Patent Publication Number: US-7707913-B2

Title: Method of disconnecting a pipe length

Description:
CROSS-REFERENCE TO PENDING APPLICATIONS 
     This application is based on PCT Patent Application No. NO02004/000380, filed on Dec. 10, 2004, which was based on Norwegian Patent Application No. 20035508, filed on Dec. 11, 2003. 
     This invention relates to a power tong. More particularly, it concerns a power tong with no radial opening, the power tong being particularly suitable for use in making up pipes during drilling in the ground as it is known from the recovery of petroleum, for example. The tong is releasably connected to a chassis and is arranged to be lifted up from a drill floor to a level higher up in order to break out a pipe from a pipe string. The invention also includes a method for the use of the power tong. 
     From the recovery of petroleum, among other things, it is known to use power tongs for making up and breaking out pipe lengths into or from a pipe string in connection with a drilling rig. It is common to use mechanized pipe tongs, which are moved, after a pipe connection has been screwed or unscrewed, essentially horizontally away from the pipe string, the pipe string being at the drilling center of the drilling rig. 
     Such a method presupposes that the power tong must be provided with a radial opening, whereby the power tong can be moved in the horizontal plane as it is removed from the pipe string. 
     It is obvious that a radial opening of this kind in a power tong that must be able to rotate about the longitudinal axis of the pipe, complicates the structure of the power tong. The opening weakens, to a substantial degree, the structure encircling the pipe. A consequence of this is that the construction will have to be dimensioned up in order to be able to absorb the relatively great forces which are transferred between the power tong and the pipe string. A relatively complicated mechanical device has to be applied to close the radial opening when the power tong is in use, and also in many cases in order to transfer forces between the side portions of the opening. 
     It is also known to use power tongs without a radial opening for work of this kind. Power tongs having no radial opening can be formed with a complete non-segmented drive ring which encircles the pipe string. When a power tong of this kind is not in use, it can be lowered down towards the slips and rotary table of the drilling device. 
     However, the fact that the power tong encircles the pipe string, may be a drawback if the pipe string gets stuck in the borehole immediately after a new pipe length has been connected in the pipe string. In some cases, in which it is not possible to pull the pipe string sufficiently up for the newly made up pipe length to be broken out, it has been necessary to cut the pipe string to be able to remove the power tong. 
     The invention has as its object to remedy or reduce at least one of the drawbacks of the prior art. 
     The object is realized according to the invention through the features specified in the description below and in the following claims. 
     A power tong according to the invention is provided with a non-divided drive ring encircling the vertical central axis of the drilling center and pipe string. The drive ring has been given a relatively large internal diameter in order for, for example, a drilling tool of a considerably larger external diameter than the pipe string to be moved through the power tong. 
     The drive ring is rotatably supported in the housing of the power tong and is preferably driven, in a manner known in itself, by means of at least one hydraulic motor. 
     In the drive ring there is arranged at least one pressure-fluid-driven radially movable clamping device (jaw). Most preferably, a number of jaws are distributed round the pipe in two groups. Each jaw group is releasably connected to the drive ring, each jaw group being arranged to be lifted out of the drive ring, for example in connection with maintenance or when a larger object is to be moved through the power tong. 
     At their portions bearing on the pipe, the jaws are preferably provided with replaceable grippers. Sets of grippers can be produced in different dimensions and designs, so that they can be adapted for the relevant pipe dimension and the desired engagement geometry between the gripper and the pipe string. 
     Most preferably, the power tong is formed by an upper assembly tong in an assembly with an underlying back-up tong. The assembly is connected by means of vertical guide columns to a horizontally movable chassis to allow the assembly to be moved away from the drilling center. 
     The power tong and the back-up tong are relatively movable in height in order to compensate for the relative axial movement of the pipes during make-up and break-out, and in order to allow work to be carried out between the tongs. It is advantageous that between the power tong and the back-up tong weight-compensating cylinders are arranged for load to be absorbed during make-up of sensitive threads. 
     The vertical guide columns are releasably connected to the chassis. Should a situation arise, in which a pipe length will have to be disconnected from the pipe string, and in which the closest accessible connection point is located at a level higher up than the normal work area of the power tong, the guide columns can be disconnected from the chassis and be locked into the back-up tong, for example. The assembly of a power tong, back-up tong and guide columns is then lifted up to the connection point of the pipe length, for example by means of so-called tugger winches. 
     During a break-out operation, in which the back-up tong clamps the lower sleeve portion of the connection point and the power tong clamps an upper sleeve portion, the guide columns absorb the torque arising between the tongs. 
     After the pipe length has been disconnected from the pipe string, the assembly may be removed, the pipe string may be released according to methods known in themselves. 
     The back-up tong may with advantage be provided with a traversing lifting device on its underside, for example in order to lift out the slips and similar. 
     Relative to the prior art, the time that it takes to make up and break out pipes can be reduced, as the time for moving the power tong to and from the drilling center will no longer be needed. The relatively simple construction of the power tong entails improved reliability and lower maintenance expenses. 
     All spinning and power operations are carried out by means of the tong and, thus, it is not necessary to use a separate so-called spinning unit. 
     The construction is compact and builds relatively little longitudinally of the pipe string. It is suitable for integrating cleaning and lubricating equipment for the threads of the pipe lengths. 
    
