US2771350A - Explosive - Google Patents

Description

United States Patent EXPLOSIVE Byron C. Baldridge, East Alton, 111., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Application March 25, 1954, Serial No. 418,747

6 Claims. (Cl. 525.1)

This invention relates generally to explosives and more particularly to a novel explosive charge adapted for use in tools such as'oil well perforated guns.

In the drilling of oil Wells, formations which appear suitable for producing oil are often by-passed in favor of drilling to greater depths in the search of more and possibly better formations. Then, after the maximum depth to which the Well is to be drilled has been reached, a casing is inserted into the oil well to the depth of the lowest formation found and the oil is pumped or otherwise removed therefrom. After all of the oil has been recovered from this formation, it is then desirable to investigate those formations which were by-passed during the drilling operation. This is accomplished by forcing projectiles or slugs through the casing and into the surrounding strata by means of one of the various perfora- 30 tor guns which are available for this purpose, such as, for example, one similar to the perforator disclosed in U. S. Patent 2,141,827. The projectile is forced from such guns by means of an explosive charge. This explosive charge must develop a large amount of energy when fired in order to force the projectile through the casing and into the surrounding strata.

Heretofore, the explosives utilized in gun perforators have contained in addition to nitrocellulose large quantities of nitroglycerine. Such explosives under ordinary circumstances outside an oil well will develop suflicient energy to satisfactorily propel a projectile. it has been found, however, that such a charge does not develop sutficient energy when it is fired in a deep oil Well to satisfactorily force the projectile from the gun perforator through the oil well casing. This is particularly true if 45 the charge is allowed to remain in the well for an appreciable time before the gun is fired. Frequently, the charge is capable of forcing the projectile only partially through the casing and as a result the perforator gun becomes lodged in the well. Furthermore, the explosive composition frequently fires prematurely as it is lowered into the oil well. It is therefore an object of this invention to provide a novel explosive charge adapted for use in tools. Another object of this invention is to provide an explosive charge having improved characteristics in deep oil wells. A further object of this invention is to provide an explosive charge for perforator guns which has advantageous characteristics under the temperature and pressure conditions ordinarily encountered in deep oil wells.

It has been found that the foregoing objects as well as others are accomplished, generally speaking, by providing an explosive charge for oil well casing perforators and similar tools composed essentially of high density particles of gelatinized nitrocellulose which has a nitrogen content of at least about 12.8 percent. The solidified particles have a surface area within the range of from about 100 to about 200 square centimeters per gram. The gravimetric density of the particles must be above about 0.800. Ordinarily, the amount of stabilizer, moisture, volatiles and like substances do not exceed more than about percent of the weight of the particles so that the particle is composed of a minimum of about 95 percent nitrocellulose and no substances are included which would impair the explosive characteristics or heat stability of 5 the particles. Suitable stabilizers include diphenylamine, the diphenyl dialkyl ureas and the like in the amounts of about 0.7 to about 1.2 percent. The particles are ordinarily coated with from about 0.1 to about 0.5 percent by weight graphite.

Contrary to the conventional practice of providing a progressive burning explosive for forcing projectiles, it has been found in accordance with this invention that the explosive charge for forcing the projectile from a gun perforator should be a neutral or non-progressive burning charge. The explosive charge must have a fast burning rate and must quickly develop a large amount of energy when the charge is fired. In order to make an explosive having a fast burning rate and one which develops a large amount of energy, it has been the practice in the art to add substantial quantities of nitroglycerine to the explosive charge. Nitroglycerine must be avoided in producing the high energy, highly heat stable charge required for satisfactory performance in an oil well. Any modifications which would tend to make the particles of smokeless powder progressive burning should also be avoided. Substantial quantities of deterrents, such as for example, dinitrotoluene and dibutylphthalate must be avoided in order to produce the explosive having the required characteristics.

Any suitable process for forming fibrous nitrocellulose into gelatinized nitrocellulose particles may be utilized, but an emulsion type of process, for example as disclosed by Schaelfer in U. S. 2,160,626 is advantageous. In accordance with this invention only those particles passing through a screen having openings of about 0.015 inch and remaining on a screen having openings therein of about 0.0075 inch are utilized for forming the explosive charge. In order to form droplets within the aforesaid size range, agitation of the emulsion must be vigorous.

In most gun perforators, an explosive charge of substantially spherical particles is preferred, but digressive burning particles of gelatinized nitrocellulose which have been rolled in accordance with conventional methods to flatten the spheres of digressive burning particles of single base nitrocellulose formed by other methods are suitable for the purpose and are, in fact particularly advantageous in some perforators.

In order better to clarify and further describe the invention the following is a description of one embodiment thereof:

About 100 parts by weight nitrocellulose composed of about parts 13.4 percent nitrogen nitrocellulose and about 40 parts 12.6 percent nitrogen nitrocellulose are suspended in about 800 parts water. About 330 parts of a suitable solvent such as ethyl acetate containing about 1 part of a stabilizer such as diphenylamine are added to the suspension. About 1 part calcium carbonate or other suitable neutralizer is added and the resulting slurry is agitated at about 70 C. until the nitrocellulose has dissolved and 8 parts gum arabic dispersed in about 50 parts water are added as agitation is continued. About onehalf hour later about 33 parts sodium sulfate dissolved in about 100 parts water are added and the slurry is rapidly agitated for about four hours after which time the temperature is gradually raised and the solvent is distilled from the slurry. After cooling the resulting solidified droplets are separated from the liquid phase.

Those solidified droplets passing through a screen having openings of about 0.015 inch and remaining on a screen having openings of about 0.0075 inch are segregated from the remaining droplets by a conventional wet screening process and are/thereafter dried in a conventional tray type steam heated dryer. These dried droplets are subsequently tumbled in a sweetie barrel with about 0.4 part graphite by means of a conventional coating process. The chemical composition of the resulting particles of gelatinized nitrocellulose of this embodiment is about:

Percent Nitrocellulose Q 97 Nitrogen in nitrocellulose 13.2 Diphenylamine 1 Calcium carbonate 0.5 Moisture 1 Graphite 0.3

The gravimetric density of the droplets is about 0.935. The surface area is about 135 square centimcters per gram.

It has been found that the non-progressive burning explosive charge of this invention contrary to the prior explosive charges containing nitrocellulose has not lost any of its energy when fired after it has been exposed to temperatures and pressures encountered in an oil well. Such an explosive is capable of developing as much as 980 calories energy per gram even after an exposure to temperatures as high as 330 F. for the period of time ordinarily required to properly locate the perforator gun in the well. In addition, this charge is capable of developing high energy without developing excessive and deleterious pressures within the gun when it is fired. Moreover, such an explosive charge is not 'only advantageous because it is capable of developing the energy required to force the projectile through the casing of the oil well but also because it has a high loading density occupying a minimum amount of space and permitting greater charge weights. Such an explosive charge is not only useful in perforator guns but is also useful in other explosive actuated tools and the like requiring the rapid development of large amounts of gas under a variety of environments.

Although the embodiments of the explosive charge of this invention have been described in detail in the foregoing many variations within the skill of the art can be made without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. As an article of manufacture, an explosive charge of non-progressive burning single base smokeless powder composed essentially of particles of gelatinized nitrocellulose having a nitrogen content of at least 12.8 percent, said particles having a surface area within the range of from about 100 to about 200 square centimeters per gram thereof with each particle having dimensions that enable it to pass through a screen opening of 0.015 inch and remain on a screen having 0.0075 inch openings, and having a gravimetric density of at least about 0.800.

2. An explosive charge composed essentially of solidified substantially spherical droplets of gelatinized nitrocellulose having a nitrogen content of at least about 12.8 percent, said droplets having a surface area within the range of from about 100 to about 200 square centimeters per gram thereof with each droplet having dimensions that enable it to pass through a screen opening of 0.015 inch and remain on a screen having 0.0075 inch openings, and having a gravimetric density of at least about 0.800.

3. In a device for forcing projectiles through the easing of an oil well, an explosive charge composed essentially of particles of gelatinized nitrocellulose having a nitrogen content of 13.2 percent, each of said particles having a surface area within the range of from about 100 to about 200 square centimeters per'gram thereof with each particle having dimensions that enable it to pass through a screen opening of 0.015 inch and remain on a screen having 0.0075 inch openings, and having a gravimetric density of at least about 0.800.

4. In a device for forcing projectiles through the easing of an oil well, an explosive charge of solidified substantially spherical droplets of gelatinized nitrocellulose having a nitrogen content of about 13.2 percent, from about 0.8 to about 1.2 percent stabilizer, a gravimetric density of about 0.935 and a surface area within the range of from about 100 to about 200 square centimeters per gram thereof with each particle having dimensions that enable it to pass through a screen opening of 0.015 inch and remain on a screen having 0.0075 inch openings.

5. An explosive charge suitable for forcing projectiles under conditions incident at the underground levels where oil well casings must be perforated, consisting essentially of a charge of solidified droplets of gelatinized nitrocellulose having a size such as to pass through a screen whose openings are 0.015 inch in diameter and tofbe retained on a screen whose openings are 0.0075 inch in diameter.

6. A non-progressive burning explosive charge adapted to force a projectile through the casing of an oil well, said charge consisting essentially of particles containing at least about nitrocellulose having a nitrogen content of at least 12.8 percent, said particles having a surface areaof from about to about 200 square centimeters per gram with each particle having dimensions that enable it to pass through a screen opening of 0.015 inch and remain on a screen having 0.0075 inch openings, and a gravimetric density of at least about 0.800.

References Cited in the file of this patent

Claims (1)

1. AS AN ARTICLE OF MANUFACTURE, AN EXPLOSIVE CHARGE OF NON-PROGRESSIVE BURNING SINGLE BASE SMOKELESS POWDER COMPOSED ESSENTIALLY OF PARTICLES OF GELATINIZED NITROCELLULOSE HAVING A NITROGEN CONTENT OF AT LEAST 12.8 PERCENT, SAID PARTICLES HAVING A SURFACE AREA WITHIN THE RANGE OF FROM ABOUT 100 TO ABOUT 200 SQUARE CENTIMETERS PER GRAM THEREOF WITH EACH PARTICLE HAVING DIMENSIONS THAT ENABLE IT TO PASS THROUGH A SCREEN OPENING OF 0.015 INCH AND REMAIN ON A SCREEN HAVING 0.0075 INCH OPENINGS, AND HAVING A GRAVIMETRIC DENSITY OF AT LEAST ABOUT 0.800.