US2351468A - Stabilized explosive composition - Google Patents

Description

Patented June 13, 1944 STABILIZED EXPLOSIVE COLIPOSITION Clifiord A. Woodbury, Media, Pa, asslgnor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application July 18, 1941, Serial No. 402,956

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This invention relates to a novel explosive composition adapted for use under extreme conditions of temperature and pressure.

For many years explosives have been used in the shooting of oil Wells to start the flow of oil or to increase it after the wen have ceased to produce paying quantities. The explosive that has been most favored in such oil well blastin in the past has been liquid nitroglycerin, which has been loaded in the desired amount into special containers to form the well-known torpedoes for use. Another form of high explosive used in oil well blasting has been the so-called solidilied nitroglycerin, or blasting gelatin, which consists of a thick viscous material resembling crude, translucent rubber, as a result of the solution of nitrocotton in nitroglycerin in the ratio of around 4 to 9 parts of nitrocotton to 90 parts of nitroglycerin.

Such explosives were generally satisfactory and reliable in the shooting of relatively shallow wells. At the present time, however, depths of 10,000 ft. to 15,000 ft. are encountered and at such depths the conditions are such that the foregoing explosives high in nitroglycerin are somewhat unreliable and hazardous unless unusual precautions are taken. Two factors come in to cause difilculties. In the first place, high pressures are met in deep hole shooting, of the order of severa1 thousand pounds per square inch. Under such pressures, the explosives show erratic behavior. They may become insensitive and fail to shoot, or may explode prematurely. Either condition is undesirable, and the presence of unexploded, potentially explosive material in the bore hole becomes a hazard, since subsequent boring into the charge would probably prove disastrous. A second troublesome factor comes in the high temperatures resulting from deep drillns. for example, up to 200 F. and higher. Whereas it is frequently the practice, after an explosive charge has been lowered into a hole, to set the time bomb for 20 or more hours, explosion may take place prematurely in 4 or 5 hours under the high temperature and pressure conditions to which the charge is exposed. Such lack of reliability is hazardous, since tamping or cementing operations may be in progress at the time of the explosion.

An object of the present invention is an explosive composition adapted for deep well shooting and possessing improved reliability of performance and markedly increased stability. A further object is a stabilized explosive compositioncapable of withstanding excessive temperature and pressure conditions while maintainin its original explosive properties. Additional ob- .iec'ts 'will be disclosed as the invention is described more at length hereinafter.

I have found that the foregoing objects are obtained by employing an explosive composition adapted for use in deep wells, and comprising more than of nitroglycerin or other liquid explosive nitric ester and a suitable amount of a weak organic base as stabilizer therefor. Preferably, the explosive will contain more than of nitroglycerin, and may comprise either liquid nitroglycerin, or a blasting gelatin type.

As stated above, a weak organic base is included as a stabilizing ingredient in the explosive composition, and I find it essential that the base be one having a dissociation constant lower than 1 x 10- since too strong a base might have a decomposing effect on the nitroglycerin or other liquid nitric ester present. Such bases are capable of serving as acid acceptors in case of decomposition of the nitric ester. The following will serve as illustrations of organic bases that fall 'within the scopeof the invention. I find it preferable to use an amount of the organic base within the range of 0.5 to 5.0% of the explosive content:

Dissociation Base constant Urea 1.5X10- Alpha-no hth lamine 9.9)(10- lBets-nap thy amin 2x10-" 1? dine 3. 3X10-' 1? enylenediamin 3. 3Xl0- o-Toluidlne 3. 3X10- Diphenylamine l l0-" sym diphenyl-dimethyl urea. 1X10- sylm-diphenyl diethyl urea. lx10- 'I iourea LlxlO- Acetanilid 4. 1X10 Dicyandiamld lXl0- While the foregoing weak bases are all applicable under the invention, I find that diphenylamine and the diphenyl-dialkyl ureas are particularly advantageous. The following examples will serve to illustrate the stabilizing efiect of such compounds when used with nitroglycerin or blasting gelatin at elevated temperatures and pressure. The efiect of the stabilizer is shown by the increased time in minutes elapsing before the explosion of the charge in question, this increase being the result of the presence of the added compound:

terial. The liquid explosive may also be com- Temperature Explosive Stabilizer Amt. Pressure Percent Lba/sq. in. Mm. Mine. 7 None 1,500 157 17 i do 3,000 82 9 Nitroglycerin Diphenylamiue 2 I 1,500 360 97 3,000 300 73 giphenyldiethylurea 2 111., $8 g8 one.. Blasting gelatm {Diphenyldimethylurea 2 3,000 330 12 I 1 91% nitroglycerin, 4.5% nitrocotton, 3.5% wood pulp, 1.0% chalk.

while at 212 F., under the same pressure-the time was increased from 82 to over 300 minutes. Likewise, at 1500 lbs/sq. in., the introduction of the same amount of dlphenylamine increased the life from 157 to more than 360 minutes at 212 F., while the increase under the same pressure at 275 F. was from 17 to 97 minutes. Similar stabilizing efiects were obtained by the use of other weak bases of the type specified. It will be understood that the conditions of testing shown in the examples are somewhat more severe than would be expected under field conditions, but the same stabilizing efiect would result.

It has been stated that the preferred amount of weak base for use as stabilizer is preferably within the range of 0.5 to 5.0%, based on the weight of the explosive compound. A smaller amount than 0.5% is insufiicient to give the desired effect, while the use of more than 5% of such material would lower the stren'gth of the explosive compound, by the introduction of so much non-explosive material. Since the base will be largely dissolved in the nitroglycerin also, its presence would tend to desensitize the composition, if too large an amount were used.

organic base can be introduced into the con tainer' in increments, if desired, and the liquid explosive be poured in in the same manner. When blasting gelatin is used, the base should be inposed entirely, if desired, of the above nitroglycol or any other suitable liquid explosive nitric ester.

It should be noted that it is not part of my invention to include these organic bases in commercial dynamite compositions.

The invention has been described in the foregoing at some length. It will be understood, however, that many variations may be introduced in Y the specific materials used and in amounts without departure from the scope of the invention. I intend to b limited therefore only by the following patent claims. a

I claim:

1. An oil well explosive composition comprising more than 60% of a liquid explosive nitric ester and between 0.5 and 5.0% of an organic base having adissociation constant lower than 1X10.

2. An oil well explosive composition comprising more than of a liquid explosive nitric ester and between 0.5 and 5.0% of an organic base having a dissociation constant lower than use in deep wells comprising more than 90% of a liquid explosive nitric ester and between 0.5 and 5.0% of diphenylamine.

8. An oil well explosive composition adapted for use in deep wells comprising more than 90% of a liquid explosive nitric ester, sufficient nitrocellulose to form a. firm gel with the liquid nitric ester, and between 0.5 and 5.0% of a diphenyldialkyl urea.

CLIFFORD A. WOODBURY.