/hr
f