Abstract:
A method and apparatus for detecting ferrous changes passing axially through a cylindrical space. In one embodiment, the method comprises surrounding the cylindrical space with a nonmagnetic cylinder having an outer wall and a cylindrical axis; creating an alternating magnetic field in the cylindrical space, the magnetic field created by a rotatable permanent magnet; monitoring the magnetic field with magnetic flux sensors placed outside the outer walls; and detecting changes in the magnetic field as ferrous matter passes axially through the cylindrical space. In other embodiments, the apparatus identifies ferrous changes as the tool joints that connect a jointed tubing string as the tubing string is moved in or out of a well bore, or as the presence or absence of a coiled tubing string in the well bore.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    In oil and gas wells, jointed pipes are conventionally inserted and stripped from a well bore under pressure. The intermittent sections that comprise the jointed pipes are typically connected by tool joints, which are generally threaded end connections.  
           [0002]    In standard operations, the jointed pipes are moved in or out of the well bore through blow out preventers (BOPs). The mounting and operation of BOPs are well known in the art. Typically, two BOPs are mounted on a spool (a “BOP spool”), with one BOP at the upper end of the spool and the other BOP at the lower end of the spool. The BOPs operate to separate the high pressure of the well bore from atmospheric pressure. Each BOP comprises a hydraulic ram that seals around the outside diameter of the pipe to pressure seal the well bore. The upper ram is normally kept closed when a pipe is stripped from the well. Because the BOP rams seal around the outside diameter of the piping, any reasonable increase in size of the piping may damage the rams and piping and may also compromise the sealing capabilities of the rams.  
           [0003]    As a tool joint enters the bottom of the spool during stripping, the upper ram is closed, and the lower ram is open. When the tool joint clears the lower ram, the stripping of the pipe is temporarily suspended. The lower ram is then closed, and the spool is depressurized to atmospheric pressure. After depressurization, the upper ram is opened, and the stripping of the piping is resumed until the tool joint exits the upper BOP ram. The upper ram is then closed, and the spool is re-pressurized to the pressure of the well bore. After re-pressurization, the lower ram is opened, and the procedure is repeated upon entry of the next tool joint into the bottom of the spool. When jointed pipe is moved into the well instead of stripped from the well, the same procedures apply in clearing the tool joints of the BOPs but in the opposite order.  
           [0004]    The movement of the tool joints through BOP spools is known to present operational problems. The rig operator is generally unable to see the tool joint enter the BOP spool. When a tool joint enters the BOP spool, if the operator does not stop the movement of the tool joint and properly open the closed BOP ram, the tool joint may contact the closed BOP ram, which may cause damage to the tool joint or BOP. If the damage is serious, the rig safety may be compromised, and a well blowout could occur. To prevent this occurrence, rig operators have historically estimated pipe lengths, and have then tallied pipe lengths between the joints to facilitate location of each tool joint as it enters the BOP spool. Errors in calculations or by the operator may cause the tool joint to strike a closed BOP ram. Further drawbacks of this process include the lack of speed at which the operator must work to prevent any such slight errors that may damage the BOP ram or tool joint.  
           [0005]    In addition to jointed pipes, coiled tubing strings are conventionally inserted and stripped from a well bore under pressure, which also presents operational problems. In standard operations, the coiled tubing string is typically moved in or out of the well bore through a crown valve and a BOP stack. The crown valve is generally the top valve on the arrangement of pipes, valves and instruments typically found at the surface of a well bore, known colloquially as the “Christmas tree.” The BOP stack may have a plurality of BOPs comprising at least one stripping BOP, which is different than the upper and lower BOP configuration that is standard for the jointed pipe operations.  
           [0006]    As the coiled tubing string is stripped from the well bore, the crown valve is open and the stripping BOPs are closed. When the last of the coiled tubing string exits the crown valve and begins to enter the BOP stack, the crown valve must be closed to maintain the well pressure. If the crown valve is not closed, the well would be open to the atmosphere and thereby increase safety and environmental risks and exposures. To prevent this occurrence, historically a friction counter will be used to estimate the coiled tubing string length. Coil tubing personnel will mechanically operate the crown valve by carefully attempting to close the crown valve to identify when the coiled tubing string exits the crown valve. Errors in calculations by the friction counter and by the coil tubing personnel may result in flooding of the well. Further drawbacks also include the lack of speed at which the operator must work to prevent any such slight errors that may cause safety and environmental exposures.  
           [0007]    Therefore, it is highly advantageous to correctly locate tool joints in the BOP spool and to correctly locate the last of the coiled tubing string to exit the crown valve. It will be understood that the presence of a pipe (for example a coiled tubing string) in a spool will cause a deviation in a magnetic field exerted across the spool. Because tool joints have larger outside diameter and mass than the pipe, the tool joints cause an even greater deviation in the magnetic field. Consequently, magnetic locators have been used in the past to identify the location of the tool joints and the presence of the coiled tubing string. For instance, magnetic sensors such as gradiometers have been used to identify the presence of tool joints in the BOP spool by sensing a change in the earth&#39;s magnetic field due to the presence of a tool joint. Problems encountered with this technology include interference from surrounding ferrous objects that may lead to false joint identification. Further, in deployments near the equator, it will be appreciated that readings of the earth&#39;s magnetic field tend towards zero, making it extremely difficult for magnetic sensors to identify the magnetic flux change due to the presence of a tool joint or the last of a coiled tubing string.  
           [0008]    Besides identifying changes in the earth&#39;s magnetic field to locate a tool joint or identify the presence of a coiled tubing string, the prior art has also utilized electromagnets to identify piping. One such device is disclosed in U.S. Pat. No. 4,964,462. In the disclosure of this patent, a magnetic field is created by electromagnets attached to a nonmagnetic BOP spool that separates upper and lower BOPs. Sensors mounted on the nonmagnetic spool identify changes in the electromagnetic field that signify the presence of a tool joint. Improvements need to be made on using electromagnets in a well bore, whose operation requires potentially unsafe voltages and currents to be deployed down hole.  
           [0009]    Consequently, there is a need for an improved method for inserting and stripping jointed pipes and coiled tubing strings from a well bore. Further, there is a need for a more safe and effective way of identifying tool joints in a BOP spool and identifying the presence of a coiled tubing string in a spool.  
         SUMMARY OF THE INVENTION  
         [0010]    These and other needs in the art are addressed in one embodiment by an inventive method for detecting ferrous changes passing axially through a cylindrical space. The method comprises surrounding the cylindrical space with a nonmagnetic cylinder having an outer wall and a cylindrical axis; creating an alternating magnetic field in the cylindrical space, the magnetic field created by a rotatable permanent magnet; monitoring the magnetic field with magnetic flux sensors placed outside the outer walls; and detecting changes in the magnetic field as ferrous matter passes axially through the cylindrical space.  
           [0011]    In another embodiment, the invention comprises an apparatus that identifies ferrous changes as a tool joint in a jointed tubing string with the tubing string moving in and out of a well bore and a plurality of the tool joints connecting sections of the jointed tubing string. The apparatus comprises a nonmagnetic cylindrical spool having a cylindrical axis, the tubing string and tool joints disposed to move axially in or out of the nonmagnetic cylindrical spool; and a sensor device attached to the nonmagnetic cylindrical spool, the sensor device having a source piece and at least one sensor piece, the source piece comprising a permanent magnet, the permanent magnet operatively rotatable.  
           [0012]    In a third embodiment, the invention provides a method of identifying ferrous changes as a plurality of the tool joints connecting a jointed tubing string move in and out of a well bore, the method comprising: (a) moving a tubing string in or out of a well bore; (b) causing the tubing string to pass through a nonmagnetic cylindrical spool; (c) creating an alternating magnetic field across the nonmagnetic cylindrical spool; (d) sensing a deviation in the alternating magnetic field; and (e) identifying the deviation in the alternating magnetic field.  
           [0013]    In a fourth embodiment, the invention provides a method of identifying ferrous changes while moving a jointed tubing string in and out of a well bore, a plurality of tool joints connecting the jointed tubing string, the method comprising: (a) moving the tubing string through an upper BOP, a lower BOP, and a nonmagnetic cylindrical spool; (b) separating the upper BOP and the lower BOP with the nonmagnetic cylindrical spool; (c) creating an alternating magnetic field across the nonmagnetic cylindrical spool; (d) sensing a deviation in the alternating magnetic field; (e) identifying the deviation in the alternating magnetic field; and (f) moving the tubing string in or out of the well bore without the tool joint contacting the upper BOP and the lower BOP.  
           [0014]    According to a fifth embodiment, the invention provides an apparatus for identifying ferrous changes in a jointed tubing string, a plurality of tool joints connecting the jointed tubing string, the tubing string moving in and out of a well bore, the apparatus comprising a nonmagnetic cylindrical spool, an upper BOP, and a lower BOP, the tubing string moving in or out of the well bore through the nonmagnetic cylindrical spool, the upper BOP, and the lower BOP; the nonmagnetic cylindrical spool separating the upper BOP and the lower BOP; the upper BOP closable around the tubing string to form a pressure lock; the lower BOP closable around the tubing string to form a pressure lock; a rotatable permanent magnet attached to the nonmagnetic cylindrical spool, the permanent magnet rotatable about an axis substantially orthogonal to the cylindrical axis of the nonmagnetic cylindrical spool; a motor secured to the nonmagnetic cylindrical spool, the motor disposed to rotate the permanent magnet; a source field shaper secured to the nonmagnetic cylindrical spool, the source field shaper disposed to shape the magnetic field created by the rotating permanent magnet; at least two sensors secured to the nonmagnetic cylindrical spool, the sensors disposed to identify changes in the magnetic field; the sensors further disposed to create a processor-readable signal that identifies the change in the magnetic field; at least one sensor field shaper attached to the nonmagnetic cylindrical spool, the sensor field shaper disposed to shield the sensors from outside magnetic interference; the upper BOP openable to allow passage of the tool joint; and the lower BOP openable to allow passage of the tool joint.  
           [0015]    In a sixth embodiment, the invention comprises an apparatus that identifies ferrous changes as a coiled tubing string moves in and out of a well bore. The apparatus comprises a nonmagnetic cylindrical spool having a cylindrical axis, the coiled tubing string disposed to move in and out of the nonmagnetic cylindrical spool along the cylindrical axis; and a sensor device attached to the nonmagnetic cylindrical spool, the sensor device having a source piece and at least one sensor piece, the source piece comprising a permanent magnet, the permanent magnet operatively rotatable.  
           [0016]    In a seventh embodiment, the invention provides a method of identifying ferrous changes as a coiled tubing string moves in and out of a well bore, the method comprising: (a) moving a coiled tubing string in and out of a well bore; (b) causing the coiled tubing string to pass through a nonmagnetic cylindrical spool; (c) creating an alternating magnetic field across the nonmagnetic cylindrical spool; (d) sensing a deviation in the alternating magnetic field; and (e) identifying the deviation in the alternating magnetic field.  
           [0017]    It will therefore be seen that a technical advantage of the invention includes a permanent magnet, thereby eliminating problems encountered by using the earth&#39;s magnetic field or by electromagnetic fields to identify changes in pipe diameter and/or mass. For instance, problems encountered with using the earth&#39;s magnetic field such as interference by surrounding ferrous objects is overcome. In addition, the magnetic reading of the present invention does not near zero at the equator, which overcomes another problem in detecting magnetic flux associated with using the earth&#39;s magnetic field. The present invention does not employ potentially unsafe voltages and currents down hole as does the use of an electromagnet. Further advantages include the rotatable permanent magnet minimizing interference from any residual magnetism of the pipe. In addition, a further technical advantage includes prevention of outside magnetic interference, which allows for identification of the ferrous changes. The invention also allows the tool joints to pass through a BOP spool without damaging the tubing string or the BOPs, which maintains the integrity of the well. In addition, the invention also allows a coiled tubing string to be inserted or stripped from a well while decreasing safety and environmental exposure risks.  
           [0018]    The foregoing has outlined rather broadly 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. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:  
         [0020]    [0020]FIG. 1 illustrates one embodiment of a tool joint locator apparatus.  
         [0021]    [0021]FIG. 2 illustrates a view of the invention showing a housing, sensor, magnet, and motor.  
         [0022]    [0022]FIG. 3 illustrates a view of the invention showing the invention with a tubing string and a tool joint.  
         [0023]    [0023]FIG. 4 depicts a waveform analysis showing presence of a tool joint.  
         [0024]    [0024]FIG. 5 illustrates a view of the invention showing blow out preventers.  
         [0025]    [0025]FIG. 6 illustrates an embodiment of the invention showing the motor connected to a magnet housing.  
         [0026]    [0026]FIG. 7 is a cross sectional view as shown on FIG. 6.  
         [0027]    [0027]FIG. 8 illustrates a view of the invention showing a housing, sensor, and a motor connected to a magnet housing.  
         [0028]    [0028]FIG. 9 illustrates a view of the invention showing the invention with a tubing string, tool joint, and a motor connected to a magnet housing.  
         [0029]    [0029]FIG. 10 illustrates a view of the invention showing blow out preventers and a motor connected to a magnet housing.  
         [0030]    [0030]FIG. 11 illustrates an embodiment of the invention showing a synchronization sensor disposed substantially diametrically across the nonmagnetic cylindrical spool from the sensor piece.  
         [0031]    [0031]FIG. 12 illustrates an embodiment of the invention showing the invention with a coiled tubing string.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    A first embodiment of the invention is described with respect to FIG. 1, in which a sensor device  5  comprises a source piece  10  and a sensor piece  15 . The source piece  10  has a permanent magnet  20  and a source field shaper  25 . The source field shaper  25  comprises a non-corrosive, soft magnetically permeable material, such as iron. Because the permanent magnet  20  exerts a magnetic field in all directions, the source field shaper  25  directs the magnetic field in the horizontal direction away from the source field shaper  25 . As shown, the sensor piece  15  comprises sensors  30  and a sensor field shaper  35 . The sensor field shaper  35  also comprises a non-corrosive, soft magnetically permeable material, again such as iron. The sensor field shaper  35  shields the sensors  30  from the effects of external magnetic fields such as the earth&#39;s magnetic field. A motor  40  is attached to the source piece  10  by a shaft  45 .  
         [0033]    In the embodiment illustrated in FIG. 1, the source piece  10  is advantageously E-shaped, with three separate horizontal sections and a vertical section. The center horizontal section is the permanent magnet  20 . The upper and lower horizontal sections and the vertical section comprise the source field shaper  25 . The source piece  10  is horizontally rotatable 360 degrees by the motor  40  and shaft  45 . The shaft  45  that connects the motor  40  to the source piece  10  is embedded into the vertical section of the source piece  10  and runs lengthwise down the vertical section. The motor  40  horizontally rotates the source piece  10  about the vertical axis of the shaft  45 , thereby creating the alternating magnetic field.  
         [0034]    With further reference to FIG. 1, the sensor piece  15  is also advantageously E-shaped, with three separate horizontal sections and a vertical section. The upper and lower horizontal sections contain the sensors  30 . The vertical section and the three horizontal sections comprise the sensor field shaper  35 . A variety of sensor technologies known in the art may be used for the sensors  30  but preferably Hall effect sensors are used. Hall effect sensors are well known in the art. Examples of available Hall effect sensors include Honeywell SS 495A and Micronas HAL800 sensors. In the alternative, Anisotropic Magnetoresistive sensors or Giant Magnetoresistive sensors could be used for sensor technology instead of Hall effect devices. The center horizontal section serves as a return for the magnetic field, which helps shape the magnetic field. In addition to containing the sensors  30 , the upper and lower horizontal sections also serve as conduit points for the return of the magnetic field thereby further helping shape the magnetic field.  
         [0035]    The invention is not limited to an E-shaped sensor piece  15  as illustrated on FIG. 1. In another embodiment of the invention (not illustrated), the sensor field shaper  35  may have a vertical section and upper and lower horizontal sections but without a center horizontal section. In a further embodiment, the sensor piece  15  is separated into an upper and lower section, each section advantageously U-shaped and comprising a sensor field shaper  35  and a sensor  30 . The sensor field shaper  35  of the upper section of the sensor piece  15  has a vertical section and upper and lower horizontal sections, with either the upper or lower horizontal sections containing the sensor  30 . Alternatively, both the upper and lower horizontal sections may contain a sensor  30 . The sensor field shaper  35  of the lower section of the sensor piece  15  also has a vertical section and upper and lower horizontal sections, with either the upper or lower horizontal sections containing the sensor  30 . Alternatively, both the upper and lower horizontal sections may contain a sensor  30 .  
         [0036]    As further illustrated on FIG. 1, an evaluation board  50  is connected to the sensors  30  by evaluation board connectors  55 . The evaluation board  50  comprises an analog to digital converter. Examples of available analog to digital converters include the Analog Devices AD7730 converter. A battery box  60  is connected to the evaluation board  50 . Examples of available battery boxes  60  include the Orga Type CCA battery box.  
         [0037]    [0037]FIG. 2 is a further view of the embodiment shown on FIG. 1. FIG. 2 illustrates a housing  65  that secures the source piece  10 , sensor piece  15 , and motor  40  to a nonmagnetic cylindrical spool  110 . The sensor piece  15  is attached to the housing  65  by bolts, screws, or other suitable fasteners. The source piece  10  is attached to the housing  65  by the shaft  45  and motor  40 . The housing  65  wraps around the outside surface of the nonmagnetic cylindrical spool  110  and is firmly secured to the outside surface of the nonmagnetic cylindrical spool  110  by Velcro, hooks and receivers, or other suitable fasteners. The source piece  10  and sensor piece  15  are oriented within the housing  65  so that when the housing  65  is secured to the nonmagnetic cylindrical spool  110 , the source piece  10  and sensor piece  15  are secured on opposite sides of the nonmagnetic cylindrical spool  110 . When the housing  65  secures the sensor piece  15  to the nonmagnetic cylindrical spool  110 , the three horizontal sections of the sensor piece  15  are pressed to the nonmagnetic cylindrical spool  110 . The source piece  10  is secured to the nonmagnetic cylindrical spool  110  but is not in physical contact with the nonmagnetic cylindrical spool  110 . The source piece  10  is horizontally rotatable about the vertical axis of the shaft  45  by the motor  40 , and so should be disposed close to, but not touching the nonmagnetic cylindrical spool  110 . The source piece  10  is connected to the motor  40  by the shaft  45  and oriented within the housing  65  so that a small space exists between the source piece  10  and the nonmagnetic cylindrical spool  110 . The motor  40  is located within the housing  65 . The motor  40  is preferably enclosed within a motor housing  85 , which motor housing  85  is attached to the housing  65 . The motor housing  85  may be attached to the housing  65  by bolts, screws, or other suitable fasteners. Advantageously, the motor  40  may be a pneumatic motor. Examples of available pneumatic motors include the Cooper Tools 21M1340-40 motor. An air supply  75  provides air to power the motor  40  through an air supply line  80 . An opening in the housing  65  allows the air supply line  80  access to the motor  40 . As shown, the shaft  45  connects the motor  40  to the source piece  10 . Alternatively, the motor  40  may be an electric motor. Examples of available electric motors include the McMaster-Carr 6331K31 motor.  
         [0038]    It will be appreciated that the invention is not limited to one sensor piece  15  secured to an opposite side of the nonmagnetic cylindrical spool  110  from the source piece  10 , as illustrated on FIGS. 2, 3,  5 ,  8 ,  9 ,  10 ,  11 , and  12 . In alternative embodiments (not illustrated), the invention may comprise more than one sensor piece  15 , with each sensor piece  15  advantageously disposed on the opposite side of the nonmagnetic cylindrical spool  110  from the source piece  10 . In these alternative embodiments, the invention may also comprise one or more of these sensor pieces  15  joined together.  
         [0039]    [0039]FIG. 3 is a further view of the embodiment depicted in FIG. 1 showing a nonmagnetic cylindrical spool  110  with a tubing string  95  and tool joint  90 . As shown, the nonmagnetic cylindrical spool  110  is a section of a riser spool  115 . The nonmagnetic cylindrical spool  110  comprises a nonmagnetic material, preferably nonmagnetic stainless steel. The source piece  10  is on the opposite side of the nonmagnetic cylindrical spool  110  from the sensor piece  15 . The tubing string  95  and tool joint  90  are movable in or out of the nonmagnetic cylindrical spool  110 .  
         [0040]    It will be seen on FIG. 3 that the source piece  10  creates an alternating magnetic field across the nonmagnetic cylindrical spool  110  by the motor  40  rotating the source piece  10  horizontally 360 degrees about the vertical axis of the shaft  45 . When the tubing string  95  is stripped through the nonmagnetic cylindrical spool  110 , the sensors  30  detect the presence of the tubing string  95 . When present, the tubing string  95  will cause a decrease in the magnetic field across the nonmagnetic cylindrical spool  110  created by the rotatable source piece  10 . Upon detection of this decrease in the magnetic field, the sensors  30  notify the evaluation board  50  (via the evaluation board connectors  55 ) of such detected decrease. The evaluation board  50  advantageously converts this information into a digital form. A remotely located computer  51  may then receive and process the information from the evaluation board  50 .  
         [0041]    With further reference to FIG. 3, the presence of a tool joint  90  in the nonmagnetic cylindrical spool  110  will cause the sensors  30  to detect an even larger decrease in the magnetic field created by the rotating source piece  10 . The evaluation board  50  receives and processes this information from the sensors  30  and then transmits this information on to the computer  51 .  
         [0042]    The computer  51  on FIG. 3 may optionally use threshold detection and waveform analysis techniques to differentiate between signals so as to detect the presence of tubing strings  95  or tool joints  90 . By threshold detection, the computer  51  evaluates the readings transmitted by the sensors  30  and compares them to predetermined values expected for the presence of tubing strings  95  and tool joints  90  and to predetermined values when no tubing strings  95  or tool joints  90  are present. Such comparisons are selected to indicate to the computer  51  whether a tool joint  90  or tubing string  95  is present, or the initial presence of the tubing string  95  in the nonmagnetic cylindrical spool  110 , or when the last of the tubing string  95  exits the nonmagnetic cylindrical spool  110 .  
         [0043]    Alternatively, the computer  51  may also evaluate the sensor  30  information by waveform analysis. In normal mode (i.e., magnet  20  rotating without tool joints  90  or tubing strings  95  present), the magnetic field creates a characteristic waveform that is known and identified by the computer  51 . The change in the magnetic field, and thereby change in waveform, by the presence of a tubing string  95  is known and identified by the computer  51 . In addition, the change in the magnetic field, and thereby further change in waveform, by the presence of the tool joint  90  is also known and identified by the computer  51 . These waveform changes are recognized by the computer  51  again with reference to predetermined changes in waveforms expected during the presence of tubing strings  95 , tool joints  90 , or when the tubing string  95  initially enters the nonmagnetic cylindrical spool  110 , or when the last of the tubing string  95  exits the nonmagnetic cylindrical spool  110 .  
         [0044]    [0044]FIG. 4 illustrates an exemplary waveform analysis of the alternating magnetic field by the computer  51  during expected normal operation of an embodiment such as is illustrated on FIG. 3. The y axis represents the sensor readings in counts. The x axis represents 0.028 seconds/sample reading. The readings in counts represent the presence of a jointed tubing string  95  with connecting tool joints  90  that are pulled through a sensor device  5 , as shown on FIG. 3. As shown, the tubing string  95  is identified when entering the sensor device  5 , registering a reading of over 3,200,000 counts. As the tubing string  95  is pulled through the sensor device  5 , sensors  30  register these readings with the evaluation board  50  and then to the computer  51  on FIG. 3, which registers these readings on FIG. 4 as waveforms. It will be understood that the computer  51  on FIG. 3 will compare the registered waveform with predetermined changes in waveforms that are expected for the presence of tubing strings  95  and tool joints  90 . With reference to the predetermined changes in waveforms, the computer  51  identifies these readings as a characteristic tubing string waveform  120 , which is illustrated on FIG. 4. As a tool joint  90  is pulled through the sensor device  5 , the sensors  30  register the decrease in counts from the magnetic reading, and the computer  51  registers these readings in waveform. Again from predetermined changes in waveforms, the computer  51  recognizes this waveform as a characteristic tool joint waveform  125 , which is illustrated on FIG. 4.  
         [0045]    [0045]FIG. 5 is a further view of the embodiment depicted in FIG. 1 showing a nonmagnetic cylindrical spool  110  and blow out preventers (BOPs)  100  and  105 . As shown, an upper BOP  100  and a lower BOP  105  are connected to a riser spool  115 . The nonmagnetic cylindrical spool  110  is a section of the riser spool  115 . The nonmagnetic cylindrical spool  110  comprises a nonmagnetic material, preferably nonmagnetic stainless steel. The nonmagnetic cylindrical spool  110  separates the upper BOP  100  from the lower BOP  105 . The source piece  10  is on the opposite side of the nonmagnetic cylindrical spool  110  from the sensor piece  15 . The tubing string  95  and connecting tool joints  90  are moveable in or out of the riser spool  115 .  
