Abstract:
A downhole magnetic clamping system for a tool is provided. The clamping system may include a first permanent magnet, and a yoke, movably positioned next to the first permanent magnet and movable to at least two positions, a first position in which a magnetic attraction force produced by the first permanent magnet on structures exterior to the tool is reduced relative to a second position. In addition, the clamping system may further include a non-linear resilient member applying a resilient force to the yoke in the direction of the second position. Further, the clamping system may include an electro-magnetic coil, operable in a first and second direction to initiate movement of the yoke between the first position and the second position.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of a related U.S. Provisional Application Ser. No. 62/261,259, filed Nov. 30, 2015, entitled “Magnetic Casing Clamping System,” to Makito KATAYAMA et al., the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    The following descriptions and examples are not admitted to be prior art by virtue of their inclusion in this section. 
         [0003]    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. When evaluating various subterranean features in fields containing hydrocarbon fluids, downhole operations such as seismic measurement are often used. Currently, a modern business trend is to have as many sensor modules as possible mounted onto an array cable, because relatively high numbers of sensor module recordings contribute to minimal operation time and providing higher quality data. For example, one company Sercel Inc. produces downhole seismic array tools which have more than 100 receiver modules included with an array structure. 
         [0004]    In order to efficiently add many receiver modules for one array, reliable, small, and cheap systems are needed for facilitation. Accordingly, it is important to simplify any of the component&#39;s mechanical structures. When considering seismic tools, clamping the sensor package onto the casing is a beneficial process used in order to detect the dynamic motion of the formation. However, the mechanical structure of current clamping systems tend to be complicated and inefficient in their ability to produce an on/off clamping force, often via a mechanical arm pushing the sensor package against the casing, or via a magnetic force using a motor and a yoke assembly. 
       SUMMARY 
       [0005]    This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. 
         [0006]    Embodiments of the claimed disclosure may comprise a downhole magnetic clamping system for a tool. The clamping system may include a first permanent magnet, and a yoke, movably positioned next to the first permanent magnet and movable to at least two positions, a first position in which a magnetic attraction force produced by the first permanent magnet on structures exterior to the tool is reduced relative to a second position. In addition, the clamping system may further include a non-linear resilient member applying a resilient force to the yoke in the direction of the second position. Further, the clamping system may include an electro-magnetic coil, operable in a first and second direction to initiate movement of the yoke between the first position and the second position. 
         [0007]    Other or alternative features will become apparent from the following description, from the drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    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 drawings illustrate only the various implementations described herein and are not meant to limit the scope of various technologies described herein. The drawings are as follows: 
           [0009]      FIGS. 1A and 1B  are schematic illustrations of a prior art magnetic clamp using a yoke; 
           [0010]      FIG. 2  is a schematic illustration of prior art magnetic clamping using a motor and graphs showing various forces on the yoke; 
           [0011]      FIG. 3  is a schematic illustration of magnetic clamping using a solenoid coil, according to an embodiment of the disclosure; and 
           [0012]      FIG. 4  is a schematic illustration of magnetic clamping using a solenoid coil and graphs showing various forces on the yoke, according to an embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Reference throughout the specification to “one embodiment,” “an embodiment,” “some embodiments,” “one aspect,” “an aspect,” or “some aspects” means that a particular feature, structure, method, or characteristic described in connection with the embodiment or aspect is included in at least one embodiment of the present disclosure. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” or “in some embodiments” in various places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, methods, or characteristics may be combined in any suitable manner in one or more embodiments. The words “including” and “having” shall have the same meaning as the word “comprising.” 
         [0014]    As used throughout the specification and claims, the term “downhole” refers to a subterranean environment, particularly in a wellbore. “Downhole tool” is used broadly to mean any tool used in a subterranean environment including, but not limited to, a logging tool, an imaging tool, an acoustic tool, a permanent monitoring tool, and a combination tool. 
         [0015]    The various techniques disclosed herein may be utilized to facilitate and improve data acquisition and analysis in downhole tools and systems. In this, downhole tools and systems are provided that utilize arrays of sensing devices that are configured or designed for easy attachment and detachment in downhole sensor tools or in modules that are deployed for the purposes of sensing data relating to the environmental and tool parameters downhole, within a borehole. The tools and sensing systems disclosed herein may effectively sense and store characteristics relating to components of downhole tools as well as formation parameters at elevated temperatures and pressures. 
