Patent Publication Number: US-9428984-B2

Title: Drive off method from subsea well with pipe retention capability

Description:
FIELD OF THE INVENTION 
     The field of the invention is deep water well drive off procedures or onshore applications where there is an emergency requiring rapid sealing off the well and more specifically a method that allows the pipe in the well to be retained without being dropped as part of sealing off the well. 
     BACKGROUND OF THE INVENTION 
     When deep water rigs experience equipment failure such as loss of power systems there is a need to quickly secure the well and drive the rig off the well. The current procedures when this occurs is to cut and drop the pipe in the hole using the shear rams and then use other blowout preventer components to secure the well before driving off. Many times there is expensive equipment on the pipe or in the well such that the act of dropping the pipe will cause an irretrievable loss of such equipment or at least severe damage if it is even possible to retrieve such equipment if the well is later reactivated. 
     Rather than dropping the pipe the present invention contemplates a method for capturing and anchoring the pipe as an initial step followed by sequential ram operation that later cuts the pipe and closes an annular preventer. In subsea applications when a rig is on location, this allows the pipe above the cut to be removed along with a marine riser so that the rig can be moved off. The pipe catcher can be of a variety of designs that can hold the pipe below the cut as long as needed. Optionally, at a later time if the well is to be reactivated, tests are performed to make sure that the well can be controlled before preventers and rams are reopened, the cut pipe reconnected before the catcher is released. A spear or overshot can grab the top of the pipe above the catcher before the catcher is released. The pipe can then be raised through the marine riser that has been replaced and repaired as needed. Those skilled in the art will better understand the method of the present invention from a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be measured by the appended claims. 
     SUMMARY OF THE INVENTION 
     This invention involves a method of securing pipe (also referred to as a “string of tools”) when driving off a subsea well or sealing off a well in onshore applications where there is an emergency by grabbing the pipe before it is cut. A pipe ram then is closed on the pipe before a shear ram is actuated to cut the pipe. In subsea applications, the top of the pipe may then be raised clear of the blowout preventer within a marine riser. A blind ram and annular preventer can then be closed above the remnant of the pipe being retained by the pipe catcher. The pipe above the cut is removed through the marine riser and the marine riser itself is then disconnected. The rig is then driven off the well. If the well is reactivated the steps are reversed but the well is safely secured before the blowout preventer components are opened. The pipe supported by the catcher is independently supported before the catcher is released and the pipe lifted through the riser. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of running pipe in the hole through a blowout preventer equipped with the pipe catcher; 
         FIG. 2  is the view of  FIG. 1  where a need for a drive off arises and the pipe catcher is activated; 
         FIG. 3  is the view of  FIG. 2  with the pipe rams closed above the pipe catcher; 
         FIG. 4  is the view of  FIG. 3  with the shear ram activated and the pipe above the cut moved above the blowout preventer; 
         FIG. 5  is the view of  FIG. 4  showing the blind ram and annular preventer closed; and 
         FIG. 6  is the view of  FIG. 5  with the marine riser disconnected allowing the rig to move off the well. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a seabed  10  having a cased borehole  12  and a blowout preventer assembly  14  mounted to the cased borehole  12  at the seabed  10 . Mounted below the blowout preventer assembly  14  is a pipe anchor or catcher  16  that can be selectively remotely operated to grab the pipe  18  that extends through the blowout preventer assembly  14  when needed. The catcher  16  can be a series of circumferentially spaced and articulated slips that can selectively move radially and bite into the pipe  18 . The blowout preventer assembly  14  has a pipe ram  20 , followed by a shear ram  22  and then a blind ram  24  followed by an annular preventer  26 . The marine riser is connected above the annular preventer  26  and extends to the rig above the water that is not shown. 
     The catcher  16  can as an alternative to simply biting the outer wall of the pipe with wickers mounted on radially movable members that are remotely hydraulically or otherwise actuated can also place slip elements on tapered ramps so that the weight of the pipe wedges the slips harder against the pipe. This design can be provided in mirror image configuration to prevent sudden rapid sting movement out of the borehole  12 . The main point is that the pipe  18  is physically supported below the blowout preventer assembly  14  before it is cut by the shear ram  22  and that the pipe  18  can later be retrieved should the well be put back in service. 
       FIG. 2  shows the catcher  16  activated to support the pipe  18 .  FIG. 3  shows the pipe ram  20  activated before the shear ram  22  is activated in  FIG. 4 . Segment  30  of the pipe  18  is now formed and moved up by the rig to clear the blowout preventer assembly  14 . Doing this allows the blind ram  24  and the annular preventer  26  to be operated as shown in  FIG. 5 . In  FIG. 6  a marine riser  28  (which may be used in subsea applications) is disconnected allowing rig (not shown) to move off the borehole  12 . The well is now secured. These steps can then be reversed if the borehole  12  is to be put back in service. After the riser  28  is reconnected and the well is re-secured above the blowout preventer assembly  14  a spear or overshot can be run in through the now opened annular preventer  26 , blind ram  24  and shear ram  22  to tag and reconnect the pipe  18  still supported by the catcher  16 . At this point the catcher  16  is released and the pipe  18  raised through the riser  28  for needed repairs and/or retrieval. 
     Those skilled in the art will appreciate that with the method of the present invention it is no longer necessary to drop the pipe for a move off the well in an emergency situation. The pipe can be initially supported and then cut and sealed off with the remnant above the cut being pulled clear of the preventer assembly so that another blind ram and an annular preventer can be closed, The marine riser can then be disconnected allowing the rig to move off the well. 
     The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: