Determining Size of Shot.—A hole 634 in. in diameter in a fine grained sandstone 25 ft. thick would require four shells 5 in. in diameter and 5 ft. 2 in. long, each containing 20 qts. of nitro glycerine. A shot for a hole which has a diameter of 43 in. and has a sand body 45 ft. thick consists of six shells 3 in. in diameter and 6 ft. 11.3 in. long of 10 qts. capacity or 60 qts. in all.
Shells are in general made in 3, 5 and 7 in. sizes holding 10, 20 and 30 qts. respectively. The following table gives some idea of the size of shells used: Firing firing shots two methods are used. One method is to use a "go devil" or jack squib which is a small shell containing nitroglycerin. This shell is dropped from the top of the hole upon the charge and is guided by the wire line with which the charge has been placed. It may be necessary to drop several "go devils" before the charge is detonated.
The second method of detonating is to use an electrical firing device. Successful results are obtained by this method but it fails sometimes through broken wires which allow contact with the casing, thus "short circuiting" the current.
is the practice of using small charges of 2 to 4 qts. of nitroglycerin for occasional shots. These shots are used particularly to stir up sluggish wells several months after the first shooting.
Many wells respond to squibbing and show a marked increase in production afterward. It is thought that squibbing burns the paraffine coatings from the walls of the hole and allows the oil to enter again freely. Some operators squib every few
months.
are thn men who put the charges in the wells and fire them. These men become very reckless in the handling of nitroglycerin. They transport the glycerin in lead-lined cans, and drive their "glycerine wagons" over rough, bumpy roads with an abandon that is foolhardy. Shooters take great chances and every once in a while the papers report "shooters" blown to atoms. It is likely such explosions are due to high heat engendered by the heat of chemical action where the glycerin still contains some free acid.
Spontaneous practice of placing charges of nitroglycerin in a hole and letting the charge explode itself is being used in North Central Texas. This was started by acci dentally leaving a shot in a hole some hours. The charge ex ploded spontaneously. Experiments were then tried and it was found that shots would explode in from '24 to 96 hr.
This method is not efficient as there must be some disintegra tion of the charge due to chemical reaction. It is also dangerous.
Action of Well after Shooting.—A well when shot may flow freely. In this case the control-casing head regulates the flow. However, if a steady flow does not follow the shot, the well must be pumped. Preparatory to pumping, the hole is bailed clean to get out the drilling sludge remaining, and to clean the residue from the shot. The well is then put on the pump as described before.