Abstract:
A method for restraining tubular members during well servicing. A first step involves monitoring a velocity of tubular members as they are withdrawn from a well. A second step involves activating a tubing restrainer when the velocity of the tubular members exceeds a predetermined threshold.

Description:
FIELD 
       [0001]    The present application relates to a method and associated apparatus for restraining tubular members during well servicing. 
       BACKGROUND 
       [0002]    During oil or gas well servicing, “snubbing” units are used to insert tubular members into the well being serviced. There are dangers associated with snubbing operations. One danger is that of a “blow out” condition, caused by fluid pressure down hole. Blowout preventers that seal around the tubular members, such as U.S. Pat. No. 3,797,570 (Leutwyler), can be used to protect against such blow out conditions. Blowout preventers are ineffective in dealing with other dangers associated with snubbing operations. 
       SUMMARY 
       [0003]    According to one aspect there is provided a method for restraining tubular members during well servicing. A first step involves monitoring a velocity of tubular members as they are withdrawn from a well. A second step involves activating a tubing restrainer when the velocity of the tubular members exceeds a predetermined threshold. 
         [0004]    The teachings of this method helps avoid problems associated with equipment failure or operator error that a blow out preventer is incapable of addressing. 
         [0005]    According to another aspect there is provided an apparatus for restraining tubular members during well servicing, which includes a body adapted for connection to a wellhead. The body has a passage adapted to permit movement of tubular members through the body, as the tubular members are inserted into or removed from a well. A controller is provided, along with at least one velocity sensor in communication with the controller and adapted to communicate to the controller a velocity of tubular members. A tubing restrainer is in communication with the controller. The tubing restrainer is adapted to restrain the tubular members moving through the passage when activated. The controller activates the tubing restrainer when the velocity of the tubular members, as indicated by the velocity sensor, exceeds a predetermined threshold. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein: 
           [0007]      FIG. 1  is a perspective view of an apparatus for restraining tubular members during well servicing installed on a well head. 
           [0008]      FIG. 2  is a side plan view of a tubing restrainer. 
           [0009]      FIG. 3  is a top plan view of the tubing restrainer shown in  FIG. 2 . 
           [0010]      FIG. 4  is a perspective view of the apparatus for restraining tubular members shown in  FIG. 1  with the speed sensor in an alternative location. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    An apparatus for restraining tubular members during well servicing generally identified by reference numeral  10 , will now be described with reference to  FIGS. 1 through 4 . 
         [0012]    Structure and Relationship of Parts: 
         [0013]    Referring to  FIG. 1 , apparatus  10  includes a body  12  to be connected to a wellhead  14 . Referring to  FIG. 2 , a flange  15  is provided for this purpose. Referring to  FIG. 3 , threaded bolt holes  17  are also provided to attach further equipment. In addition, body  12  has a central passage  16  through body  12 . Referring to  FIG. 1 , passage  16  is adapted to permit movement of tubular members  18  through body  12  as tubular members  18  are inserted into or removed from a well. There is also a controller  20  with a velocity sensor  22  in communication with controller  20  to communicate the velocity of tubular members  18  to controller  20 . Velocity sensor  22  may either be mounted on body  12  as shown in  FIG. 1  or spaced from body  12  as shown in  FIG. 4 . Referring to  FIG. 4 , velocity sensor  22  is positioned within a slip cylinder  23 , which is part of the equipment  38  used to move tubular member  18  up and down.  FIG. 1  shows another arrangement of equipment  38  that may be used, while other types may also be used as is known in the art. An example of a suitable velocity sensor  22  includes a contact wheel positioned against tubular member  18  connected to a rotary encoder. Other suitable sensors will be apparent to those skilled in the art. Referring again to  FIG. 1 , controller  20  is also in communication with a tubing restrainer  24 , which is adapted to restrain tubular members  18  moving through passage  16  when activated. Tubing restrainer  24  is activated by controller  20  when the velocity of tubular members  18  as indicated by velocity sensor  22  exceeds a predetermined threshold. Referring to  FIG. 3 , tubing restrainer  24  has restraining elements  26  in the form of fluid activated pistons  28  with serrated grips  29  positioned radially about passage  16 . Alignment pins  30  are used to align restraining elements  26 . Different sizes of pistons  28  with serrated grips  29  may be provided depending on the size of tubular members  18 . Referring to  FIG. 1 , tubing restrainer  24  is fluid-activated with a fluid source that includes an accumulator  32  connected to a supply of inert gas  34 . An equal pressuring valve  36  is also connected between accumulator  32  and fluid-activated pistons  28  to ensure that each piston  28  receives an equal amount of pressure. 
         [0014]    The accumulator contains pressurized gas, which can be fed into the item to which it is connected, such as a hydraulic or pneumatic system. The energy produced by the release of the gas serves as a motive force in the system to do the work, such as moving the fluid or actuating a valve. 
         [0015]    Operation: 
         [0016]    Referring to  FIGS. 1 through 4 , the use and operation of apparatus  10  as described above will now be given. Referring to  FIG. 1 , body  12  is installed on wellhead  14  with tubular member  18  passing through passage  16  (seen in  FIG. 3 ). Equipment  38  above wellhead  14  and body  12  causes tubular member  18  moves up and down, while velocity sensor  22  monitors its velocity. If the velocity of tubular member  18  goes beyond a predetermined threshold for whatever reason, controller  20  activates tubing restrainer  24 . Supply of inert gas  34  supplies accumulator  32  with inert gas, which is then allowed to flow through equal pressuring valve  36  to activate fluid-activated pistons  28 . Serrated grips  29  on fluid-activated pistons  28  then engage tubular member  18  to stop its motion. 
         [0017]    Advantages: 
         [0018]    Current safety devices merely react to high pressures downhole. The present teachings act to protect workers in situations where tubing is travelling at dangerous speeds for a number of different reasons, such as operator error, slip failure, equipment failure, or a blowout. 
         [0019]    In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. 
         [0020]    It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiment without departing from the spirit and scope defined in the Claims.