         [0016]    The sensing systems herein may be incorporated in tool systems such as wireline logging tools, measurement-while-drilling and logging-while-drilling tools, permanent monitoring systems, drill bits, drill collars, sondes, among others. For purposes of this disclosure, when any one of the terms wireline, cable line, slickline or coiled tubing or conveyance is used it is understood that any of the referenced deployment means, or any other suitable equivalent means, may be used with the present disclosure without departing from the spirit and scope of the present disclosure. 
         [0017]    Embodiments of the proposed clamping system incorporate the use of a magnet and a yoke to control the magnetic force emanating from the magnet. The theory may be described as part of a seismic sensing array with a plurality of sensor packages, but any sensing or measuring device incorporating clamping may include aspects of the present disclosure and are considered within the scope of this application. 
         [0018]    Referring generally to the exemplary  FIGS. 1A and 1B , this schematic illustrates a basic concept behind a magnet and yoke clamping system. As seen in the left side of the figure, a permanent magnet  150  is fixed in position relative to the housing  110  of a sensor package  100 . A metallic yoke  140  is configured and positioned so as to fully cover the sides and one surface of the magnet  150 . The sensor package  100  is suspended by means of a cable  130  that is attached to two ends of the housing  110 . Although not illustrated in this figure, the portion of the sensor package and cable shown may represent one of a plurality of sensor packages attached to one another through the use of a cable. 
         [0019]    When the sensor package  100  is deployed downhole, there is little need to clamp the sensor package to the casing  120  lining a wellbore. In fact, if the magnet  150  were to exert a strong attractive force towards the casing  120 , the sensor array may require weight or a tractor to fully deploy downhole. But with a permanent magnet  150 , the magnetic force  160  is constantly generated, and use of an electro-magnet for clamping force would require additional components and the expenditure of large amounts of energy, either from an internal battery or from the cable. In order to control or reduce the level of magnetic attraction produced by the permanent magnet  150  during deployment, a metallic yoke  140  is positioned to couple with the magnet  150 , in some cases, the opposing surfaces may be designed to contact one another. 
         [0020]    When the yoke  140  is surrounding the sides of the permanent magnet  150  and abutting the surface of the permanent magnet  150 , the magnetic field  160  is constrained by the yoke  140  to flow around the magnet  150 , as seen in the figure. By providing a pathway for the magnetic field  160 , the attraction force between the magnet  150  and the casing  120  is reduced, allowing for ease of travel of the sensor package  100  and array during deployment. 
         [0021]    Referring generally to the right side of the figure, the yoke  140  is moved apart from the permanent magnet  150 , allowing the magnetic force  160  to emanate from the permanent magnet  150  and apply a clamping force against an inner surface of the casing  120 . The magnetic force  160  can be illustrated as indicated by the arrows in the figure. When the yoke  140  is displaced from the permanent magnet  150 , the clamping system is ‘on’. When the yoke  140  is coupled or attached to the permanent magnet  150 , the clamping system is ‘off’. 
         [0022]    Turning now to prior art  FIG. 2 . Conventional implementations of a permanent magnet  150  and yoke  140  system use a motor  180  and a threaded attachment to the yoke. As seen in this figure, a gear box  170  takes an input from the motor  180  and uses a threaded connection to apply a force F d  to the yoke  140 . When the F d  exceeds the force of the permanent magnet F m , the yoke  140  moves apart from the magnet  150  and the clamping system is switched ‘on’ as previously explained. 
         [0023]    However, with this system and as shown by the graph on the right side of the figure, F d , as generated by the motor  180  and the threaded gear box assembly  170 , is relatively constant. But F m  from the permanent magnet  150  is greatest when the yoke  140  is contacting the magnet  150  and then falls exponentially as the yoke  140  moves away from the magnet  150 . The result is that the application of the force F d  from the motor  180  is significantly inefficient relative to the travel position of the yoke  140 . While a relatively strong motor  180  is need to initially break the contact between the yoke  140  and the permanent magnet  150 , the strength required rapidly diminishes as the yoke  140  gains in distance away from the magnet  150 . At the end of the travel, the difference between the two levels of force is quite large. 
         [0024]    Embodiments of the current disclosure have attempted to increase the efficiency of moving a yoke between an ‘on’ and ‘off’ position. As seen in exemplary  FIG. 3 , embodiments of a sensor package  300  may include a housing  315 . Within the housing  315  is a yoke  340  surrounding and in some cases contacting at least one surface of a permanent magnet  350 . The permanent magnet  350  may be fixed in position relative to the housing  315 . 
