Abstract:
The subject matter of this specification can be embodied in, among other things, a system for removably attaching an optical fiber sensor loop onto a tubular member, which includes an optical fiber sensor loop having a continuous optical fiber positioned arranged in a plurality of loops, each of said loops having a first end turn and a second end turn, a first and a second turn guide each including a plurality of turn grooves increasing outwardly in increasing radii, each of said turn grooves configured to receive an end turn portion of the optical fiber, a first and a second supporting wedge each having a planar first surface configured to receive a turn guide and a curved second surface configured to be received on the tubular member, and a connector configured to couple the first mounting wedge to the second mounting wedge.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application is a Divisional of U.S. application Ser. No. 14/411,198 filed on Dec. 24, 2014, entitled “PORTABLE ATTACHMENT OF FIBER OPTIC SENSING LOOP,” currently pending; which application is a U.S. National Stage of International Application No. PCT/US2014/017983, filed Feb. 24, 2014, entitled “PORTABLE ATTACHMENT OF FIBER OPTIC SENSING LOOP,” both of which are commonly assigned with the present invention and incorporated herein by reference. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    This present disclosure relates to an apparatus for mounting of fiber optic sensing elements on pipe sections. 
       BACKGROUND OF THE INVENTION 
       [0003]    In connection with the recovery of hydrocarbons from the earth, wellbores are generally drilled using a variety of different methods and equipment. According to one common method, a drill bit is rotated against the subsurface formation to form the wellbore. The drill bit is rotated in the wellbore through the rotation of a drill string attached to the drill bit and/or by the rotary force imparted to the drill bit by a subsurface drilling motor powered by the flow of drilling fluid down the drill string and through downhole motor. 
         [0004]    The flow of drilling fluid through the drill string can exhibit variations in pressure including pressure pulses. These pressure variations can cause dimensional changes in solid structures such as piping that carries the drilling fluid to and from the drill string. Strain gauges are sometimes used for detecting and measuring absolute dimensional changes of solid structures, such a piping for drilling fluid. Such changes can occur gradually, however, and may be challenging to observe and quantify. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a perspective view of an example optical sensor mounting system. 
           [0006]      FIG. 2  is a perspective view of an example optical sensor loop. 
           [0007]      FIG. 3  is perspective view of an inner surface of an example optical sensor loop turn guide. 
           [0008]      FIG. 4  is perspective view of an outer surface of an example optical sensor loop turn guide. 
           [0009]      FIG. 5  is a perspective view of an example optical sensor in a partially assembled state. 
           [0010]      FIG. 6  is a perspective view of an example optical sensor in an assembled state. 
           [0011]      FIG. 7  is a perspective view of an example mount wedge. 
           [0012]      FIG. 8  is a perspective view of a collection of example tension rods. 
           [0013]      FIG. 9  is a perspective view of another example optical sensor mounting system. 
           [0014]      FIG. 10  is an exploded perspective view of another example optical sensor mounting system. 
           [0015]      FIGS. 11 and 12  are side and top views of the example optical sensor mounting system of  FIG. 10 . 
           [0016]      FIGS. 13-15  are various cross-sectional side views of the example optical sensor mounting system of  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    This document describes systems and techniques for mounting sensor attachments to drilling fluid piping on drilling rigs. The assemblies described in this document can be used, for example, to mount optical sensors such as sections of Sagnac loop interferometers to measure expansion and contraction of the piping due to pressure variations in the fluid flowing within the piping. The Sagnac Loop interferometer is a sensor that can be used to detect mechanical or thermal disturbances or vibrations. The Sagnac interferometer operates by generating a light signal with a predetermined wavelength, transmitting the light signal through an optical fiber loop, and detecting the resulting coherent light phase shift. Measurements of the shifts in the coherent light phase provide information regarding physical disturbances or vibrations along the loop of the Sagnac interferometer. 
         [0018]    In general, optical sensor mounts clamp, attach, or are otherwise affixed to an outside surface of one or more pipes in the drilling fluid piping system. Fluid (for example, drilling fluid) flowing through the pipe exerts a pressure force outward against the pipe, which causes small changes in the diameter of the pipe that vary with the pressure of the fluid within. The optical sensor mounts mechanically transfer, and in some implementations, amplify or reduce, changes in pipe diameter to one or more sensors. The signal outputs of such sensors can then be processed to observe changes in the diameter of the pipe. The changes in diameter of the pipe diameter may be processed using known physical characteristics of pressure pipes, and detection of said changes can allow for downhole pressure pulse detection whereas said pressure pulses can convey the specific information or data content. 
         [0019]      FIG. 1  is a perspective view of an example optical sensor mounting system  100 . In general, the mounting system  100  simplifies attachment and removal of an optical sensor  101 , such as a fiber optic loop section of a Sagnac Loop interferometer, a Mach-Zehnder interferometer, a distributed Acoustic Sensing System (DASS), or any other appropriate sensor that includes one or more loops of fiber optic cable, to and from a pipe  102  while preserving signal fidelity and rotational signal rejection of the optical sensor  101 . 
         [0020]    The optical sensor mounting system  100  includes a pair of mount wedges  110   a  and  110   b . The optical sensor  101  is wrapped around the periphery of the pipe  102 , and is removably affixed to the mount wedges  110   a ,  110   b  by a pair of sensor loop turn guide assemblies  120   a  and  120   b . The mount wedges  110   a ,  110   b  are flexibly interconnected by a collection of tension rods  130 . The optical sensor  101  is wrapped around the pipe  102  and is adjusted to a predetermined pre-tension by adjustment of the linkage between the tension rods  130 . The optical sensor  101  is configured to detect changes in the length of the optical sensor  101  (e.g., stretching). In the illustrated configuration, expansion or contraction of the circumference and diameter of the pipe  102  due to changes in the pressure of a fluid within the pipe  102  will apply changes in tension on the optical sensor  101  that can be measured and used to determine changes in the fluid pressure within the pipe  102 . The optical sensor  101 , the mount wedges  110   a  and  110   b , the sensor loop turn guide assemblies  120   a - 120   b , and the tensioning rods  130  with associated linkage will be discussed further in the descriptions of  FIGS. 2-9 . 
         [0021]      FIG. 2  is a perspective view of an example optical sensor loop  200 . The optical sensor loop  200  includes a fiber optic cable  210  arranged in an elongated spiral having a middle section  220  in which the fiber optic cable  210  is arranged as a collection of generally planar and substantially parallel strands, and two end sections  230  in which the fiber optic cable  210  is arranged as a collection of generally planar and curved pathways. In some implementations the curved pathways may be arranged substantially concentric and semi-circular and/or in a partial elliptical arrangement. 
         [0022]    The fiber optic cable  210  is terminated at each end by a pair of optical couplers  240 . The optical couplers  240  provide connecting points to which light sources, optical detectors, and other appropriate equipment can be optically coupled to the fiber optic cable  210 . 
         [0023]      FIGS. 3 and 4  are perspective views of an example optical sensor loop turn guide  300 .  FIG. 3  shows an optical sensor loop lower turn guide  301  and  FIG. 4  show an optical sensor loop upper turn guide  302 . In general, the optical sensor loop lower turn guide  301  and the optical sensor loop upper turn guide  302  are coupled together to form the example sensor turn guide assembly  120   a  of  FIG. 1 , and the optical sensor loop lower turn guide  301  and the optical sensor loop upper turn guide  302  are coupled together to form the example sensor turn guide assembly  120   b.    
         [0024]    Referring to  FIG. 3 , an inner face  310  of the optical sensor loop lower turn guide  301  is shown. The optical sensor loop lower turn guide  301  includes a bore  330  and a collection of bores  350 . The inner face  310  includes a collection of grooves  320 . The grooves  320  are arranged as a collection of ridges and troughs formed on the inner face  310  in a curved pathway. The grooves  320  are non-intersecting, and increase outwardly with increasing radii. In some implementations the curved pathways may be arranged substantially concentric and semi-circular and/or in a partial elliptical arrangement. Each of the grooves  320  is configured to receive a portion of the optical fiber  210  at one of the end sections  230 . 