         [0046]    It will be seen on FIG. 5 that the source piece  10  creates an alternating magnetic field across the nonmagnetic cylindrical spool  110  by the motor  40  rotating the source piece  10  horizontally 360 degrees about the vertical axis of the shaft  45 . When the tubing string  95  is stripped through the nonmagnetic cylindrical spool  110 , the sensors  30  detect the presence of the tubing string  95 . When present, the tubing string  95  will tend to cause a decrease in the magnetic field across the nonmagnetic cylindrical spool  110  created by the rotating source piece  10 . Upon detection of this decrease in the magnetic field, the sensors  30  notify the evaluation board  50  (via the evaluation board connectors  55 ) of such detected decrease. The evaluation board  50  processes this information and transmits it to the computer  51 .  
         [0047]    With further reference to FIG. 5, the evaluation board  50  and battery box  60  are located adjacent to the sensor piece  15 . Alternatively, the evaluation board  50  and battery box  60  are remotely located, preferably on a structure supported by the Christmas tree. The computer  51  is shown located remotely from the sensor piece  15 . In this embodiment, the computer  51  is also connected to an audio and/or visual alarm by a cable. The audio and/or visual alarm will preferably be located near an operator. This audio and/or visual alarm indicates to the operator the presence of the tool joint  90  in the nonmagnetic cylindrical spool  110 . Upon this alarm, the operator may halt the movement of the tubing string  95  and open and close the appropriate BOPs. This audio and/or visual alarm may also notify the operator of the presence of the tubing string  95 , or when the tubing string  95  initially enters the nonmagnetic cylindrical spool  110 , or when the last of the tubing string  95  exits the nonmagnetic cylindrical spool  110 .  
         [0048]    The following describes an exemplary application of the present invention as embodied and illustrated on FIG. 5. In operation, as the tubing string  95  is stripped from the well bore, it can be seen on FIG. 5 that the tubing string  95  is pulled upwards through the riser spool  115 . The lower BOP  105  is open, and the upper BOP  100  is closed. Both the upper BOP  100  and the lower BOP  105  are openable and closable around the tubing string  95 , separating the high pressure of the well bore from the lower atmospheric pressure. The sections of the tubing string  95  are connected by tool joints  90 . As the motor  40  rotates the permanent magnet  20 , the permanent magnet  20  creates an alternating magnetic field across the nonmagnetic cylindrical spool  110 . The sensors  30  measure the alternating magnetic field created by the permanent magnet  20  and transmit a signal to the evaluation board  50 , which advantageously converts the signal into digital form. The evaluation board  50  then transmits this information to the computer  51 , which continually monitors and processes these sensor  30  readings. When a tubing string  95  enters the nonmagnetic cylindrical spool  110  during stripping, the lower BOP  105  remains open, and the upper BOP  100  remains closed. The sensors  30  transmit a signal to the evaluation board  50  indicating presence of the tubing string  90  in the nonmagnetic cylindrical spool  110 . The evaluation board  50  processes this signal and transmits this signal to the computer  51 , which monitors and further processes the information. As a tool joint  90  enters the nonmagnetic cylindrical spool  110 , the lower BOP  105  remains open, and the upper BOP  100  remains closed. The sensors  30  will identify the lower reading of the magnetic field caused by the tool joint  90 . The sensors  30  will transmit the reading to the evaluation board  50 . The evaluation board  50  will process this reading and transmit the reading to the computer  51 , which will monitor and further process the reading. By analysis using techniques such as threshold detection or waveform analysis, the computer  51  will identify the presence of the tool joint  90  and notify the operator of the tool joint&#39;s  90  presence by audio and/or visual alarm.  
         [0049]    Notified of the presence of the tool joint  90  in the nonmagnetic cylindrical spool  110  of FIG. 5, the operator will temporarily halt the stripping of the tubing string  95 . With the upper BOP  100  remaining closed, the lower BOP  105  is then closed, and the nonmagnetic cylindrical spool  110  is depressurized to atmospheric pressure. After the nonmagnetic cylindrical spool  110  is depressurized, the lower BOP  105  remains closed, and the upper BOP  100  is opened. The stripping of the tubing string  95  is then resumed. When the tool joint  90  exits the upper BOP  100 , the sensors  30  will transmit to the evaluation board  50  the increased magnetic readings. The evaluation board  50  will process this information and then transmit the information to the computer  51 . The computer  51  will identify that no tool joint  90  is within the nonmagnetic cylindrical spool  110 . The computer  51  will then notify the operator by audio and/or visual alarm that no tool joint  90  is present in the nonmagnetic cylindrical spool  110 . The operator will then temporarily halt the movement of the tubing string  95 . With the lower BOP  105  remaining closed, the upper BOP  100  will be closed, and the nonmagnetic cylindrical spool  110  will be re-pressurized to the pressure within the riser spool  115 . After re-pressurization, the upper BOP  100  will remain closed, and the lower BOP  105  will be opened, followed by resumption of the stripping of the tubing string  95 . When a tubing string  95  is moved into the well instead of stripped from the well, the same procedures apply in clearing the tool joints  90  of the BOPs but in converse order.  
         [0050]    [0050]FIG. 6 is a further embodiment of the invention showing a sensor device  5  comprising a source piece  10 , sensor piece  15  and with a motor  40  attached to a magnet housing  21 . The source piece  10  includes a magnet housing  21  and a source field shaper  25 . A permanent magnet  20  is enclosed within the magnet housing  21 . The magnet housing  21  and source field shaper  25  comprise a non-corrosive, soft magnetically permeable material, such as iron. Because the permanent magnet  20  exerts a magnetic field in all directions, the source field shaper  25  directs the magnetic field in the horizontal direction away from the source field shaper  25 . As shown, the sensor piece  15  comprises sensors  30  and a sensor field shaper  35 . The sensor field shaper  35  also comprises a non-corrosive, soft, magnetically permeable material, again such as iron. The source field shaper  25  includes a void section  26 . The void section  26  comprises a removed section of the source field shaper  25 . The magnet housing  21  is advantageously disposed within the void section  26 . A motor  40  is attached to the magnet housing  21  by a shaft  45 .  
         [0051]    In the embodiment illustrated in FIG. 6, the source piece  10  comprises three sections, upper and lower horizontal sections and a vertical section. These three sections comprise the source field shaper  25 . Alternatively, the source field shaper  25  may have more than two horizontal sections. The void section  26  and magnet housing  21  are located within the vertical section. The magnet housing  21  is rotatable 360 degrees by the motor  40  and shaft  45 . The shaft  45  is secured to the magnet housing  21  by bolts, screws, or other suitable fasteners. The motor  40  rotates the magnet housing  21  about the horizontal axis of the shaft  45 , thereby creating the alternating magnetic field. As further illustrated, an evaluation board  50  is connected to the sensors  30  by evaluation board connectors  55 . A battery box  60  is connected to the evaluation board  50 .  
