Patent Publication Number: US-7913770-B2

Title: Controlled pressure equalization of atmospheric chambers

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to downhole tools which incorporate one or more atmospheric chambers. 
     2. Description of the Related Art 
     A number of downhole tools rely upon the hydrostatic pressure of the wellbore in order to be actuated. These downhole tools include packers and locks that are set using hydrostatic pressure. Typically, such tools incorporate at least one collapsible atmospheric chamber into their setting mechanism. When the tool is constructed at the surface prior to being run into the well, the atmospheric chamber is usually enclosed and sealed off so that it contains an amount of fluid (usually air) at atmospheric pressure. 
     During setting of the tool, the atmospheric chamber is collapsed due to a pressure differential between the atmospheric chamber and surrounding hydrostatic and applied pressure within the wellbore. Following collapse, the atmospheric chamber continues to retain a small amount of fluid. A significant pressure differential between the atmospheric chamber and surrounding pressure is desirable to ensure positive actuation of the tool. The inventors have recognized, however, following actuation of the tool, a significant pressure differential can act to reduce the rating of the tool. 
     SUMMARY OF THE INVENTION 
     The invention provides methods and devices for equalizing an atmospheric chamber within a well tool in a controlled manner following the operation of setting the well tool. In a preferred embodiment, the well tool comprises a packer setting tool. In a currently preferred embodiment, a packer setting tool having a setting mechanism with an atmospheric chamber is provided with an equalization assembly to permit the pressure differential between the atmospheric chamber and the surrounding annulus to be substantially equalized. The equalization assembly includes a fluid passage that provides fluid communication between the atmospheric chamber and a setting chamber that is in fluid communication with the surrounding annulus. Preferably, entry of fluid into the setting chamber from the annulus is selectively blocked by a frangible rupture member. Preferably also, the fluid passage is provided with a fluid restrictor. One exemplary fluid restrictor is a porous plug member which is disposed within the fluid passage. In a preferred embodiment, the porous plug member is substantially formed of a sintered metal which provides interstices through which fluid may be communicated by seepage. During actuation of the setting tool, the rupture member is ruptured to permit fluid communication into the setting chamber from the surrounding annulus. This results in rapid compression of the atmospheric chamber. Thereafter fluid pressure between the atmospheric chamber and the surrounding annulus is substantially equalized in a controlled manner as fluid is communicated into the atmospheric chamber via the fluid passage. The equalization is controlled due to the flow restriction provided by the fluid restrictor. Equalization is delayed and occurs over an extended length of time, so that the setting process is not disrupted by rapid pressure equalization. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages and further aspects of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing and wherein: 
         FIG. 1  is a side, cross-sectional view of an exemplary unset packer device and packer setting assembly constructed in accordance with the present invention. 
         FIG. 2  is a side, cross-sectional view of the packer device and setting assembly, now with the packer device in a set condition. 
         FIG. 3  is a side, one-quarter cross-sectional view of the atmospheric pressure chamber portion of the setting tool of  FIGS. 1 and 2 . 
         FIG. 4  is a side, one-quarter cross-sectional view of the atmospheric pressure chamber portion of the setting tool shown in  FIG. 3  now in a collapsed condition. 
         FIG. 5  depicts an exemplary porous plug member in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates an exemplary packer device  10  and affixed hydraulic packer setting tool  12 . Those of skill in the art will understand that the packer device  10  is used to form a fluid seal within a wellbore, the inner surface of which is indicated at  11 , and that the setting tool  12  is used to set the packer within the wellbore  11 . An annulus  13  is defined between the wellbore  13  and the packer device  10  and setting tool  12 . As the annulus  13  contains wellbore fluids such as drilling mud and hydrocarbons, it is under hydrostatic pressure. 
     The packer device  10  includes a central packer mandrel  14  which defines a central axial bore  16 . A compression-set packer element  18  radially surrounds the packer mandrel  14 . The packer element  18  is preferably formed of an elastomeric material, although other suitable materials may be used. A setting collar  20  radially surrounds the packer mandrel  14  and abuts the packer element  18 . The packer device  10  is affixed by threaded connection  22  to the setting tool  12 . 
     The setting tool  12  includes a setting tool mandrel  24  and a radially-surrounding setting sleeve  26  which is axially moveable with respect to the setting tool mandrel  24 . The outer radial surface  28  of the setting tool mandrel  24  includes a radially reduced portion  30  and a radially enlarged portion  32 . A sloped shoulder  34  is defined between the radially enlarged portion  32  and the radially reduced portion  30 . The setting sleeve  26  is better seen with further reference to  FIGS. 3 and 4  and includes an upper sleeve section  36  and a lower sleeve section  38 . The upper and lower sleeve sections  36 ,  38  are affixed to one another by threaded connection  40  and set screw  42 . A fluid communication port  44  is disposed through the upper sleeve section  36  and is initially closed off by a frangible rupture member, such as rupture disc  46 . The rupture disc  46  is selected to rupture at a predetermined pressure differential applied to the rupture disc  46 , thereby selectively permitting fluid to flow through the port  44 . The lower sleeve section  38  features a lower, enlarged-diameter interior portion  48  and a reduced-diameter interior portion  50  which are separated by sloped shoulder  51 . The lower sleeve section  38  presents a compression end  52 . 