         [0025]    Referring to  FIG. 4 , the optical sensor loop upper turn guide  302  of the sensor loop turn guide  300  is shown. The optical sensor loop upper turn guide  302  includes the bore  330  and the bores  350 . In some implementations, the optical sensor loop upper turn guide  302  is a substantially flat plate that, when assembled to the optical sensor loop lower turn guide  301 , contacts the ridges or the grooves  320  to substantially enclose and constrain the fiber optic cable  210  with each of the grooves  320 . 
         [0026]      FIG. 5  is a perspective view of the example optical sensor  101  in a partially assembled state. As is best seen in reference to the sensor loop turn guide assembly  120   a , each loop of the end sections  230  of the sensor loop  200  is placed in one of the corresponding grooves  320  of the optical sensor loop lower turn guide  301 . The optical sensor loop upper turn guide  302  is placed adjacent the optical sensor loop lower turn guide  301 , as is best seen in reference to the sensor loop turn guide assembly  120   b . In the assembled configurations of the sensor loop turn guide assemblies  120   a ,  120   b , each mating pair of the optical sensor loop lower turn guide  301  and the optical sensor loop upper turn guide  302  substantially surrounds and constrains a corresponding loop of the sensor loop  200 . 
         [0027]    A bottom sheath  510  is provided to support and protect the middle section  220  of the sensor loop  200 . Referring now to  FIG. 6 , which is a perspective view of the example optical sensor  101  in an assembled state, a top sheath  610  is provided to support and protect the middle section  220  of the sensor loop  200 . The top sheath  610  includes holes  620 . The fiber optic cable  210  passes through the holes  620  to expose the optical couplers  240 . 
         [0028]    The top sheath  610  and the bottom sheath  510  are flexible to allow the sensor loop to be bent into a curve. In some embodiments, the top sheath  610  and the bottom sheath  510  can have a flexible stiffness that limits the bending radius of the sensor loop  200 . For example, fiber optic cable  210  may have a maximum bending radius which, if exceeded, could damage the fiber optic cable  210  in a way that prevents light from passing through and thus possibly causing the sensor loop  200  to malfunction. The top sheath  610  and bottom sheath  510 , however, can have a stiffness and bending radius that are greater than that of the fiber optic cable  210 , so that the sensor loop  200  will follow the relatively lesser bending radius of the sheaths  510 ,  610  when flexed. 
         [0029]    Referring now to  FIGS. 3-6 , the sensor loop turn guides  300  also include the collection of bores  350 . During assembly, pairs of the sensor loop turn guides  301  and  302  are mated to align the bores  350 , and a collection of fasteners (not shown) (e.g., bolts, screws) are passed through the bores  350  to removably attach the pairs to each other to form the sensor loop turn guide assemblies  120   a  and  120   b . During assembly, the collection of fasteners are also passed through the bores  350  to removably assemble the sensor loop turn guide assemblies  120   a  and  120   b  to the mount wedges  110   a  and  110   b.    
         [0030]      FIG. 7  is a perspective view of an example mount wedge  700 . In some embodiments, the mount wedge  700  can be the mount wedge  110   a  or the mount wedge  110   b  of  FIG. 1 . The mount wedge  700  includes a bottom face  710 , a back face  720 , and a mount face  730 . 
         [0031]    The bottom face  710  is formed with a longitudinal concave curvature. In some embodiments, the radius of the bottom face  710  approximates the radius of the pipe  102  of  FIG. 1 . The back face  720  is a substantially flat planar surface that intersects the bottom face  710  at an approximately perpendicular angle. The front face  730  is a substantially flat planar surface that intersects the back face  720  at an approximately 45 degree angle and intersects the bottom face  710  at an angle approximately tangent to the curvature of the bottom face  710 . In some embodiments, the angle at which the front face  730  and the back face  720  intersect can be determined from the diameter of pipe  102 . 
         [0032]    The front face  730  includes a groove  740 . The groove  740  is a semi-cylindrical, concave recess formed along the longitudinal length (e.g., relative to the axis of curvature of the bottom face  710 ) of a distal end  702  of the mount wedge  700 . A slot  750  cut out of the distal end  702 , intersecting the groove  740  near a midpoint substantially perpendicular to the groove  740 . A longitudinal bore  760  is formed through the mounting wedge substantially parallel to the faces  710 ,  720 , and  730 . The groove  740 , the slot  750 , and the bore  760  will be discussed further in the descriptions on  FIGS. 8 and 9 . 
