Low debris perforating gun system for oriented perforating

Disclosed herein is a reinforcing system for a shaped charge assembly for use in a perforating gun. The shaped charge assembly includes a shaped charge combined with a longitudinal reinforcing system extending along a portion of a perforating gun barrel. The reinforcing system comprises a spine with a recess formed to receive the shaped charge of a perforating gun. The reinforcing system further comprises a compression zone coaxially disposed around a portion of the shaped charge. The compression zone is formed between a bushing and a retaining shell that also coaxially circumscribe a portion of the shaped charge and on one of their respective ends connect to the spine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to an apparatus that connects perforating guns. Yet more specifically, the present invention relates to a perforating gun connector utilizing corresponding tapered ends to facilitate connections thereof. Yet even more specifically, the present invention relates to an automated method of connecting perforating guns with a perforating gun connector.

2. Description of Related Art

Perforating guns are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore, and the casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore.

Included with the perforating guns are shaped charges that typically include a housing, a liner, and a quantity of high explosive inserted between the liner and the housing. When the high explosive is detonated, the force of the detonation collapses the liner and ejects it from one end of the charge at very high velocity in a pattern called a “jet”. The jet penetrates the casing, the cement and a quantity of the formation.

Due to the high force caused by the explosive, the shaped charge often shatters into many fragments that exit the perforating gun into the fluids within the wellbore. These fragments can clog as well as damage devices such as chokes and manifolds, thereby restricting the flow of fluids through these devices and possibly hampering the amount of hydrocarbons produced from the particular wellbore. Therefore, there exists a need for an apparatus and a method for conducting perforating operations that reduces fragmentation of shaped charges and also provides a manner of retaining fragments of shaped charges produced during the perforation sequence.

BRIEF SUMMARY OF THE INVENTION

The present invention involves a reinforcing system for a shaped charge comprising, a reinforcing buttress, a recess on the reinforcing buttress formed to receive the closed end of the casing of the shaped charge, and a shock absorbing collar seated on the reinforcing buttress formed to coaxially circumscribe at least a portion of the shaped charge casing. The shock absorbing collar includes a shock absorbing material therein. The shock absorbing material may be rubber, foam, cotton, cork, and/or mixtures thereof. Moreover, the shock absorbing material may be comprised of a corrugated element.

The shock absorbing collar may further include supporting structure circumscribing the inner and outer radius of the shock absorbing material. The supporting structure may comprise a bushing in coaxial cooperation with at least a portion of the outer surface of the casing, and a retaining shell coaxially circumscribing the bushing, wherein an annular void is formed between the outer radius of said bushing and the inner radius of said retaining shell. It is within the annular void wherein the shock absorbing material may reside. The casing includes a space capable of receiving an amount of explosive, and the casing is formed into a generally tubular shape.

The reinforcing system is capable of retaining substantially all casing fragments produced during detonation of the explosive. The reinforcing system may further comprise at least one other shaped charge. The reinforcing system may further include a gun body, wherein the presence of the reinforcing buttress and the casing produce an asymmetric radial weight distribution around the axis of the gun body.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawings herein, inFIG. 1a cross sectional view of one embodiment of a reinforcing system for a shaped charge assembly of the present invention is shown. The reinforcing system ofFIG. 1comprises a spine16, a retaining shell14, and a bushing18. A compression zone57is formed between the annular space between the retaining shell14and the bushing18. As is well known, when assembled these components are preferably positioned and used within a gun body22. For the purposes of reference and not to serve as any limitation of the scope of the present invention, a dashed line is included withFIG. 1representing an axis42of the shaped charge assembly10. As will be described herein, it is preferred that many of the components of the shaped charge assembly10be bisected by the axis42in the embodiment ofFIG. 1.

The casing12is comprised a base24and walls25, where the walls25are generally a tube-like section that extend up and away from the outer circumference of the base24. The space28between the walls25and the base24is formed to receive explosive32and a liner30. Preferably the base24is shaped similar to a bowl in that it has inner and outer surfaces that curve parallel to the axis of the base24as the surfaces travel away from the axis42. The walls25and the base24meet approximately at the point where the inner surface of the casing12is substantially parallel to the axis42. It is also preferred that the thickness of the base24and the walls25be roughly the same at the region where they meet. However, the thickness of the walls25can decrease as the walls25approach the open end26of the casing12.

Rounding the outer surface of the base24combined with decreasing the thickness of the walls25results in a generally crucible shaped casing12, this enhances the fit between the casing12and the recess17formed in the spine16. Further, the generally curvilinear shaped of the base24also helps to equalize the forces that are subjected to the casing12, this helps to reduce fragmentation of the casing12during detonation of the explosive32. This shape also works to produce fragments that are more uniform in size. Both of these effects result in minimization of metal fragments escaping the gun body22. However the present invention can accommodate a casing12made from any one of a number of different shapes, such as one that has a largely rectangular cross section, a hemispherical shape, or a cross section where the inner and outer surface have different cross sections, such as an outer surface with a rectangular cross section and an inner surface having rounded edges, or vice versa.

As illustrated in a cross sectional view inFIG. 1, the spine16of one embodiment of the present invention has a generally curved outer surface38formed to fit a portion of the inner surface40of the gun body22. Preferably the spine16should be somewhat hemispherical so that when situated within the gun body22its mass coupled with the base24, retaining shell14, and the bushing18, will produce an eccentric moment of inertia around the axis of the gun body22. While the outer surface38of the spine16has mostly the same radius along its circumference, the shape of the spine's16inner surface37varies along its circumference. The shape of the inner surface37surrounding and proximate to the axis42is largely curved and forms a recess17. The shape of the recess17should closely match the shape of the outer surface of the base24such that a majority of the base24can be positioned within the recess17.

A ledge44is positioned at the outer edge of the recess17, the contour of the ledge44is primarily perpendicular to the axis42. When viewed from the axis, the ledge44has a generally annularly shaped surface with a radius that extends from the terminal edge of the recess17up to the threaded portion46. As can be seen inFIG. 1, the length of the ledge44should be able to accommodate the ends of both the retaining shell14and the bushing18when they are positioned coaxially around the casing12. The threaded portion46of the spine16is mostly parallel with the axis42having threads49, such as National “N” threads, formed along its surface. The length of the threaded portion46will depend on the particular size of shaped charge assembly10involved as well as the type of threads used, but the length should be sufficiently long to ensure a tight and secure coupling of the threads50of the retaining shell14with the threaded portion46. An annularly shaped shoulder48connects the inner surface of the gun body22with the threaded portion46. The shoulder48circumscribes the threaded portion46and preferably has a surface that is largely parallel to the surface of the ledge44. However the shape and contour of the shoulder48is not critical, but can be any shape. The shoulder48though should have a large enough radius to provide sufficient material so that when the threads49are formed on the threaded portion46the spine16can still structurally support the addition of the retaining shell14.

When viewed along the axis42, the bushing18is has a mostly annular cross section. While the outer radius of the bushing18is preferably constant along its length, its inner radius can vary in size to match the contour of the outer radius of the casing12. In the embodiment of the present invention shown inFIG. 1, the outer radius of the casing12decreases as it approaches the open end26. Since it is desired that the inner radius of the bushing18closely circumscribe the outer surface of the casing12, the inner radius of the bushing18is shown to correspondingly decrease proximate to the open end26, while the outer radius remains relatively constant. Thus the thickness of the bushing18increases along its length from the ledge44towards the open end26. However the shape of the inner radius is not limited to that shown inFIG. 1, but can be of any contour, but it should closely match the contour of the outer radius of the particular casing12included with the present invention—which as noted above can be of various types.

As previously noted, threads50on the outer circumference of one edge of the retaining shell14are included to mate with the threads of the threaded portion46. The corresponding threads (49and50) provide a means of releasably attaching the retaining shell14to the spine16, either by hand or with the aid of an associated tool. A retaining lip15is provided on the inner radius of the retaining shell14on the side opposite the threads50. The retaining lip15extends inward towards the axis42from the inner radius of the retaining shell14having a surface that is generally at an angle oblique from the axis42. Similarly, a beveled edge19is provided on the outer surface of the bushing18such that when the retaining shell14and the bushing18are assembled within the shaped charge assembly10, the angle of the beveled edge19is substantially the same as the angle of the retaining lip15. The combination of the retaining lip15and the beveled edge19provide a means of enabling the retaining the bushing18within the shaped charge assembly10when the retaining shell14is secured to the shaped charge assembly10. It is believed it is well within the scope of those skilled in the art to design and implement adequate dimensions and angles for both the retaining lip15and the beveled edge19without undue experimentation.

It should be noted that the inner radius of the retaining shell14increases along its length such that its width is smaller proximate to its threaded end than proximate to the retaining lip15. This increase in radius combined with a constant outer radius of the bushing18produces an annular void between the bushing18and the retaining shell14. Within the void shock absorbing material can be placed. Examples of shock absorbing material include rubber, cotton, foam, sponge, cork, and combinations thereof. The foam open or closed cell foam and can selected from any known or later developed foam materials. Potential foam compositions include polyethylene foam (both high and low density), polystyrene, neoprene, and urethane, among others.

As shown inFIG. 4, the shock absorbing material may optionally be comprised of a corrugated element situated within the annular void. The corrugated element can be comprised of metals such as steel, iron, copper, as well as metal alloys. Optionally, the element may also be comprised of corrugated paper such as cardboard. Further, a honeycomb structure (not shown) may be provided within the space of the annular void. The combination of the bushing18, the retaining shell14, and the shock absorbing material form a shock-absorbing collar23that absorbs shock produced during detonation of the explosive32.

In operation of the preferred embodiment of the present invention, the shaped charge assembly10is assembled, then combined with a gun body22, and integrated into a perforating gun8. As is known in the art, the perforating gun8is inserted into a wellbore5preferably by a wireline6. The perforating gun8can also be inserted into the wellbore5and lowered to the spot where perforations are desired. The perforating gun8can be tethered by a slickline, by tubing, or any now known or later developed insertion/suspension technique or devices. Once the surface personnel have determined that the perforating gun8has been lowered to the region where perforations are to be conducted, perforating operations can be commenced. Generally perforating is initiated by sending a signal down the wireline6from the surface to the perforating gun8. As is well known, initiators (not shown) within the perforating gun8receive that surface signal and in turn transfer a detonative force though the detonation cord34that in turn initiates detonation of the explosive32within the shaped charge assembly10. Detonation of the explosive32collapses the liner30and transforms the solid liner into a metal jet11that exits the wall of the gun body22and penetrates the inner surface of the wellbore5. The metal jet11pierces the inner surface of the wellbore5thereby producing perforations9in the formation13that surrounds the wellbore5.

During detonation of the shaped charge assembly10of the present invention, the likelihood of fragments of the casing12entering the wellbore5after detonation of the explosive32is highly reduced over that of prior art shaped charges. During detonation, the shock absorbing material within the compression zone57compresses due to the shock of the detonation thereby relieving the casing12of at least a portion of the detonation shock it may typically experience during detonation. Since the implementation of the shock-absorbing collar23transfers detonation stresses away from the casing12, this shock-absorbing feature necessarily results in less fragmentation of the casing12due to explosive detonation.

Furthermore, with regard to the fragmentation that may occur, the presence of the spine16combined with the retaining shell14serves to contain the fragments of the casing12well within the gun body22and not allow them to enter the wellbore5where the fragments might likely cause clogging or congestion problems. The spine16and its associated recess17act as a reinforcing buttress that supports the base24of the casing12during detonation of the explosive32to prevent fracturing or fragmentation of the base24.

The spine16also can aid in orientation of the perforating gun8in which it is integrated. The eccentric loading of the spine16produces an asymmetric mass distribution around the axis (not shown) of the gun body22. This is important when the perforating gun is in deviated section7of the wellbore5, such that when allowed to rotate about its axis, the gravitational pull on the gun body22will attempt to orient it such that the spine16is located proximate to the lowermost portion21of the wellbore5.

The components of the present invention should have the capability of withstanding downhole conditions, such as high pressures and temperatures, as well as the ability to withstand attach by corrosive agents. Accordingly steel is a suitable material for the components of the present invention.

The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, the corrugated strip58can also be formed from other malleable metals such as aluminum, lead, combinations thereof, and alloys made from these substances. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.