Abstract:
Methods and apparatus for receiving a telemetry signal with a receiver that is moveably disposed within a drillstring. In certain embodiments, the system comprises a surface module coupled to the upper end of a drillstring, an upper module detachably connected to the surface module, and a lower module moveably disposed within the drillstring. The lower module is coupled to the upper module by an extendable cable. A telemetry signal receiver is disposed on said lower module, which also includes a tractor assembly for moving the lower module through the drillstring.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not Applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable. 
   FIELD OF THE INVENTION 
   The present invention relates generally to methods and apparatus for receiving downhole telemetry data. More specifically the present invention relates to a telemetry receiver mounted within the drill pipe and selectively locatable at a position below the drill floor. 
   BACKGROUND 
   Modern petroleum drilling and production operations demand a great quantity of information relating to parameters and conditions downhole. Such information typically includes characteristics of the earth formations traversed by the wellbore, along with data relating to the size and configuration of the borehole itself. The collection of information relating to conditions downhole, which commonly is referred to as “logging”, can be performed by several methods. In conventional wireline logging, the drill string is removed from the wellbore and a probe containing selected instrumentation is lowered into the wellbore on a wire that supports the instruments and provides a direct communication link to the surface. 
   It is often desired to collect data during the drilling process while the drill string is in the wellbore, thus allowing the driller to make accurate modifications or corrections as needed to optimize performance. Designs for measuring wellbore conditions and formation parameter during drilling have come to be known as “measurement-while-drilling” (MWD) or “logging while drilling” (LWD) techniques. While distinctions between MWD and LWD may exist, the terms MWD and LWD often are used interchangeably. For the purposes of this disclosure, the term MWD will be used with the understanding that this term encompasses both the collection of formation parameters and the collection of information relating to the movement and position of the drilling assembly. 
   Data gathered by MWD tools is typically transmitted to the surface by sensors or transducers located at the lower end of the drill string. While drilling is in progress, these sensors continuously or intermittently monitor selected drilling parameters and formation data and use some form of telemetry to transmit the information to a detector located at the surface. There are a number of telemetry systems in the art that seek to transmit information regarding downhole parameters up to the surface without requiring the use of a physical connection, such as a wire. 
   Acoustic telemetry is one of the systems used for MWD applications and operates by creating acoustic signals that travel to the surface along the drill string or through the fluid in the well. The acoustic telemetry signal is received at or near the surface using an accelerometer, or some similar device that is sensitive to motion. When acoustic telemetry is attempted through the drill pipe, each pipe joint acts as a reflector of acoustic radiation. The net effect of all these reflections is the creation of a comb-like structure of pass bands and stop bands where the range of frequencies of any of the pass bands is fairly narrow. The combined effect of a narrow frequency band and multiple reflections causes nodes and anti-nodes to be distributed along the pipe, where the signal is strongest at a node and weakest at an anti-node. 
   The transmission of data can be negatively affected by pulse spreading, distortion, attenuation, modulation rate limitations, and other disruptive forces, such as the ambient noise in the drill string. The largest source of ambient noise in the drill string is the drilling rig. Thus, receivers located at or near the surface are subjected to high levels of ambient noise generated by the drilling rig. These high levels of noise can interfere with the reception of telemetry signals and often require additional filtering or other processing of the received signals before useful analysis can be performed. 
   Therefore, while receiving telemetry signals at the surface is an important aspect of MWD or LWD processes, the inherent noise of the drilling rig often makes the surface one of the least desirable locations for placing a receiver. Accordingly, there remains a need to develop telemetry signal receiving methods and apparatus that overcome certain of the foregoing difficulties while providing more advantageous overall results. 
   SUMMARY OF THE PREFERRED EMBODIMENTS 
   The embodiments of the present invention are directed to methods and apparatus for receiving a telemetry signal with a receiver that is moveably disposed within a drillstring. In certain embodiments, the system comprises a surface module coupled to the upper end of a drillstring, an upper module detachably connected to the surface module, and a lower module moveably disposed within the drillstring. The lower module is coupled to the upper module by an extendable cable. A telemetry signal receiver is disposed on said lower module, which also includes a tractor assembly for moving the lower module through the drillstring. 
