Draw works ( drilling rig ) – Readyzone

Fig. 1Draw works

The draw works represent the heart of the rig, enabling equipment to be run in and out of the hole and also providing power for making or breaking pipe joints. The principle components of a draw work comprise drum shaft group; cat shaft and coring reel group; main drive shaft and jack shaft group; rotary counter shaft group; and controls ( refer to Figure 1 ).Fig. 1

draw - works

Fig. 1 – The Draw Works

Drum shaft group

As can be seen from Figure 1, the main components of the drum shaft group are as follows.

 Hoisting drum

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 Brakes

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Draw - Works

Fig. 2 – Schematic of the brake syatem.

Cooling system

The braking action caused by the brake blocks contacting the rims of the drum flanges generates a great deal of heat. This heat must be dissipated quickly, to avoid damage to the rims and brake blocks.

All draw works manufacturers employ a water-cooling system for removing the heat generated during braking. Figure 3 gives a schematic diagram of a typical water cooling system. Important features of Figure 3 include a motor pump which circulates water through a piping system to the water-jacketed rims and to the auxiliary brake. Finally, the water is returned to the suction tank.

Draw - works

Fig. 3 – Typical water cooling system for draw works and eddy current brake.

 Auxiliary brakes

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Hydrodynamic ( or Hydromatic ) auxiliary brake

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Draw - Works

Fig. 4 – Schematic of auxillary brake; (a) hydromatic brake; (b) eddy brake. (Courtesy of Oil and Gas Journal)

Eddy current auxiliary brake

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Comparison of hydromatic and eddy current brake

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Cat shaft and coring reel group

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Main drive shaft and jack shaft group

On many modern rigs the prime movers are of the diesel-electric type, in which diesel engines are used to generate electricity. Electric cables are used to deliver power to motors attached to the main drive shaft( Figure 1 ), rotary table and mud pumps. The main drive shaft is equipped with two sprockets connected by roller chains to high and low drive sprockets on the jack shaft. The jack shaft is connected to the cat shaft and drum shaft through roller chain and sprockets, as depicted in Figure 1.

Engagement of the high or low drive sprockets, cat shaft or hoisting drum shaft is achieved by sliding gear clutches.

With the combination of high and low drive sprockets on the jack shaft plus high and low air clutches on the drum shaft, the hoisting drum is, in effect, driven from a four-speed gear box. Reverse is obtained by reversing the rotation of the d.c. electric motors. Speed control is by a foot or hand throttle at the driller’s position.

Rotary counter shaft group

When the rotary table is powered directly from the draw works, a rotary counter shaft is required. The rotary counter shaft group comprises all the components required to transfer rotary motion to the rotary table. The equipment includes the rotary counter shaft drive chain and sprockets, air clutch, inertia brake and controls. In most modern rigs, however, the rotary table is independently powered by a separate d.c. motor and drive shaft assembly.

Related Links:-

*  Derrick             *  Drill collar            *  Kelly Drive

*  Drill pipe          *  Rotary table         *  Swivel

*  Tool joint          *  Drum shaft group

*  Cat shaft and coring reel group      *  Hoisting drum

*  Auxiliary brake                                     *  Brakes

Reference : H. Rabia, Oil Well Drilling engineering-Principles and Practice

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