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BACKGROUND OF THE INVENTION 
     1. Field of Invention 
       [0001]    The present invention relates generally to measuring down-hole bores and in particular to an apparatus and method for measuring well bores in line with a tool string. 
       2. Description of Related Art 
       [0002]    In oilfield applications, tubular wells (boreholes or wellbores) are directionally drilled through the earth using a drilling string suspended from a drilling rig. A drilling string is a collection of assembled parts including drill pipe, drill collars, tools and the drill bit. The parts are threadably coupled together to form the drill string, with the drill bit on the distal end of the string. The drilling rig may include equipment to rotate the drilling string, or the drilling string may include a mud motor, which uses hydraulic energy from drilling fluid to turn the drill bit, independent of the drill string. The drilling fluid, also known as drilling mud, passes through the interior of the drilling string, exiting the string at the drill bit and is subsequently pumped back to the surface around the exterior of the drilling string, carrying the drill cuttings with it for treatment and disposal. 
         [0003]    It is desirable and common practice to measure the physical properties of the wellbore during or following drilling operations. Information may be obtained about the well path and position, depth, bottom-hole location, geophysical properties of the rock, etc. This information can be used to optimize the efficiency of the wellbore placement and provide information for future well use as well as any remedial steps which must be performed on the well bore. 
         [0004]    Measurement while drilling (MWD) components may include a variety of sensors which allow for continued drilling operation while collecting data with the sensors. It should be noted that in the art it is known to distinguish between the terms “measurement while drilling” (MWD) and “logging while drilling” (LWD) in that the MWD term generally refers to measurements relating to the progress of the drilling operation (such as the trajectory, rate of penetration, etc.), whereas LWD relates to information about the wellbore physical properties (such as the porosity of the rock, vertical seismic profile, etc.). For the purpose of the description of the present invention, “wellbore measurement” is intended to cover both classifications of sensors, without limiting the type of sensors that may be described below. 
         [0005]    Conventional methods of wellbore measurement have included tools with multiple sensors. However, many of these tools are separate from the drill string, not permitting a fluid bypass, and thus drilling operation must be ceased and the drill string may need to be removed before such tools can be inserted for measurements to be taken. Examples of such devices with multiple sensors include CN102337884 CN202194563 and CN20241128, U.S. Pat. No. 7,6989,937 to Neidhardt, U.S. Pat. No. 4,673,890 to Copeland et al., U.S. Pat. No. 7,281,578 to Nakajima et al. And US Patent Application Publication No. 2014/0138084 to Al-Mulhem. 
         [0006]    Applicant is aware of wall contact caliper instruments for use in a drilling string which includes a bypass passage through the tool such that the drilling operation does not need to be ceased while measurements are taken. Such devices do not detect the profile of the well bore directly, but rather detect the difference in the height between the top and bottom of the tool to measure the average diameter of the bore. Examples of such devices may be found in U.S. Pat. No. 8,024,868 to Brannigan et al. 
       SUMMARY OF THE INVENTION 
       [0007]    According to a first embodiment of the present invention there is disclosed an apparatus for measuring a well bore wall comprising a casing connectable in line with a tool string having a central passage therethrough and extending between first and second ends and a plurality of longitudinally extending biasing elements extending longitudinally along the body between first and second ends wherein each of the second end of the biasing elements is connected to the casing body. The apparatus further comprises a sensor located along a midpoint of each of the biasing elements and an engagement body located within the central passage of the casing longitudinally displaceable therein between first and second positions, wherein the engagement body is connected to the first end of each of the biasing elements such that displacement of the engagement body within the central passage from the first to the second positions compresses and radially extends the biasing elements so as to engage the sensors against the well bore wall. 
         [0008]    The central passage may have a first portion proximate to a first end of the casing and a second portion at a middle thereof. The second portion of the central passage may be larger than the first portion. The first and second portions of the central passage may include an annular shelf extending therebetween. 
         [0009]    The engagement body may comprise a disk. The disk may have a diameter larger than the first portion so as to be retained within the second portion. The disk may include a plurality bores therethrough. The plurality of bores may be positioned to be sealed by the disk when the disk is engaged thereon. 
         [0010]    The casing may include a plurality of longitudinal slots extending therealong. The apparatus may further include a carriage located in each slot. Each of the carriages may be connected to the engagement body. The biasing elements may extend along the slot. The biasing elements may extend between the carriage and a distal end of the slot. The biasing elements may comprise springs. 
         [0011]    The apparatus may further comprise a transfer body positioned within the first portion of the central passage being displaceable therein. The transfer body may have leading edge adapted to receive a dropped ball thereon. The transfer body may have a length selected to be located within the second portion of the central passage at the second position of the engagement body. 
         [0012]    According to a further embodiment of the present invention there is disclosed a method for measuring a well bore wall comprising providing a casing in line within a tool string and displacing an engagement body within a central passage of the casing from a first position to a second position to compress and radially extend a plurality of longitudinally extending biasing elements connected thereto. The method further comprises recording at least one measurement of the well bore wall with a sensor located on each of the radially extended biasing elements. 
