Abstract:
A tongs monitor for monitoring the tightening of tubing, casings, and sucker rods of a well is selectively operable in a learning mode and a monitoring mode. A target tightness value is determined during the learning mode. Subsequent tightness values are then compared to the target value. For example, a first connection is tightened in a conventional manner, while its tightness is monitored during the learning mode. If the tightening process went well, then an operator pushes a button that tells the monitor to remember how tight the first connection was tightened. The tightness value of that first joint then becomes the target tightness value for any subsequent joints. As additional joints are tightened, their tightness are monitored and compared to the first one to ensure that all the joints are as good as the first one within an allowable tolerance.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject invention generally pertains to assembling threaded sucker rods and tubulars of oil wells and other wells, and more specifically pertains to a device that monitors the operation of a set of tongs. 
     2. Description of Related Art 
     Oil wells and many other types of wells often comprise a well bore lined with a steel casing. A casing is a string of pipes that are threaded at each end to be interconnected by a series of internally threaded pipe couplings. A lower end of the casing is perforated to allow oil, water, gas, or other targeted fluid to enter the interior of the casing. 
     Disposed within the casing is another string of pipes interconnected by a series of threaded pipe couplings. This internal string of pipes, known as tubing, has of a much smaller diameter than casing. Fluid in the ground passes through the perforations of the casing to enter an annulus between the inner wall of the casing and the outer wall of the tubing. From there, the fluid forces itself through openings in the tubing and then up through the tubing to ground level, provided the fluid is under sufficient pressure. 
     If the natural fluid pressure is insufficient, a reciprocating piston pump is installed at the bottom of the tubing to force the fluid up the tubing. A reciprocating drive at ground level is coupled to operate the pump&#39;s piston by way of a long string of sucker rods that is driven up and down within the interior of the tubing. A string of sucker rods are typically comprised of individual solid rods that are threaded at each end so they can be interconnected by threaded couplings. 
     Since casings, tubing and sucker rods often extend thousands of feet to generally the full depth of the well, it is imperative that their respective coupling connections be properly tightened to avoid costly repair and downtime. Couplings for tubulars (i.e., couplings for tubing and casings), and couplings for sucker rods are usually tightened using tools know as tongs. Tongs vary in design to suit its particular purpose, i.e., tightening tubulars or rods, however, tongs all share a common purpose of torquing one threaded element relative to another. Tongs typically include a hydraulic motor that delivers a torque to a set of jaws that grip the element or elements being tightened. 
     Various control methods have been developed in an attempt to ensure that sucker rods and tubulars are properly tightened. However, properly tightened joints can be difficult to consistently achieve due to numerous rather uncontrollable factors and widely varying specifications of tubulars and sucker rods. For instance, tubing, casings and sucker rods each serve a different purpose, and so they are each designed with different features having different tightening requirements. 
     But even within the same family of parts, numerous variations need to be taken into account. With sucker rods, for example, some have tapered threads, and some have straight threads. Some are made of fiberglass, and some are made of stainless steel. Some are a half-inch in diameter, and some are over an inch in diameter. With tubing, some have shoulders, and some do not. 
     And even for a given part, other conditions may vary. For instance, when tightening the first few sucker rods at the beginning of a day, the hydraulic fluid driving the tongs may be relatively cool and viscous. Later in the day, the hydraulic fluid may warm up, which may cause the tongs to run faster. The hydraulic fluid changing temperature or changing from one set of tongs to another may result in inconsistent tightening of the joints. Even supposedly identical tongs of the same make and model may have different operating characteristics, due to the tongs having varying degrees of wear on their bearings, gears, or seals. Also, the threads of some sucker rods may be more lubricated than others. Some threads may be new, and others may be worn. These are just a few of the many factors that need to be considered when tightening sucker rods and tubulars. 
     It can be very difficult to provide a control method for tongs that takes into consideration all the various factors that affect the process of tightening tubulars and sucker rods. Since many factors cannot be readily quantified by those who specify the torque to which a particular part should be tightened, specifying a particular torque is risky. 
     Consequently, a need exists for a control or monitoring system that adapts to various conditions at a well site where sucker rods, casings, or tubing are being tightened. 
     SUMMARY OF THE INVENTION 
     To provide a monitor or control system that adapts to various conditions at a well site where sucker rods, casing, or tubing is being tightened, it is an object of the invention to provide such a system with a learning mode wherein the system develops a target tightness value based on tightening a particular connection. 
     Another object of some embodiments of the invention is to provide a monitor system that allows an operator to determine when a set of tongs is turned on and off, rather than being determined by an automatic control. 
     Another object is to provide a monitor or control system that includes a time delay as a way of factoring in the effects of wind loading. 
     Yet another object is to provide a monitor or control system that can be used when tightening sucker rods, casing, and tubing. 
     A further object of the invention is to provide a monitor system for threaded tubulars and sucker rods, wherein an operator does not have to enter a predetermined target tightness value. 
     A still further object is to provide a monitor or control system that does not need to know the size, grade, or other design specifications of the tubular or sucker rod being tightened. 
     Another object is to provide a monitor system that does not need to know what type of tongs is being monitored. 
