Steel bull wheels and calf wheels are now being employed for deep wells. The advantage of steel lies in its longer life as 8 or 10 wells may be drilled without relining the wheels.
The band brake consists of a steel band 10 in. wide. One end of the steel band is fastened to the floor of the derrick and the other passes around the brake wheel of the bull wheels, and is attached to the lower arm of the brake lever. This lever con trols the band brake. Pushing down on the brake checks or stops the bull wheels and thus controls the speed of the tools when they are let into the hole. If the tools are let into the hole rapidly the band brake may become red hot. To avoid this a water spray plays upon the band brake.
The headache post is a small post which is placed under the walking beam and keeps the walking beam from striking the driller's head if the beam is displaced from its saddle. The headache post rests on the nose sill.
The four legs of the derrick do not rest on the floor but upon blocks of wood or concrete bases sunk in the ground.
Girts are the horizontal pieces that bind the derrick legs together. Braces are the cross pieces extending at an angle of 45 deg. from leg to leg.
Some very heavy rigs have double sets of braces and girts, and heavily reinforced legs.
A hole is cut through the floor, just under the end of the walking beam. This hole is the start of the prospective oil well.
Rig Irons.—All the metal parts used in the construction of a derrick, with the exception of the nails, bolts, sand reel, and guy wire, are known collectively as the "rig irons," and designated by the size of the crank shaft that carries the band wheel.
The crank shafts vary from 3)4 to in. in diameter. The 3%, 4, 4M, and 5-in. rig irons are used on light rigs for drilling from 1000 to 2500 ft. in depth. Heavier rig irons of the 6-in. type and extra heavy 7j in. are used on deep wells from 2500 ft. and deeper, especially under difficult drilling conditions, as found in California. Six-inch irons are now being used in Texas and in the deeper fields of Oklahoma.
Main Operations in main operations of oil well drilling are: 1. Cutting the rock material.
2. Removing the cut material.
3. Casing the hole.
4. Fishing out lost tools or casing.