         [0013]    Displacing the engagement body may comprises engaging a blocking body upon a transfer sleeve above the engagement body, applying a pressure to a top side of the blocking body and the transfer body and displacing and the engagement body under the pressure. The method may further comprise uncovering at least one bypass port through the engagement body at the second position. 
         [0014]    Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    In drawings which illustrate embodiments of the invention wherein similar characters of reference denote corresponding parts in each view, 
           [0016]      FIG. 1  is a cross sectional view of a wellbore having a drilling string therein which includes an apparatus for measuring the well bore wall. 
           [0017]      FIG. 2  is a perspective view of a well bore measuring apparatus for use in the drilling string of  FIG. 1 . 
           [0018]      FIG. 3  is a cross-sectional view of the apparatus of  FIG. 2  taken along line  3 - 3  in a first or disengaged position. 
           [0019]      FIG. 4  is a cross-sectional view of the apparatus of  FIG. 2  taken along the line  3 - 3  in a second or extended position. 
           [0020]      FIG. 5  is a cross sectional view of the apparatus of  FIG. 2  as taken along the line  5 - 5  of  FIG. 4 . 
           [0021]      FIG. 6  is a detailed cross sectional view of one of the slots of the apparatus of  FIG. 2  as taken along the line  5 - 5  of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Referring to  FIG. 1 , a wellbore  10  is drilled into the ground  8  by known methods. The production zone may contain a horizontally extending hydrocarbon bearing rock formation or may span a plurality of hydrocarbon bearing rock formations such that the wellbore  10  has a path designed to cross or intersect each formation. As illustrated in  FIG. 1 , the wellbore includes a drilling rig  12  at a top end thereof and a drilling or bottom hole assembly  14  at a distal end of a drill string  16  extending therebetween. As illustrated in  FIG. 1 , a wellbore measuring apparatus  20  is located within the drill string  16  for measuring the properties and characteristics of the well bore wall  18  as will be further described below. 
         [0023]    Turning to  FIGS. 2 through 4 , an apparatus  20  for measuring a well bore as set out above comprises a casing  22  extending between first and second ends,  24  and  26 , respectively and including a middle or cage portion  28  at a middle thereof. As illustrated in  FIGS. 3 and 4 , the apparatus  20  includes a plurality of spring biased sensors  30  extendable by the displacement of an actuating plate  40  therein into contact with, or proximity to the well bore wall  18  as will be described further below. 
         [0024]    The casing  22  is sized to be coupled within the drill string  16 , and having internal end threading  32  at the first end  24  and external end threading  34  at the second end  26 . The internal and external threading,  32 ,  34 , are selected to correspond to and be matable with other drill string threading, as are commonly known. The casing  22  defines an interior passage  36  therethrough having a lead portion  42  proximate to the first end  24  and a cage portion  28  located at the midpoint thereof. The diameter of the lead portion  42  of the interior passage  36  is less than the diameter of the cage portion  28 . An inward annular shoulder  44  defines the separation between the lead portion  42  and cage portion  28 . A bottom portion  46  of the interior passage  36 I located proximate to the second end  26  end and matches the diameter of the lead portion  42 , with an annular shoulder  48  between the cage and bottom portions  28 ,  46 . 
         [0025]    As shown best on  FIG. 5 , the cage portion  28  of the casing  22  includes a plurality of longitudinal slots  50  extending through the casing  22  which may be distributed axially around the casing  22  at the cage portion  28 . The quantity of slots  50  may range from 10 to 18, although it may be appreciated that other quantities may be useful, as well. As illustrated, the slots  50  may be arranged radially at regular angles around the casing although it will be appreciated that other configurations may be useful as well. The slots  50  extend between a first end  52  located towards the first end  24  of the casing  22  and slot second end  54  located towards the second end  26  of the casing  22 . A carriage  56  is located within each slot. A leaf spring  58 , or other biasing member, may be fixed to the carriage  56  and to the casing  22  at the second end  54  of the slot  50 . Each slot  50  is sealed with an anticorrosive rubber seal  60  located therein which incorporates a slit  62  through which each carriage  56  may be connected to the actuating plate  40  as illustrated in  FIG. 6 . The carriages  56  may include a narrowed portion  57  extending through the slit  62  to the actuating plate  40 . Sensors  30  may be attached to each leaf spring  58  and may be extended therefrom. As illustrated, the sensors  30  may be located at a midpoint of the leaf spring  58  span, although other locations may be useful as well. As illustrated in  FIG. 3 , the leaf spring  58  may be sized to substantially span the length of the slot  50  when in the resting or inert position so as to position the carriage proximate to the first end  52  of the slot  50  at such position. 
