US3237706A - Well perforator - Google Patents

Description

March 1966 A. A. VENGHIATTIS 3,237,706

WELL PERFORATOR 8 Sheets-Sheet 1 Filed Jan. 8, 1964 HOIST a CONTROL EQUIPMENT FIG.

FIG. Z-A FIG. 2-8

INVENTOR.

ALEXIS A. VENGHIATTIS BY ATTORNEY March 1966 A. A. VENGHlA'fTIS 3,237,706

WELL PERFORATOR Filed Jan. 8, 1964 5 Sheets-Sheet 2 FIG. l-B

INVENTOR.

ALEXIS A. VENGHIATTIS ATTORNEY March 1966 A. A. VENGHIATTIS 3,237,705

WELL PERFORATOR 3 Sheets-Sheet 5 Filed Jan. 8, 1964 INVENTOR.

ALEXIS A. VENGHIATTIS FIG. 4

ATTORNEY United States Patent D 3,237,706 WELL PERFORATOP Alexis A. Venghiattis, Houston, Tex. assignor to Dresser Industries, Inc, Dailas, Tera, a corporation of Delaware Filed Jan. 8, 1964, Ser. No. 336,469 2 Qlairns. (Cl. 1754.5)

This invention relates to well completion apparatus for oil and gas wells, and more particularly relates to an improved bullet perforator for puncturing the casing, cement and rock formation surrounding a cased borehole in the earth.

It is well known that boreholes are drilled into the earth for the purpose of recovering oil and gas which may be trapped in subsurface rock formations or strata. After a well has been drilled to its desired depth, a steel casing is inserted in the well throughout its entire length, and thereafter cement is inserted between the casing and the face of the borehole to seal off all fluid-bearing rock formations. After the casing and cement have been properly located, however, it is necessary to puncture the casing and cement adjacent the formation sought to be tapped, in order to drain the fluids trapped in the selected formation. This technique is commonly referred to as cornpleting the well, since it is substantially the last step performed below the surface for obtaining a producing oil or gas well.

It has been found necessary, to obtain an adequate fluid flow, not only to perforate the casing and cement adjacent the selected formation, but to puncture the formation itself. Accordingly, many different means and methods have been developed to achieve substantial penetration of the rock formation, as well as penetration of the casing and cement, in order to provide adequate passage of the fluid from the formation into the casing. Originally, perforation was obtained solely by discharging one or more metal bullets outwardly through the casing and cement, and into the formations. These bullets generally achieved good penetration of the casing and cement, but often insuflicient penetration of the more compacted formation. Furthermore, the bullet itself would often create an obstruction to fluid flow at the point where it would lodge in the formation. Thus, well perforating apparatus was developed which employed shaped explosive charges, rather than bullets, which would provide a tongue or jet of penetrating flame when exploded. This jet effectively burns a channel through the casing and cement and deep into the formation. Although shaped charge perforating generally achieves substantially deeper penetration in all but the least consolidated formations, it usually achieves such penetration without fracturing the region about the channel. Accordingly, it has been necessary to use bullet perforators to perforate the more compacted or harder formations because the fractures produced in such formations by bullets will greatly improve the flow rates obtained in the well.

Due to the necessity for using bullet perforators, much has been done to eliminate or reduce the undesirable features of this type of Well completion. It has been found that an ogivally-pointed bullet achieves substantially greater penetration than is achieved by bullets having rounded or comically-pointed bullets. Furthermore, it has been found that a sharp pointed bullet will achieve greater penetration than will a blunt-nosed bullet. However, a sharp pointed bullet all cut a smaller hole, and the tip will often break off during penetration. On the other hand, a blunt-nosed bullet will often shatter before penetrating adequately into the formation. Consequently, the bullets presently in general use in the industry are those having ogivally-pointed tips, since these bullets achieve good penetration without shattering or breaking,

3,2317% Patented Mar. 1, 1966 and since they generally achieve at least some fracturing of the penetrated formations. However, ogivally-pointed bullets produce relatively small holes in the casing and formation, and therefore it is often necessary to use larger caliber bullets, and consequently larger propellant charges, than would otherwise be necessary.

These disadvantages of the prior art are overcome with the present invention, and novel bullet-type perforating apparatus is provided which produces a hole of a substantially greater cross-sectional area than that of the bullet, and which achieves greater fracturing of the formation than that achieved by bullets in present use.

Accordingly, it is an object of the present invention to provide more effective means for perforating a well casing in an oil or gas well.