         [0052]    [0052]FIG. 7 is a cross sectional frontal view as shown on FIG. 6. FIG. 7 illustrates the source piece  10  comprising a permanent magnet  20 , magnet housing  21 , and source field shaper  25 . As shown, the permanent magnet  20  is disposed within the magnet housing  21 . The motor  40  rotates the permanent magnet  20  and magnet housing  21 .  
         [0053]    [0053]FIG. 8 illustrates a further view of the embodiment depicted on FIG. 6 showing a housing  65  that secures the source piece  10 , sensor piece  15 , and motor  40  to a nonmagnetic cylindrical spool  110 . The sensor piece  15  is attached to the housing  65  by bolts, screws, or other suitable fasteners. The source piece  10  is attached to the housing  65  by bolts, screws, or other suitable fasteners. The housing  65  wraps around the outside surface of the nonmagnetic cylindrical spool  110  and is firmly secured to the outside surface of the nonmagnetic cylindrical spool  110  by Velcro, hooks and receivers, or other suitable fasteners. The source piece  10  and sensor piece  15  are oriented within the housing  65  so that when the housing  65  is secured to the nonmagnetic cylindrical spool  110 , the source piece  10  and sensor piece  15  are secured on opposite sides of the nonmagnetic cylindrical spool  110 . When the housing  65  secures the sensor piece  15  to the nonmagnetic cylindrical spool  110 , the three horizontal sections of the sensor piece  15  are pressed to the nonmagnetic cylindrical spool  110 . When the housing  65  secures the source piece  10  to the nonmagnetic cylindrical spool  110 , the two horizontal sections of the source piece  10  are also pressed to the nonmagnetic cylindrical spool  110 . The magnet housing  21  is disposed within the void section  26  and is rotatable about an axis that is orthogonal to the cylindrical axis of the nonmagnetic cylindrical spool  110 . FIG. 8 illustrates that such orthogonal rotation is about shaft  45  of motor  40 . The source piece  10  is connected to the motor  40  by the attachment of the shaft  45  to the magnet housing  21 . The motor  40  is located within the housing  65 . The motor  40  is enclosed within a motor housing  85 , which motor housing  85  is attached to the housing  65 . The motor housing  85  may be attached to the housing  65  by bolts, screws, or other suitable fasteners. Advantageously, the motor  40  may be a pneumatic motor. An air supply  75  provides air to power the motor  40  through an air supply line  80 . An opening in the housing  65  allows the air supply line  80  access to the motor  40 . As shown, the shaft  45  connects the motor  40  to the source piece  10 . Alternatively, the motor  40  may be an electric motor.  
         [0054]    [0054]FIG. 9 is a further view of the embodiment illustrated in FIG. 6 showing a nonmagnetic cylindrical spool  110  with a tubing string  95  and tool joint  90 . The nonmagnetic cylindrical spool  110  comprises a nonmagnetic material, preferably nonmagnetic stainless steel. As shown, the nonmagnetic cylindrical spool  110  will be understood to be a section of a riser spool  115 . The source piece  10  is on the opposite side of the nonmagnetic cylindrical spool  110  from the sensor piece  15 . The tubing string  95  and tool joint  90  are movable in or out of the nonmagnetic cylindrical spool  110 .  
         [0055]    It will be seen on FIG. 9 that the source piece  10  creates an alternating magnetic field across the nonmagnetic cylindrical spool  110  by the motor  40  rotating the magnet housing  21 , which encloses the permanent magnet  20 . The rotation of the magnet housing  21  is 360 degrees about shaft  45 , and the axis of rotation is disposed orthogonal to the cylindrical axis of the nonmagnetic cylindrical spool  110 . When the tubing string  95  is stripped through the nonmagnetic cylindrical spool  110 , the sensors  30  detect the presence of the tubing string  95 . When present, the tubing string  95  will cause a decrease in the magnetic field across the nonmagnetic cylindrical spool  110  created by the rotatable permanent magnet  20 . Upon detection of this decrease in the magnetic field, the sensors  30  notify the evaluation board  50  (via the evaluation board connectors  55 ) of such detected decrease. The evaluation board  50  advantageously converts this information into digital form. A remotely located computer  51  then receives and processes this information from the evaluation board  50 .  
         [0056]    With further reference to FIG. 9, the presence of a tool joint  90  in the nonmagnetic cylindrical spool  110  will cause the sensors  30  to detect an even larger decrease in the magnetic field created by the rotating permanent magnet  20 . The evaluation board  50  receives and processes this information from the sensors  30  and then transmits this information on to the computer  51  for further processing.  
         [0057]    [0057]FIG. 10 is a further view of the embodiment depicted in FIG. 6 showing a nonmagnetic cylindrical spool  110  and blow out preventers (BOPs)  100  and  105 . As shown, an upper BOP  100  and a lower BOP  105  are connected to a riser spool  115 . The nonmagnetic cylindrical spool  110  is a section of the riser spool  115 . The nonmagnetic cylindrical spool  110  comprises a nonmagnetic material, preferably nonmagnetic stainless steel. The nonmagnetic cylindrical spool  110  separates the upper BOP  100  from the lower BOP  105 . The source piece  10  is on the opposite side of the nonmagnetic cylindrical spool  110  from the sensor piece  15 . The tubing string  95  and connecting tool joints  90  are moveable in or out of the riser spool  115 .  
         [0058]    It will be seen on FIG. 10 that the source piece  10  creates an alternating magnetic field across the nonmagnetic cylindrical spool  110  by the motor  40  rotating the magnet housing  21 , which encloses the permanent magnet  20 . The rotation of magnet housing  21  is 360 degrees about shaft  45 . When the tubing string  95  is stripped through the nonmagnetic cylindrical spool  110 , the sensors  30  detect the presence of the tubing string  95 . When present, the tubing string  95  will tend to cause a decrease in the magnetic field across the nonmagnetic cylindrical spool  110  created by the rotatable magnet  20 . Upon detection of this decrease in the magnetic field, the sensors  30  notify the evaluation board  50  (via the evaluation board connectors  55 ) of such detected decrease. The evaluation board  50  processes this information and transmits it to the computer  51  for further processing.  
         [0059]    With further reference to FIG. 10, the evaluation board  50  and battery box  60  are shown located adjacent to the sensor piece  15 . Alternatively, the evaluation board  50  and battery box  60  may be located remotely, preferably on a structure supported by the Christmas tree. The computer  51  is remotely located from the sensor piece  15 . In this embodiment, the computer  51  is also connected to an audio and/or visual alarm by a cable. The audio and/or visual alarm will preferably be located near an operator. This audio and/or visual alarm indicates to the operator the presence of the tool joint  90  in the nonmagnetic cylindrical spool  110 . Upon this alarm, the operator may halt the movement of the tubing string  95  and open and close the appropriate BOPs. This audio and/or visual alarm may also notify the operator of the presence of the tubing string  95 , or when the tubing string  95  initially enters the nonmagnetic cylindrical spool  110 , or when the last of the tubing string  95  exits the nonmagnetic cylindrical spool  110 .  
         [0060]    In operation, FIG. 10 is analogous to the application depicted in FIG. 5 except that the motor  40  rotates the magnet housing  21  and thereby rotates the enclosed permanent magnet  20 .  
         [0061]    [0061]FIG. 11 illustrates an alternative embodiment of the invention depicting a synchronization sensor  31  disposed to monitor the rotation of the permanent magnet  20 , which is enclosed within the magnet housing  21 . The synchronization sensor  31  is pressed to the nonmagnetic cylindrical spool  110  and secured by the housing  65 . The synchronization sensor  31  is attached to the housing  65  by bolts, screws, or other suitable fasteners. A variety of sensor technologies known in the art may be used for the synchronization sensor  31  but preferably conventional Hall effect sensors are used. In the alternative, Anisotropic Magnetoresistive sensors or Giant Magnetoresistive sensors could be used for sensor technology instead of Hall effect devices.  
         [0062]    It will be seen on FIG. 11 that the source piece  10 , sensor piece  15 , and synchronization sensor  31  are oriented within the housing  65  so that when the housing  65  is secured to the nonmagnetic cylindrical spool  110 , the source piece  10  and synchronization sensor  31  are disposed on the opposite side of the nonmagnetic cylindrical spool  110  from the sensor piece  15 . The synchronization sensor  31  is disposed in close proximity to the source piece  10 . The synchronization sensor  31  and sensor piece  15  are connected to the evaluation board  50  by evaluation board connectors  55 . When the motor  40  rotates the magnet housing  21  and thereby rotates the permanent magnet  20 , an alternating magnetic field is created across the nonmagnetic cylindrical spool  110 , which alternating magnetic field results in alternating maximum magnetic flux values and minimum magnetic flux values being detectable and measurable across the nonmagnetic cylindrical spool  110 .  
         [0063]    It will be seen on FIG. 11 that the synchronization sensor  31  measures the magnetic field created by the source piece  10 . The synchronization sensor  31  does not measure the magnetic field across the nonmagnetic cylindrical spool  110 , which is measured by the sensor piece  15 . Instead, the synchronization sensor  31  continuously monitors the magnetic field created by the source piece  10  and transmits measured flux values to the evaluation board  50  via the evaluation board connectors  55 . The evaluation board  50  will receive this signal and transmit it to the computer  51 , which computer  51  will process and evaluate this information to determine whether a maximum or minimum magnetic flux value is at that instant being exerted. Upon an evaluation that the source piece  10  is creating a maximum magnetic flux value, the computer  51  transmits a signal via the evaluation board  50  to the sensors  30 . Upon receipt of this signal identifying the maximum magnetic flux value, the sensors  30  will take their reading of the magnetic field across the nonmagnetic cylindrical spool  110 . Unless the sensors  30  receive the signal from the computer  51  identifying a maximum magnetic flux value, the sensors  30  will not take their reading. A technical advantage of synchronizing the sensor  30  readings to the maximum magnetic flux value is that the effects of electrical and magnetic noise interferences are averaged out and minimized.  
         [0064]    In an alternative embodiment that is not illustrated, the synchronization sensor  31  may be attached to the source field shaper  25 . In this alternative embodiment, the synchronization sensor  31  may be connected to the source field shaper  25  by bolts, screws, or other suitable fasteners.  
         [0065]    [0065]FIG. 12 illustrates a further embodiment of the invention showing a coiled tubing string  130 , a crown valve  135 , and a BOP stack  140 . The crown valve  135  is the top valve in the Christmas tree of a well. As shown, an adapter spool  145  connects the nonmagnetic cylindrical spool  110  to the crown valve  135 . The nonmagnetic cylindrical spool  110  separates the BOP stack  140  from the adapter spool  145  and crown valve  135 . The BOP stack  140  may have a plurality of BOPs comprising at least one stripping BOP. The different types of BOPs comprising the BOP stack are well known in the art. Examples of available BOPs include stripping, blind, and cutter BOPs. The source piece  10  is on the opposite side of the nonmagnetic cylindrical spool  110  from the sensor piece  15 . The coiled tubing string  130  is moveable in or out of the crown valve  135  and the BOP stack  140 .  
         [0066]    It will be seen on FIG. 12 that the source piece  10  creates an alternating magnetic field across the nonmagnetic cylindrical spool  110  by the motor  40  rotating the magnet housing  21 , which encloses the permanent magnet  20 . The rotation of magnet housing  21  is 360 degrees about shaft  45 . When the coiled tubing string  130  is stripped through the nonmagnetic cylindrical spool  110 , the sensors  30  detect the presence of the coiled tubing string  130 . When the last of the coiled tubing string  130  exits the nonmagnetic cylindrical spool  110 , the exit of the coiled tubing string  130  will tend to cause an increase in the magnetic field across the nonmagnetic cylindrical spool  110  created by the rotatable magnet  20 . Upon detection of this increase in the magnetic field, the sensors  30  notify the evaluation board  50  (via the evaluation board connectors  55 ) of such detected increase. The evaluation board  50  processes this information and transmits it to the computer  51  for further processing.  
