Patent Publication Number: US-2015083438-A1

Title: Downhole tool shock absorber with electromagnetic damping

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present document is based on and claims priority to U.S. Provisional Application Ser. No. 61/882,992, filed Sep. 26, 2013, which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Hydrocarbon fluids such as oil and natural gas are obtained from a subterranean geologic formation, referred to as a reservoir, by drilling a well that penetrates the hydrocarbon-bearing formation. Once a wellbore is drilled, various forms of well completion components may be installed to control and enhance the efficiency of producing the various fluids from the reservoir. During drilling, production, and/or other phases of operation, downhole tools may be subjected to mechanical impact and/or perforation induced shock loads which can be detrimental to the integrity and functionality of the tool string and tools/instruments carried by the tool string. Shock absorbers have been employed in tool strings, but existing shock absorbers are based on mechanical or hydraulic systems. For example, downhole shock absorbing systems may be made of crushable elements, e.g honeycomb structures, crushable noses, or crushable coils, which offer one-time shock absorption. Springs also have been used as shock absorption elements, but springs are not able to dissipate energy and may provide undesirable bouncing/recoil upon external excitation. 
     SUMMARY 
     In general, the present disclosure provides a system and method for absorbing shock in a borehole. The technique comprises coupling a tool into a tool string sized for delivery into the borehole. A shock absorber is positioned along the tool string to absorb shock loads incurred by the tool. The shock load experienced by the tool induces an electromagnetic force in the shock absorber which acts in a direction to mitigate the shock load. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying figures illustrate various implementations described herein and are not meant to limit the scope of various technologies described herein, and: 
         FIG. 1  is a schematic illustration of an example of a tool string deployed in a borehole and having a tool subject to shock loads, the tool working in cooperation with a shock absorber employing electromagnetic damping, according to an embodiment of the disclosure; 
         FIG. 2  is a schematic illustration of an example of a shock absorber for use in absorbing shocks along a tool string, according to an embodiment of the disclosure; 
         FIG. 3  is a schematic illustration of another example of a shock absorber for use in absorbing shocks along a tool string, according to an embodiment of the disclosure; 
         FIG. 4  is a schematic illustration of another example of a shock absorber for use in absorbing shocks along a tool string, according to an embodiment of the disclosure; and 
         FIG. 5  is a schematic illustration of another example of a shock absorber for use in absorbing shocks along a tool string, according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of some illustrative embodiments of the present disclosure. However, it will be understood by those of ordinary skill in the art that the system and/or methodology may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     The disclosure herein generally relates to a system and methodology for absorbing shock in a borehole. For example, a variety of tools may be used in many well related operations or other borehole related operations and those tools can be subjected to shock forces or loads in a variety of situations. For example, undesirable shock loading may occur through mechanical impact, downhole perforation activities, and/or other activities which subject the tools to high force loads. The shock loading may occur in drilling operations, completion operations, production operations, well servicing operations, and/or a variety of other well related operations. 
     Generally, a tool is coupled into a tool string which is sized for delivery into the borehole. The tool is moved downhole via the tool string and operated downhole to perform a desired function. A shock absorber is positioned along the tool string to absorb shock loads incurred by the tool. The shock load experienced by the tool induces an electromagnetic force in the shock absorber which acts in a direction to mitigate the shock load. 
     In embodiments described herein, shock absorption is performed via a shock absorption technology based on the use of electromagnetic damping to reduce the effects of shock forces. With electromagnetic damping, an electromagnetic force is induced in the shock absorber due to a relative motion between a conductor and a nearby magnetic field. The induced force is oriented in a direction opposed to the relative motion and, at least in some cases, is nearly proportional to the motion velocity. As a result, abrupt velocity changes are suppressed and the shock load is mitigated, e.g. damped. The shock absorber effectively converts kinetic energy to electrical energy, and this electrical energy can be dissipated via electrical heating so as to avoid undesirable bouncing or recoil. In some embodiments, the shock absorber has a first component and a second component which induce the electromagnetic force when moved relative to each other and the first component and second component can operate without physical contact. This approach provides a robust and low maintenance shock absorbing system. 
     According to an embodiment, the shock absorber comprises an electromagnetic damper which handles repetitive and/or reciprocating shock loads because the electromagnetic force is able to continuously act against the direction of relative movement between shock absorber components. The embodiment also is able to convert kinetic energy to electrical energy which can be dissipated to electrical heating or otherwise used or stored, e.g. stored in a battery. In some applications, high-temperature magnets and conductors may be used in the shock absorber to ensure reliable performance at high, downhole temperatures. In some embodiments, the relative movement which creates the electromagnetic force may be accomplished between components which remain physically separate, i.e. limited or no physical contact occurs between the moving components. 
