Abstract:
Method for overcoming friction between a coiled tube and the wall of a well by an oil- or gas well, and for enabling application of impact energy to loosen stuck objects in a well. Pressure changes are applied to a liquid flowing in the coiled tube by periodically shutting off the liquid flow at or near the outlet of the coiled tube. Pressure changes, pressure strokes, are applied by means of a valve device comprising a valve body ( 31 ) arranged to seal against a valve seat ( 45 ) and to shut off the liquid flow whenever the flow rate exceeds a predetermined value, and to remain shut until the pressure in the liquid upstream of the valve body ( 31 ) is lower than a predetermined value, and that the valve body ( 31 ) has a slide ( 3 ) arranged thereto, which is arranged to open for a liquid flow past the valve body ( 31 ), to reduce, thereby, the pressure in the liquid upstream of the valve body ( 31 ) whenever the pressure in the liquid upstream of the valve body ( 31 ) exceeds a predetermined value. A damping device in which pistons in the form of collars ( 25, 26 ), channels ( 27, 28 ) and check valves ( 29, 30 ) are moved in annular spaces ( 17, 18, 19 ) filled with liquid, contributes to the valve device being closed long enough for a pressure rise to spread in the liquid in the coiled tube, and being open long enough for full liquid flow to be established before the next shut-off.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to PCT Application No. PCT/NO97/00147 filed Jun. 6, 1997 which claims priority from Norwegian Patent Application No. 962429 filed Jun. 6, 1996. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a method and a device for facilitating the insertion of a coiled tube into an oil or gas well, and for applying of impact energy to stuck objects in an oil or gas well. 
     On inserting a coiled tube into an oil or gas well, in the following referred to as a well, the length of insertion is limited by friction between the coiled tube and the wall of the well. Even if the coiled tube is straightened in a separate straightening apparatus before being introduced into the well, it will adopt the form of a wave or a helix in the well. As the coiled tube is being pushed further and further down the well, and there are more points of contact between the coiled tube and the wall of the well, the total friction increases to a level at which the end of the coiled tube does not proceed further into the well. Further supply of coiled tube only leads to more turns being formed in the helix adopted by the coiled tube. 
     As is quite natural, the problem arises especially in wells of long horizontal stretches, in which weights at the end of the coiled tube will not contribute to stretching out the coiled tube. 
     It is known to mount a remotely controlled, motor driven propulsion device, a well tractor, at the end of the coiled tube to draw the coiled tube into the well. A well tractor is expensive and complex, and operational disturbances may easily occur. Furthermore, it is difficult to construct well tractors which are able to proceed and provide sufficient force in wells of small cross-sections. The cross-section is always smallest at the innermost/downmost part of a well, and long wells may also have the smallest cross-sections. 
     Objects that are stuck in a well, are most commonly loosened by applying impact energy to them. An impact tool which has been arranged to a drill string or a coiled tube, is inserted down to the stuck object and is activated. Known impact tools use a pre-tensioned spring which accelerates a mass, a hammer, which after having achieved appropriate speed, strikes against a stop transferring impact energy to the stuck object. Before each stroke the spring is tensioned by means of a hydraulic mechanism which is activated by a pressure liquid in the drill string or the coiled tube. The spring energy is released when the pre-tensioning has reached a predetermined value. A drawback of this known solution is that very powerful and space-consuming springs have to be provided to achieve the required impact energy. Another known type of impact tool is periodically extended and lifts the drill string or coiled tube which is above the impact tool, and then lets the drill string or coiled tube drop again, so that the mass of the drill string or the coiled tube causes a hammer effect. This type of impact tool has the unfavourable effect that impacts are transferred to the hole drill string or coiled tube in such a way that the couplings and other equipment arranged thereto, may be damaged. 
     The object of the invention is to provide a method and a simple, inexpensive device for facilitating the insertion of a coiled tube into a well, and for applying impact energy to objects which are stuck in a well. The aim is reached through features as indicated in the following description and subsequent claims. 
     According to the invention the aim is reached through applying impact changes or pressure strokes to a liquid flowing through a coiled tube or drill string. A pressure stroke in a coiled tube will contribute to briefly overcoming frictional forces between a coiled tube and the wall of the well, so that the coiled tube may be introduced a little further into the well by each pressure stroke. 
     Pressure strokes may be transferred to a stuck object by the coiled tube or drill string in a known manner being lead into contact with, and possibly attached to, the stuck object. Pressure strokes may also be used to accelerate a mass, a hammer, which in a manner known in itself, strikes against a stop which transfers impact energy to the stuck object. 
     Pressure strokes is achieved, according to the invention, by periodical shut-off of a liquid flow in the coiled tube or drill string, a valve device being located at or near the outlet of the coiled spring. The valve device may advantageously be such, that it is activated once the liquid flow exceeds a predetermined flow rate. Then it is possible to carry out ordinary well operations by a lower and normal flow rate, and if a need for pressure changes arises, the flow rate is increased to activate the valve device. 
     To achieve the best possible effect, the valve device should be such, that after having shut off, it remains shut long enough for the pressure rise to spread in the liquid, and so that after having opened, it remains open long enough to re-establish full flow rate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of a preferred valve device for the periodical shut-off of the liquid flow in a coiled tube or a drill string is described in the following with reference to the accompanying drawings, in which 
     FIG. 1 schematically shows a sectional side view of a part of a valve device in its opened starting position; 
     FIG. 2 shows the valve devised in closed position; 
     FIG. 3 shows the valve device as it is about to open and revert to its starting position; 
     FIG. 4 schematically shows a cross-section of the housing and valve body of the valve device; 
     FIG. 5 schematically shows a cross-section of a damping device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1 reference numeral  1  indicates a valve device which can open and close periodically for a liquid flow. The valve device  1  which is shown in vertical position, comprises an external tubular housing  2 , in which are provided movable parts. 
     Before the invention is described further, it should be mentioned that the shown housing  2  and said movable parts are shown schematically. This provides a clearly set out figure, and the way of working of the invention will be easily understood. In practice, the housing  2  will be divided into several parts which are typically joined up as a housing  2  by means of threaded couplings which are made pressure tight by means of seals. Shoulders and other items which in the figure appear as parts of the housing  2 , may in practice be separate parts which in known manner are secured inside the housing  2 . Further, movable parts in the housing  2  may in the same way be made up of several parts. The division is necessary to enable production of the valve device in machine tools or other production equipment. Division is also necessary to enable mounting of movable parts in the housing  2 . It is common that down-hole tools have an external tubular housing, and that within the housing are arranged both fixed and movable parts. A skilled person will undertake a division suitable for the equipment that he wants to use for the production, and at the same time take into account that the device shall be mountable and dismountable. 
     The housing  2  is further shown without end couplings as such are well known from other down-hole equipment. 
     Inside the housing  2  is arranged an axially displaceable slide  3  which at its lower end is provided externally with three separate annular seals  4 ,  5 ,  6  mentioned from the top downwards. A channel  7  in the slide  3  ends at its bottom end in the lower end surface of the slide  3 , and at the top in a transverse hole in the slide  3 , between the seals  4 ,  5 . 
     The slide  3  is retained in an upper starting position by a pre-tensioned spring  9  which is supported by a first annular shoulder  10  inside the housing  2 , and works on the underside of an external shoulder  11  at the upper end of an axially displaceable cylindrical sleeve  12 , which at its lower end is attached to the slide  3 . The sleeve  12  is at its bottom provided with openings  13 , so that liquid can flow through the sleeve  12 . Below the shoulder  10  there is, inside the housing  2 , a second annular shoulder  14 . The shoulders  10 ,  14  are provided with respectively seal  15  and  16 , which are arranged to form a sliding tightening against the outer surface of the sleeve  12 . The shoulders  10 ,  14  define an upper annular space  17 , a central annular space  18  and a lower annular space  19 . At the central annular space  18  the housing  2  has a larger internal diameter than the adjacent annular spaces  17  and  19 . The housing  2  may have the same internal diameter at the annular space  17  as at the annular space  19 . 
     Below the shoulder  14  there is in the annular space between the housing  2  and the sleeve  12  an annular piston  20  with seals  21 ,  22  which rest tighteningly against the housing  2  and the sleeve  12 , respectively. The underside of the shoulder  14  and the top side of the piston  20  thus define a portion  23  of the annular space between the housing  2  and the sleeve  12 . A channel  24  in the shoulder  14  connects the portion  23  of the annular space with the annular spaces  17 ,  18 ,  19  above the shoulder  14 . 
     The annular spaces  17 ,  18 ,  19  and  23  are filled with hydraulic oil or another liquid. The underside of the piston  20  is exposed to the liquid which is conveyed by the valve device  1 , and ensures that always the same pressure prevails in the liquid in the annular spaces  17 ,  18 ,  19  and  23  as in the rest of the valve device  1 . The annular space  23  with the piston  20  serves as a reservoir and a pressure accumulator for the annular spaces  17 ,  18 ,  19 . 
     The sleeve  12  is externally provided with an upper collar  25  and a lower collar  26  which are both located between the shoulders  10 ,  14 . The stroke length of the sleeve  12  is restricted by the collars  25 ,  26  abutting the shoulders  10 ,  14 . The diameter of the upper collar  25  is adapted to the diameter of the housing  2  at the upper annular space  17 , and the diameter of the lower collar  26  is adapted to the diameter of the housing  2  at the lower annular space  19 , so that there is little clearance between the housing  2  and the collars  25 ,  26 . The distance between the collars  25 ,  26  is such, that they may be brought, separately or simultaneously, into the central annular space  18  by displacing the sleeve  12  axially in the housing  2 . When the collars  25 ,  26  are in the annular space  18 , there will, due to the larger outer diameter of the annular space  18 , be a greater clearance outwards towards the housing  2 , than when the collars  25 ,  26  are in the annular spaces  17  and  19 , respectively. 
     In each of the collars  25 ,  26  has been provided, in the form of a relatively narrow channel  27  and  28 , respectively, or in another manner, a limited cross-section, by which liquid may flow through or past the collars  25 ,  26  when these are moved within the annular space  17  and  19 , respectively. In each of the collars  25 ,  26  is further arranged a check valve  29  and  30 , respectively, of a larger cross-sections than the channels  27 ,  28 . The flow resistance past the collars  25 ,  26  thus become direction dependent when the collars  25 ,  26  are moved in the annular space  17  and the annular space  19 , respectively. In one direction liquid may pass the collar  25  through both channel  27  and check valve  29 , and the flow resistance is small. In the opposite direction liquid may only pass the collar  25  in a restricted cross-section provided by the channel  27  and the clearance between the collar  25  and the housing  2 . When the collar  25  is in the annular space  17 , this provides great flow resistance. This is correspondingly also the case for the collar  26  when it is in the annular space  19 . 
     The check valve  29  in the collar  25  is arranged to open for liquid from the upper side of the collar  25  to its underside. The check valve  30  is arranged opposite, to open for liquid from the underside of the collar  26  to its upper side. If the sleeve  12  is displaced, this entails great flow resistance for the one of the collars  25 ,  26  which is being moved in the direction towards the annular space  18 , and little resistance for the collar  25 ,  26  which is simultaneously being moved in the direction from the annular space  18 . A collar  25 ,  26  which is in the annular space  18 , provides little flow resistance independently of the direction of motion, as liquid may pass outside the collar. If the sleeve  12  is subjected to a downward force which is greater than the force from the spring  9 , the sleeve  12  (and thereby the slide  3 ) will move slowly downwards because of the flow resistance in the channel  27  in the collar  25 . When the collar  25  enters the annular space  18 , the flow resistance is reduced, and the sleeve  12  is quickly moved to a lower end-position, in which the lower collar  26  abuts the shoulder  14 , as the check valve  30  will open for the liquid flow. If the downward force is removed, the spring  9  will seek to bring the sleeve  12  and the slide  3  back into the upper position. The check valve  30  will then close, and the speed of the sleeve  12  is restricted by the flow resistance in the channel  28 . The channels  27 ,  28  serve as flow resistors. The check valve  29  in the upper collar  25  will open for liquid flow, so that there will be little flow resistance when the collar  25  is displaced in the annular space  17 . When the collar  26  enters the annular space  18 , the flow resistance is reduced, and the sleeve  12  is quickly displaced towards the upper end-position. 
     An axially displaceable tubular valve body  31  encloses the lower part of the slide  3 , so that the seals  4 ,  5 ,  6  form a sliding tightening against the inner surface of the valve body  31 . The seals  4 ,  5 ,  6  thus define an upper annular space  32  and a lower annular space  33  between the slide  3  and the valve body  31 , and thereby liquid cannot flow directly through the valve body  31 . In the side wall of the valve body  31 , above the area of the seal  4 , are arranged gates  34 ,  35 , so that liquid flowing into the upper end of the valve body  31 , may flow through the gates  34  and  35  out into an annular space  36  between the valve body  31  and the housing  2 . Further, in the side wall of the valve body  31 , below the area of the seal  4 , are arranged further gates  37 ,  38 , so that liquid may flow from the annular space  36  into the annular space  32  or the annular space  33 , depending on the position of the slide  3  relative to the valve body  31 . A pre-tensioned spring  39 , resting on the shoulder  41  inside the housing  2 , works against the underside of an external shoulder  42  on the valve body  31 , retaining the latter in an upper starting position. 
     Below the gates  37 ,  38 , the valve body  31  is provided with a flow restriction  42 ′ in the form of an increased outer diameter, which limits the cross-section of the annular space  36  at the lower end of the valve body  31 . At the flow restriction  42 ′ the valve body  31  is provided with external ribs  43  slidably resting on the housing  2 , see FIG.  4 . 
     The lower end of the valve body  31  is provided with a seal surface  44  arranged to be capable of tightening against a valve seat  45  in the housing  2 , when the valve body  31  is displaced to a lower position. 
     When both the slide  3  and the valve body  31  are in the starting position, the annular space  33  communicates with the annular space  36  through the gates  37 ,  38 , as is shown in FIG.  1 . 
     Liquid may flow into the upper end of the valve device  1 , down through the sleeve  12 , through the openings  13 , into the valve body  31  at the upper end thereof, through the gates  34 ,  35 , out into the annular space  36 , past the flow restriction  42 ′, further past the seal surface  44  and valve seat  45 , out through the lower part of the valve device  1 . 
     If the flow rate is increased, the flow restriction  42 ′ will cause such a great pressure fall that a resulting force working on the valve body  31 , will overcome the force from the spring  39  and displace the valve body  31  to a lower position, in which its sealing surface  44  seals against the valve seat  45 , see FIG.  2 . 
     The liquid flow through the valve device  1  comes to a stop, which results in a pressure rise in the liquid above the valve seat  45 . An increasing pressure difference from the upper side to the underside of the valve seat  45  is caused, and this effects an increasing downward force which works on the valve body  31  and retains the seal surface  44  against the valve seat  45 . It also effects an increasing downward force working on the slide  3 . When the resulting force against the slide  3  exceeds the force from the spring  9 , the slide  3  is displaced downwards, and the sleeve  12  is brought along. 
     At the beginning the slide  3  will be displaced slowly downwards because of the flow resistance when the collar  25  is displaced downwards in the annular space  17 . After some time, greatly determined by the cross-section of the channel  27  and the length of the annular space  17 , the collar  25  enters the annular space  18 . The sleeve  12  and the slide  3  is then displaced quickly towards a lower position, as already explained. 
     As a consequence of the slide  3  being displaced downwards in the valve body  31 , communication between the annular space  36  and the annular space  32  is established through the channels  37 ,  38 , see FIG.  3 . Liquid may then flow from the annular space  36  to the annular space  32  and further through the bore  8  and the channel  7  out through the lower part of the valve device  1 . 
     The liquid flow established entails a pressure fall on the upper side of the valve seat  45 , and the spring  39  will, after a short while, lift the valve body  31 , so that it does not tighten against the valve seat  45 . 
     Thereby, liquid may flow past the flow restriction  42  as well as through the gates  37 ,  38 , the bore  8  and the channel  7 , and the pressure may be equalized in the valve device  1 . 
     The spring  9  seeks to lift the sleeve  12  and the slide  3  to the upper starting position, but the flow resistance of the collar  26  in the annular space  19  makes this happen slowly. After a while, which is greatly determined by the cross-section of the channel  28  and the length of the annular space  19 , the collar  26  enters the annular space  18 . The flow resistance is reduced as liquid may pass outside the collar  26 , and the spring  9  quickly brings the sleeve  12  and the slide  3  to the upper starting position, see FIG.  1 . 
     The process is periodically repeated as long as a sufficiently great liquid flow is being pressed through the valve device  1 . 
     The collars  25 ,  26  with channels  27 ,  28 , check valves  29 ,  30  and the annular spaces  17 ,  18 ,  19 , filled with liquid, constitute a damping device limiting the speed of the valve body  31  during part of the movement of the valve body  31 . 
     An alternative embodiment of a damping device is described in the following with reference to FIG. 5, in which reference numerals of values exceeding one hundred are used, and so that components having the same or corresponding functions as those of the damping device already described, have been given the same reference numerals plus one hundred. Thus, in FIG. 5, is shown a part of a tubular housing  102 , corresponding to the housing  2 , and in which the upper part of a slide  103 , corresponding to the slide  3 , is shown. The slide  103  is kept in an upper starting position by a pre-tensioned spring  109  which rests on an annular shoulder  110  inside the housing  102  and works against the underside of a plate  111  attached to the slide  103  at the upper end thereof. Liquid may pass the plate  111  through openings  113  in the plate  111 . 
     Below the shoulder  110  there is provided in the housing  102  a concentric fixed sleeve  112 . There is a clearance between the housing  102  and the sleeve  112 , external radial lugs or ribs  112 ′ supporting the sleeve  112  internally in the housing  102 , so that liquid may pass outside the sleeve  112 . 
     The slide  103  runs through the sleeve  112  which is open at its upper end. In the sleeve  112  is arranged a shoulder  114  with a seal  115  which slidingly tightens against the slide  103 . At the lower end of the sleeve  112  is arranged a seal  116  with also tightens slidingly against the slide  103 . The seals  115 ,  116  define an upper annular space  117 , a central annular space  118  and a lower annular space  119  between the slide  103  and the sleeve  112 . At the central annular space  118  the sleeve  112  has a larger internal diameter than at the adjacent annular spaces  117 ,  119 . The sleeve  112  may have the same internal diameter at the annular space  117  as at the annular space  119 . 
     Above the shoulder  114 , in the sleeve  112  there is an annular piston  120  with seals  121 ,  122  slidingly tightening against the sleeve  112  and the slide  103 , respectively. The underside of the piston  120  and the upper side of the shoulder  114  thus define a portion  123  of the annular space between the slide  103  and the sleeve  112 . A channel  124  in the shoulder  114  connects the portion  123  of the annular space to the annular spaces  117 ,  118 ,  119  below the shoulder  114 . The annular spaces  117 ,  118 ,  119  and the annular space portion  123  are filled with hydraulic oil or another liquid. The upper side of the piston  120  is exposed to the liquid conveyed in the valve device  1 , and ensures that always the same pressure prevails in the liquid in the annular spaces  117 ,  118 ,  119  and  123  as in the rest of the valve device. The annular space portion  123  serves as reservoir and pressure accumulator for liquid in the annular spaces  117 ,  118 ,  119 . 
     The slide  103  is externally provided with a fixed upper collar  125  and a fixed lower collar  126  located between the seals  115 ,  116 . The diameter of the upper collar  125  is adapted to the annular space  117 , and the diameter of the lower collar  126  is adapted to the annular space  119 , so that there is little clearance between the sleeve  112  and the collars  125 ,  126 . The distance between the collars  125 ,  126  is such that they may be brought, separately or simultaneously, into the central annular space  118  through axial displacement of the slide  103 . When the collars  125 ,  126  are in the annular space  118 , there will be larger clearance between the sleeve  112  and the collars  125 ,  126  than when the collars  125 ,  126  are in the annular space  117 ,  119 . 
     In each of the collars  125 ,  126  is provided, in the form of a relatively narrow channel  127  and  128 , respectively, a limited cross-section by way of which liquid may flow through or past the collars  125 ,  126  when these are moved in the annular space  117  and  119 , respectively. The channels  127 ,  128  serve as flow restrictors. In each of the collars  125 ,  126  is further provided a check valve  129  and  130 , respectively, of a larger cross-sections than the channels  127 ,  128 . The flow resistance past the collars  125 ,  126  is thus direction dependent when the collars  125 ,  126  are in the annular space  117  and  119 , respectively. When the slide is forced downwards by the pressure created when the valve body  31  closes, the annular spaces  117 ,  118 ,  119  filled with liquid, the collars  125 ,  126  with channels  127 ,  128  and check valves  129 ,  130 , will delay the movement of the slide  103  in a manner corresponding to that explained for the annular spaces  17 ,  18 ,  19  and the collars  25 ,  26  with channels  27 ,  28  and check valves  29 ,  30 .