METHODS OF SHOOTING WELLS In order to allow the setting of plugs it is most advantageous to shoot wells where oil and water bearing formations are penetrated by casing which can not be removed. It is necessary to shoot wells which have one or more strings of sidetracked casing (which may serve to conduct water into or between oil-bearing formations) in order that all holes may be converted into one large cavity, which must then be plugged to prevent the passage of water. It sometimes becomes necessary to first shoot with a small amount of explosive to create a " pocket " in which to place a charge large enough to obtain the desired results. In cases where the " pocket " has been made torpedoes of comparatively short lengths are con nected by a wire so as to allow them to rest alongside of each other in the hole.
The method of shooting wells for repair work, such as has been mentioned, is somewhat different from the common practice in shooting new wells and is well described by M. J. Kirwan as "Previous to the year 1910 oil wells in California were generally shot in the following manner: "A shell, or container, was made of ordinary galvanized, light sheet iron. Sticks of stock 60 per cent. dynamite, usually from ";,i to 1% inches in diameter by 8 inches in length, were loaded into the shell which was lowered into the well to the desired depth by the sand line. The charge of dynamite was detonated by the use of a blasting cap lighted with a fuse. The length of the fuse was regulated so as to allow sufficient time to lower the shell to the desired shooting depth before detonation. The diameter of the shell was governed by the size of the casing through which it had to be run and the length of the shell by the amount of dynamite used.
"In some instances a piece of casing was used for a container of the dynamite. This container was lowered into the well to the desired depth by an attached string of tubing extending to the surface. The charge of dynamite was exploded by dropping a squib-shot through the tubing. Squib-shots usually consist of a short piece of pipe about one
inch in diameter containing one or two sticks of dynamite with cap and lighted fuse attached. The explosion of the squib-shot detonated the main charge of dynamite previously lowered into the well.
"The foregoing described methods of shooting wells are still used in some cases. The results obtained by employing such methods have, in many instances, been unsatisfactory, and in some cases detrimental to the well on account of casing having been shot at the wrong depth as a result of premature explosion. There are cases in which workmen en gaged in shooting have been killed or injured, while using one of these methods, on account of accidental explosions at the surface.
"The modern method of shooting oil wells is accomplished by the use of a specially prepared blasting gelatin, an explosive much safer than dynamite or nitroglycerin, on account of its insensitiveness to heat, fric tion or concussion. Straight blasting gelatin is a nitroglycerin and gun-cotton composition, and is not especially adapted to well shootingon account of its tendency to so harden shortly after manufacture that it can not be made to conform to the size or shape of the desired shellor container.
"Blasting gelatin, for well-shooting purposes, is prepared by the addition of wood pulp in certain proportions in order to make it suffi ciently plastic that it can be properly shaped for the container.
"Electric detonators, which are especially prepared to withstand the pressure to be contended with in oil-well shooting, are embedded in the blasting gelatin and then connected in series so as to insure a simulta neous explosion of the entire charge. The torpedo or container, when loaded, is lowered into the well to the shooting depth by the sand line, and the waterproof leading wires from the electric detonators are connected to a blasting machine, or power circuit, at the surface. The charge of gelatin is then detonated by electric current at the desired moment.