Patent Application
20090151589
The present invention relates in general to explosive devices and more particular to devices and systems for shielding devices from the stress energy propagated from explosions by dissipating the propagated stress energy.
It is often necessary to use explosives during wellbore operations, in particular during the drilling of a well. For example, it may be desired to obtain a sidewall core before the well is completed. To obtain a core, an explosive charge may be detonated to propel a coring device into the wall to obtain a sample. It is also commonly required to provide communication between the wellbore and the surrounding formation after the well is completed with a casing. To provide the necessary communication, perforations are created through the casing, cement and into the formation. The perforations are commonly created with shaped explosive charges.
These explosive devices may be lowered and positioned at the desired location in various manners. In the simplest of operations the explosive charge may be positioned by measuring the length of the conveyance, carrying the explosive charge, that is run into the well until it is believed that the explosive charges are properly positioned.
In many instances it is desired or necessary to include electronic instrumentation or other mechanical packages in close proximity to the explosive charges or other working packages that may be sensitive to the explosive shock waves. For example, in high-angle wells and horizontal wells it may be necessary to include locating electronics with the conveyance and explosive device for proper positioning. Electronic equipment and the like are also desirable for locating thin zones and positioning of the explosive device. Further, in deep wells the stretch of conveyance (wireline or pipe) alone may necessitate the use of locating equipment for positioning. Additionally, it is often desired to perform multiple operations in a well without running into and then out of the well between operations, in these cases it is desirable to include electronic equipment in the tool string.
The firing of the explosive charges produces a large shock wave that propagates through the wellbore and perforating assembly. These shock waves can exert massive forces upon the electronic instrumentation and other downhole equipment, often resulting in damage to or failure of the equipment. It may be desired to shield any number of various devices, or packages, from the shock waves propagated from the explosive device. Packages to be shield from the explosive shock waves may include, without limitation to, sensors, gauges, logging instruments, telemetry devices, additional explosives, and valves.
Examples of apparatus, devices, systems and method for dissipating a stress wave to shield a package such as, without limitation, an electronic system or working member from the stress wave. In one example, an apparatus for dampening a stress wave includes a first interface formed between a first layer of material and a second layer of material, the first and second layers of material having dissimilar acoustic impedances.
In another example, a wellbore tool string includes an explosive device, a package, and a shock dissipater positioned between the explosive device and the package, the shock dissipater includes a first interface formed between a first layer of material and a second layer of material, the first and second layers of material having dissimilar acoustic impedances. Additional layer of alternating acoustic impedance material can be add to further reduce the shock.
In another example, a method of dampening stress waves propagated from the detonation of an explosive device in a wellbore to protect a device positioned downhole includes the steps of positioning a shock dissipater between an explosive device and a package; detonating the explosive device propagating a stress wave toward the shock dissipater and the package; and reflecting a portion of the stress wave in the shock dissipater back to the originating device and propagating a smaller portion of the shock wave through the device.
The foregoing has outlined some of the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.
The foregoing and other features and aspects of the present invention will be best understood with reference to the following detailed description of a specific embodiment of the invention, when read in conjunction with the accompanying drawings, wherein:
Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views.
As used herein, the terms “up” and “down”; “upper” and “lower”; and other like terms indicating relative positions to a given point or element are utilized to more clearly describe some elements of the embodiments of the invention. Commonly, these terms relate to a reference point at the surface from which drilling operations are initiated as being the top point and the total depth of the well being the lowest point.
In the illustrated example, tool string 12 includes an explosive device 18, a shock dissipater 20, and a package 22. Explosive device 18 is illustrated as a perforating gun; however explosive device 18 may be without limitation a coring device, a cutting tool or other device that includes an explosive charge or other element that produces a shock wave upon activation.
Package 22 may be any device, tool or system that it is desired to be protected from the shock waves propagated from the detonation or activation of explosive device 18. For purposes of description herein, package 22 is often referred to generally as an electronics package. For example, package 22 may include electronics and instrumentation for sensing pressure or temperature. Package 22 may be an electronics package such as, without limitation, logging instruments, telemetry equipment, and positioning instruments. However, it is recognized that package 22 may include any other device that may need to be shielded from the shock waves of the explosive device, including without limitation, valves and explosive devices.
Shock dissipater 20 is provided for dampening shock energy generated by downhole explosive device 18, thus providing a means for running packages 22 in tool string 12. In
Refer now to
Dissipater 20, which will be described in more detail below with reference to
Referring now to
Layers 30 are positioned in contact with one another to form interfaces 32. Adjacent layers 30 have dissimilar acoustic impedance, and are referred to herein as dissimilar layer or members. Thus, layer 30a has an impedance Ia and layer 30b has an impedance of Ib. Similarly, 30c has an impedance Ic, which is different from and therefore dissimilar to its adjacent layer 30b. Layer 30c has an impedance that is dissimilar to layer 30b, and that may be the same as or different from the impedance of layer 30a.
Upon detonation of explosive device 18, shock or stress waves, illustrated by arrows 36, propagate through the first dissipating layer 30a encountered. Stress waves 36 include a tensile portion and a compressive portion. When shock waves 36 encounter interface 32ab, a portion of the stress energy is transmitted into the adjacent layer 30b, illustrated by the arrow 36t, and a portion is reflected, illustrated by the arrow 36r. When stress energy 36t encounters interface 36bc a portion is transmitted and a portion is reflected. Any of the interfaces could be angled so as to deflect shock or stress waves coming from any potential direction as necessary.
At each interface 32, provided the adjacent acoustic impedances are different, a portion of the stress wave is transmitted and a portion of the stress wave is reflected. When the impedance of the first layer encountered is less than the impedance of the second layer encountered (Ia<Ib) a tensile stress wave is reflected. When the impedance of the first layer encountered is greater than the impedance of the second layer encountered (Ia>Ib) a compressive stress wave is reflected.
A coefficient of reflection, KR, and a coefficient of transmission, KT, is provided below wherein I1 is the impedance of the first layer encountered by the stress wave and I2 is the impedance of the layer across the interface from the first layer.
With reference to
From the foregoing detailed description of specific embodiments of the invention, it should be apparent that a system for dissipating impulse stress energy propagated from an explosive device to shield a device from the stress energy that is novel has been disclosed. Although specific embodiments of the invention have been disclosed herein in some detail, this has been done solely for the purposes of describing various features and aspects of the invention, and is not intended to be limiting with respect to the scope of the invention. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed embodiments without departing from the spirit and scope of the invention as defined by the appended claims which follow.
