Abstract:
The present invention concerns a pressure containment device for use in a lubricator. The device includes a housing having a first main bore extending throughout its length a number of transversal bores intersecting the main bore. Pairs of opposing rams are located in the transversal bores to grip and seal around a cable in the main bore.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a pressure control device. More particularly the invention relates to a compact pressure control device for use in a subsea lubricator stack.  
       BACKGROUND OF THE INVENTION  
       [0002]     When developing subsea oil and gas wells there are stringent demands to the control and containment of the well during all aspects of the work, be it drilling, production or later intervention. The needs for control of well pressure have lead to requirements for safe barriers in the well and/or above ground, both during production and during intervention work.  
         [0003]     During the lifetime of the well various types of work may be carried out to enhance production or to measure conditions in the well. Well intervention may be difficult, as existing barriers have to be removed to gain entry into the well. There are in most countries strict rules regarding the size and number of barriers needed to keep control of the well during intervention. To gain access to a living well a blowout preventer, containing a number of valves, must be connected to the well before the well barriers can be opened. In addition, a number of pressure containment devices ensure control over the well during the work.  
         [0004]     One of the methods for gaining entry into a live well is by using a lubricator. This employs a tool attached to the end of a wire or cable and inserted into the well. This equipment includes means whereby grease can be injected under pressure to seal around and lubricate the wire or cable during rising or lowering of the tool, hence the name lubricator.  
         [0005]     Lubricators are in use both on surface and on subsea wells. U.S. Pat. No. 4,993,492 shows an example of a surface lubricator, while U.S. Pat. No. 3,638,722 and International Patent Application no. WO 0125593 shows examples of subsea lubricators. In for example WO 0125593 there is shown a subsea lubricator consisting of the afore-mentioned blowout preventer, called a Lower Intervention Package (LIP), a tool housing (or lubricator pipe), and a pressure control head which includes a grease injector assembly. When lowering a tool into the well using this equipment, the wire or cable is inserted through the pressure control head and the tool attached to the end of the wire. Then the whole assembly is lowered to the seabed and the tool guided into the tool housing while the LIP valves and Christmas tree valves are closed. Then the grease injector is closed around the wire above the tool. The LIP valves and Christmas tree master valve can now be opened so that the tool can be lowered into the well.  
         [0006]     The tool housing must be of a length capable of holding the full length of the tool, and is can be up to 30 meters long. The whole lubricator assembly may be up to 50 meters long.  
         [0007]     To ensure a greater degree of safety, an additional blow out preventer is mounted on top of the tool housing. One common type is a shear/blind ram in combination with one (or two) wireline rams. The shear ram is used to cut the wire or cable in an emergency. The wireline ram(s) are designed to grip and hold the wire and include facilities for grease injection, see for example U.S. Pat. No. 4,938,290. The main disadvantage with these is their large size and weight. Its weight mounted on top of a (up to) 30 meters column, exerts a large bending moment on the lubricator and necessitates stronger (and therefore heavier) tool housing and connectors.  
         [0008]     A stuffing box is also normally included in a lubricator assembly located above the grease injector. The stuffing box is intended to grip and hold the wire or cable in the event of gas leaking past the grease injector. Examples of known stuffing boxes are shown in GB 2,214,954 and U.S. Pat. No. 2,943,682. In U.S. Pat. No. 5,863,022, a stripper/packer including a split bonnet is shown. The packer also serves as a blowout preventer. The packer can be axially activated to achieve a radial sealing, and the function of the packer is similar to a stuffing box. The present invention can be used together with a packer of this type.  
         [0009]     To reduce some of this weight the lubricator described in WO 0125593, uses only the shear/blind ram in conjunction with a second high pressure stuffing box with grease injection, the stuffing box being a replacement for the wireline ram. However, a stuffing box in this position will have well pressure acting on the lower surface of the rubber cylinder, thereby adding to the forces keeping the rubber in compression. There are also higher frictional forces. This makes it difficult to control the stuffing box properly. One consequence has been that it has proved difficult to reopen the stuffing box, forcing the operator to cut the wire and retrieve the whole lubricator to the surface. This can be a costly operation.  