     Embodiments described herein also provide flexibility for use in various applications and environments because the energy absorption capacity can be modeled and optimized. For example, the energy absorption capacity can be modeled and optimized by manipulating system parameters such as coil density, magnetic strength, resistance load in a circuit, geometric dimensions, and/or other system parameters. 
     Referring generally to  FIG. 1 , an example of a shock load absorbing system  20  is illustrated. In this embodiment, a tool string  22  is deployed in a borehole  24  and has a tool  26 , e.g. a well tool, which may be subjected to shock loads. The tool  26  may comprise a drill bit, a bottom hole assembly component, a completion component, a landing component, and/or a variety of other components which may be utilized in a borehole and subjected to unwanted forces due to shock loads. The tool  26  works in cooperation with a shock absorber  28 , and shock absorber  28  employs electromagnetic damping to dissipate the unwanted shock loads. The shock absorber  28  may be coupled directly with tool  26  or mounted at another location along the tool string  22  such that shock loads incurred by tool  26  can be transmitted to the shock absorber  28 . 
     Referring generally to  FIG. 2 , an example of shock absorber  28  is illustrated. In this example, shock absorber  28  comprises a first component  30  and a second component  32  which are able to move relative to each other to induce an electromagnetic force, as discussed in greater detail below. In the embodiment illustrated, the first component  30  comprises an electromagnetic coil  34  and the second component  32  comprises a permanent magnet  36 , such as a stack of permanent magnets  36 . The permanent magnet(s)  36  is positioned for relative movement with respect to the electromagnetic coil  34  when shocks are incurred by the well tool  26 . In other words, movement of tool  26  is transmitted to one of the components  30 ,  32  to create the relative movement with respect to the other of the components  30 ,  32 . The relative movement induces an eddy current in the electromagnetic coil  34  which generates a magnetic field resisting the relative movement between first component  30  and second component  32 . The resistance to the relative movement has sufficient force to absorb the shock forces, while the electrical energy generated is dissipated to avoid detrimental recoil or bounce. 
     In the embodiment of  FIG. 2 , the first component  30  is in the form of an outer sleeve  38  containing the electromagnetic coil  34  and the second component  32  is in the form of an inner rod  40  containing a stack of the permanent magnets  36 . The inner rod  40  is slidably received within outer sleeve  38 . In some embodiments, the inner rod  40  is received within outer sleeve  38  without physically contacting the outer sleeve  38  and, in such a configuration, the components of shock absorber  28  may be coupled together and supported by other mechanisms. Other embodiments of the shock absorber  28  also may be constructed in a manner such that the first component  30  and the second component  32  remain out of physical contact during relative movement between the first and second components  30 ,  32 . 
     When there is relative motion between inner rod  40  and surrounding sleeve  38  due to external excitation, e.g. a shock load incurred by tool  26 , eddy current is induced in the electromagnetic coil  34 . The induced eddy current then generates a magnetic field which opposes the relative motion between the inner rod  40  and the outer sleeve  38  to effectively slow down the movement. During this process, kinetic energy is converted to electrical energy which is dissipated, e.g. dissipated through electrical heating. In some embodiments, an external resistor  42  may be placed in a circuit  44  of electromagnetic coil  34 . The external resistor  42  may be selected to adjust or set a rate of energy dissipation. 
     Depending on the application, a spring  46  may be attached between first component  30  and second component  32  to help buffer the shock load, i.e. to store part of the kinetic energy in case the electromagnetic coil  34  is unable to dissipate the energy quickly enough. The spring  46  can be used to reduce the overall length of the shock absorber  28  by helping buffer the shock load. Spring  46  also may be used to bias the permanent magnet  36  back toward a predetermined position relative to the electromagnetic coil  34 . In the example illustrated, spring  46  is positioned within outer sleeve  38  between outer sleeve  38  and inner rod  40 . In this manner, spring  46  is able to help buffer the shock load while also serving to bias the inner rod  40  and the outer sleeve  38  back toward a desired relative position. In other words, the spring  46  may be used to reset the position of inner rod  40  within outer sleeve  38  following activation. The resetting ensures that shock absorber  28  is ready for the next shock absorption with consistent performance. 
