STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Drilling Bits and Downhole Tools 785
Mill tooth bits, each $ 260.00
insert bits 1,250.00
Mud, per day 500.00
Water, per day 200.00
Desilter, per day 150.00
Supervision, per day
Total daily cost
250.00
$2,6 10.00
Hourly rig cost $ 108.00
Trip time is 0.7 per hour per 1,000 ft.
The cost equation is
C = B/F + C,T,/F + CtT,/F (4-75)
where C = drilling cost per foot in $/ft
B = bit cost in $
F = footage drilled in ft
C, = rig cost for drilling in $/hr
T, = drilling time in hr
Tt = trip time in hr
Cc = rig cost for trip in $/hr
Assumptions are (1) comparable lithology, (2) C, = Ct = $108/hr, and (3) the
well in question is to be deepened from 6000 to 7650 ft.
The bit record from the offset control well is presented in Table 4-96.
The cost per foot for each bit run is calculated as follows:
Bit No. 1
Drilling hours = 10.5
Trip hours = (0.7 hr/1000 ft)(5.958 x 1000 ft) = 4.1 hr
Total hours = 14.6 hr
Total footage = 160 ft
Therefore.
C = 1/F [B + C,(T, + T,)] = 1/160 ft[$260 + $108/hr (10.5 + 4.l)hrl
= $11.51/ft
Table 4-96
Cost of Steel Tooth Bits [34]
Bit No Depth out, ft Footage, ft Bottom time, hr
1 6008 174 19.0
2 6268 260 19.5
3 6518 250 25.0
4 7444 926 99.75
5 7650 206 25.5
Copyright PennWell Books, 1986.