Abstract:
A system for cementing a tubular member in a well bore includes a cementing plug. The cementing plug includes at least one sensor. The system transmits a value measured by the sensor to a surface location. The system may transmit the value measured by the sensor through a cable connected between the plug and the surface location. Alternatively, the system may transmit the value measured by the sensor acoustically to the surface location.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. application Ser. No. 09/706,072, filed Nov. 3, 2000, titled INSTRUMENTED CEMENTING PLUG AND SYSTEM (abandoned). 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of oil and gas well cementing. More particularly, the present invention relates to an instrumented cementing plug and a system for sending to a surface location data measured by the instrumentation of the cementing plug. 
     DESCRIPTION OF THE PRIOR ART 
     During the drilling and at the completion of every oil and gas drilling operation, it is necessary that cementing be done in the borehole. More particularly, the casing or liner must be cemented in the hole in order to support the casing or liner and the hole and to prevent the flow of fluids between formations. 
     The operations associated with setting and cementing casing and liners in the borehole are generally well known in the art. At the completion of a phase of drilling, the cased and open portions of the well bore are filled with drilling fluid. A casing or liner string is assembled and run into the well bore. Then, a spacer or displacement plug is inserted into the top of the casing or liner above the drilling fluid. The displacement plug serves to separate and prevent mixing of the drilling fluid below the displacement plug and a cement slurry that is pumped into the casing or liner above the displacement plug. After a predetermined quantity of cement slurry has been pumped into the casing or liner, a cementing plug is inserted above the cement slurry. Then, drilling fluid is pumped into the casing above the cementing plug to force the slug of cement slurry down the casing or liner and up the annulus between the casing or liner and the borehole. After cementing, the displacement and cementing plugs, the cementing shoe, and any residual cement in the casing are drilled out. 
     Good cementing jobs are essential to the successful drilling and completion of oil and gas wells. Currently, operators rely upon proper equipment and skill of personnel in order to achieve a good cementing job. However, occasionally, bad cementing jobs occur. Some of the causes of bad cementing jobs are over-displacement or under-displacement of the cement slurry, which results in the formations not be properly isolated from each other. Another cause of bad cementing jobs channeling within the cement, which results in flow paths within the cement between formations. 
     Various tests are performed to determine whether or not the cementing job is good. If a cementing job is not good, then remedial operations, such as squeeze jobs, must be undertaken. However, remedial operations, tend to be expensive in terms of equipment and supplies and time. 
     It is an object of the present invention to provide a system for improving the quality of cementing operations. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system for cementing a tubular member, such as a casing or liner string, in a well bore. The system of the present invention includes a cementing plug. The cementing plug includes at least one sensor. The system transmits a value measured by the sensor to a surface location. The system may transmit the value measured by the sensor through a cable connected between the plug and the surface location. Alternatively, the system may transmit the value measured by the sensor in a wireless manner to the surface location. In a cable-connected embodiment, an optical transmitter may be coupled to the sensor and the cable may include an optical fiber. In a wireless embodiment, the signal may be acoustically coupled to the surface. For example, an explosive device for producing an acoustic signal may be coupled to the sensor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial representation of one embodiment of the system of the present invention. 
     FIG. 2 is a block diagram of the system of FIG.  1 . 
     FIG. 3 is a pictorial representation of an alternative embodiment of the system of the present invention. 
     FIG. 4 is a block diagram of the system of FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and first to FIG. 1, a casing string  11  is shown inserted into a well bore  13 . Casing string  11  is of the type generally well known in the art, and it includes a plurality of casing sections  15  connected together by casing collars  17 . A cementing shoe  19  is affixed to the bottom end of casing string  11 . A plug container  21  is affixed to the upper end of casing string  11 . Plug container  21  is of the type generally well known in the art, and it includes a cement inlet  23  and a drilling fluid inlet  25 . Plug container  21  is adapted to launch a displacement plug  27  and an instrumented cementing plug  29  into casing string  11 . 
     Cementing plug  29  is generally cylindrical and it includes an upper surface and a lower. The side surfaces of cementing plug  29  are in the form of wipers that engage the inside wall of casing string  11 . Cementing plug  29  performs its normal displacement and separation functions. Additionally, as will be explained in detail hereinafter, cementing plug  29  includes various sensor and telemetry instrumentation. 
     In the embodiment illustrated in FIG. 1, plug container  21  includes a lubricator  31 . Lubricator  31  is adapted to sealingly and slidingly engage a cable  33  connected to cementing plug  29 . In the preferred embodiment, cable  33  includes an optical fiber. Lubricator  31  allows cable  33  to be run into casing string  11  as cementing plug  29  is pumped downwardly. Cable  33  is preferably releasably connected to cementing plug  29  so that cable  33  may be retrieved through lubricator  31 . 
     Referring now to FIG. 2, there is shown a block diagram of a system according to the present invention. In the embodiment shown in FIG. 2, cementing plug  29  includes a plurality of sensors. An upper pressure sensor  41  and an upper temperature sensor  43  are positioned to sense pressure and temperature, respectively, at the upper surface  45  of cementing plug  29 . A lower pressure sensor  47  and a lower temperature sensor  49  are positioned to sense pressure and temperature, respectively, at the lower surface  51  of cementing plug  29 . The operation and construction of pressure and temperature sensors are generally well known. 
     Pressure sensors  41  and  47 , and temperature sensors  43  and  49 , are adapted to output an electrical signal indicative of the pressure or temperature that they sense. The difference in pressure measured by pressure sensors  41  and  47  is useful in determining if there is bypass of displacement fluid around cementing plug  27 . Fluid bypass can result in effective over-displacement or under-displacement of the cement slurry or mixing of displacement fluid and the cement slurry, which can cause channeling or an otherwise ineffective cement job. 
     The setting of cement involves exothermic reactions. Thus, the progress of the setting of the cement can be monitored with reference to the temperature measured by sensors  43  and  49 . Those skilled in the art will recognize other information that may be obtained from the pressure and temperature sensors. 
     Cementing plug  29  also includes a location sensor  53 . Location sensor  53  preferably operates magnetically to detect the casing collar. Whenever cementing plug  29  passes a casing collar, location sensor  53  puts out a particular signal. The output of location sensor  53  enables an operator to know the location of cementing plug  29  within casing string  11 . Location information is essential to prevent over- or under-displacement of the cement slurry. Location information may also be obtained by measuring the length of cable  33  run into the hole. 
     The outputs of the sensors are coupled to a processor  55 . Processor  55  converts the signals received from pressure sensors  41  and  47  and from temperature sensors  43  and  49  to pressure and temperature values, respectively. Processor  55  counts the signals received from location sensor  53 , thereby to determine the location of cementing plug  29  within the casing. Processor  55  also packages the pressure, temperature, and location data according to an appropriate communications protocol for transmission to a surface location. Processor  55  may also perform other processing. For example, processor  55  may compute pressure or temperature differentials between upper surface  45  and lower surface  51  of cementing plug  29 . 
     Cementing plug  29  also includes a communication interface  57  coupled to processor  55 . In the embodiment shown in FIG. 2, communications interface  57  is coupled to an optical transmitter  59  and to an optical receiver  61 . Optical transmitters and receivers are generally well known in the art. The output of optical transmitter  59  and the input of optical receiver  61  are coupled to a multiplexer  63 . Multiplexer  63  is coupled to a releasable optical coupler  65 , which in turn is coupled to optical cable  33 . In the embodiment shown in FIG. 2, coupler  65  is operated to release cable  33  by a signal from processor  55 . A power supply indicated generally by the numeral  67  supplies power to the components of cementing plug  29 . 
     Cementing plug  29  is expendable in that it is not intended to be retrieved at the completion of use. Also, the instrumentation components of cementing plug  29  that are left downhole after optical cable  33  has been retrieved are drillable so that they may be drilled out. While the sensors and processors have been illustrated as discrete components, the sensing and processing functions may be integrated into a smart sensor built on a single semiconductor chip. 
     The system illustrated in FIG. 2 includes surface equipment, indicated generally by the numeral  71 . Surface equipment  71  includes a multiplexer  73  coupled to optical cable  33 . Multiplexer  73  is coupled to an optical transmitter  75  and an optical receiver  77 . The output of optical receiver  77  and the input of optical transmitter  75  are coupled to a communications interface  79 , which in turn is coupled to a workstation or personal computer  81 . Workstation  81  is adopted to run an operating system, such as Windows 98 (tm) or Windows NT (tm), and various application programs according to the present invention. The application programs provide a user interface that displays data and enables an operator to interact with the system. The application programs also process data received from cementing plug  29 , to calculate and display location, pressure, and temperature information. As is apparent, the system of FIG. 2 enables bi-directional communication between surface location  71  and cementing plug  29 . The bi-directional communication enables, among other things, an operator at surface to cause the actuation of coupler  65  to release cable  33 . Preferably, coupler  65  includes an explosive element adapted to release cable  33 . 
     Referring now to FIG. 3, there is illustrated an alternative embodiment of the present invention. The embodiment of FIG. 3 is similar to the embodiment of FIG. 1, except that information from cementing plug  29   a  is coupled to surface equipment acoustically, rather than optically. Thus, plug container  21   a  includes a transducer  93  that is coupled to surface equipment by a cable  95  that passes through a stuffing box  91 . 
     Referring now to FIG. 4, there is shown a block diagram of the system of FIG.  3 . Cementing plug  29   a  includes a location sensor  91  that operates substantially in the same way as the location sensor of the system of FIG.  2 . The output of location sensor  91  is coupled to a processor  93 . Processor  93  is coupled to a detonator  95 , which is adapted to selectively detonate explosive caps  97 . Explosive caps  97  are disposed in an array adjacent the upper surface  99  of cementing plug  29 A. In the preferred embodiment, each cap  97  has a distinctive acoustic signature that enables the signal of a particular cap  97  to be distinguished from that of another. Thus, the detonation of caps  97  may be coded with information obtained from location sensor  91 . 
     Generally, the acoustic coupling of the system of FIG. 4 provides lower bandwidth than the optical coupling of the system of FIG.  2 . Thus, in FIG. 4, only the location sensor  91  is shown. However, by increasing the size of the array of caps  97  additional information may be transmitted and the number and types of sensors may be increased. A power supply  101  supplies power to the components of cementing plug  29   a.    
     The system of FIG. 4 includes surface equipment, designated generally by the numeral  111 . Surface equipment  111  includes transducer  93 , which is coupled to an audio interface  113 . Audio interface  113  is coupled to a workstation or processor  115 . Surface equipment  111  receives and processes acoustic signals from cementing plug  29   a . In the system illustrated with respect to FIG. 4, an operator is provided with location information. Those skilled in the art will recognize other wireless downhole telemetry systems, such as mud pulse and electromagnetic systems. 
     From the foregoing, it will be apparent that the present invention provides an improved cementing system. The system of the present invention provides real-time measurements of downhole conditions and plug locations, thereby enabling an operator to take corrective actions before the cement has set. The system of the present invention thus reduces or eliminates the need for costly post-cementing remedial actions. 
     The system of the present invention has been illustrated and described with respect to presently preferred embodiments. Those skilled in the art will recognize, given the benefit of the foregoing disclosure, alternative embodiments. Accordingly, the foregoing disclosure is intended for purposes of illustration rather than limitation.