     An atmospheric chamber  54  is defined radially between the setting tool mandrel  24  and the setting sleeve  26 . It is noted that the use of the term “atmospheric chamber” herein, as it relates to the chamber  54 , is not meant to be limited strictly to a chamber that is filled with a fluid that is maintained at one standard atmosphere of pressure. Instead, the terms “atmospheric chamber” and “atmospheric pressure” are meant to refer to a pressure that is markedly lower than the hydrostatic pressure that exists within the annulus  13 . Thus, it is contemplated that the chamber  54  could be pressurized above a standard atmosphere or reduced in pressure below a standard atmosphere or placed into vacuum at the surface  14  prior to run in and still be encompassed within the term “atmospheric chamber,” so long as a significant pressure differential between the chamber  54  and the hydrostatic pressure within the wellbore  10 . The atmospheric chamber  54  is bounded at its upper axial end by annular fluid seal  56  and at its lower axial end by fluid seal  58 . The atmospheric chamber  54  includes a collapsible volume portion  60  which is adjoined by annular space  62 . 
     An annular setting chamber  64  is also defined radially between the setting tool mandrel  24  and the setting sleeve  26 . The setting chamber  64  is bounded at its upper axial end by annular fluid seal  66  (visible in  FIG. 4 ) and at its lower axial end by seal  56  and annular fluid seals  68 . It is noted that the fluid communication port  44  interconnects the setting chamber  64  with the annulus  13 . 
     A fluid passage  70  extends through the lower sleeve section  38  and interconnects the setting chamber  64  with the annular space  62  of the atmospheric chamber  54 . A fluid restrictor is operably associated with the fluid passage  70 . In a preferred embodiment, the fluid restrictor is a porous plug member  72  that is disposed within the fluid passage  70 . In alternative embodiments, the porous plug member  72  may be located at one or both ends of the fluid passage  70  rather than within it. In a preferred embodiment, the plug member  72  is formed of a sintered metal which permits fluids to pass through the passage  70  slowly. A sintered metal provides interstices through which fluid may seep.  FIG. 5  depicts an exemplary plug member  72 . In a further preferred embodiment, the plug member  72  includes external radial threading  74  to permit it to be threadedly secured within the fluid passage  70 . 
     In operation, the packer device  10  and setting tool  12  are assembled at the surface of a wellbore so that the atmospheric chamber  54  is filled with a fluid, such as air, at atmospheric pressure. The porous plug member  72  is disposed into the fluid passage  70 , and then the upper setting sleeve section  36  is secured by threaded connection  40  to the lower setting sleeve section  38 , which blocks fluid communication through the fluid passage  70  and ensures that the fluid within the atmospheric chamber  54  remains at atmospheric pressure. The set screw  42  is then inserted to further secure the upper and lower sections  36 ,  38  to one another. The packer device  10  and setting tool  12  are then disposed into the wellbore  11  in the unset condition depicted in  FIGS. 1 and 3 . 
     When it is desired to set the packer device  10  within the wellbore  11  the annulus is pressured up to a pressure level sufficient to cause the rupture disc  46  to be ruptured. High pressure fluid from the annulus  13  will enter the setting chamber  64  via the fluid communication port  44 . The increased pressure in the annulus  13  will bear upon the upper end of the lower sleeve portion  38  and cause the setting sleeve  26  to shift with respect to the setting tool mandrel  24  as the collapsible chamber portion  60  of the atmospheric chamber  54  is collapsed. Movement of the setting sleeve  26  will cause the packer device  10  to be set as the compression end  52  of the setting sleeve  26  to contact the compression ring  20  and axially compress the packer element  18 , in a manner known in the art. 
     Following setting of the packer device  10 , the pressure differential between the now high-pressure annular setting chamber  64  and the low-pressure atmospheric chamber  54  will be equalized over an extended period of time. It is preferred that pressure equalization not occur immediately, as this might disrupt the operation of setting the packer device  10 . Generally, a period of about five to ten minutes is desired to ensure that the packer device  10  becomes completely set although the particular amount of time will vary depending upon the particular packer device  10  and setting tool  12  being used. During the setting operation, it is important that the pressure differential between the atmospheric chamber  54  and the setting chamber  64  be maintained at a significant level. Following the setting process, wellbore fluid seeps through the porous plug member  72  and reduces the pressure differential. The amount of time for equalization to occur will vary depending upon the viscosity of the fluids present in the wellbore, the porosity of the plug member  72  and the degree of pressure differential. It is currently preferred that the porosity of the plug member  72  is such that the pressure differential between the atmospheric chamber  54  and the setting chamber  64  is maintained at about 80% or higher of the initial differential pressure level for around five to ten minutes following rupture of the rupture member  46 . The fluid passage  70  and plug member  72  may be collectively considered an equalization assembly that permits controlled entry of fluid into the atmospheric chamber  54  and equalization of pressure between the atmospheric chamber  54  and the setting chamber  64  and surrounding annulus  13 . The setting chamber  64 , fluid communication port  44 , and the rupture member  46  may be collectively considered to be an actuation mechanism that initiates both movement of the setting tool  12  from the unactuated position to the actuated position as well as the process of equalizing the pressure differential between the atmospheric chamber  54  and the well fluids within the surrounding setting chamber  64  and the annulus  13 . 
     The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however to those skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention.