My good friend Scott Hirshey recently gave me a copy of an old pamphlet he obtained from the estate of the late Harry Horner, the well-known oil field engine enthusiast who passed away last year. The pamphlet, Driiling, Getting Acquainted with Your Company's Operations, was written by professor CM. Young and printed by The Columbia Gas System in 1949. I've excerpted portions of the pamphlet for this issue, as I think it gives a good description of the cable-tool drilling method under which most of our old oil field engines labored.
Standard and Rotary Drilling
There are two principal methods of drilling wells; the cable tool method and the rotary method. In the cable tool method a heavy drill is dropped upon the rock, which is broken by the blow. In the rotary method a drill is pressed against the rock with great force and turned, and the rock is worn away by the concentration of pressure in a small area.
The Standard Rig
The walking beam is driven by the engine and gives motion to the tools. As finally developed it was an oak beam 26 feet long, supported at the middle on a Samson post with one end directly over the hole. A pitman at the other end is connected to the wrist pin of the band wheel crank and the band wheel is driven by a belt from the engine.
On the side of the derrick opposite the band wheel is the bull wheel on which the drilling cable is wound. On one side of the bull wheel is a grooved wheel that carries the bull rope, by which the bull wheel is driven from the band wheel. The other side has a brake drum for control of the tools when they are run in the hole.
In order to allow the cable to be fed out as the hole is deepened it is attached to the walking beam by a temper screw; a screw allowing six feet of travel through a split threaded box, the two halves of which are held together by a clamp. When the screw has been let out its full length of travel, that is, when a 'screw' has been drilled, this split box is opened and the screw is raised through it, and the box is again clamped onto the screw. This raises the rope clamp by which the temper screw is attached to the rope.
To make this change the bull rope is thrown onto the bull wheel and the cable wound up until the tools are supported a little above the bottom of the hole. Then the rope clamp is moved upward and tightened on the cable, the bull wheel released and some slack thrown into the cable, and drilling is carried on again.
When exceptionally heavy strings of casing have to be handled, a rig with a calf wheel is used. The calf wheel is similar to the bull wheel but is on the band-wheel side of the derrick and is driven from the band wheel by chain and sprocket, with the use of the calf wheel, and with multiple sheaves at the top of the derrick and in the traveling block that supports the casing, heavy strings can be handled.
When no calf wheel is used the top of the derrick, called the water table, carries two sheaves; one for the sand line (which handles the bailer) and one for the drilling cable. Thus, it will be seen that the drilling cable runs up from the bull wheel over the crown pulley and down to the tools. The sand line sheave is set to one side and the line runs from the bailer up over this sheave and down to the sand reel, which is commonly driven by friction from the band wheel.
The sand line and bailer are used in removing cuttings from the hole. The bailer is a long tube with an upward-opening valve at the bottom. This valve has a dart, which extends a few inches below the bottom of the bailer and raises the valve when the bailer reaches bottom.
The bits are steel forgings made in various sizes and designs to fit different conditions. The cutting edge is forged to a distinct edge. The angle of the sides runs from about 90 to 100 degrees, depending upon the kind of rock that is being drilled. The bit does not cut the rock, but breaks it.
Since the bit is forged to an edge, the result is that great pressure is suddenly concentrated on the narrow line on which the bit strikes the rock. This concentrated pressure is so great that the strength of the rock is overcome and chips are broken off. Thus the essence of drilling by the standard method is a series of blows against the rock.
In order to prevent the accumulation of cuttings on the bottom of the hole where they would simply be pulverized by following blows, water is poured into the hole if it is not already present. The finest cuttings make this water into a mud, which hinders the settling of the coarse cuttings, and the whole is constantly stirred up by the up-and-down movement of the tools.
When drilling begins, there is not room for tools below the end of the walking beam, so the walking beam cannot be used. The tools are hung on the cable and a jerk line is attached to the cable above the bull wheel and run to the wrist pin on the band wheel crank. Then when the crank revolves the cable is pulled out of line and let back again, and the tools are raised and dropped. A spudding shoe is used to protect the cable, and this is especially necessary when a wire line is used. The beginning of a hole is always called 'spudding in,' even when a rotary rig is used.
Conductor Pipe and Drive Pipe
When the hole is started a conductor pipe is set in the ground and carefully plumbed. This is necessary to keep out the surface soil and to start the hole in a truly vertical direction. Also sometimes drive pipe is used. This is a pipe that extends from the surface to the first solid rock, and because it sometimes has to be driven down it is called drive pipe. If the material below the loose surface soil stands well at all, the drive pipe is not used.
The Rotary Method
Very briefly, it consists of pressing a bit against the rock and turning it. At the same time a stream of mud is pumped down through the hollow drill pipe that turns the bit. This mud cools the bit and carries the cuttings to the surface. Also, because there is a column of heavy liquid in the hole, gas, oil or water cannot flow in from the beds passed through and the caving off of fragments of rock is prevented, or at least hindered.
The bits used after hard rock is met have a set of wheels much like cog wheels with sharp teeth. These roll around against the rock and are pressed against the rock by the weight of the drill pipe. Thus, great pressure is concentrated on the teeth and the rock is broken by this pressure. The drill pipe is turned at the surface by a rotary table that is driven by a steam engine or other motor. The drill pipe slides down through the rotary table and new lengths are added at the top as needed. Thus drilling is almost continuous. But the changing of bits, when this is necessary, is a long job because all of the drill pipe has to be pulled out of the hole and then run back again. Since it is not necessary to shut out water, little casing is run until the hole is finished. Drilling is more rapid than with a standard rig, but the rig costs much more and much more power is required, as well as a larger crew. It is the saving in time, which has led to the use of the rotary in those fields to which it is suited.
I hope you enjoyed this brief description. As ever, anyone interested in an OFES society membership please write or e-mail at the address below.
Contact the Oil Field Engine Society at: 1231 Banta's Creek Road, Eaton, OH 45320-9701. On the Web at www.oilfieldengine.com or e-mail at: firstname.lastname@example.org