STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

600,000
9,
Hoisting System 525
block weighs 9,000 lb and the traveling block weighs 4,500 lb. Assume that there
are no other tools hanging in the derrick and that the deadline is attached to
the rig floor across from the drawworks in its normal position (see Figure 4-7).
Assume the standard deduction of 2% per working line to calculate eh.
eh = 1.00 - 0.02(8) = 0.84
From Equation 4-13
+
F, = 604,500 + --
600 + 000
0.84(8) 8
ooo
= 604,500 + 89,286 + 75,000 + 9,000
= 786,786 lb
Drawworks
The drawworks is the key operating component of the hoisting system. On
most modern rotary drilling rigs, the prime movers either operate the hoisting
drum within the drawworks or operate the rotary table through the transmission
within the drawworks. Thus the drawworks is a complicated mechanical system
with many functions [1,7].
Functions
The drawworks does not carry out only hoisting functions on the rotary
drilling rig. In general, the functions of the drawworks are as follows:
1. Transmit power from the prime movers (through the transmission) to its
hoisting drum to lift drill string, casing string, or tubing string, or to pull
in excess of these string loads to free stuck pipe.
2. Provide the braking systems on the hoist drum for lowering drill string,
casing string, or tubing string into the borehole.
3. Transmit power from the prime movers (through the transmission) to the
rotary drive sprocket to drive the rotary table.
4. Transmit power to the catheads for breaking out and making up drill string,
casing string, and tubing string.
Figure 4-9 is a schematic of drawworks together with the prime mover power
source.
Design
The drawworks basically contains the hoist drum, the transmissions, the brake
systems, the clutch systems, rotary drive sprocket, and cathead. Figure 410 shows
a schematic of the drawworks.
The power is provided to the drawworks by the prime movers at the master
clutch (see Figure 49) and is transmitted to the master clutch shaft via sprockets
and roller chain drives. The speed and the torque from the prime movers are
controlled through the compound. The compound is a series of sprockets, roller
chain drives, and clutches that allow the driller to control the power to the