    
     
       In what follows will be described a non-limiting example of a preferred embodiment and method which are visualized in the accompanying drawings, in which: 
         FIG. 1  shows in perspective an assembly of a power tong, in which a jaw group has been removed for illustrative reasons, and a back-up tong on a horizontally movable chassis, the assembly having been moved into its upper position; 
         FIG. 2  shows, on a larger scale, a back-up tong from which an upper cover has been removed; 
         FIG. 3  shows the same as  FIG. 1 , but here the assembly is in its lower position; and 
         FIG. 4  shows the assembly during the break-out of a pipe length from the pipe string, the break-out point being at a level higher up than the normal work area of the power tong. 
     
    
    
     In the drawings the reference numeral  1  identifies an assembly of a power tong  2  and a back-up tong  4  located on a drilling rig  6 , coaxially to the drilling center  8  of the drilling rig  6 . The assembly  1  is connected, vertically movable, to two diametrically opposite guide columns  10  relative to the drilling center  8 . 
     The guide columns  10  are releasably connected to a chassis  12 , which is horizontally movable by means of wheels  14  and hydraulic motors, not shown, on rails  16  connected to the drilling rig  6 . 
     In its active position the assembly  1  is thus just above the slips  18  of the drilling rig  6 , a pipe string  20  extending up through the slips  18  and further up through the assembly  1 . The pipe string  20  is formed by pipe lengths  22  screwed together. 
     The power tong  2  includes a power tong housing  24  which is provided with a through guide  26  corresponding to the guide columns  10 , and a supported, undivided drive ring  30 . 
     The drive ring  30  is rotated about the drilling center  8  by means of two hydraulic motors  34 . 
     In the drive ring  30  and co-rotating therewith, are arranged two crescent-shaped jaw groups  36 , only one of which is illustrated in the drawings for illustrative reasons. 
     Each jaw group  36  is typically provided with three hydraulically movable jaws  38  distributed about the well center  8 . 
     The back-up tong  4 , see  FIG. 2 , comprises a back-up tong housing  40  with guides  42  corresponding to the guide columns  10 , and a supporting ring  44  for two not shown jaw groups. At the guides  42  are arranged cogwheels  46  engaging the respective pitch racks  48  of the guide columns  10 . 
     The cogwheels  46  are each driven by a respective hydraulic motor  50  via gears  52 , and the guide columns  10  are arranged to be locked into the back-up tong housing  40  by means of corresponding locking mandrels  54  movable in the back-up tong housing  40 . 
     A pair of hydraulic cylinders  56  are arranged to adjust the vertical distance between the power tong  2  and the back-up tong  4 . 
     When a pipe length  22  is to be joined to the pipe string  20 , the assembly  1  is moved vertically on the guide columns  10  by means of the hydraulic motors  50 , gears  52 , cogwheels  46  and pitch racks  48  until, in a known manner, the back-up tong  4  corresponds with the upper sleeve portion, not shown, of the pipe string  20 . The vertical distance between the back-up tong  4  and the power tong  2  is adjusted in such a way that the jaw groups  36  correspond with the lower sleeve portion of the pipe length  22 . 
     The jaws  38  are moved towards the pipe length  22  by means of pressurized fluid, thereby gripping their respective pipe portions as the hydraulic motors  34  rotate the drive ring  30  and the jaw groups  36  about the drilling center  8 . 
     The power tong  2  is moved down towards the back-up tong  4  as the make-up proceeds. 
     After the desired tightening torque has been achieved, the rotation of the drive ring  30  is stopped and the jaws  38  are withdrawn. 
     The assembly  1  is thereby disengaged from the pipe string  20  and may, if desired, be moved into its lower position, see  FIG. 3 . 
     When a pipe length  22  is to be broken out of the pipe string  20 , the operation is carried out in reverse order in a manner corresponding to that described above. 
     If drilling tools or other objects having larger external diameters than the pipe string  20 , are to be moved through the assembly  1 , the jaw groups  36  can relatively easily be lifted out of the drive ring  30 . 
     Should the pipe string  20  get stuck, so that the upper pipe length  22  will have to be unscrewed from the pipe string  20  while the nearest accessible pipe joint is at a level higher up than the normal work area of the assembly  1 , the guide columns  10  are disconnected from the chassis  12  and locked into the back-up tong  4  by means of the locking mandrels  54 . The assembly  1  of a power tong  2 , back-up tong  4  and guide columns  10  is then lifted up to the connecting point  58  of the pipe length  20 , for example by means of not shown tugger winches and lifting lugs  60 . 
     During the break-out operation, in which the back-up tong  4  clamps the lower sleeve portion of the connecting point  58  and the power tong  2  clamps the upper sleeve portion of the connecting point  58 , the guide columns  10  absorb the torque that arises between the tongs  2 ,  4 . It is advantageous that the guide columns  10  are positioned on diametrically opposite sides of the well center  8  in order to absorb the torque in the best possible way. 
     When the pipe length  22  is unscrewed from the pipe string  20 , the assembly  1  may be removed from the drilling center  8 .