   In one embodiment, a wellbore telemetry system comprises a surface module coupled to the upper end of a drillstring, an upper module detachably connected to the surface module and disposed within the drillstring, a lower module moveably disposed within the drillstring and coupled to the upper module, and a telemetry signal receiver disposed on said lower module. The lower module further comprises a tractor assembly adapted to move the lower module through the drillstring. A detachable electrical connector couples the surface module to the upper module, which further comprises a cable reel, wherein a cable is spooled onto the cable reel and coupled to the lower module and the upper module. 
   In an another embodiment, a method for receiving telemetry signals comprises disposing a receiver array within a drillstring, moving the receiver array within the drillstring to improve reception of telemetry signals, and relaying the received signals to a data analysis system. The receiver array is disposed on one or more tractor assemblies adapted to move the array within the drillstring. The method further comprises disposing an upper assembly in the drillstring, wherein the receiver array is coupled to the upper assembly by a cable; connecting a surface module to the upper end of the drillstring; and detachably connecting the upper assembly to the surface module. The received signals are relayed from the receiver array through the cable to the upper assembly, from the upper assembly to the surface module, and from the surface module to the data analysis system. 
   In another embodiment, a method for using a telemetry receiver system comprises installing a telemetry receiver system on a drillstring. The telemetry receiver system comprises a surface module coupled to the upper end of a drillstring, an upper module detachably connected to the surface module and disposed within the drillstring, and a lower module moveably disposed within the drillstring and coupled to the upper module. The lower module comprises a receiver. The method further comprises moving the lower module within the drillstring to a location optimizing the reception of telemetry signals and relaying telemetry signals from the receiver to a data analysis system through the upper module and the surface module. 
   Thus, the present invention comprises a combination of features and advantages that enable it to overcome various shortcomings of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein: 
       FIG. 1  illustrates a schematic elevation view showing a pipe mounted telemetry receiver; 
       FIG. 2  illustrates a top view of the receiver of  FIG. 1 ; and 
       FIGS. 3   a - 3   e  illustrate drilling operations with a pipe mounted telemetry receiver. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. 
   In particular, various embodiments described herein thus comprise a combination of features and advantages that overcome some of the deficiencies or shortcomings of prior art telemetry systems. The various characteristics mentioned above, as well as other features and characteristics described in more detail below, will be readily apparent to those skilled in the art upon reading the following detailed description of preferred embodiments, and by referring to the accompanying drawings. 
   Referring now to  FIG. 1 , one embodiment of a telemetry receiver system  10  is shown disposed in a pipe  12 . System  10  includes surface module  14 , upper module  16 , and lower module  18 . Each module  14 ,  16 , and  18  has one or more fluid paths  15  allowing fluid to be circulated through the pipe. Surface module  14  comprises a body  20  including a pipe connection  22  and support frame  24 . An electrical wet connector  26  is suspended from support frame  24 . Cable  28  extends from support frame  24  and provides a communications link to a data analysis system. Cable  28  may extend through a pipe wall to a transmitter on the outside of the unit or may extend to a rotating transformer that is fixed to the swivel and provides communication with the data analysis system. 
   Upper module  16  includes base  30  supporting an electrical wet connector  32  and a bobbin or reel  34  supporting a cable  36 . Reel  34  preferably includes a level wind apparatus that controls the winding of cable  36  onto and off of the reel. In the current context bobbin and reel may be used interchangeably to describe the component of upper module  16  on which cable  36  is stored and wound to and from. In some embodiments, upper module  16  may include a tractor assembly or anchor assembly to control the location of the upper module within pipe  12 . 
   Lower module  18  includes tractor assembly  38  supporting interface  40  and accelerometer array  42 . Interface  40  includes an electronics module and any electromechanical components required to operate tractor assembly  38  and enable communication with array  42 . Tractor assembly  38  has tracks  44  pushed against pipe  12  by spring  46  and serves to hold lower module  18  in place within the pipe. Tractor assembly  38  provides traction within pipe  12  but also preferably retracts to release tracks  44  from the pipe. Tracks  44  are preferably motorized so as to move lower module  18  up and down pipe  12 , as desired. 
   Tractor assembly  38  provides sufficient force to hold lower module  18  in position when fluid is being circulated down through pipe  12  and to move the assembly upward through the pipe when fluid is being circulated downward. In certain embodiments tractor assembly  38  may include a safety braking system to prevent the descent of the assembly into pipe  12  should tracks  44  unexpectedly release from the wall of the pipe. 
   Surface module  14  connects to the upper end of pipe  12  through connection  22 . Upper module  16  is supported by and electrically coupled to support frame  24  by electrical connectors  26  and  32 . Cable  36  is connected to interface  40 . Thus, communication between the data analysis system and accelerometer array  42  is along cable  28 , through connectors  26  and  32 , and through cable  36  to interface  40 , which is coupled to accelerometer array  42 . This communications link provides direct, two-way communication between accelerometer array  42  and the data analysis system. 
   Referring now to  FIGS. 3   a - 3   e , a sequence of events is shown illustrating the use of telemetry system  10  during drilling operations. A signal generating tool is disposed within the weilbore on drill string  50 . This signal generating tool may transmit acoustic signals along drill string  50 , within the drilling fluid (mud pulse telemetry), or any other downhole-to-surface communication method. In  FIG. 3   a , telemetry system  10  is shown disposed within drill string  50 , when the upper end  52  of the drill string is above drill floor  54 . Surface module  14  is connected to the upper end  52 . Surface module  14  is connected to upper module  16 , which is connected to lower module  18 . From this initial configuration, a signal is given to the lower incdule  18  to disconnect from upper module  16  and move downward within drill string  50 , as shown in  FIG. 3   b.    
   As lower module  18  moves away from upper module  16 , cable  36  provides communication between the modules. Lower module  18  can move up or down within drill string  50  in order to optimize reception of telemetry signals traveling up the drill string or through the wellbore. In some embodiments, lower module  18  moves to a position below drill floor  54  in order to reduce the noise generated by the surface drilling equipment. In the preferred embodiments, a group of sensors is used to enhance signal reception and noise rejection in order to improve and optimize the signal to noise ratio. 
   For example, two or more of the accelerometers or transducers in the array can be operated so as to discriminate between upgoing and downgoing acoustic energy and utilized in accordance with U.S. Pat. No. 4,590,593, which is hereby incorporated by reference herein. In addition, the lower module  18  can be located such that the array is located at an antinode of acoustic radiation coming from downhole. Further, the moveable lower module  18  allows for the location to be adjusted to a position where the telemetry signal will be the strongest and noise from the drilling rig can be minimized. 
   As drilling progresses and upper end  52  approaches drill floor  54 , lower module  18  is moved back up drill string  50  to engage upper module  16 , as shown in  FIG. 3   c . A command is given to disengage upper module  16  from surface module  14 . This command, and other communication once upper module  16  is separated from surface module  14 , may be transmitted acoustically, and received by array  42 , or via an electrical or electromechanical signal.  FIG. 3   d  illustrates that once upper module  16  has been engaged by lower module  18  and disengaged from surface module  14 , it is lowered down drill string  50  by lower module  18 . Surface module  14  is then disconnected from drill string  50 . As shown in  FIG. 3   e , additional drill pipe  56  is then connected to drill string  50  and surface module is reconnected to the new upper end  52  of the drill string. Lower module  18  then moves upper module  16  back to upper end  52  so that the upper module can reconnect to surface module  14  and reestablish the initial position as shown in  FIG. 3   a.    
   While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied, so long as the hydraulic retention system and apparatus retain the advantages discussed herein. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.