US3367429A - Perforating gun for small diameter bullets - Google Patents

Description

Feb. 6, 1968 F. v. PORTER PERFORATING GUN FOR SMALL DIAMETER BULLETS Filed Oct. 21, 1965 INVENTOR FORREST V. PORTER BY 2 5 Jew/ 4;

' ATTORNEY United States Patent 3,367,429 PERFORATING GUN FOR SMALL DIAMETER ULLETS Forrest V. Porter, Houston, Tex., assignor to Dresser Industries, Inc., Dallas, Tern, a corporation of Delaware Filed Oct. 21, 1965, Ser. No. 499,670 4 Claims. (Cl. 1754.58)

ABSTRACT OF THE DISCLOSURE A 'bullet perforating gun assembly for firing small diameter bullets utilizing a propellant charge compounded for firing regular size bullets. The gun assembly including a cylindrical gun body having laterally oriented barrel members that include a central longitudinal bore for containing the bullet and a plurality of venting bores extending longitudinally through the barrel member parallel to the central longitudinal bore. The combined cross-sectional area of the bores is substantially equal to the area of a regular size bullet to control the chamber pressure and avoid damage to the gun body. A shear disc, located between the charge and the bores, shears after detonation of the charge and after a predetermined pressure increase in the chamber, whereby the peak chamber pressure is held below a magnitude that would damage the body.

This invention relates to bullet perforating guns utilized in oil field operations.

Although bullet perforating guns have been used in perforating well'bore casings for many years, the design of such guns are fraught with many difiiculties not ordinarily found in ballistics. For example, the diameter of the gun body is extremely limited. It has to be run inside oilfield casing which in many cases has an inside diameter of 55 /2" and, in cases of tubing, even less. This results in a gun body with an over-all diameter of 4 and an efiective barrel length of only about 2". With a standolf from zero to 1 /2" maximum, the bullet then has to penetrate a /8" steel casing and several inches of cement before it reaches its ultimate target, the formation where it is expected to penetrate many more inches.

One of the bullet perforators that has been successful in the industry is constructed in accordance with the dis closure of F. V. Porter, U.S. Patent 2,953,971 dated Sept. 27, 1960. In such patent, the bullet customarily used is approximately Recently there has been a demand for a smaller diameter bullet. By balancing chamber volume versus barrel volume, it has been possible to obtain very satisfactory results with a bullet. However, barrel volume decreases rapidly with a decrease in diameter, and it was found that if the bullet is decreased to A" or /8", the density of the powder load would have to drastically reduce in order to keep the peak pressure within safe limits. However, a decrease in load density results in reduced burning rate and average pressure with the result that the velocity of the bullet and its penetration are correspondingly reduced.

Throughout this application the term regular size bullet will be used to define bullets having a diameter in the approximate range of A5" to and the term small diameter bullets will be used to define bullets having a diameter in the approximate rangev of to /1".

While it would be possible to design an entirely new gun for small diameter bullets, such a procedure is expensive. It requires the carrying of an inventory of more guns and also more cartridges. Moreover, operations one day may call for regular size bullets and the next day for small 3,367,429 Patented Feb. 6, 1968 diameter size or a fixture of both may be required. With the advent of replaceable barrels, such as disclosed in U.S. Patent 2,953,971, the life of gun bodies have substantially increased. Further, replaceable barrels permit the same gun body to be used for a range of different size bullets. Therefore, it is very desirable for eificient and economical operation that the same gun body used for regular size bullets be also used for small diameter bullets. The present invention is directed to novel apparatus which permits the regular bullet perforating guns to be utilized to fire small diameter bullets.

It is an object of the present invention to provide a bullet perforating gun for small diameter bullets in which there is means to compensate for the small barrel volume.

It is another object to provide a bullet perforating gun for small diameter bullets in which there is means to develop a high average pressure and at the same time relieve such pressure to prevent peak pressures of excessive duration.

It is a further object to provide a bullet perforating gun for small diameter bullets in which there is means to develop highest peak pressure at the rear of the bullet and additional means to relieve chamber pressure.

In order to accomplish the above objects, and other objects which will become apparent from the detailed description to follow, the bullet perforating gun of the present invention is formed of a gun body provided with a plurality of laterally extending openings forming individual guns. Each individual gun has a charge chamber accommodating a propellant charge and ignition means therefor, and a removably secured generally tubular barrel member. The barrel member has a central bore forming a barrel adapted to receive a small diameter bullet and a plurality of additional small bores circumferentially spaced about the central bore. A shear disc positioned between the charge chamber and the barrel member extends across the central bore and circumferentially spaced bores. Discharge of the propellant creates a pressure which breaks the shear disc at the central bore and circumferentially spaced bore discharging the bullet and relieving the chamber pressure.

A preferred embodiment of the invention is illustrated in the accompanying drawings in which:

FIGURE 1 is an elevational view of a typical bullet perforating gun embodying the features of the present invention.

FIGURE 2 is a cross sectional view of an individual gun shown in position in the well bore.

FIGURE 3 is an enlarged elevational view of an individual gun.

FIGURE 4 is a cross sectional view of an alternate form of shear disc.

Referring now to the drawings, and, in particular, to FIG. 1, it can be seen that a bullet perforating gun assembly 10 is comprised of a generally cylindrical tubular gun body 12 having a plurality of individual guns 14. The assembly 10 is adapted to be lowered into a well borehole 16 by a conductor cable 18 containing an insulated conductor or conductors through which the firing of the individual guns 14 may be controlled. As indicated in FIG. 1, between the gun body 12 and the conductor cable 18, there is provided a cable head 20 to receive the cable 18 and various interconnecting subs. One of these subs may be the casing collar locator 22 and the firing control head 24. These subs are not part of the present invention and are all well known in the art. If desired, the gun assembly 10 may be also in the form shown in my copending application S.N. 412,487, filed Nov. 19, 1964, now U.S. Patent No. 3,327,793, issued June 27, 1967.

The gun body 12 may be formed of a generally elongated substantially solid steel cylinder of sufficient strength and solidity to withstand the pressures generated by the firing of the gun. The gun body 12 is provided with a plurality of laterally extending coaxial bores 26 and 28. The smaller diameter bore 26 extends innermost and forms the charge chamber for each gun 14. Positioned in the charge chamber 26 is an annular shaped propellant charge 34. A bore 36 having an initial tapered portion 38 extends from the rear wall of the charge chamber 26 to a cylindrical recess or cavity 40 in the peripheral wall of the gun body 12. The tapered portion 38 of the bore 36 accommodates the head of a firing pin 42 which extends through the bore 36 into the cavity 40 when the electrical connection to the firing pin 42 is made. A seal 44 is engaged with the wall of the cavity 40 to form a seal for the cavity and prevent the entrance of well fluid into the gun 14.

The cylindrical wall of the outer bore 28 is formed into female threads to engage with the male threads of a generally tubular barrel member 46.

The essence of the present invention resides in providing a regular bullet well perforating gun assembly of the above design with the capability of firing small diameter bullets while utilizing the standard gun body and propellant charge.

As previously set forth, the conditions under which a bullet perforating gun operates is far from optimum. The bullet fired by the gun is required to penetrate a steel casing, a varying amount of cement, and then substantially extends into the formation itself, which may be hard. All of this is required from a gun having a two inch barrel, the end of which may be virtually in contact with the steel casing. Accordingly, it has been found desirable to have a propellant charge of fairly heavy density. A 200 grain charge per cubic inch of charge chamber has been found satisfactory. Such a charge will produce an average pressure in a gun with a barrel of approximately 190,000 pounds with peak pressure often exceeding 350,000 pounds. Due to the limitations in diameter, the peak pressure often approaches the limit of the material surrounding the charge chamber. However, the pressure is at its peak only momentarily, and the material is able to withstand the pressure for such a short duration.

It has been found that if the density of the propellant charge is materially reduced, the pressure generated is also reduced and the velocity imparted to the bullet is insufiicient to accomplish required penetration. However, if the charge is allowed to remain the same and a small diameter bullet is used, the barrel volume is too small to quickly In accordance with the present invention, the tubular barrel member is provided with a central longitudinally extending bore 48 forming a barrel. The diameter of the barrel 48 is such as to receive a small diameter bullet 50; i.e., a bullet having a diameter in the neighborhood of A3" to A. A plurality of additional longitudinally extending bores 52 are crcumferentially spaced about the central bore 50. The total volume of the bores 52 plus the volume of the barrel 48 approximate the volume of a /8 barrel.

Positioned between the propellant charge 34 and the back of the barrel member 46 is a steel shear disc 54 ap* proximately 50 thousandths of an inch in thickness. The shear disc 54 covers the central bore 48 and the circumferentially spaced bores 52. The shear disc initially retains the pressure generated by the firing of the propellant charge 34. However, as the pressure reaches its peak, it bursts the shear disc 54 opposite the barrel 48 and bores 52, thereby imparting velocity to the bullet 50 and also relieving the pressure in the chamber 26.

By having the relief ports formed by the bores 52, it is possible to utilize the standard propellant charge used for a regular size bullet perforating gun without unduly endangering the gun. Also, the charge generates a pressure of sufficient force to propel the bullet with sufficient velocity so that maximum penetration results.

A plug 56 of soft material may be used to retain the bullet 50 in its proper position. If a /s bullet is used, an alternate shear disc 58 may be used which has a reduced portion 60 opposite the bullet. This portion will shear prior to the portion positioned opposite the relief ports. Therefore, the highest peak pressure will be directly behind the bullet to impart maximum force to it. Yet, shortly thereafter, the portions of the disc opposite the relief ports will shear again providing necessary pressure relief to the charge chamber to prohibit damage.

Summarizing, the present invention, generally speaking, provides vent ports in the barrel which permit the discharge of pressure generated in the charge chamber by the firing of the propellant charge. A shear disc designed to burst at the desired pressure is positioned between the charge chamber and barrel permitting build up of pressure to a desired maximum before delivering it to the bullet. Thereby, the force reacting on the bullet is such that maximum velocity results. With such construction, a high density propellant charge may be utilized to generate the desired pressure at the same time the peak pressure is eliminated by the vent ports.

I claim:

1. In a bullet perforating gun formed of a generally cylindrical gun body provided with at least one laterally extending opening having an inner portion forming a charge chamber accommodating a propellant charge compounded to propel a regular size bullet and ignition means, and an enlarged outer portion in which is removably secured a generally cylindrical barrel member, the improvement which comprises: I

the barrel member having a central longitudinal bore forming a barrel adapted to receive a small diameter bullet and a plurality of longitudinal venting bores, each being smaller in cross-sectional area than the cross-sectional area of said central longitudinal bore; and,

a shear disc positioned between the charge chamber and the barrel member, the disc extending across all of the bores of the barrel member, the thickness of the shear disc being such that it shears at the bores in the barrel upon the pressure in the charge chamber reaching a desired level to prevent damage to the gun body.

2. The bullet perforating gun of claim 1 wherein the combined cross-sectional area of the bores extending through the barrel member substantially equals the crosssectional area of a regular size bullet.

3. In a bullet perforating gun formed of a generally cylindrical gun body provided with at least one laterally extending opening having an inner portion forming a charge chamber accommodating a propellant charge compounded to propel a regular sized bullet and ignition means, and an enlarged outer portion in which is removably secured a generally cylindrical barrel member, the improvement which comprises:

the barrel member having a central longitudinal bore forming a barrel adapted to receive .a small diam-- eter bullet and a plurality of longitudinal venting, bores; and,

a shear disc positioned between the charge chamber and the barrel member, the disc extending across the extent of the charge chamber and having a portion of reduced thickness opposite the central longitudinal bore whereby such portion shears first to direct the initial force to the bullet.

4. In a bullet perforating gun formed of a generally cylindrical gun body provided with at least one laterally extending opening having an inner portion forming a charge chamber accommodating a propellant charge compounded to propel a regular size bullet and ignition means, and an enlarged outer portion in which is removably se- 5 6 cured a generally cylindrical barrel member, the improve- References Cited ment which comprim UNITED STATES PATENTS 'ijgfj 2 5 33355232 3 central-longltudmal 2,266,345 12/1941 Turechek 175 4.s9

pted to receive a small dram eter bullet and a vplurality of longitudinal venting 5 2336819 12/1943 Turechek bores; and, OTHER REFERENCES a shear disc positioned betweenthe charge chamber Bahn F 0 Smamdiameter Perforating Method i the barrel the dlsc h p a reduced Aids Sand Control, The Oil and Gas Journal, June 15, thickness opposite the central longltudlnal bore, the 1964 72 and 73 disc shearing first at the central longitudinal bore 10 and after imparting force to the bullet then shear- CHARLES OCONNELL, Primary Examiner ing at the venting bores to relieve pressure in the I charge chamben DAVID H. BROWN, Exammer.

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