         [0010]     In U.S. Pat. No. 6,394,460, a one-piece ram element block for wireline blowout-preventers is shown. The ram element block is a part of a BOP housing with a generally vertically oriented bore for a wireline. The BOP housing defines a pair of opposed ram element bores wherein linearly movable ram elements are located. Here, high pressure grease is injected into the flow passage between the upper and lower ram elements, thereby effecting a proper wireline seal when the rams are actuated to their closed positions. The ram elements are not located in separate bores and can not be independently controlled.  
         [0011]     An object of the present invention is therefore to produce a pressure containment device in place of the stuffing box which can be positively and exactly balanced and will give a better control over the gripping forces than existing stuffing boxes. As the shear/blind ram function is also built into the device it will eliminate the need for the upper blowout preventer. It is small and compact and will therefore reduce the overall bending moments on the lubricator. This in turn makes it possible to reduce the strength and size of the tool housing and connectors.  
         [0012]     The present invention utilises positively closing and opening rams to grip and hold the cable or wire. It also includes a shear/blind ram so that it will cut the wire or cable in a emergency. Because the unit is located in the pressure control head, e.g. above the tool housing, the internal size can be related to the wire diameter and not, as in the present, the tool diameter.  
       SUMMARY OF THE INVENTION  
       [0013]     The invention thus provides for pressure containment device comprising a main housing, first longitudinal through bore arranged to receive a wire or cable slidingly therethrough, at least two spaced apart transversal through bores intersecting the main bore, each transversal bore carrying a pair of opposing rams  
         [0014]     The bore of the ram is preferably lined with a cylindrical sleeve, enabling several sizes of wire to be used by only changing the sleeves.  
         [0015]     The invention will in the following be explained with a preferred embodiment which is one not limiting example of how the invention may be employed, with reference to the drawings. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  shows a lubricator of prior art type.  
         [0017]      FIG. 2  shows the invention used in the pressure control head  
         [0018]      FIG. 3  shows the grease injector  
         [0019]      FIG. 4  is a detail of the grease injector. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]     In  FIG. 1  is shown a prior art type subsea lubricator  1 . This consists of blowout preventer  2  (LIP). Attached to the LIP is an Emergency Disconnect Package (EQDP)  3 . A lubricator tool housing  4  is connected to the EQDP. The tool housing is in the form of a pipe of a length that will contain a tool before lowering into the well. A pressure control head  5  is connected to the tool housing. The pressure control head includes grease injectors  6 , a line wiper  7 , and a stuffing box (not shown). An upper blowout preventer  8  is located on top of the tool housing  4 .  
         [0021]     When used on a surface well, the EQDP is omitted.  
         [0022]      FIG. 2  shows the pressure control head assembly  20  according to the invention. This consists of, from bottom to top, a connector  21  for coupling to the tool housing, a tool catcher unit  22 , the pressure control device  30  (that will be described in more detail later), first  23  and second  24  grease inlets, a grease return  25  and a combined upper stuffing box and line wiper  26 . The numerals  27 - 29  depicts grease tubes. The upper stuffing box and line wiper  26  can, as an example, be of the type shown in U.S. Pat. No. 5,863,022.  
         [0023]     During intervention work this unit acts as the primary seal barrier preventing hydrocarbons from escaping into the environment. Grease is injected under pressure through inlets  23  and  24  travels up along grease tubes  27 - 29 , sealing and lubricating the wire and returned through grease outlet  25 . The stuffing box is only used when there is a need to clamp and hold the wire securely, as can happen if hydrocarbons leak past the grease tubes. The tool catcher unit holds the tool during raising and lowering from the surface to the seabed.  
         [0024]     In  FIG. 3  is shown the pressure containment device according to the invention. The unit consists of a solid housing  31 , in the form of a rectangular solid metal block. The housing may have coupling parts such as flanges (not shown) at each end for connecting the housing with the rest of the pressure control head assembly. A main bore  32  extends through the length of the housing. When assembled into the pressure control head the main bore is aligned with the bore above and below to give a fluid path through the lubricator.  
         [0025]     Auxiliary bores  33 ,  34 ,  35 ,  36  and  37  extends transversally through the housing  31 . The auxiliary bores intersect the main bore  31 . As shown bores  33 - 37  may be located in the same vertical plane as the axis of main bore  31 . Grease supply bores  38  and  39  also located in the same plane extends from the side but ending in ports (only port  40  is shown) in main bore  31 . As seen on  FIG. 3 , bore  38  is located between bores  33  and  34  while bore  39  is located between bores  35  and  36 .  
         [0026]     As an alternative, the bores can be staggered around the sides of main housing  31 , for example can by bore be located perpendicular to the next bore, or the bores can be distributed stepped from each other.  
         [0027]     In each bore  33 - 36  a pair of opposing rams  41 ,  42  ( FIG. 4 ) are arranged to move towards each other as is well known. Each ram consists of a main cylindrical part  43  with a sliding fit within its bore. A rod  44  attached to cylindrical part  43  is intended to be connected to an actuator (not shown) that can be bolted onto the housing. A cylindrical body  45  of an elastic material such as rubber is fixed to the front of part  43  as shown in  FIG. 4 . Rubber body  45  preferably has an outer diameter so that it will seal against its bore. Rubber body  45  has a front surface  46  with a vertical slot  47 . When the two rams are in their fully closed position, surfaces  46  will abut and seal against each other except for the slots  47  which will define a circular opening for the passage of wire or cable.  
         [0028]     In bore  37  there is located a shear/blind ram for cutting wire or cable as is well known in the art. Bores  38 ,  39  are connected to a pump (not shown) for supplying grease under pressure to bore  31 .  
         [0029]     Main bore  31  has an inner sleeve lining. As can be seen from  FIGS. 3 and 4  the sleeve consists of a number of smaller sleeves. Upper sleeve  51  extends from top of housing  31  to first ram bore  33 . First intermediate sleeve  52  extends between first  33  and second  34  ram bores. Sleeve  52  may be in two parts separated by a gap  54  located in the area of grease injection bore  38 , as shown on  FIG. 4 , or alternatively may have a port oriented in line with grease through bore  38 . Second intermediate sleeve  53  extends between second  34  and third  35  ram bores. Third intermediate sleeve (not shown) between ram bores  35  and  36  is identical to sleeve  52  while fourth intermediate sleeve (not shown) between ram bores  36  and  37  is identical to sleeve  53  and lower sleeve (not shown) is identical to upper sleeve  51 .  
         [0030]     Each sleeve is a sliding fit within main bore  31 , that is, the sleeves are position in bore  31  with a very small clearance. When mounted each sleeve is oriented in the correct angular position and fixed in place, for example with screws or latches. Moreover, each sleeve has an inner diameter corresponding to the outer diameter of the wire or cable in use so that the wire has a small clearance within the sleeves.  
         [0031]     The sleeves have two functions. They are exchangeable and can therefore be sized to fit the size of the wire or cable in use to obtain the desired tight fit. Therefore, when using another size cable or wire, the sleeves can easily and quickly be exchanged with sleeves tailored to the wire size. The sleeves will also prevent the rubber on the rams from extruding into main bore  31  when subjected to pressure when grease in pumped into main bore  31 .  
         [0032]     The rams  33 - 35 , and the shear rams  36  and  37 , are actuated by means of controllable actuating means (not shown). The actuating means are preferably hydraulically or mechanically driven, where the force from the controllable actuating means on the rams is controllable. Moreover, the force from the controllable actuating means can be controlled independently for each of the rams. A detecting device, such as a gas detector, television camera etc, is preferably used to detect the conditions in the well. The controllable actuating means can be controlled based on the detected condition.  
         [0033]     In use, rams  33 - 35  will be actuated to close around the wire or cable to hold it securely. At the same time, grease is injected through grease injection ports  38 ,  39  by means of grease injection means, to seal between wire and sleeve. The grease injection means is controlling the pressure of the injected grease.  
         [0034]     If necessary, shear ram  37  will be activated to shear off wire, allowing the main valve in the LIP and the Christmas tree master valve to be closed.  
         [0035]     The use of rams allow for a precise control of the tightness around the wire. If so desired, the rams can be positioned with slightly reduced pressure to allow the wire to be drawn through the rams while maintaining control over grease pressure. This allows the tool to be moved to a safer location, for example into the tool housing while still maintaining control of the well. The continuous injection of grease under high pressure makes it possible to control and contain the well pressure.  
         [0036]     In an emergency the shear ram will be activated to cut the wire or cable. This will cause the tool to fall into the well and allow the lubricator to be disconnected and removed.