     In some applications, a magnetic cushion  48  may be used to complement spring  46  and to provide more buffering of the shock load via magnetic cushioning. However, the magnetic cushion  48  also may be used in lieu of spring  46 . By way of example, the magnetic cushion  48  may comprise a pair of permanent magnets  50  arranged with opposing poles to provide a kinetic cushioning during relative movement of first component  30  and second component  32 , e.g. during movement of inner rod  40  farther into outer sleeve  38 . The magnetic cushion  48  effectively works in parallel with the electromagnetic coil  34  and the permanent magnet  36 . 
     Referring generally to  FIG. 3 , another embodiment of shock absorber  28  is illustrated. In this embodiment, the first component  30  comprises outer sleeve  38  containing at least one and often a stack of the permanent magnets  36  and the second component  32  comprises inner rod  40  containing the electromagnetic coil  34 . Similar to the previously described embodiment, the inner rod  40  is slidably received within outer sleeve  38  and, in some cases, may interact with outer sleeve  38  without physically contacting the outer sleeve  38 . 
     When there is relative motion between inner rod  40  and surrounding sleeve  38  due to external excitation, e.g. a shock load incurred by tool  26 , eddy current is induced in the electromagnetic coil  34  of inner rod  40 . The induced eddy current again generates a magnetic field which opposes the relative motion between the inner rod  40  and the outer sleeve  38  to effectively slow down the movement. During this process, kinetic energy is converted to electrical energy which is dissipated, e.g. dissipated through electrical heating. Depending on the application, a spring  46  and/or magnetic cushion  48  may be used in combination with the inner rod  40  and outer sleeve  38  to help buffer the shock load and to reset the relative positions of the electromagnetic coil  34  and permanent magnets  36 . The external resistor  42  also may be employed in a manner similar to that described above with reference to the embodiment illustrated in  FIG. 2 . 
     Referring generally to  FIG. 4 , another embodiment of shock absorber  28  is illustrated. In this embodiment, the first component  30  and the second component  32  are constructed such that the electromagnetic coil  34  and the permanent magnet  36  are not positioned coaxially. By way of example, the first component  30  and the second component  32  may be constructed so that the electromagnetic coil  34  and the permanent magnet  36  move relative to each other along a parallel plane. 
     As with the embodiments of  FIGS. 2 and 3 , relative motion between first component  30  and second component  32  due to external excitation, e.g. a shock load incurred by tool  26 , induces an eddy current in the electromagnetic coil  34 . The induced eddy current again generates a magnetic field which opposes the relative motion between the first component  30  and the second component  32  to effectively slow down the movement. During this process, kinetic energy is converted to electrical energy which is dissipated through electrical heating or through other techniques. The spring  46  and/or magnetic cushion  48  may be positioned between the first component  30  and the second component  32  to help buffer the shock load and to reset the relative positions of the electromagnetic coil  34  and permanent magnets  36 . The external resistor  42  also may be employed in a manner similar to that described above with reference to the embodiment illustrated in  FIG. 2 . 
     Referring generally to  FIG. 5 , another embodiment of shock absorber  28  is illustrated. In this embodiment, the first component  30  comprises outer sleeve  38  which may be formed out of a suitable metal material. The second component  32  comprises inner rod  40  which is formed with a pair of rod portions  52  coupled to a piston  54  slidably mounted within outer sleeve  38 . The electromagnetic coil  34  may be positioned along piston  54  as illustrated. The rod portions  52  also may be supported by bearing structures  56  which are sealed to both rod portions  52  and to outer sleeve  38  via appropriate seals  58 . The bearing structures  56  enclose piston  54  and create a cavity  60  which may be filled with magneto-rheological fluid  62 . 
     When there is relative motion between inner rod  40  and surrounding sleeve  38  due to external excitation, e.g. a shock load incurred by tool  26 , the relative motion induces a magnetic field in the coil  34 . The magnetic field aligns the micro-particles of the magneto rheological fluid  62  and thus increases the viscosity of fluid  62 . The increased viscosity acts against the relative movement, thus creating a force acting in a direction which mitigates the shock load. 
     The various components of shock absorber  28  may be formed from a variety of materials and in a variety of configurations. In some applications, for example, the inner rod  40  may be made of iron or with iron elements instead of magnets. Additionally, the electromagnetic coil density, magneto-rheological fluid, magnetic strength, resistance load in the circuit  44 , geometric dimensions of the components, and other system configurations and system parameters may be selected or changed to adjust the shock absorber  28  so as to accomplish a targeted performance. 
     Although a few embodiments of the system and methodology have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims.