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BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention generally pertains to oil wells and more specifically to a system for servicing oil wells. 
     2. Description of Related Art 
     After a well is set up and operating to draw petroleum, water or other fluid up from within the ground, various service operations are periodically performed to maintain the well. Such service operations may include replacing worn parts such as a pump, sucker rods, inner tubing, and packer glands; pumping chemical treatments or hot oil down into the well bore; and pouring cement into the well bore to partially close off a portion of the well (or to shut it down entirely). Since wells are often miles apart from each other, the maintenance or service operations are usually performed by a mobile unit or service vehicle having special onboard servicing equipment suited to perform the work. Some examples of service vehicles include a chemical tank truck or trailer, a cement truck or trailer, a hot-oiler tank truck or trailer, and a portable work-over service rig having a hoist to remove and install well components (e.g., sucker rods, tubing, etc.). 
     Service vehicles are often owned by a contractor that the well owner hires to service the wells. Typically, the contractor performs the work and invoices the owner. For many service operations, it is difficult for the owner to confirm exactly what work was actually done or how well it was done, without actually witnessing the work while it is in progress. In the case of pumping a chemical treatment down into a well bore, it is virtually impossible to confirm how much chemical was dispensed after the fact. Other examples would include not being able to confirm the temperature or quantity of a hot oil treatment, the quantity and position of replaced sucker rods or tubing, and the torque used in tightening sucker rods or tubing. There are numerous other possible service operations that are difficult to confirm after the work has been reported as having been completed. Unfortunately it is impractical the well owner to travel to the various remote well sites, arrive at the right moment, and wait around until the work is complete. Consequently, the well owner often relies on the integrity of the contractor. However, even the most reputable contractor (e.g., Fred Newman of Midland, Tex.) can make an honest mistake, as it can be difficult to accurately keep a myriad of process data readings in order and correctly associated with the right oil well, especially when they look so similar. 
     SUMMARY OF THE INVENTION 
     To avoid the problems and limitations of existing well servicing systems, it is an object of the invention to provide a well servicing system that reliably monitors the performance of a well servicing operation, properly associates the operation to the correct well, and secures the combined results to protect against unauthorized changes or tampering of data. 
     A second object is to provide a secure record that can be relied upon at a later date to resolve a maintenance problem, resolve a question of theft, or determine the cause of an accident that may have occurred at the well site. 
     A third object is to provide a well servicing system for use on a mobile well servicing vehicle. 
     A fourth object is to provide a durable well identification device that stores a digital well identification value without having to maintain the device with a source of electrical power. 
     A fifth object is to provide a well servicing system that minimizes a temptation for others to improperly alter data. 
     A sixth object is to provide a well servicing system that lends itself well to a wide variety of processes. 
     A seventh object is to eliminate much of the paper shuffling that is often associated with an invoice created by several people manually comparing handwritten work reports to purchase orders, contracts, and a myriad of other documents. 
     These and other objects of the invention are provided by a novel well servicing system that includes a mobile transducer that senses a parameter of a service operation performed at a plurality of well sites, and includes a memory that stores information provided by the transducer with reference to a well site identifier at each well site to associate the information with the proper well site at which the service operation was performed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a well servicing system, according to one embodiment of the invention, showing a service vehicle at a first well site. 
     FIG. 2 is another schematic view of the system of FIG. 1, but showing the service vehicle traveling between two well sites. 
     FIG. 3 is the same as FIG. 1, but showing the service vehicle at a second well site. 
     FIG. 4 is a schematic view of another embodiment. 
     FIG. 5 is a schematic view of another embodiment. 
     FIG. 6 is a schematic view of another embodiment. 
     FIG. 7 is a schematic view of another embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A first oil well  10  separated several miles from a second oil well  12  are shown in FIGS. 1-3 being serviced by a service vehicle  14 . Vehicle  14  is shown servicing well  10  in FIG. 1, servicing well  12  in FIG. 3, and traveling along a road between wells  10  and  12  in FIG.  2 . Wells  10  and  12  each includes a pivoting beam  16  that raises and lowers a string of sucker rods  18  to operate a pump submerged deep within a well bore  20 . 
     Once a well is set up and operating to draw petroleum, water or other fluid up from within the ground, various service operations are periodically performed to maintain the well. Such service operations include, but are not limited to, replacing worn parts such as a pump, sucker rods, inner tubing, and packer glands; pumping chemical treatments or hot oil down into the well bore; and pouring cement into the well bore to partially close off a portion of the well (or to shut it down entirely). 
     Such services are usually performed by an appropriately equipped service vehicle of which some examples would include, but not be limited to, a chemical tank truck or trailer, a cement truck or trailer, a hot-oiler tank truck or trailer, and a portable work-over service rig having a hoist to remove and install well components (e.g., sucker rods, tubing, etc.). All of these examples of service vehicles and more are schematically/generically represented by vehicle  14  of FIGS. 1-3. For example, vehicle  14  includes a pump  22  that pumps a fluid (e.g., hot oil, cement, or chemical) from a tank  24 , through a hose  26  and down into well bore  20 . The pumping process and a variety of other service operations can be monitored by several transducers that sense various process parameters. The term, “parameter” used in relation to performing a service operation or process on a well represents any detectable feature that reflects at least some condition or status of the process. 
     For example, for a fluid being pumped (e.g., hot oil, chemical, gas, water, steam, cement, etc.) one transducer  28  monitors the flow rate, a second transducer  30  monitors the pressure, a third transducer  32  monitors the temperature, a fourth transducer  34  (removably attached to the well head) monitors any one of a variety of other parameters, such as fluid acidity or concentration. In some service operations, such as the removal and replacement of sucker rods  18 , packer glands, tubing anchors, etc., transducer  34  could count the number of parts being removed or installed to monitor inventory. When replacing sucker rods  18  or other well components, a fifth transducer  36  could monitor the force or weight being applied to vehicle  14  (e.g., a portable work-over service rig having a hoist to remove and install well components). Transducer  36  in conjunction with a sixth transducer  38  monitoring a hoist engine speed could monitor the force and horsepower required to pull a rod  18  from well bore  20 . 
     In response to sensing the various parameters, transducers  28 ,  30 ,  32 ,  34 ,  36  and  38  provide analog feedback signals  40  (i.e.,  40   a ,  40   b ,  40   c ,  40   d ,  40   e  and  40   f  respectively) that an analog to digital converter  42  periodically converts to digital feedback values  44  (i.e.,  44   a ,  44   b ,  44   c ,  44   d ,  44   e  and  44   f  respectively). Analog feedback signals typically take the form of voltage (e.g., 0-5 VDC) or current (e.g., 4-20 mA), however other forms of analog feedback could also be used. The term, “digital feedback value” as used throughout this disclosure is equivalent and interchangeable with the term “digital feedback signal” both of which encompass a quantity that if varied, varies in discrete increments. Digital feedback values and digital feedback signals can take a wide variety of forms including, but not limited to, binary voltage, alphanumeric data (e.g., whole numbers, decimals, letters, and combinations thereof, etc.), bar code and magnetic recording. It should be appreciated by those skilled in the art, that incorporating an analog to digital converter within the transducer itself is well within the scope of the invention. In some embodiments of the invention, a conventional microprocessor circuit  46  (well known to those skilled in the art) periodically conveys digital feedback values  44  to a memory  48  where the values are stored. The term, “memory” used herein and below represents any data storage device and its ancillary elements that facilitate its use. Memory  48  is schematically illustrated to represent the wide variety of forms that it can assume, which include, but are not limited to, a hard drive of a computer; a floppy disc; a CD (compact disk); ZIP drive/cartridge, an electronic chip such as RAM, EPROM, or EEPROM and variations thereof; and magnetic tape. In one embodiment, a clock  50  provides a digital time stamp  52  that circuit  46  also conveys to memory  48  to provide digital feedback values  44  with a time reference. Although circuit  46 , clock  50  and memory  48  can be provided by any one of a wide variety circuits, in one embodiment, devices  46 ,  50  and  48  comprise a computer. In another embodiment, however, devices  46 ,  50  and  48  include a “POCKET LOGGER” by Pace Scientific, Inc. of Charlotte, N.C. 
     To associate the data collected on the service operation with the particular well on which the work was performed, each well  10  and  12  includes a well identifier  54  (e.g.,  54   a ,  54   b ,  54   c  and  54   d ). The term “well identifier” used herein and below represents any value or feature that can be referenced to distinguish one well from another. Some examples of well identifier  54  include, but are not limited to, a bar code label (as commonly used on retail merchandise, e.g., labels  54   a  and  54   b ), data stored on a magnetic or electromagnetic strip (similar to a common credit card or some building access security badges, e.g., item  54   c ), and data stored on an integrated circuit chip (similar to an electromagnetic implant used for animal identification). Other examples of a well identifier include data stored on a memory  54   d  such as a hard drive of a computer; a floppy disc; a CD (compact disk); ZIP drive/cartridge, an electronic chip such as RAM, EPROM, or EEPROM and variations thereof; and magnetic tape. 
     Information of well identifier  54  preferably takes the form of a digital well site value  56  (e.g.,  56   a ,  56   b ,  56   c  and  56   d ). In the example of bar code label  54   a  of FIGS. 1-3, digital well site value  56   a  is represented by a series of bars of varying width and/or pitch. The digital well site value is conveyed to memory  48  by way of a communication link  58  (e.g.,  58   a ,  58   b ,  58   c ,  58   d  and  58   e ). In the case of bar code label  54   a , communication link  58   a  includes a visual scan  60  of label  54   a  by way of a conventional bar code scanner  62  and a cable  64  electrically coupled to memory  48 . Well site value  56   a  and digital feedback values  44  are stored in memory  48  in reference to each other, i.e., values  56   a  and  44  can be referenced later in relation to each other, such that one knows which digital feedback values go with which well site value. 
     In operation then, referring first to FIG. 1, vehicle  14  drives up to well  10 , and an operator scans bar code label  54   a . The scanned digital well site value  56   a  is conveyed to memory  48  by way of communication link  58   a . The operator connects a hose  26  to well bore  20  and sets up transducers  34  and  36  as shown. Some (or all) of the transducers may already be set up upon arrival of vehicle  14 , such as transducers  28 ,  30 ,  32  and  38  in this case. The service operation process is performed (e.g., pumping a fluid into well bore  20  through hose  26 ), while data provided by the transducers is recorded in memory  48  in the form of digital feedback values  44 . Clock  50  can provide various time stamps  52  to indicate when vehicle  14  arrived at the site to scan label  54   a , when the service process began and stopped, when the digital feedback values  44  were sampled, and when vehicle  14  departed. 
     Upon departing, hose  26 , scanner  62 , and transducers  34  and  36  can be disconnected and/or stored for transport with vehicle  14 . As vehicle  14  travels along a road  64  from well  10  to well  12 , as shown in FIG. 2, clock  50 , transducer  38  and other transducers could continue to feed memory  48  with data to provide a record of information such as travel time, speed, travel distance, etc., if desired. 
     Upon arriving at well  12 , the setup and operation can proceed as just described in relation to well  10 , or an entirely different service operation can be performed, depending upon the service needs of well  12  and the capabilities of service vehicle  14 . However, with well  14 , the scanned digital value  56   b  of label  54   b  would be different than that of well  10 , so that whatever data is collected at well  12  would not be confused with the data that had been gathered and recorded at well  10 . 
     Alternate embodiments of the invention are shown in FIGS. 4-7. In FIG. 4, well site identifier  54   c  includes an electromagnetic element such as magnet strip  66 , and communication link  58   b  includes an appropriate electromagnetic detector  68  that senses digital well site value  56   c  of strip  66 . Otherwise, the overall operation of the embodiment of FIG. 4 is generally the same as that of FIGS. 1-3. 
     In FIG. 5, the well identifier is memory  54   d  of a computer  69 . Memory  54   d  is able to store an entered digital well site value  56   d . In this example, memory  54   d  and memory  48  are combined. Feedback from the transducers are conveyed to memory  48  by way of communication link  58   c  that includes a readily disconnectable cable  70 . Although A/D converter  42  is shown closely associated with vehicle  14  with cable  70  conveying digital feedback, it should be appreciated by those skilled in the art that converter  42  could optionally be closely associated with computer  69  with cable  70  conveying analog feedback instead. Either way, as vehicle  14  travels between well sites, the transducers travel with vehicle  14 , while each well site has its own resident memory  48  and  54   d    
     The embodiment of FIG. 6 is similar to that of FIG. 5, however cable  70  is replaced by an electromagnetic communication link  58   d  provided by an electromagnet transmitter  72  and an electromagnetic receiver  74 . However, it is well within the scope of the invention to switch the locations of transmitter  72  and receiver  74  depending on the resident location of memory  48  (i.e., at the well site or on the vehicle). The operation of this embodiment can vary, but in one example, transmitter  72  emits a radio signal that receiver  74  receives and computer  69  interprets as an indication that a specifically identified vehicle  14  has arrived at the well site. In response, computer  69  provides an indication (e.g. a green light) to the operator of the vehicle that his vehicle has been recognized and that computer  69  is ready to receive transducer feedback data. The operator performs the service operation on the well, while transducer feedback is transmitted to computer  69  for storage in memory  48 . 
     The data is stored with limited access (e.g., lock and key and/or a computer password, all of which are depicted by numeral  76 ) for security purposes to prevent unauthorized tampering or altering of the data. In other words, those performing the service operation are inhibited from falsifying the data collected at the well site. Later, an owner of the well or a representative thereof with sufficient security clearance can access the stored data and use the information for a variety purposes including, but not limited to automatically creating an invoice  77  specifying the amount of payment due as a function of the data collected at the well site. A database memory  81  (e.g., a hard drive of a computer; a floppy disc; a CD (compact disk); ZIP drive/cartridge, an electronic chip such as RAM, EPROM, or EEPROM and variations thereof; and magnetic tape) stores data (i.e., plurality of digital feedback signals in reference to well site values) that has been collected over a period of days or years to provide a record  83  that serves as a history of the work performed at various wells. The use of invoice  77 , database memory  81  and record  83  are optionally applicable to all embodiments of the invention. 
     The embodiment of FIG. 7 is similar to those of FIGS. 5 and 6; however, communication link  58   e  includes physically carrying a portable data storage element  78  between vehicle  14  and the well site. Portable data storage element  78  is schematically illustrated to represent the wide variety of forms that element  78  can assume, which include, but are not limited to a memory chip, such as RAM, EPROM, EEPROM and variations thereof; a magnetically recordable tape; a magnetically recordable disc such as a floppy disc; and a CD. The operation of this embodiment can vary, but in one example, transducer feedback is stored on a floppy disc at a disc drive  80 . After the service operation is performed, the floppy disc with the transducer feedback data is then carried to computer  69  that is kept at the well site to serve as a well site identifier. Computer  69  reads and stores the transducer feedback data for later reference. 
     Although the invention is described with reference to a preferred embodiment, it should be appreciated by those skilled in the art that various modifications are well within the scope of the invention. Therefore, the scope of the invention is to be determined by reference to the claims that follow.

Summary:
A well servicing system includes a vehicle that travels to perform a service operation at several well sites while monitoring and recording data that reflects the performance of the operation at each site, and then associates that data with unique well site identifiers. The information is stored and secured against tampering to provide a reliable record of what work was done at each particular well site.