         [0026]    Referring to  FIGS. 3, 4 and 5 , the cage portion  28  contains a disk shaped actuating plate  40  sized to fit therein. The diameter of the actuating plate  40  is sized to slide within the cage portion  28 , having a larger diameter than the lead portion  42  of the interior passage, such that the actuating plate  40  will not slide past annular shoulder  44 . The actuating plate  40  may have a thickness ranging such as from 1 to 2 inches (25.4 to 50.8 mm), although it may be appreciated that other thicknesses may be useful, as well. A plurality of bypass bores  60  are positioned in a circular array proximate to the exterior edge of the actuating plate  40 , such that they are positioned to be covered by the annular shoulder  44  when the actuating plate  40  is located at the first position as illustrated in  FIG. 3 . A central bore  41  is located in the centre of the actuating plate  40  to permit fluid to pass therethrough prior to a ball being dropped into contact with the ball seat as set out below. The plurality of carriages  56  may be attached to the actuating plate  40  such that they are seated within the plurality of slots  50 . 
         [0027]    A cylindrical engagement sleeve  70  is sized to fit within the lead portion  42  such that it can slide therein. The engagement sleeve  70  extends between lead and second ends  72  and  74 , respectively, with a central bore  76  defining a passage  78  therethrough. The passage  78  continues through central bore  41  in the actuating plate  40 . The central bore  76  has a profiled ball seat  79  at the lead end  72  such that an engagement ball  80  can be seated therein, thus sealing passage  78 , as shown in  FIG. 4 . The length of engagement sleeve  70  may range such as from 6 to 24 inches (152 to 610 mm), although it may be appreciated that other lengths may be useful, as well. The engagement sleeve  70  is maintained in position by spring loaded wedges  84  located below the ball seat  70 . After the ball seat  70  is shifted downwardly within the interior passage  36 , the wedges  84  will return to their extended position as illustrated thereby preventing an upward return of the ball seat  70  to the run in position. It will also be appreciated that other devices for retaining the ball seat  70  at the run in position illustrated in  FIG. 3  may also be utilized such as, by way of non-limiting example, shear pins or the like. 
         [0028]    In operation the apparatus  20  may be located within a drill string  16  and the drilling operation performed as is commonly known. When an operator desires to activate the apparatus  20 , an engagement ball  80  is released within the drill string  16 . The ball  80  is sized to pass through the interior passage of all drill string  16  components, and to be seated snugly within the ball seat  79  of the engagement sleeve  70 . As the ball  80  is seated within engagement sleeve  70 , the hydraulic fluid builds pressure on the now sealed engagement sleeve  70 , which shifts down past the pressure gradient mechanisms to engage upon the actuating plate  40 . Further pressure thereon displaces the actuating plate  40  and engagement sleeve  70  within cage portion  28 , longitudinally sliding the carriages  56  within the slots  50  and subsequently extending leaf springs  58  with attached sensors  30  through the slits in the rubber seals. As the actuating plate  40  is displaced within the cage portion  28 , bypass bores  60  are exposed, allowing hydraulic fluid to pass therethrough once the engagement sleeve  70  has been displaced past annular shoulder  44 , as indicated at  100  on  FIG. 4 , while maintaining sufficient pressure to continuously maintain the sensors at the extended position. Hydraulic fluid continues to pass through passages  36  and  82 , allowing continued operation of the drill string during wellbore measurement with the sensors  30 . 
         [0029]    Sensors  30  may be radius proximity sensors, or other sensor types commonly used in the art, depending on the desired data outcome. As there are a plurality of sensors on the cage portion  28 , a variety of sensor types could be mounted on leaf springs  58 . The sensors  30  may be connected, as is commonly known, by wire to a memory card  90  enclosed within the casing  22 . It will be appreciated that the sensors  30  may be selected to measure a desired characteristic of the well bore as are commonly known in the art. The memory card  90  could store data received from the sensors  30  until the apparatus  20  is removed from the wellbore  10  for review following the drilling operation. Alternately, signals from the sensors  30  may be communicated to the surface over a signal line, within wired drill pipe, or through any other method as is commonly known in the art. 
         [0030]    The casing  22  may be fabricated using metal composites, using any common forming methods, such as casting, molding, or machining, by way of non-limiting example. It will be appreciated that all components of the present device will be required to be formed of materials and in sufficient thicknesses and dimensions to withstand the torque stress, pressure, temperature and anticorrosive standards of bottom hole assemblies as are commonly known. 
         [0031]    While specific embodiments of the invention have been described and illustrated, such embodiments should be considered illustrative of the invention only and not as limiting the invention as construed in accordance with the accompanying claims.

Summary:
An apparatus for measuring a well bore wall comprises a casing connectable in line with a tool string having a central passage therethrough and extending between first and second ends and a plurality of longitudinally extending biasing elements extending longitudinally along the casing between first and second ends wherein each of the second end of the biasing elements is connected to the casing. The apparatus further comprises a sensor located along a midpoint of each of the biasing elements and an engagement body located within the central passage of the casing longitudinally displaceable therein between first and second positions, wherein the engagement body is connected to the first end of each of the biasing elements such that displacement of the engagement body within the central passage from the first to the second positions compresses and radially extends the biasing elements so as to engage the sensors against the well bore wall.