Fiber optic cable in det cord

Abstract

An apparatus and method for providing a fiber optic cord in a perforating gun.

Description

BACKGROUND OF THE INVENTION

Generally, when completing a subterranean well for the production of fluids, minerals, or gases from underground reservoirs, several types of tubulars are placed downhole as part of the drilling, exploration, and completions process. These tubulars can include casing, tubing, pipes, liners, and devices conveyed downhole by tubulars of various types. Each well is unique, so combinations of different tubulars may be lowered into a well for a multitude of purposes.

A subsurface or subterranean well transits one or more formations. The formation is a body of rock or strata that contains one or more compositions. The formation is treated as a continuous body. Within the formation hydrocarbon deposits may exist. Typically a wellbore will be drilled from a surface location, placing a hole into a formation of interest. Completion equipment will be put into place, including casing, tubing, and other downhole equipment as needed. Perforating the casing and the formation with a perforating gun is a well known method in the art for accessing hydrocarbon deposits within a formation from a wellbore.

Explosively perforating the formation using a shaped charge is a widely known method for completing an oil well. A shaped charge is a term of art for a device that when detonated generates a focused explosive output. This is achieved in part by the geometry of the explosive in conjunction with an adjacent liner. Generally, a shaped charge includes a metal case that contains an explosive material with a concave shape, which has a thin metal liner on the inner surface. Many materials are used for the liner; some of the more common metals include brass, copper, tungsten, and lead. When the explosive detonates the liner metal is compressed into a super-heated, super pressurized jet that can penetrate metal, concrete, and rock.

A perforating gun has a gun body. The gun body typically is composed of metal and is cylindrical in shape. Within a typical gun tube is a charge holder or carrier tube, which is a tube that is designed to hold the actual shaped charges. The charge holder will contain cutouts called charge holes where the shaped charges will be placed.

A shaped charge is typically detonated by a booster or primer. Shaped charges may be detonated by electrical igniters, pressure activated igniters, or detonating cord. One way to ignite several shaped charges is to connect a common detonating cord that is placed proximate to the primer of each shaped charge. The detonating cord is comprised of material that explodes upon ignition. The energy of the exploding detonating cord can ignite shaped charges that are properly placed proximate to the detonating cord. Often a series of shaped charges may be daisy chained together using detonating cord.

In addition to a detonating cord running through the perforating gun, a wire may also run through the detonating cord. The wire is used to enable power to the different switch systems. The wires of multiple perforating guns connected together may also be connected. The wire is sometimes run to control device on gun string or sometimes it is run to a location at the surface with a controller. Additionally, each perforating gun may have its own control device for independent activation.

The problem with the wire is that is has poor reliability due to shock and vibration. Also, the wire may increase inductance that can inhibit communication signals along the gun string. This inhibition can limit the length of the wire, which may limit the depth of the drill string. Furthermore, the wire can suffer from insulation loss. Insulation loss may result in sparking or arcing between the wire and another conductor. The arcing or sparking may cause pre-detonation of the explosive shaped charges, detonation cord, or interfere with the electronics generally. Finally, the wire is susceptible to radio frequency (RF) interference. RF interference may cause unintended detonation of the explosives in the perforating gun. As a result, the transportation of loaded perforating guns maybe made safer by the removal of the wire.

SUMMARY OF EXAMPLES OF THE INVENTION

In this invention a fiber optic cable is used instead of a wire to communicate with equipment on the perforating gun. Fiber optics have been around for a long time, but they have not been used in downhole perforating guns because of complexity, reliability issues, and the difficulty of getting a powerful signal to the shaped charges that has not been degraded by the Stimulated Brioullin Scattering (SBS) effect. The Stimulated Brioullin Scattering effect causes the transmission of signals in a fiber optic cable to scatter and reflect in adverse ways that negates the ability of a fiber optic cable to transmit enough power downhole to cause a detonation. Newer fiber optic cables overcome these problems and provide the potential for using a fiber optic over many miles in length to communicate with a perforating gun located in a harsh environment. This invention aims to provide a fiber optic cable as an effective replacement for a wire on a perforating gun.

An example of the invention may include an elongated detonating cord comprising an explosive encased in a sheath and a fiber optic cable. The sheath and encased explosives may be substantially cylindrical. The fiber optic cable may be substantially parallel to the sheath. The example may further comprise an optical shield between the fiber optic cable and the explosive. The fiber optic cable may be substantially coaxial with the sheath. The fiber optic cable may be affixed to the sheath. The fiber optic cable may be encased by the sheath. The fiber optic cable may be embedded in the sheath. The fiber optic cable may be spirally wound around the sheath. The fiber optic cable may be offset from the centerline. The fiber optic cable may be single mode or multi-mode. The fiber optic cable may include one or more optical fibers encased in a shield.

Another example of the invention may include a method of perforating an oil well comprising assembling a string of perforating guns including a fiber optic cable, conveying the string of perforating guns into a subterranean well, communicating with the perforating guns using the fiber optic cable. The example may further comprise sending a detonation signal to the perforating guns using the fiber optic cable and detonating the perforating guns in response to the detonation signal. The fiber optic cable may be single mode or multi-mode. The fiber optic cable may include one or more optical fibers encased in a shield.

Another example of the invention may include an integrated ballistic and optic communications cable comprising a tubular sheath, an explosive contained within the sheath, and a fiber optic cable. The sheath may be substantially cylindrical. The fiber optic cable may be substantially parallel to the sheath. The fiber optic cable may be substantially coaxial with the sheath. The fiber optic cable may be affixed to the sheath. The fiber optic cable may be encased by the sheath. The fiber optic cable may be embedded in the sheath. The fiber optic cable may be spirally wound around the sheath. The fiber optic cable may be offset from the centerline. The example may further comprise an optical shield between the fiber optic cable and the explosive. The fiber optic cable may be single mode or multi-mode. The fiber optic cable may include one or more optical fibers encased in a shield.

BRIEF DESCRIPTION OF THE DRAWINGS

For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings in which reference numbers designate like or similar elements throughout the several figures of the drawing. Briefly:

FIG. 1 is a detonating cord with an internally located coaxial fiber optic cable.

FIG. 2 is a detonating cord with an internally located off-centered fiber optic cable.

FIG. 3 is a cross section of a detonating cord with an internally located off-centered fiber optic cable.

FIG. 4 is a detonating cord bundled to a fiber optic cord.

FIG. 5 is a charge tube wrapped with a detonating cord bundled to a fiber optic cord.

DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION

In the following description, certain terms have been used for brevity, clarity, and examples. No unnecessary limitations are to be implied therefrom and such terms are used for descriptive purposes only and are intended to be broadly construed. The different apparatus, systems and method steps described herein may be used alone or in combination with other apparatus, systems and method steps. It is to be expected that various equivalents, alternatives, and modifications are possible within the scope of the appended claims.

A typical perforating gun comprises a gun body that houses a charge tube, which further houses the shaped charges. The gun body contains end fittings which secure the charge tube inside the perforating gun. The charge tube has charge holes and apex holes for installing shaped charges. The gun body may have threaded ends that allow it to be connected to a series of perforating guns or to other downhole tubulars. Typically the detonating cord runs the majority of the length of the gun body. One or more shaped charges can be placed in the charge tube. Sometimes the shaped charges can all point in the same direction, other times some or all may be oriented in different directions about the center axis of the charge tube. Different orientations of the shaped charges may have different angles between each shaped charge. The detonating cord wraps around the charge tube to accommodate the different orientations of the shaped charges in phased perforating guns.

The shaped charges include a shaped charge case that holds the energetic material, a liner and an explosive. The shaped charge case typically is composed of a high strength metal, such as alloy steel. The liner is usually composed of a powdered metal that is either pressed or stamped into place. The metals used in liner may include brass, copper, tungsten, and lead.

An example of an embodiment of the invention may include a perforating gun with a charge tube located within the perforating gun. The charge tube would contain cutouts for each shaped charge. The fiber optic cable may be adapted to interface with the shaped charges located in the charge tube. The fiber optic cable may wind around the charge tube such that all of the shaped charges are connected to the same fiber optic cable.

The fiber optic cable in this example could terminate at either end of the charge tube and interface with another communication device or another fiber optic cable. The fiber optic could eventually reach the surface where the operator can control the perforating gun. The perforating gun could be detonated by sending a signal downhole through the fiber optic cable. The detonation command could be achieved by a single pulse or a series of pulses. The pulses could be used to detonate all the shaped charges, individual shaped charges in a unique sequence, or individual perforating guns.

Referring to FIG. 1, a fiber optic cable 52 is located within a detonating cord 51. Detonating cord 51 includes explosive material 59 enclosed in a sheath 58. The fiber optic cable 52 may include one or more optical fibers 60 encased in a shield 61. The fiber optic cable may be single mode or multi-mode. In this example the fiber optic cable 52 is located substantially centrally within the detonating cord 51. The fiber optic cable 52 may have one or more Application Specific integrated Circuit (referred to as “ASIC”) devices 53 attached that could be capable of interfacing with a device outside of the detonating cord 51. The ASIC device 53 may be secured to the fiber optic cable 52 by snapping, screwing, adhering to, or press fitting.

In another example, as shown in FIG. 2, the fiber optic cable 52 is located off-center within the detonating cord 51. Detonating cord 51 includes explosive material 59 enclosed in a sheath 58. At one or more locations along the fiber optic cord 52 there may be an ASIC device 53 attached as shown in FIG. 3. In the example shown, a signal could be sent or received through the fiber optic cable 52 and that signal could then be sent to a device outside of the detonating cord 51. Types of devices that could be attached to the ASIC device 53 may include sensors, detonators, switches, or communication devices. In this example the ASIC device 53 is configured to allow the fiber optic cable 52 to communicate with other electronics outside of the detonating cord sheath 58. The fiber optic cable offers the advantage of being radio frequency (RF) interference free as opposed to a conductive wire because a fiber optic does not transmit electricity, therefore it is considered safer that a conductor such as a wire.