It is also an object of the present invention to provide bullet perforation of a well casing, in a manner to produce a large hole relative to the cross section of the bullet, and at the same time to produce good penetration and fracturing of the formation aggregate.

It is further an object of the present invention to provide an improved bullet for use in perforating oil well casing.

It is a specific object of the present invention to provide bullet perforating apparatus wherein the bullet is of an improved design such as to achieve good penetration into and fracturing of the formation, and also to produce a very large hole as compared to the cross section of the bullet, without the necessity for employing a propelling charge of abnormally large strength or size.

These and other objects and features of the present invention will be apparent from the following detailed description, wherein reference is made to the accompanying drawings.

In the drawings:

FIGURE 1-A shows a pictorial representation of a gun perforator incorporating the present invention and disposed in a well bore.

FIGURE lB shows a cross section view of the gun perforator depicted in FIGURE 1A.

FIGURE 2-A shows one view of the bullet contained in the gun perforator depicted in FIGURES 1-A and 1-H.

FIGURE 2B shows another view of the bullet depicted in FIGURE 2-A.

FIGURE 3 depicts a cross section view of the borehole shown in FIGURE 1-A after the bullet has been discharged into the earth.

FIGURE 4 depicts another view of the channel cut into the earth by the discharged bullet shown in FIG- URE 3.

The advantages of the present invention are preferably attained by means of gun perforating apparatus including a bullet of a novel design, wherein the tip or nose of the bullet is shaped in the manner of two converging planes, rather than in the manner of an ogival surface of revolution, and wherein the angle at which the two planes converge is selected to provide for optimum penetration without shattering or breaking of the tip of the bullet during such penetration. As will be clearly apparent from the following description, such a bullet achieves improved penetration of the casing as well as of the formation, and provides for much greater flow rates from the formation through the holes in the well casing.

Referring now to FIGURE 1-A, there may be seen a cross sectional view of a typical borehole 2 drilled into the earth 4 past at least one fluid-bearing formation 6. The borehole 2 is lined with a steel casing 8, and contains cement 10 inserted in the annulus of the borehole 2 so as to seal off the formation 6. Accordingly, a conventional gun perforator 12 having a plurality of bullets 14 is lowered into the casing 8 by means of a conventional well cable 16 until the perforator 12 is at a depth which places it adjacent the formation 6 sought to be trapped.

As may be seen, the perforator 12 is suspended at one end of the cable 16, and the cable 16 is supported at its other end by means of a sheave wheel 18 for connection to any suitable hoist and control equipment 20. The hoist and control equipment 20 may be of any suitable type, and is therefore depicted functionally in FIGURE 1-A.

The gun perforator 12 may be designed so as to be actuated by means of an electrical signal from the hoist and control equipment 20, which signal is transmitted to the perforator 12 by means of one or more electrical conductors in the logging cable 16. The gun perforator 12 responds to the signal by discharging a plurality of explosive charges (not shown) which serve, respectively, as propelling charges for the various bullets 14 carried by the gun perforator 12. In FIGURE 1-A, the bullets 14 are shown arranged in all directions about the gun perforator 12. to employ a mono-directional gun perforator 12 having its bullets 14 arranged linearly along the axis of the perforator 12. In either case, the explosion of the propelling charges will project the bullets 14 laterally into the formation 6 in Whatever direction they may be aimed at the instant of their discharge. If the perforation is successful, at least a substantial number of the bullets 14 will each puncture the casing 8, and will penetrate through the cement 1t) and into the formation 6 to a substantial depth, to provide individual channels through which fluids may flow from the formation 6 and into the casing 8.

The gun perforator 12 comprises a generally elongated, substantially solid steel cylinder of sufficient strength and solidity to withstand the explosive forces of the firing of the gun charges. Laterally directed gun units are mounted in the cylindrical gun body at longitudinally spaced intervals. As illustarted in FIGURE 1B, each unit comprises an internally threaded, laterally directed barrel opening 116 which receives the externally threaded barrel member 117. Preferably, the lateral depth of the barrel opening 116 and the length of the barrel member 117 are such that the barrel member is wholly received within the opening, flush with the surface of the gun body, when fully seated and tightened therein, so as not to present any laterally projecting parts when the gun is fully assembled in the manner shown in FIGURES 1-A and l-B.

The rear or inner end of the barrel member 117 is formed with a smooth, thread-free end 119 of slightly reduced external diameter adapted to be received concentrically within an inner, thread-free, counterbored end recess 121 of the barrel opening 116. This provides a short annular end recess between the surfaces 119 and 121 containing resilient ring 122 in order to seal the barrel member within the barrel opening and to preclude leaking of any well fiuid inwardly from between the threaded portion of the barrel opening 116 and the external surface of the barrel member 117.

