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FIELD OF THE INVENTION  
         [0001]    This invention relates to oil and gas well drilling as well as to completion and production of the same, and more particularly to pressure containment for using cools in under balanced drilling and snubbing operations.  
         BACKGROUND OF THE INVENTION  
         [0002]    In the drilling, completion, and production of oil and gas wells, it is common practice to work with formation pressure. There are various stages and conditions of an oil or gas well during which access to the inside of the well is required. In underbalanced drilling, drilling occurs without restricting pressure from the well bore. Completion is a stage during which the well is perforated by shooting holes in the casing, while well servicing occurs during workover operations. In all of these cases, when drilling, completion or workover operations are performed, it is necessary in order to prevent hydrocarbons from leaking to atmosphere, to provide a containment device to contain gas within the well bore. This containment is important at all times but more particularly during snubbing operations when tool strings or tubing is jacked into and out of the well while the well is live. During snubbing, a stripping device is required for containment of the hydrocarbons, and the well bore pressure. Some standard containment approaches include a Blow Out Preventer (BOP) or an annular preventer, which comprise a piston which squeezes rubber to seal mechanically and may sit above a BOP. These systems may also be rotating pressure control systems. The standard approaches have limits with respect to the size or diameter of tool string or tubing that can be stripped in and out of the containment device for access to the well bore. Often if tool strings or tubing are of widely differing diameters, multiple annular containment spools are required, increasing costs incurred by the purchase and maintenance of multiple devices, and delays and lost production time due to the need to fit a new spool or containment device which fits the new tool string or tubing. This is particularly the case when switching between different tool strings and tubing used in drilling and work over operations. Due to the limits of the ranges of tool string and tubing shaft sizes compatible with standard devices, safety also becomes an issue when the size of a tool string or tubing is not within the safe range of shaft sizes compatible with the containment device. Size of the containment device itself is also an issue as it is more desirable to have a closely configured hydraulic jacking system.  
           [0003]    It would be desirable in drilling and snubbing operations for there to a be a single stripping and containment device which has a wide range of tool string or tubing size compatibility. This is desirable for safety reasons and for cost efficiency. It is also desirable to find a single device which can be used for well bore pressure containment during underbalanced drilling, completion and work over operations. It is also more desirable to implement a smaller device than standard existing ones.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention provides a single stripping and containment device which has a wide range of tool string and tubing shaft size compatibility, can be used for well bore pressure containment during underbalanced drilling, completion and work over operations, and can be integrated into rotating pressure control systems, and moreover is in general smaller in size than existing pressure control systems.  
           [0005]    According to a first broad aspect the invention provides an apparatus for use in containing well bore pressure, comprising: a spool having a wall defining a passage therethrough for receiving a shaft; a seal disposed within said passage and having a flexible wall having first and second opposed surfaces, the first surface defining an aperture for receiving the shaft, the flexible wall being capable of flexing away from the spool wall to sealably engage the shaft in response to a force applied thereto, the second surface of the seal wall being accessible for receiving a controllable force directed away from the spool wall and towards said aperture for urging the seal wall inwardly of said passage.  
           [0006]    According to a second broad aspect the invention provides an apparatus according to claim 19 further comprising: a rigid annular piston sealably receivable within said spool; an outer spool having an outer spool wall extending outside and about the spool; a plurality of cylindrical guiding fingers; an outer rigid annular piston sealably receivable inside of the outer spool and extending sealably about the spool and capable of translating in a direction along the axis of the spool; wherein an outer surface of the wall of the bladder, an inner surface of the outer spool wall, and a first end surface of the rigid annular piston define a chamber adapted for a fluid for use in exerting the controllable force, wherein the bladder is sealably fixed at one end to an inner surface of the spool, and is sealably secured to the first end surface of the rigid annular piston at the other end of the bladder, wherein the rigid annular piston is capable of translating in a direction along an axis of the spool in response to variations in a pressure of a fluid in the chamber, wherein the spool comprises an upper portion a lower portion with a gap therebetween, wherein an axis of each cylindrical guiding finger lies in a plane passing through an axis of the spool, and wherein the plurality of cylindrical guiding fingers are fixed at respective first ends to the inner surface of the outer spool wall, and are secured to the outer annular piston at respective second ends, and wherein the plurality of cylindrical guiding fingers are adapted to be controllably deformed to forceably engage the outer surface of the wall of the bladder at portions thereof located at the gap in the spool using pressure exerted on the outer annular piston in a direction toward the first ends of the plurality of cylindrical fingers, thereby providing centering forces to the outer surface of the wall of the bladder.  