         [0025]    Applying a force to the yoke  340  and away from the permanent magnet  350  is a non-linear spring  375 . The non-linear spring  375  may have an incremental increase in spring constant or may be composed of two or more sections of relatively constant but greater spring constants. Attached to the other end of the yoke  340  is another permanent magnet  355  that is configured to move along with the yoke  340 . The other permanent magnet  355  may be attracted by an electro-magnetic coil  385 , fixed in position relative to the housing  315 . Although another permanent magnet  355  and an electro-magnetic coil  385  have been shown, these components may be replaced with functional or other types of equivalent components performing the same general functions. 
         [0026]    Now generally referring to  FIG. 4 , this exemplary figure shows an embodiment of the clamping system along with the forces acting on the yoke  340  generated by the various components. The forces are also shown in two graphs on the right side of the figure. The primary forces include the force of the permanent magnet F m  being opposed by the force of the non-linear spring F s . The first graph shows the interaction of these two forces. When X c  (displacement of the yoke  340  from the permanent magnet  350 ) is zero, the force of the permanent magnet F m  exceeds the force of the linear spring F s  and the yoke  340  is coupled to the magnet  350  and the clamping system is ‘off’. 
         [0027]    At the other end of the travel of the yoke  340 , when X c  is at its largest value, the force of the spring F s  exceeds the force of the magnet F m  and the yoke  340  remains in the ‘on’ position. As shown in the first graph, the two forces are much more closely aligned to one another, so that the system is not significantly over or under specified during the entire length of travel of the yoke  340 . The slight difference at either end of travel allow the system to stably remain in an ‘on’ or ‘off’ position. Therefore, only a small force is required to initiate the travel of the yoke  340  in either direction. 
         [0028]    As seen in this exemplary embodiment, the small force required to initiate the travel of the yoke  340  is produced by an electro-magnetic coil  385  that can be operated in two directions by changing the polarity of an applied current. When operated in the direction as shown, the electro-magnetic coil produces a force F e  in the same direction as the F s . This force is enough to exceed the difference between the magnetic force F m  and the non-linear spring force F s . In reverse, when the yoke  340  is moving from the ‘on’ position to the ‘off’ position, the electro-magnetic F e  provides a slight push (in the direction of the magnetic force F m ). The electro-magnetic force F e  is able to overcome the spring force to start the motion of the yoke  340  so that the clamping system is switched ‘off’. 
         [0029]    Turning to the second graph, the difference between the magnetic force F m  and the non-linear spring force F s  is shown as essentially a straight line. This is due in part to the incremental nature of the spring force F s  being selected to correspond to the drop off in the magnetic force F m . The difference between the forces is shown located between the application of the electro-magnetic coil force F e  in both a positive (e.g., above the axis) and reverse polarity (e.g., below the axis) direction. In one direction, a higher current may be applied to the electro-magnetic coil than the other direction. Another permanent magnet  355  applied to one end of the yoke  340  to enhance the effect from the electro-magnetic coil  385 . The other permanent magnet  355  may be sized so as to optimize the specification of the elecro-magnetic coil  385  and the power requirements of the electro-magnetic coil  385 . 
         [0030]    Referring to the far right side graph shown in  FIG. 4 , the far right side graph shows the application of the electro-magnetic coil  385  adding a force F e  to the difference between the force from the permanent magnet  350  and the non-linear spring  375 , F m -F s , to initiate the movement of the yoke  340  from the ‘off’ position to the ‘on’ position. The electro-magnetic coil  385  only needs to be applied until the force from the non-linear spring F s  begins to exceed the force from the permanent magnet F m . After which, the yoke  340  will continue to travel on its own until it reaches the ‘on’ position at the highest value of distance X c . For reverse operation, the polarity is switched at the electro-magnetic coil  385  and a smaller current is applied to begin the movement of the yoke  340  from the ‘on’ position to the ‘off’ position. 
         [0031]    The use of a non-linear spring  375  reduces the overall force required to induce motion in the yoke  340 . Although embodiments of the current disclosure show the combination of a non-linear spring  340  with an electro-magnetic coil  385 , other mechanisms may be used to initiate motion in the yoke  340 . As previously stated, although a non-linear spring  375  with an incremental spring constant may be one of the more optimized methods of creating embodiments of this disclosure, springs with step increases in spring constant may be considered within the scope of the disclosure. 
         [0032]    Moreover, inventive aspects lie in less than all features of a single disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment. 
         [0033]    Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this disclosure. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. 
         [0034]    In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.