The barrel member 117 is formed with a concentric barrel bore 123 having at the front or muzzle end thereof a short portion of slightly enlarged diameter forming a shallow recess 124 having an annular shoulder 126. Seated within the recess 124 and making sealing engagement against the shoulder 126, there is provided a sealing disc 127 for preventing admission of well fluid into the barrel bore. The disc 127 may be seated and sealed in any suitable manner well known in the art and may In some cases, however, it is desirable be formed of any suitable material, such as brass or steel. In operation, when the propellant charge 132 is ignited and the bullet 14 fired, the seal 127 is ejected from the recess 124 either as a unit or in fragments and forms substantially no obstacle to the discharge of the bullet 14.

Barrel bore 123 is formed with a frusto-conical enlarged end portion 128 at the inner end thereof. A

correspondingly shaped frusto-conical restraining annulus 129 fits within the end portion 128. A cylindrical socket 131, formed in the gun perforator 12 at the rear of the barrel opening 116, accommodates a propellant charge which comprises a compressed, molded or otherwise consolidated or pelletized tubular shaped body of combustible propellant 132 formed with an opening 133 extending centrally therethrough from end to end. The propellant body 132 is surrounded and contained within a container sleeve or shell 134 which may be composed of any suitable material, preferably non-metallic, such as, for example, a paper or cloth-base, phenolic-impregnated tubing.

Igniter head 136 fits within the reduced diameter rear portion 137 of socket 131 and opening 138 in shell 134 and is positioned in close proximity to propellant 132. Igniter head 135 forms a part of conventional igniter 139 of the type well known in the art and may, for example, be of the type shown and describer in US. Patent 2,649,- 736 to R. A. Phillips. Igniter 139 is actuated electrically through conductor 14 1 positioned within the passage 142 and electrically connected to firing control apparatus through the conductors of cable 16.

A bullet 14 preferably comprises a forward piercing nose portion 3 preferably of the form depicted in FIG- URES 2-A and 2B and a body or rearward shank portion 32, preferably of uniform diameter extending from the nose portion 34 to a transverse rear end or butt 32. The bullet 14 is preferably made of hardened steel or is steel jacketed in a manner well known in the industry to provide adequate casing and formation piercing ability.

The bullet 14 is mounted through the annulus 129 which forms a tight, press fit therewith near the forward end of shank portion 30. The bullet 14- also makes a tight, press fit within central opening formed in the cartridge cover 14-8 which is provided with a peripheral flange 14-9 fitting around the forward open end of shell 13%. The fit of bullet 14- within restraining annulus 129 is preferably sufficiently tight to retard the bullet 14 until the most of the propellant 132 has been consumed.

Referring now to FIGURES ?.A and 2-B, respectively, there may be seen two views of a preferred form of the bullet 14 depicted generally in FIGURE 1B, wherein the bullet 14 is shown as having a circular body with fiat butt 32 and a chisel-shaped tip 34. At the tip 34, there are two fiat surfaces 36 which are defined by two planes converging at a preselected angle. Preferably, the edge 38 of the tip 34 does not terminate in the manner of knife-edge, but is squared off substantially parallel with the butt 32 end of the bullet 14. The two fiat surfaces 36 preferably converge at an angle which provides for optimum penetration of the bullet 14 into the formation 6, and yet minimum probability of breakage of the tip 34. A suitable angle has been found to be degrees.

Referring now to FIGURES 3 and 4, there is depicted therein a pictorial representation of the cased borehole shown in FIGURE 1-A, after the bullet 14 has been discharged through the cement 10 and easing 8, and after the gun perforator 12 has been removed. Accordingly, it may be seen that, due to the shape of its nose portion 34, the bullet 14 has carved a channel into the earth 6 which is substantially three times as wide as the diameter of the shank portion 319 of the bullet 14-. FIGURE 4 shows in particular how the broad portion of the channel 41}! is perpendicular to the cutting edge 38 of the nose 36 of the bullet 14, whereas the width of the channel 40- measuring parallel with the cutting edge 38 of the bullet 14-is only about as Wide as the diameter of the bullet 14. It is this phenomenon which amplifies the utility of the present invention, since the bullet 14 may be rotated appropriately in the gun perforator 12 prior to firing, to provide for coincidence of the tilt of the channel 40 to conform with the angle of dip (or bedding plane) of the formation 6. This substantially increases the flow rate of the fluids which flow through the puncture 46 in the casing 8. Another advantage of the bullet 14 having a nose portion 34 formed in the manner of two converging planes, is the fact that substantial cracking or fracturing is produced in the areas of the formation 6 immediately surrounding the channel 40. The fissures 42 thereby produced greatly increase the flow rate into the channel 40, and accordingly, into the casing 8. Furthermore, the bullet 14 itself in no way obstructs flow through the channel 40, as is apparent from FIGURES 3 and 4.

It may also be seen in FIGURE 4 that the channel 4%) has a cross sectional shape which tends to be a lemniscate, depending substantially upon the force with which the bullet 14 is projected into the formation 6, and depending to some extent, perhaps, upon the angle formed by surfaces 36 on the bullet 14. Accordingly, if the nose portion 34 of the bullet 14 be formed in the manner of a three or four sided pyramid, then the cross sectional shape of the channel 443 should assume a different shape, since the enlarged portions 50 of the channel 40 appear to be directly related to the surfaces 36 on the nose 34 of the bullet 14. Accordingly, a bullet 14 having a nose 34 formed in the manner of two converging planes, i.e., formed in the manner of a chisel, appears to best utilize the pressuring effect had on the formation 6 by the fiat surfaces, and therefore appears to cut the best shaped channel 40 insofar as flow rate is concerned.

A further advantage accruing to the chisel bullet 14 may be seen in the fact that the burrs which are produced in the puncturing of the casing are not of a character such as to obstruct fluid flow through the channel 40. Referring to FIGURE 3, there may be seen that two large burrs 44 are created by the bullet 14 on each side of the puncture 46 in the casing 8, but substantially none at the top and bottom of the puncture 46. The bottom edge 48, of the puncture 46, is indeed quite ragged. However, any burrs which originate along the bottom edge 48 (or along the top edge) are quite small and few in number. The large burrs 44 at the sides, on the other hand, seldom break loose from the casing 8.

Numerous other variations and modifications may be made without departing from the scope of the present invention. Accordingly, it should be clearly understood that the forms of the invention described herein and shown in the figures of the accompanying drawings are illustrative only and are not intended to be construed as limitations.

What is claimed is:

1. Apparatus for perforating casing in a borehole, said apparatus comprising a gun perforator means for discharging a bullet through said well casing,

a cable means for disposing said perforator means in said well casing at a preselected depth in said borehole, and

cylindrically-shaped bullet means in said gun perforator for boring a hole having a generally lemniscatelike cross sectional configuration extending through said casing and into said earth formation,

said bullet means having a cylindrical shank portion of constant diameter and a cutting nose formed in the manner of two planes intersecting the cylindrical surface of said shank portion and converging along the cross section diameter of said bullet.

2. Apparatus of the character described in claim 1 wherein said hole has a cross sectional shape such that one diameter is substantially equal to the cylindrical diameter of said bullet means and such that the other perpendicular diameter is substantially three times as great as the cylindrical diameter of said bullet means.

References Cited by the Examiner UNITED STATES PATENTS 2,612,108 9/1952 Schmidt 10252 2,806,442 9/1957 Temple 891 2,953,971 9/1960 Porter 89-1 3,062,294 11/1962 Huith et al 166-421 X BENJAMIN A. BORCHELT, Primary Examiner. SAMUEL W. ENGLE, Examiner.

Claims (1)

1. APPARATUS FOR PERFORATING CASING IN A BOREHOLE, SAID APPARATUS COMPRISING A GUN PERFORATOR MEANS FOR DISCHARGING A BULLET THROUGH SAID WELL CASING, A CABLE MEANS FOR DISPOSING SAID PERFORATOR MEANS IN SAID WELL CASING AT A PRESELECTED DEPTH IN SAID BOREHOLE, AND CYLINDRICALLY-SHAPED BULLET MEANS IN SAID GUN PERFORATOR FOR BORING A HOLE HAVING A GENERALLY LEMNISCATELIKE CROSS SECTIONAL CONFIGURATION EXTENDING THROUGH SAID CASING AND INTO SAID EARTH FORMATION, SAID BULLET MEANS HAVING A CYLINDRICAL SHANK PORTION OF CONSTANT DIAMETER AND A CUTTING NOSE FORMED IN THE MANNER OF TWO PLANES INTERSECTING THE CYLINDRICAL SURFACE OF SAID SHANK PORTION AND CONVERGING ALONG THE CROSS SECTION DIAMETER OF SAID BULLET

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