In another example, as shown in FIG. 4, the fiber optic cable 52 is affixed to the outside of a detonating cord 51 to make an integrated communications cable 55. The fiber optic cable 52 is bundled to the detonating cord 51 using a fastening device 54. The fastening device 54 shown is a tie that wraps around both the fiber optic cable 52 and the detonating cord 51. The fastening device 54 may be a metal or plastic tie, a cable, a wire, u-bolt, a ring, additional sheath, tape, heat shrink, tubing, conduit, adhesive or a similar fastening mechanism.

The integrated communications cable 55 may then be wrapped around a charge tube 57 as shown in FIG. 5. A charge tube 57 holds shaped charges and is then placed inside a perforating gun. In a typical perforating job, shaped charges may be lined up along the charge tube 57 all pointing the same direction, which is referred to as zero phase. The shaped charges may be offset from each other by rotating a certain number of degrees about the center of the charge tube 57 from one shaped charge to the next. The offset angle is referred to as the phase angle. Because the charges are often offset from each other and therefore pointing in different directions, the integrated communications cable 55 has to wrap around the gun such that the detonating cord 51 and the fiber optic cable 52 may interface with each and every shaped charges apex. The shaped charge apex may have additional equipment or devices attached to it. Generally the shaped charge apex will be located at an apex hole on the shaped charge.

In the example of FIG. 5, the integrated communications cable 55 may be attached to the charge tube 57 using a variety of fastening devices 54 including ties, wires, cables, rings, u-bolts, or similar fastening mechanisms. Further, the fiber optic cord 52 may be individually secured to the charge tube 57 using a variety of fastening devices 56 including metal or plastic tie, a cable, a wire, a ring, additional sheath, tape, heat shrink, tubing, u-bolts, conduit, adhesive or a similar fastening mechanism. The integrated communications cable 55 may also be fastened to the shaped charges directly.

Although the invention has been described in terms of particular embodiments which are set forth in detail, it should be understood that this is by illustration only and that the invention is not necessarily limited thereto. Alternative embodiments and operating techniques will become apparent to those of ordinary skill in the art in view of the present disclosure. Accordingly, modifications of the invention are contemplated which may be made without departing from the spirit of the claimed invention.

Claims

1. An elongated detonating cord comprising: an explosive encased in a sheath;a fiber optic cable.

2. The detonating cord of claim 1 wherein the sheath and encased explosives are substantially cylindrical.

3. The detonating cord of claim 1 wherein the fiber optic cable is substantially parallel to the sheath.

4. The detonating cord of claim 1 further comprising an optical shield between the fiber optic cable and the explosive.

5. The detonating cord of claim 3 wherein the fiber optic cable is substantially coaxial with the sheath.

6. The detonating cord of claim 3 wherein the fiber optic cable is affixed to the sheath.

7. The detonating cord of claim 3 wherein the fiber optic cable is encased by the sheath.

8. The detonating cord of claim 3 wherein the fiber optic cable is embedded in the sheath.

9. The detonating cord of claim 3 wherein the fiber optic cable is spirally wound around the sheath.

10. The detonating cord of claim 7 wherein the fiber optic cable is offset from a centerline of the sheath.

11. A method of perforating an oil well comprising: assembling a string of perforating guns including a fiber optic cable;conveying the string of perforating guns into a subterranean well;communicating with the perforating guns using the fiber optic cable.

12. The method of claim 11 further comprising: sending a detonation signal to the perforating guns using the fiber optic cable;detonating the perforating guns in response to the detonation signal.

13. An integrated ballistic and optic communications cable comprising: a tubular sheath;an explosive contained within the sheath;a fiber optic cable.

14. The integrated ballistic and optic communications cable of claim 13 wherein the sheath is substantially cylindrical.

15. The integrated ballistic and optic communications cable of claim 13 wherein the fiber optic cable is substantially parallel to the sheath.

16. The integrated ballistic and optic communications cable of claim 13 wherein the fiber optic cable is substantially coaxial with the sheath.

17. The integrated ballistic and optic communications cable of claim 13 wherein the fiber optic cable is affixed to the sheath.

18. The integrated ballistic and optic communications cable of claim 13 wherein the fiber optic cable is encased by the sheath.

19. The integrated ballistic and optic communications cable of claim 13 wherein the fiber optic cable is embedded in the sheath.

20. The integrated ballistic and optic communications cable of claim 13 wherein the fiber optic cable is spirally wound around the sheath.

21. The integrated ballistic and optic communications cable of claim 18 wherein the fiber optic cable is offset from a centerline of the sheath.

22. The integrated ballistic and optic communications cable of claim 13 further comprising an optical shield between the fiber optic cable and the explosive.

23. The integrated ballistic and optic communications cable of claim 13 wherein the fiber optic cable is a single mode fiber optic cable.

24. The integrated ballistic and optic communications cable of claim 13 wherein the fiber optic cable is a multi-mode fiber optic cable.