         [0033]    The front face  730  also includes a mounting post  770 . The mounting post  770  protrudes out from the mount wedge  700  at an angle substantially perpendicular to the front face  730 . The mounting post  770  is configured to mate with the bores  330  of the sensor loop turn guides  300 , as will be discussed further in the descriptions on  FIG. 9 . In some embodiments, the mounting post  770  may be a threaded member that can be removably threaded into a corresponding threaded receptacle in the front face  730 . 
         [0034]      FIG. 8  is a perspective view of the collection of example connector rods  130 . The collection includes an outer rod  810   a , an outer rod  810   b , a center rod  820 , a through-wedge rod  830   a , and a through-wedge rod  830   b . The outer rods  810   a  and  810   b  have a diameter that approximates or is less than that of the groove  740  of the example mount wedge  700  of  FIG. 7 . The outer rods  810   a ,  810   b  and the center rod  820  each include a bore  840 . The bores  840  are formed near the midpoints and perpendicular to the longitudinal lengths of their corresponding rods  810   a ,  810   b , and  820 . 
         [0035]    The through-wedge rods  830   a  and  830   b  have a diameter that allows the rods  830   a ,  830   b  to be inserted into the bore  760 . The through-wedge rods  830   a  and  830   b  each also include a pair of bores  850 , with each bore  850  formed near an end and perpendicular to the longitudinal lengths of their corresponding through-wedge rods  830   a  and  830   b . The collection of rods  130  will be discussed further in the description of  FIG. 9 . 
         [0036]      FIG. 9  is another perspective view of the example optical sensor mounting system  100  in a partly assembled form. During assembly, the mount wedges  110   a  and  110   b  are arranged such that their bottom faces  710  are in contact with the pipe  102 , and their back faces  720  are facing each other. The sensor loop turn guide assembly  120   a  is brought into contact with the mount wedge  110   a  such that the mount post  770  passes through the bores  330  such that one of the bottom faces  710  contacts the front face  730 . A fastener (not shown) (e.g., bolt, screw, rivet) is passed through each of the bores  350  to removably attach the sensor loop turn guide assembly  120   a  to the mount wedge  110   a.    
         [0037]    The optical sensor  101  is wrapped around the pipe  102 , and the sensor loop turn guide assembly  120   b  is assembled to the mount wedge  110   b  in a manner similar to the assembly of the turn guide assembly  120   a  and the mount wedge  110   a  (e.g., as illustrated in  FIG. 1 ). The through-wedge rod  830   a  is inserted into the bore  760  in the mount wedge  110   a , and the through-wedge rod  830   b  is inserted into the bore  760  in the mount wedge  110   b.    
         [0038]    The outer rod  810   a  is placed in the groove  740  of the mount wedge  110   a , and the outer rod  810   b  is placed in the groove  740  of the mount wedge  110   b . The center rod  820  is placed between the mount wedges  110   a  and  110   b . The bores  840  in outer rod  810   a , the outer rod  810   b , and the center rod  820  are aligned with the slots  750  and with each other. A fastener (not shown) (e.g., a bolt, a screw) is passed through the aligned bores  840  and is adjustably tensioned. Tension on the fastener draws the mount wedges  110   a  and  110   b  toward each other, which in turn applies an adjustable pre-tension on the optical sensor  101 . In some embodiments, the bores  850  of the rods  830   a  and  830   b  can be aligned, a collection of fasteners (not shown) can be passed through the bores  850  and adjustably tensioned to pre-tension the optical sensor  101  instead of or in addition to use of the outer rods  810   a ,  810   b.    
         [0039]      FIG. 10  is an exploded perspective view of another example optical sensor mounting system  1000 .  FIGS. 11 and 12  are side and top views of the optical sensor mounting system  1000 .  FIGS. 13-15  are various cross-sectional side views of the optical sensor mounting system  1000 . 
         [0040]    With reference to  FIGS. 10-15 , the optical sensor mounting system  1000  removably attaches an optical sensor loop (not shown), such as the example optical sensor loop  200  of  FIG. 2 , to the pipe  102 . The optical sensor mounting system  1000  includes a support wedge  1010  having a bottom face  1012 , a side face  1014   a , a side face  1014   b , and a groove  1016 . 
         [0041]    The bottom face  1012  is formed with a concave angular or curved profile that approximates the outer diameter of the pipe  102 . The side faces  1014   a ,  1014   b  are substantially planar faces that intersect the bottom face  1012  at angles approximately tangent to the outer diameter of the pipe  102 , and approach but do not intersect each other at the groove  1016 . 
         [0042]    The optical sensor mounting system  1000  includes a tension bar  1020 . A collection of load transfer pins  1022  extend laterally outward from the tension bar  1020 . The tension bar  1020  is positioned in the groove  1016  such that the load transfer pins  1022  align with and extend through a corresponding collection of lateral slots  1018  formed in the side faces  1014   a  and  1014   b , intersecting the groove  1016 . A collection of bores  1024  are formed through the tension bar  1020  perpendicular to the load transfer pins  1022 . 
         [0043]    A collection of fasteners  1030  (e.g., bolts) are passed through and protrude out the bottoms of the bores  1024 . A collection of springs  1032  are placed about the protruding ends of the fasteners  1030 , and the fasteners  1030  are threaded into a collection of bores  1019  formed in the groove  1016 , capturing the springs  1032  between the support wedge  1010  and the tension bar  1020 . The fasteners  1030  are tensioned to adjustably draw the tension bar  1020  toward the support wedge  1010  against the bias of the springs  1032 . As the tension bar  1020  is drawn into the groove  1016 , the load transfer pins  1022  are drawn along the lateral slots  1018  toward the pipe  102 . 
         [0044]    The optical sensor mounting system  1000  includes a sensor loop turn guide  1040   a  and a sensor loop turn guide  1040   b . The sensor loop turn guides  1040   a ,  1040   b  each have a front face  1042  and a back face  1044 . The back faces  1044  are substantially flat surfaces. Each of the front faces  1042  includes a collection of grooves  1046 . The grooves  1046  are arranged as a collection of concentric, semi-circular ridges and troughs formed on the front faces  1042 . The grooves  1046  are non-intersecting, and increase outwardly with increasing radii. Each of the grooves  1046  is configured to receive a portion of the optical fiber  210  of  FIG. 2  at one of the end sections  230 . 
         [0045]    The sensor loop turn guide  1040   a  is removably assembled to the support wedge  1010  by placing the back face  1044  in contact with the side face  1014   a . The load transfer pins  1022  extend through a collection of bores  1048  formed through the sensor loop turn guide  1040   a . Similarly, the sensor loop turn guide  1040   b  is removably assembled to the support wedge  1010  by placing the back face  1044  in contact with the side face  1014   b . The load transfer pins  1022  extend through a collection of bores  1048  formed through the sensor loop turn guide  1040   b.    
         [0046]    In an assembled form, the sensor loop turn guides  1040   a  and  1040   b  draw the optical sensor loop  200  about a section of the outer periphery of the pipe  102 . As the fasteners  1030  are partly unthreaded, the springs  1032  urge the tension bar  1020  away from the pipe  102 , adjustably tensioning the optical sensor  200  about the pipe  102 . 
         [0047]    In operation, pressurization of a fluid within the pipe  102  can cause the pipe  102  to expand. Expansion of the pipe  102  can provide additional tension to the optical sensor loop  200  as it is held to the pipe  102  by the mounting system  100  of  FIGS. 1-9  or the mounting system  1000  of  FIGS. 10-15 . In some implementations, light passing through the optical sensor loop  200  can be affected by varying the tension applied to the optical sensor loop  200 , and these effects can be measured. For example, by measuring the effects of tension on the light being passed through the optical sensor loop  200 , expansion and contraction of the pipe  102  caused by pulses of fluid pressure within the pipe  102  can be measured. 
         [0048]    Although a few implementations have been described in detail above, other modifications are possible. For example, the assembly flows discussed in the descriptions of the figures do not require the particular order described, or sequential order, to achieve desirable results. In addition, other steps may be provided, or steps may be eliminated, from the described flows, and other components may be added to, or removed from, the described systems. Accordingly, other implementations are within the scope of the following claims.