         [0067]    With further reference to FIG. 12, the evaluation board  50  and battery box  60  are shown located adjacent to the sensor piece  15 . Alternatively, the evaluation board  50  and battery box  60  may be located remotely, preferably on a structure supported by the Christmas tree. The computer  51  is remotely located from the sensor piece  15 . In this embodiment, the computer  51  is also connected to an audio and/or visual alarm by a cable. The audio and/or visual alarm will preferably be located near an operator. This audio and/or visual alarm indicates to the operator the exit of the last of the coiled tubing string from the nonmagnetic cylindrical spool  110 . Upon this alarm, the operator may halt the movement of the coiled tubing string  130  and close the crown valve  135 . This audio and/or visual alarm may also notify the operator when the coiled tubing string  130  initially enters the nonmagnetic cylindrical spool  110 . The invention is not limited to the nonmagnetic cylindrical spool  110  separating the adapter spool  145  and crown valve  135  from the BOP stack  140 . Alternatively, a spacer spool (not illustrated) may separate the BOP stack  140  from the nonmagnetic cylindrical spool  110 .  
         [0068]    The following describes an exemplary application of the present invention as embodied and illustrated on FIG. 12. In operation, as the coiled tubing string  130  is stripped from the well bore, it can be seen on FIG. 12 that the coiled tubing string  130  is pulled upwards through the crown valve  135 , nonmagnetic cylindrical spool  110 , and the BOP stack  140 . The crown valve  135  is open and the stripping BOPs of the BOP stack  140  are closed. Both the crown valve  135  and the stripping BOPs of the BOP stack  140  are openable and closable, with the stripping BOPs of the BOP stack  140  openable and closable around the coiled tubing string  130 , separating the high pressure of the well bore from the lower atmospheric pressure. As the motor  40  rotates the permanent magnet  20 , the permanent magnet  20  creates an alternating magnetic field across the nonmagnetic cylindrical spool  110 . The sensors  30  measure the alternating magnetic field created by the permanent magnet  20  and transmit a signal to the evaluation board  50 , which advantageously converts the signal into digital form. The evaluation board  50  then transmits this information to the computer  51 , which continually monitors and processes these sensor  30  readings. When the coiled tubing string  130  is passing through the nonmagnetic cylindrical spool  110  during stripping, the crown valve  135  remains open and the stripping BOPs of the BOP stack  140  remain closed. The sensors  30  transmit a signal to the evaluation board  50  indicating the presence of the coiled tubing string  130  in the nonmagnetic cylindrical spool  110 . The evaluation board  50  processes this signal and transmits this signal to the computer  51 , which monitors and further processes the information. As the last of the coiled tubing string  130  exits the nonmagnetic cylindrical spool  110 , the crown valve  135  may be closed and the stripping BOPs of the BOP stack  140  remain closed. The sensors  30  will identify the higher reading of the magnetic field caused by the exit of the coiled tubing string  130 . The sensors  30  will transmit the reading to the evaluation board  50 . The evaluation board  50  will process this reading and transmit the reading to the computer  51 , which will monitor and further process the reading. By analysis using techniques such as threshold detection or waveform analysis (as functionally described earlier), the computer  51  will identify the exit of the coiled tubing string  130  and notify the operator of the coiled tubing string&#39;s  130  exit by audio and/or visual alarm.  
         [0069]    Notified of the exit of the coiled tubing string  130  from the nonmagnetic cylindrical spool  110  of FIG. 12, the operator will temporarily halt the stripping of the coiled tubing string  130 . With the stripping BOPs of the BOP stack  140  remaining closed, the crown valve  135  is then closed, and the adapter spool  145  and nonmagnetic cylindrical spool  110  are depressurized to atmospheric pressure. After the nonmagnetic cylindrical spool  110  and adapter spool  145  are depressurized, the crown valve  135  remains closed, and the stripping BOPs of the BOP stack  140  remain closed. The stripping of the coiled tubing string  130  is then resumed. When the coiled tubing string  130  exits the BOP stack  140 , the stripping BOPs of the BOP stack  140  may be opened. When a coiled tubing string  130  is moved into the well instead of stripped from the well, the same procedures apply in maintaining the well pressure but in converse order.  
         [0070]    It will be understood that the invention is not limited to a magnet housing  21  that encloses a permanent magnet  20 . In alternative embodiments that are not illustrated, the permanent magnet  20  is not enclosed within a magnet housing  21 . The permanent magnet  20  may be secured directly to the shaft  45  instead. The permanent magnet  20  may be secured to the shaft  45  by bolts, screws, or other suitable fasteners.  
         [0071]    It will be further understood that the invention is not limited to an evaluation board  50  and computer  51  that receive and evaluate magnetic readings from the sensors  30 . One alternative embodiment (not illustrated), may comprise an analog to digital conversion board and a control panel. A suitable example of a control panel includes but is not limited to the MEDC Ltd. GP2 control panel. The analog to digital converter is remotely located from the sensors  30 , and preferably the analog to digital converter may be secured within the housing  65 . The control panel is remotely located from the sensors  30 , preferably on a structure supported by the Christmas tree. The analog to digital converter will process readings from the sensors  30  and/or the synchronization sensor  31  and then transmit these processed signals on to the control panel. The control panel may optionally use threshold detection and waveform analysis (as functionally described earlier) to differentiate between readings during the insertion or stripping of tubing strings  95  so as to detect the presence of tool joints  90 , tubing strings  95 , or the initial presence of the tubing string  95  in the nonmagnetic cylindrical spool  110 , or to detect when the last of the tubing string  95  exits the nonmagnetic cylindrical spool  110  and during the insertion or stripping of coiled tubing strings  130  so as to detect when the last of the coiled tubing string  130  exits the nonmagnetic cylindrical spool  110  or to detect the initial presence of the coiled tubing string  130  in the nonmagnetic cylindrical spool  110 . The control panel may also evaluate the reading of the synchronization sensor  31  and determine whether a maximum magnetic flux value is at that time being detected and may then in turn notify the sensors  30  of such reading.  
         [0072]    Even though the above disclosure describes identifying the location of tool joints  90  in a tubing string  95  and identifying the presence of a coiled tubing string  130  in the nonmagnetic cylindrical spool  110 , the present invention is expressly not limited to such applications, and may be useful in various other applications. The present invention would prove useful, for example, for identifying the initial presence of a tubing string  95  in a BOP spool or another predetermined section of pipe. For instance, the computer  51  or control panel may also give an audio and/or visual signal to the operator signifying the initial presence of the tubing string  95  in the predetermined section of pipe and also when the last of the tubing string  95  exits the predetermined section of pipe. The present invention is further not limited to use in a well bore. It will be appreciated that the invention may detect changes in mass and/or diameter of ferrous objects passing through a cylindrical space in any technology or application calling for such functionality.  
         [0073]    Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.