     These and other objects of the invention are provided by a monitor for tongs that includes a learning mode and a monitoring mode. Tightness readings taken during the monitoring mode are compared to a target tightness value established during the learning mode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a system that monitors a set of tongs tightening a string of elongated members. 
     FIG. 2 is a side view of a set of tongs about to tighten two sucker rods into a coupling. 
     FIG. 3 is a cut-away top view of the tongs of FIG.  2 . 
     FIG. 4 in algorithm for a tongs monitor that illustrates a method of tightening a plurality of joints during a monitoring mode of the tongs monitor and comparing their tightness values to that of a target value determined during a learning mode of a tongs monitor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A monitor  10  for monitoring the tightening operation of a set of tongs  12  is shown in FIG.  1 . Monitor  10  includes a learning mode that enables the monitor to adapt to various tongs and operating conditions. After temporarily operating in the learning mode, monitor  10  shifts to a monitoring mode. Readings taken during the monitoring mode are compared to those taken during the learning mode to determine whether any changes occur during the tightening operation. 
     Tongs  12  are schematically illustrated to represent various types of tongs including, but not limited to, those used for tightening sucker rods, tubing or casings. In FIG. 1, tongs  12  are shown used in assembling a string of elongated members  14 , which are schematically illustrated to represent any elongated member with threaded ends for interconnecting members  14  with a series of threaded couplings  16 . Examples of elongated members  14  include, but are not limited to sucker rods, tubing, and casings. Tongs  12  include at least one set of jaws for gripping and rotating one elongated member  14  relative to another, thereby screwing at least one elongated member into an adjacent coupling  16 . A drive unit  18  drives the rotation of the jaws. Drive unit  18  is schematically illustrated to represent various types of drive units including those that can move linearly (e.g., piston/cylinder) or rotationally and can be powered hydraulically, pneumatically or electrically. 
     In a currently preferred embodiment, monitor  10  comprises an electrical circuit  20  that is electrically coupled to an output  21  and four inputs. Electrical circuit  20  is schematically illustrated to represent any circuit adapted to receive a signal through an input and respond through an output. Examples of circuit  20  include, but are not limited to, computers, programmable logic controllers, circuits comprising discrete electrical components, circuits comprising integrated circuits, and various combinations thereof. 
     The inputs of circuit  20 , according to some embodiments of the invention, include a first input  22  electrically coupled to a first sensor  24 , a second input  26  electrically coupled to a second sensor  28 , a learn input  30 , and a tolerance input  32 . However, it should be noted that monitors with fewer inputs or with inputs other than those used in this example are well within the scope of the invention. 
     In response to the rotational action or tightening action of tongs  12 , sensors  24  and  28  provide input signals  34  and  36  respectively. The term, “rotational action” refers to any rotational movement of any element associated with a set of tongs. Examples of such an element include, but are not limited to, gears, jaws, sucker rods, couplings, and tubulars. The term, “tightening action” refers to an effort applied in tightening a threaded connection. Sensors  24  and  28  are schematically illustrated to represent a wide variety of sensors that respond to the rotational or tightening action of tongs  12 . Examples of sensors  24  and  28  include, but are not limited to a pressure sensor (e.g., for sensing hydraulic pressure of a hydraulic motor); strain gage (e.g., for sensing strain as the tongs exert torque) limit switch (e.g., used as a counter for counting passing gear teeth or used in detecting a kickback action of the tongs as it begins tightening a joint); hall effect sensor, proximity switch, or photoelectric eye (e.g., used as a counter for counting passing gear teeth); and a current sensor (e.g., for measuring the power or electrical current delivered to an electric motor that in cases where an electric motor serves as the tongs&#39; drive unit). 
     Learn input  30  and tolerance input  32  are user interface elements that allow a user to affect the operation of monitor  10  in ways that will be explained later. 
     For illustration, monitor  20  will be described with reference to a set of sucker rod tongs  12 ′ used for screwing two sucker rods  38  and  40  into a coupling  42 , as shown in FIGS. 2 and 3. However, it should emphasized that monitor  20  can be readily used with other types of tongs for tightening other types of elongated members. In this example, a hydraulic motor  18 ′ is the drive unit of tongs  12 ′. Motor  18 ′ drives the rotation of various gears of a drive train  44 , which rotates an upper set of jaws  46  relative to a lower set of jaws  48 . Upper jaws  46  are adapted to engage flats  50  on sucker rod  40 , and jaws  48  engage the flats  52  on rod  38 . So, as jaws  46  rotate relative to jaws  48 , upper sucker rod  40  rotates relative to rod  38 , which forces both rods  38  and  40  to tightly screw into coupling  42 . 
     In the example of FIGS. 2 and 3, sensor  24 ′ is a conventional pressure sensor in fluid communication with motor  18 ′ to sense the hydraulic pressure that drives motor  18 ′. The hydraulic pressure increases with the amount of torque exerted by tongs  12 ′, so sensor  24 ′ provides an input signal  34 ′ that reflects that torque. Sensor  28 ′, in this particular example, is a conventional Hall effect sensor that generates a pulse with every gear tooth  54  that rotates past sensor  28 ′. The pulses provide an input signal  36 ′ that monitor  20  counts to obtain an indication of how far jaws  46  rotates. Although either input signal  34 ′ or  36 ′ alone can provide an indication of the tightening action of tongs  12 ′, in a preferred embodiment of the invention, both signals  34 ′ and  36 ′ are used to provide an even more accurate idea of how well a connection is tightened. 
     More specifically, monitor  20  generally follows a control algorithm  56  of FIG.  4 . After starting in block  58 , control block  60  directs monitor  20  to interpret input signals  34 ′ and  36 ′ to determine the tightness of a first connection  62  (FIG.  1 ). Connection  62  may be tightened in any conventional manner, such as performing the following sequenctial steps: manually engaging tongs  12 ′ with sucker rods  38  and  40 , operating a manual trigger to start motor  18 ′, and manually releasing the trigger when tongs  12 ′ appears to have stalled. 
     During the tightening process, monitor  20  calculates a tightness value, Tn. Tn could simply be the final torque or pressure as sensed by sensor  24 ′. However, in a preferred, more accurate method, Tn is determined based on the relative angular rotational displacement of two sucker rods being turned into a common coupling. To disregard any rotation prior to the connection reaching its shoulder point (e.g., the point at which the connection becomes hand-tight or begins to strain), monitor  20  only counts pulses from sensor  28 ′ after the torque, as measured by sensor  24 ′, excedes a predetermined minimum threshold. After reaching the shoulder point, monitor  20  counts gear tooth pulses until the the tongs&#39; trigger is released manually or automatically. 
     In control box  20 , monitor  64  measures a TDn, which is the amount of time that Tn was above a set point or target tightness value. Since such a set point has not yet been determined, the value of the measured time delay is currently meaningless. 
     A setpoint or target tightness value can be set by control block  66 . For example, if the operator is satisfied with how the first connection  62  was just tightened, the operator may activate learn input  30 , which can simply be a push button or some other appropriate input device. Activating learn input  30  places monitor  20  in a learning mode  68  where in block  70  a setpoint SP is assigned the most recent value of Tn, which in this case is the tightness of first connection  62 . Next, in blocks  72  and  74 , a Tmin and a Tmax are defined as the SP plus or minus a TOL tolerance value. The TOL tolerance value specifies an allowable tolerance range for the target tightness value. The TOL value may be+5%, 10% or any other desired tolerance chosen by the user. The user enters the desired TOL value through tolerance input  32 , which may be a dial, keyboard, selector push buttons, etc. In a currently preferred embodiment, tolerance input  32  is a two-position toggle switch, wherein one position the toggle switch sets the tolerance to 5% and the other position sets the tolerance to 10%. 
     Next, control transfers from the learning mode in block  74  to a monitoring mode  76  in block  78 . Here, if Tn is within the allowable range between Tmin and Tmax, and if Tn was within that range for a duration or time delay TDn that excedes a predetermined or user selectable minimum duration TDmin, then block  82  creates an output signal  80  on output  21  to indicate that the connection is acceptable. The actual value of TDmin can be a predetermined value stored in monitor  20 , or may be a user selectable value entered by yet another input of monitor  20 . TDmin may help offset the negative effects of wind acting on the sucker rod and other conditions that might create a momentary spike in torque. 
     If control block  78  determines that Tn is beyond the allowable range of Tmin to Tmax, or if Tn was not within that range a duration of TDmin, then block  84  creates an output signal  80  on output  21  that indicates the connection is unacceptable. The signal for acceptable or unacceptable connections may be visable, such as a red light  86  for unacceptable and a green light  88  for acceptable. The output signal may also be an audible alarm, such as a horn  90 . 
     From blocks  82  or  84 , control shifts to block  92  where “n” is indexed for the next connection  94 . As an operator tightens connection  94 , block  60  senses its tightness value Tn, which will be a number of pulses past the shoulder point. The duration over which Tn was above TDmin is noted in block  64 . By not activating learn input  30 , block  66  transfers control to block  78  of monitoring mode  76 . If Tn is between Tmin and Tmax, and if Tn was within that range for a duration of at least TDmin, then block  82  causes green light  88  to come on momentarily. If, however, Tn is beyond the allowable range of Tmin to Tmax, or if Tn was not within that range a duration of TDmin, then block  84  turns on red light  86 . Afterwards, control returns to block  92  to again index “n” for the next connection  96 . 
     This cycle continues for as long as the operator desires. At any time, however, the operator may choose to reset the target tightness setpoint SP to another Tn value by simply reactivating learn input  30 . 
     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. For example, instead of one red light  86  and one green light  88 , two like sets of red and green lights can be connected to monitor  20 . One red/green set of lights could indicate whether an acceptable amount of torque has been applied to a joint (e.g., as sensed by sensor  24 ′), and the other set of red/green lights could indicate whether the joint has undergone a proper degree of rotation (e.g., as sensed by sensor  28 ′). Two sets of lights for distinguishing between torque and rotation helps in identifying the source of a problem when the tongs fail to properly tighten a joint. Therefore, the scope of the invention is to be determined by reference to the claims that follow.