           [0007]    According to a third broad aspect the invention provides a method of operating a seal for sealing to a shaft in a well bore, comprising the steps of providing: a seal having a flexible wall, said seal wall having first and second opposed surfaces, the first surface defining an aperture for receiving said shaft, and applying a force to said second surface to urge said seal wall against said shaft.  
           [0008]    Other aspects and features of the present invention will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The invention will now be described in greater detail with reference to the accompanying diagrams, in which:  
         [0010]    [0010]FIG. 1A is a side view of a well bore pressure containment device according to the invention;  
         [0011]    [0011]FIG. 1B is a side view of a well bore pressure containment device according to the invention rotated 90 degrees around the vertical axis relative to the view shown in FIG. 1A;  
         [0012]    [0012]FIG. 1C is a top view of a well bore pressure containment device according to the invention;  
         [0013]    [0013]FIG. 2 is an isometric view of the well bore pressure containment device of FIGS. 1A, 1B, and  1 C in use, with the containment device shown sectioned along its length to expose its interior;  
         [0014]    [0014]FIG. 3 is an isometric view of the well bore pressure containment device of FIGS. 1A, 1B, and  1 C in an unpressurized state, with the containment device shown sectioned along its length to expose its interior;  
         [0015]    [0015]FIG. 4A is a side view of an alternate well bore pressure containment device incorporating bladder guiding polyurethane fingers;  
         [0016]    [0016]FIG. 4B is a side view of the alternate well bore pressure containment device according to the invention rotated 90 degrees around the vertical axis relative to the view shown in FIG. 4A; and  
         [0017]    [0017]FIG. 4C is a top view of the alternate well bore pressure containment device according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    Referring to FIGS. 1A, 1B,  1 C, and  3 , a well bore pressure containment device constructed according to the invention is described in terms of its structure. The well bore pressure containment device, generally indicated by  10 , comprises an annular pressure spool  100  and a bladder  106 . The spool  100  is an annular metal spool which consists of an annular flange  102  at one end of a hollow cylinder comprising an annular spool wall  104 . Inside the annular spool  100  and extending concentric therewith is located the bladder  106  which is constructed as a hollow cylinder and may be made of rubber, polyurethane, or other appropriate flexible material. The bladder  106  has an outer radius smaller than that of the annular spool wall  104 . An end of the bladder  106  is bonded to the flange end of the annular spool  100  and the opposite end of the bladder  106  is free floating. The floating end is secured to an annular sliding piston  108  which floats freely within the annular spool  100 . The piston has an annular seal  110  which serves to seal the piston against the inner surface of the annular spool wall  104 . Two holes are located in the annular spool wall  104  at positions along its height which overlap with the bladder, one hole serving as an inlet valve  112  and the other serving as an outlet valve  114 . The annular flange  102  has an aperture  117  for passage of a tool string or tubing therethrough. In the preferred embodiment, the annular flange  102  has holes located exterior to the annular spool wall  104  for mounting the annular spool  100  to other equipment which in the preferred embodiment of the invention is the rig BOP which serves as a backup system for pressure containment.  
         [0019]    Referring now to FIG. 2 the operation of the pressure containment device  10  shown in FIGS. 1A, 1B,  1 C, and  3 , is described. The device may be pre-set to withstand different pressure demands for different jobs, and may accommodate tool strings and tubing of differing diameters. FIG. 2 depicts the pressure containment device  10  with a tool string  118  present. In order to maintain pressure and contain the hydrocarbons a seal must be made between the inner surface of the bladder and the outer surface of the tool string. By pumping and releasing pressure respectively through the inlet valve  112  and the outlet valve  114  respectively into and out of the space interstitial of the bladder and the annular spool wall using a special hydraulic or pneumatic valving system, the bladder  104  may be made to expand or contract to varying degrees between a cylindrical tube-like shape and a roughly hyperbolic shape. The bladder  104  is able to freely deform in this manner due to one of its ends being a floating end secured to the floating piston  108  which is free to move along the axis of the annular spool. In this way pumping and releasing fluid pressure through the valves enables the diameter of the inner surface of the bladder to constrict at the bladder&#39;s apex (halfway along its length) to the diameter of the tool string  118  passing through the device. The pressure and may be pre-set to the required pressure to maintain a sufficient seal for the particular operation. In some embodiments, additional guiding elements are provided to ensure the bladder concentrically engages the tool string in a symmetric manner.  
         [0020]    Referring to FIGS. 4A, 4B, and  4 C an alternative embodiment of the pressure containment device  10  utilizing polyurethane fingers to help guide the bladder  106  and ensure that it concentrically engages the tool string passing therethrough, is described. To house the system by which the guide fingers are provided, the alternate embodiment has an outer spool  200  which is an annular metal spool concentric with the annular spool  100  having a diameter larger than that of the annular spool  100 . One end of the outer spool  200  is fixed to the flange  102 , the other end is fixed to the annular spool  100  via an annular member  220 . The flange  102  is modified in this embodiment in that it is of a larger diameter. The annular spool  100  is modified in this embodiment to consist of two portions with a gap between them. An upper portion  100   a  of the annular spool  100  is fixed to the outer spool  200  via the annular member  220 , and engages the annular sliding piston  108  as described in association with FIGS. 1A, 1B,  1 C,  2 , and  3 . A lower portion of the annular spool  100   b  is fixed to the flange  102 . An outer fixed piston  202  is fixed to the outer surface of the annular spool wall  104  of the lower portion  100   b  of the annular spool  100  and the inner surface of an outer spool wall  204  of the outer spool  200 . An outer sliding piston  208 , floats freely between the outer surface of the annular spool wall  104  of the upper portion  100   a  of the annular spool  100 , and the inner surface of the outer spool wall  204 . The outer sliding piston  208  has an inner annular seal  210   a  which serves to seal the outer sliding piston  208  against the outer surface of the annular spool wall  104 , and an outer seal  210   b  which serves to seal the outer sliding piston  208  against the inner surface of the outer spool wall  204 . Twelve cylindrical polyurethane fingers  206  have respective first ends bonded to the outer fixed piston  202  at evenly spaced angular positions. The second ends of the polyurethane fingers  206  are secured to the outer sliding piston  208  also at evenly spaced angular positions. The gap between the upper and lower portions  100   a,    100   b  of the annular spool  100  exposes the bladder  106  to a first hydraulic chamber  118  in which the polyurethane fingers  206  are situated. Two holes are formed in the outer spool wall  204 , one serving as the outlet valve  214  and the other serving as the inlet valve  212  to the first hydraulic chamber  118 . The outer sliding piston  208 , the upper portion  100   a  of the annular spool  100 , the annular member  220 , and the outer spool  200  define a second hydraulic chamber  216 . Two apertures  218  and  220  are situated in the outer spool wall  204 , one serving as a second hydraulic chamber outlet valve  220  and the other serving as a second hydraulic chamber inlet valve  218  to the second hydraulic chamber  216 . In some embodiments a stop is located at a lower edge of the upper portion  100   b  of the annular spool  100  to prevent either or both of the annular sliding piston  108  and the outer sliding piston  208  from disengaging from the upper portion  100   b  of the annular spool  100 .  
