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 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'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 is 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, so as to extend 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 (referred to collectively herein as “rods” or “sucker rods” are usually tightened using a tool known as tongs. Tongs vary in design to suit particular purposes, i.e., tightening tubulars or rods, however, each variety of tongs shares 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 are properly tightened. However, properly tightened joints can be difficult to consistently achieve due to numerous rather uncontrollable factors and widely varying specifications of 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 steel. Some are one-half inch in diameter, and some are over one inch in diameter. With tubing, some have shoulders, and some do not. 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.
Furthermore, variations in the speed that the tongs generate on the sucker rods during each make-up and at different times during each portion of the make-up process can affect whether the make-up is successful and whether a proper torque is generated at the connection point. In addition, these variations in speed can affect the torque readings being received for evaluation and can result in inconclusive or incorrect analysis as to the quality of the rod, the threads on the rod or coupling, and/or the success of the make-up process for that rod.
Another problem with conventional tongs systems is that, while they provide some level of reference for how tight each connection is made up it is typically done by putting a pressure gauge or electronic pressure transducer on the hydraulic supply to the motor on the tongs. Monitoring this pressure gives an inferred reading of how much torque was applied to each rod connection. Substantial variation and error is introduced using this method due to variations in hydraulic performance (oil viscosity, contamination, flow rates, motor wear, cavitation, leakage) and drive train (friction, wear, lubrication, slip). For a given pressure reading of hydraulic supply to the motor, it cannot be definitive that the torque output was correct.
Consequently, a need exists in the art for a system and method for monitoring and controlling the speed generated by the tongs on a rod or other elongated member during a make-up process. In addition, a need exists in the art for a system and method that maximizes the efficiency of the make-up process while also controlling the speed of the tongs during key portions of the make-up process. Furthermore, a need exists in the art for a system and method for measuring the actual torque generated by tongs on sucker rods during the make-up and/or breakout process.