ACTION OF TOOLS In drilling, the striking action of the tools must be likened to the lash of a whip. The back lash or snap of the drilling cable drives the bit into the rock and drills the hole. The tools when in the hole must swing free of bottom at their lowest point. As the beam rises and falls there is vibratory action in the elastic cable that causes the line to stretch. The tools will lash out 4 or 5 ft. and strike bottom with terrific force. Experienced drillers tell from the feel of the tools whether or not the bit is striking a solid blow. The "pick up" of the cable is the measure of the blow.
"Pick up" is the feel of the tension on the drilling cable, sand, line or measuring line. If the drilling tools are allowed to rest on the bottom of the hole and then raised there will be a slight jerk perceptible to the eye or to the hand just as the tools are lifted from the bottom of the hole. The same is true of the bailer or the plumb bob on a measuring line. This "pick up" is most important for drillers, not only in measuring hole but in order to know whether or not the tools are striking bottom or swinging free in the hole.
When the screw is "extended" to its full length, which varies from 2 to 6 ft., the bull rope is thrown on the bull wheels and band wheel. The cable is then unclamped from the rope clamps, and pulled from the hole.
Two bull ropes at a time are used in pulling tools from deep holes.
Bailing.—The bailer is next run. The bailer (see Fig. 11a) is a long tube, much like a joint of casing or pipe. It has a valve in its bottom, and a bail at the top to which is attached the sand line.
The sand line, which is used to lift the bailer, is wound on a spool or drum called the sand-line reel or drum and runs over a pulley on top of the derrick called the sand-line sheave. The ' sand-line drum is driven from the band wheel by friction drive. On one end of the sand line shaft is a drive wheel which, when pulled against the revolv ing band wheel, raises the sand line. A lever operated from the derrick floor pulls the drive wheel against the face of the ' band wheel.
When the brake is neutral or upright the bailer drops of its own weight. The friction drive is only used to brake the bailer or to lift it from the bottom of 1 the hole.
The bailing operation is a simple one. The bailer is first lowered to bottom and fills with fluid. When raised the bottom valve closes. The bailer is raised and dumped and then lowered again. This is I repeated several times until the driller is satisfied that the hole is clean, when the drilling tools are again introduced.
Casing the Hole.—When it is desired to insert casing, the tools are withdrawn and tied back in the derrick.
Then the elevators, which are suspended from the top of the derrick by cables called the casing lines, are lowered to the floor. A joint of casing is rolled into the derrick and the elevators are clamped around the casing under a collar. The elevators are now raised to bring the casing over the hole, and the casing is next lowered into it.
A casing spider (see Fig. 12) is set on a pair of sills in the cellar of the derrick. The casing is guided through the hole in the spider. The spider lugs are then placed. The casing is eased down until the lugs grip the pipe. The elevators are then unclamped and raised for another joint. When the second joint is screwed into the top of the first joint the casing is lifted a trifle, the spider is knocked free with a sledge hammer, and the lugs are withdrawn. The two joints are now lowered until the collar of the second joint is near the spider. The casing is then caught in the spider, and the elevator is released. This procedure is repeated until the necessary casing is placed in the hole.
Cellars.—With the modern cable-tool system of drilling, a good cellar is essential. The floor of the cellar serves as the main rest or support for heavy strings of casing, instead of putting such strains on the derrick floor. The cellar is usually 20 ft. deep and 6 ft. square. Its walls are lined with timber or concrete. A ladder extends from the floor of the derrick into the cellar. A pair of heavy sills is laid in it, and a heavy casing spider rests on them. (See Fig. 33, page 89, Chapter IV.) When casing is handled one man stays in the cellar and puts in the lugs which grip the casing, and puts on or releases the elevators from the hook.