         [0021]    The pressure containment device  10  functions in a similar manner to that described in association with FIGS. 1A, 1B,  1 C,  2 , and  3 . By pumping and releasing pressure respectively through the inlet valve  212  and the outlet valve  214  respectively into and out of the first hydraulic chamber, the bladder  106  may be made to expand or contract to varying degrees between a cylindrical tube-like shape and a roughly hyperbolic shape. The bladder  106  is able to freely deform in this manner due to one of its ends being a floating end secured to the floating piston  108  which is free to move along the axis of the annular spool within the upper portion  100   a  of the annular spool. To assist in guiding the annular spool into symmetric and concentric engagement with a tool string or tube passing therethrough, polyurethane fingers  206  are made to forceably engage the outer surface of the bladder  106  by pumping and releasing pressure respectively through the second hydraulic chamber inlet valve  218  and the second hydraulic chamber outlet valve  220  respectively into and out of the second hydraulic chamber  216 , to move the outer sliding piston  208  towards or away from the outer fixed piston  202 . The movement of the outer sliding piston  208  in relation to the position of the outer fixed piston  202  causes the polyurethane fingers to bend or straighten to varying degrees between a bow-shaped cylindrical shape and a roughly straight cylindrical shape. The polyurethane fingers  206  are biased towards bending towards the axis of the annular pressure spool  100  by having in their relaxed state a slight bend inwards towards said axis. Each of the axes of the polyurethane fingers during their entire range of movement lies in a plane passing through the axis of the annular spool  100 . By pumping and releasing fluid pressure through the second hydraulic chamber input and output valves, the polyurethane fingers engage and apply a force to the outer surface of the bladder  106 , thereby keeping it engaged to the tool or tubing in a symmetric and concentric manner. The pressure may be pre-set to that required to maintain a sufficient force against the bladder  106 . In a preferred embodiment the control of the hydraulic pressures in the first and second hydraulic chambers  118  and  216  is coordinated so that the proper pressure is applied to the bladder  106  while at the same time the outer piston  208  is movable in the desired direction.  
         [0022]    In a preferred embodiment, the pressure containment device  10  sits above a BOP, and is mounted thereon using bolts passing through holes  116  of the flange  102  of the annular spool  100 , and can be integrated into a rotating pressure control system. The pressure containment device  10  is flexible with respect to the size or diameter of tool string or tubing that can be stripped in and out of the pressure containment device  10  for access to the well bore. Tool strings and tubing of widely differing diameters may be accommodated by the pressure containment device  10  avoiding the increased costs incurred by the purchase and maintenance of multiple standard containment devices, and delays and lost production time due to the need to fit new standard spools or containment devices which fit each new tool string or tubing. This pressure containment device  10 , due to its flexibility may be used in drilling and work over operations. Due to the flexibility of the pressure containment device, safety is increased since a wider range of sizes of tubing and tool strings are within the safe range of sizes compatible with the pressure containment device  10 . Due to its design, the pressure containment device  10  is also smaller than standard devices and therefor lends itself to closely configured hydraulic jacking systems.  
         [0023]    Although the preferred embodiments have been described as using a fluid to flex the bladder against the tool string or tubing passing therethrough, it should be understood that other mechanisms for applying a controllable force against the bladder, directed away from the spool wall and towards a tool passing therethrough, are possible. In fact, mechanical pressure exerted by rigid or semi-rigid fingers similar those described in association with the alternate embodiment could be used, or other mechanical members.  
         [0024]    What has been described is merely illustrative of the application of the principles of the invention. Other arrangements and methods can be implemented by those skilled in the art without departing from the spirit and scope of the present invention.

Summary:
A well bore pressure containment device is provided. Operating as a single stripping and containment device compatible with a wide range of tool string and tubing sizes, the containment device may be integrated with rotating pressure control systems, and be used during completion and work over operations. The containment device has a spool, and a flexible bladder extending about the interior of the spool. The bladder may be controllably deformed to seal against a tool string passing through the device using an inwardly directed pressure, which preferably is exerted by a fluid in the interstitial space between the spool and the bladder.