Abstract:
A wireless casing collar locator includes a pipe coupling detector configured to be conveyed through a wellbore. A detection device is associated with the pipe coupling detector. The detection device generates an output indicative of detection of a pipe coupling in response to the output of the pipe coupling detector. The locator includes an acoustic transmitter functionally associated with the detection device. The transmitter is configured to apply an acoustic impulse to a conveyance device used to move the locator along the wellbore in response to communication to the transmitter of the output of the detection device. A surface receiver and processing unit used to convert acoustic energy into electrical energy for processing in real time to determine the location of the pipe detector in wellbores.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION  
       [0003]    1. Field of the Invention 
         [0004]    The invention relates generally to the field of wellbore instruments used to determine the position within a wellbore of threaded connections between adjacent casing segments (or “joints”). Such instruments are referred to in the art as “casing collar locators”, irrespective of whether the casing joints are coupled to each other using internally threaded sleeve connectors (“collars”) or alternating externally and internally threaded casing joint ends (“pin” and “box” connections). More specifically, the invention relates to casing collar locators that communicate to the Earth&#39;s surface without using an electrical conductor or optical fiber cable for a signal communication channel. 
         [0005]    2. Background Art 
         [0006]    A casing collar locator is a instrument deployed in a wellbore which finds or locates the collars or casing joint ends which join together the individual joints to form a “string” of well casing. After a wellbore has been drilled, and as part of the wellbore completion procedure, the wellbore typically is “cased”, which means a length of steel or other high strength material pipe is inserted into the wellbore and is typically cemented in place. Casing is assembled by joining individual, discrete length segments (“joints”) together end to end. The joints are normally joined using an internally threaded coupling or “collar” which threads to the externally threaded ends of each of a pair of adjacent casing joints. The collar typically has a larger external diameter than the casing joints and is thus easy to locate using magnetic detection apparatus. Improvements in the design of threaded couplings in some instances enables the collars to be omitted, by incorporation of a different type of thread construction on the longitudinal ends of the casing joints, namely, a “pin and box” thread connection between adjacent joints. The pin end is externally threaded and is inserted into the internally threaded or “box” end of the adjacent casing joint. Pin and box casing connections reduce the mass of metal proximate the threaded connection. It provides a more uniform wall thickness while reducing the mass of metal around the connection of joints. 
         [0007]    It is important to correctly locate the collars or joints so that the depth or location of a tool in the cased well can be determined. Given the fact that casing joints have uniform spacing, the depth of a particular instrument or device suspended in the wellbore can be determined if the casing collars or joints can be correctly counted. 
         [0008]    An example of a casing collar locator that can generate an electrical signal when the locator moves past a collar or past a pin and box connection is described, for example, in U.S. Pat. No. 4,808,925 issued to Baird. Other types of casing collar locators are well known in the art. 
         [0009]    Irrespective of the configuration of the threaded connection used in any casing string, as known in the art, it is necessary to provide an electrical and/or optical signal channel to communicate the output of the casing collar locator to the Earth&#39;s surface, so that a record with respect to depth in the well of the collar locator signal can be produced. For this reason, casing collar locators are ordinarily used with “wireline”, which is an armored cable having at least one insulated electrical conductor therein. There are configurations of wireline known in the art that also include optical fibers. 
         [0010]    It is known in the art to perform wellbore intervention services using instrument conveyances that do not provide such signal channel. Such conveyance methods include, for example, coiled tubing, production tubing and slickline, for example. It is known in the at to use electromagnetic signal communication (radio) for signal communication over slickline. See, for example, U.S. Pat. No. 7,224,289 issued to Bausov et al. It is believed that the radio transmission device disclosed &#39;289 patent may have limited applicability in wellbores having highly conductive fluid therein, particularly at great depth (in excess of about 5,000 feet). It is also known in the art to make a slickline in the form of a tube having an insulated electrical conductor therein. See, for example, U.S. Pat. No. 5,495,755 issued to Moore. Making a slickline as described in the Moore &#39;755 patent is difficult and expensive, and requires that a spooling device or winch, used to deploy the slickline in the wellbore, include some form of slip ring or similar device that enables the winch drum to rotate while making electrical (or optical) connection to a rotationally fixed position in the unit used to detect signals from the instrument in the wellbore. 
         [0011]    There continues to be a need for casing collar location devices that do not require an electrical or optical signal channel to communicate detection of a casing collar or connection to the surface, and do not require modification of conventional “slickline units” to include a slip ring or similar fixed-to-rotating electrical and/or optical coupling. 
         [0012]    The ability to know in real time the location of a tool string in a well when the tool string is deployed using a coil tubing or slickline is critical to compensate for the elongation of the tubing string as it is deployed in the wellbore. The incorrect determination of the location of the tool string when performing a service in the wellbore can cause the string to fail in such services as hydraulic fracturing work due to excessive pressure that could be exerted onto the tool string. 
       SUMMARY OF THE INVENTION  
       [0013]    A wireless casing collar locator according to one aspect of the invention includes a pipe coupling detector configured to be conveyed through a wellbore. A detection device is associated with the pipe coupling detector. The detection device generates an output indicative of detection of a pipe coupling in response to the output of the pipe coupling detector. The casing collar locator includes an acoustic transmitter functionally associated with the detection device. The acoustic transmitter is configured to apply an acoustic impulse to a conveyance device used to move the collar locator along the wellbore in response to communication to the acoustic transmitter of the output of the detection device when a collar is detected. 
         [0014]    A method for detecting a pipe coupling according to another aspect of the invention includes moving a pipe coupling detector along the interior of a pipe disposed in a wellbore. An output of the coupling detector is conducted to a signal detector. The signal detector generates a pulse in response to detection by the coupling detector of a pipe coupling in the wellbore. Output of the signal detector is coupled to an acoustic telemetry transmitter. The transmitted is then caused to impart an acoustic signal to an instrument conveyance device in response to output of the signal detector. 
         [0015]    Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows an example of a casing collar locator being conveyed into a wellbore by slickline. 
           [0017]      FIG. 2  shows components of the casing collar locator of  FIG. 1  in more detail. 
           [0018]      FIG. 3  shows signal detection components disposed at the Earth&#39;s surface for determining placement of a collar or other pipe connection using the instrument shown in  FIGS. 1 and 2 . 
       
    
    
     DETAILED DESCRIPTION  
       [0019]    A typical wellbore intervention operation including one example of a casing collar locator  18  according to the invention is shown in  FIG. 1 . The casing collar locator  18  may be disposed in a sealed, pressure resistant housing (not shown separately) which includes therein a pipe coupling detection device  18 A and a signal detection, processing and telemetry unit  18 B. The foregoing device  18 A and unit  18 B will be explained in more detail with reference to  FIG. 3 . In the present example, the casing collar locator  18  is inserted into and withdrawn from a wellbore  10  drilled through subsurface formations  12  at the end of a “slickline”  20 . Slickline is essentially a solid steel wire that is round in cross section. It should be understood that the present invention may be used with other forms of conveyance, such as tubing, coiled tubing, drill pipe or the like, or any other conveyance that does not include an electrical or optical signal channel for communicating signals from the collar locator  18  to the Earth&#39;s surface. 
         [0020]    The wellbore  10  includes a steel pipe or casing  14  inserted therein. The casing  14  is typically formed by threadedly coupling end to end a plurality of segments or “joints” of such pipe or casing. In some examples, the casing joints include male threads (pin ends) at both longitudinal ends, and the joints are threadedly coupled by connecting two adjacent joints to a casing collar  16 . A casing collar is essentially an internally threaded sleeve configured to mate with the pin (externally threaded) end of each adjacent casing joint. It should be clearly understood that so called “flush joint” casing having one end internally threaded (a “box end”) and configured to mate with the pin end of the adjacent casing joint may also be used with the invention. One example of a casing collar locator particularly suited to detect flush joint threaded connections is described in U.S. Pat. No. 7,224,289 issued to Bausov et al. 
         [0021]    The slickline  20  can be extended from and withdrawn onto a winch or similar spooling device (not shown separately) forming part of a slickline unit  26 . The slickline unit  28  may include a spooling head  28  or similar laterally movable extension arm with rollers (not shown) that enables the operator thereof to guide the slickine  20  so that it is wound neatly on a winch drum (not shown). In some examples, a motion detector  54 , such as an accelerometer, is coupled to the spooling head  28  such that an axial acceleration of the slickline  20  is measured. As will be further explained with reference to  FIG. 3 , the motion detector  54  may be used to detect an acoustic signal imparted to the slickline  20  by the collar locator  18  when a collar or threaded connection is detected. As will be readily appreciated by those skilled in the art, the slickline  20  can be passed through an upper sheave  22  and a lower sheave  24  so that certain forces acting on the slickline  20  are properly distributed. However, the configuration shown in  FIG. 1  for inserting the slickline into the wellbore is not intended to limit the scope of the invention. 
         [0022]    In the example of  FIG. 1 , as the collar locator  18  is moved past collars  16  or any other threaded coupling (e.g., “flush joint” connections) of casing joint to casing joint, a magnetic field is imparted to the casing  14  by one or more magnets (not shown) inside the collar locator  18 . A wire coil (not shown) is disposed proximate the magnet and will have voltages induced therein when the collar locator  18  passes by a casing collar  16 . In the present example, when a collar  16  is located by moving the collar locator  18  by a collar  16 , the telemetry unit  18 B imparts an acoustic wave to the slickline  26  so that the position of the collar  16  can be determined. The acoustic wave imparted to the slickline  20  is detected by the motion detector  54 , the output of which is coupled to suitable detection and recording circuitry (collectively referred to as a recording system  56 ) disposed inside the slickline unit  26 . The detected acoustic wave indicate the presence of a casing collar or other type of threaded connection at the depth of the collar locator  18  at the time of signal detection. 
         [0023]    An example of circuitry that may be included in some examples of a casing collar locator are shown schematically in  FIG. 2 . A pipe coupling detection device  32  may be any type of magnetic casing collar locator device known in the art. One such collar locator is described in U.S. Pat. No. 7,224,289 issued to Bausov et al. as explained in the Background section herein. Such pipe coupling detection devices include one or more magnets for inducing a magnetic field in the casing, and a detection coil. Because of the change in magnetic field distribution in the vicinity of collars or threaded couplings, when a detection coil is moved through such altered distribution magnetic field, a voltage is induced in the coil. The detected voltage is interpreted to determine the position of the threaded connection. 
         [0024]    It is also possible to use contact arm-type caliper tools as a pipe coupling detection device. One such contact arm caliper is disclosed in U.S. Pat. No. 4,299,033 issued to Kinley et al. Inside a pipe coupling, there is typically at least a small longitudinal segment having a different internal diameter than the adjacent pipe joints. Momentary increase in measured internal diameter may be indicative of a pipe coupling. 
         [0025]    Irrespective of the type of collar locator device used, the output of the pipe coupling detection device  32  is coupled to a detection circuit  34 . The detection circuit  34  is configured to determine from the signal sent from the pipe joint detection device whether the device  32  has passed a connection between adjacent pipe joints (collar or otherwise), and in response thereto provides a pulsed output that is indicative of a casing collar or other threaded connection in the casing ( 14  in  FIG. 1 ). Output of the detection circuit  34  is coupled to a controller  36 , which may be any microprocessor based controller. The controller  36  may be programmed and reprogrammed by connection to an external signal communication port  38  when the collar locator ( 18  in  FIG. 1 ) is at the Earth&#39;s surface. For example, the controller  36  may be programmed to cause a telemetry transmitter (explained below) to operate when an input pulse from the detection circuit  34  is conducted to the controller  36 . Electrical power to operate the foregoing devices, and other devices to be explained further below, may be provided by batteries  46 . 
         [0026]    During periods of time when the telemetry transmitter is not operating, the batteries  46  charge, through a current regulator  44 , a bank of capacitors  42 . The capacitors  42  store energy to be released quickly through the telemetry transmitter to cause a large amplitude acoustic pulse to be imparted to the slickline ( 20  in  FIG. 1 ). The capacitors  42  are also coupled to a transmitter driver  48 . When instructed by the controller  36 , the transmitter driver  48  couples the capacitors  42  to one side of transformer  50 , the other side of which is coupled to the acoustic transmitter. In the present example, the acoustic transmitter can be a stack of piezoelectric disk elements  52  in acoustic coupling with the collar locator housing. When electrically actuated by application thereto of the energy in the capacitors  42 , the piezoelectric elements  52  generate an acoustic pulse which is ultimately imparted to the slickline ( 20  in  FIG. 1 ). In one example, the controller  36  and the transmitter driver  48  are configured to cause the piezoelectric elements  52  to emit a pulse of essentially monochromatic 1500 Hz acoustic energy, such pulse corresponding to detection of a casing collar or threaded coupling. Such acoustic pulse is detected at the surface, as will be explained below with reference to  FIG. 3 . 
         [0027]    The surface recording system  56  may include detection circuitry configured to detect and interpret acoustic pulses imparted to the slickline (or other conveyance) by the collar locator ( 18  in  FIG. 1 ). The previously mentioned accelerometer  54  is preferably mounted on the spooling arm or otherwise placed in contact with the slickline ( 20  in  FIG. 1 ) such that it is responsive to axial motion of the slickline ( 20  in  FIG. 1 ). The AC (non zero frequency) output of the accelerometer  54  may be coupled though a capacitance coupler  58  to a digital signal processing unit (“DSP”)  64 , such as one sold under model designation TMS320C33 by Texas Instruments, Inc., Dallas, Tex. The DSP  64  is configured to interpret the output of the accelerometer  54  to determine when an acoustic pulse has been applied to the slickline ( 20  in  FIG. 1 ) by the casing collar locator ( 18  in  FIG. 1 ). A power converter  60  may convert standard house current or standard rig current (e.g., 120, 208, 240 or 480 volt AC) to suitable direct current for operating the various devices in the recording system  56 . Data output from the DSP  64  may be conducted to a portable computer  66  such as a notebook computer for making a record with respect to depth of the detected casing collars or threaded couplings. An output driver  62  may provide signal output that can be used by a system operator or system customer. 
         [0028]    A casing collar locator system according to the invention can provide casing collar or threaded coupling location in a wellbore without the need to provide an electrical or optical signal channel. Such capability may provide casing collar detection in environments not well suited for electrical and/or optical signal transmission. 
         [0029]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.