Patent Publication Number: US-2009229832-A1

Title: Pressure Compensator for Hydrostatically-Actuated Packers

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to downhole tools, including packer devices. In particular aspects, the invention relates to methods of actuating downhole tools. 
     2. Description of the Related Art 
     Some downhole tools use absolute well pressure activation to operate. They are also referred to as hydrostatically actuated tools. In absolute well pressure activation, the to absolute pressure in the wellbore is the sum of the hydrostatic pressure and any additional pressure generated from the surface of the well. To use absolute pressure activation, the tool to be actuated is constructed to hold atmospheric air pressure in an atmospheric chamber. The tool is then run to depth. A rupture disc separates the atmospheric chamber from the wellbore fluid, which is under hydrostatic pressure. When the absolute pressure in is the well exceeds the differential pressure rating of the rupture disc, the disc ruptures to permit fluid to enter the atmospheric chamber. Typically, the pressurized well fluid entering the actuation chamber is applied to a setting piston to set the packer device or otherwise actuate the downhole tool. Tools which can be operated using absolute well pressure activation are described in, for example, U.S. Pat. No. 6,779,600. 
     SUMMARY OF THE INVENTION 
     In preferred embodiments, the invention provides a design and method for operating downhole tools in response to absolute pressure. In a described embodiment, a well packer device is provided with a packer element and slip elements which are set by axial compression. The packer device has an actuation chamber which is in communication with a pressure compensator reservoir. The actuation chamber has a fluid communication port which allows fluid communication between actuation chamber and the annulus surrounding the packer device. The pressure compensator reservoir and actuation chamber are charged with a pressurized fluid, such as nitrogen. The fluid pressure within the pressure compensator reservoir and actuation chamber is higher than atmospheric pressure. The tool is actuated when the external wellbore pressure exceeds the burst pressure rating of the rupture disc plus the fluid pressure contained within the pressure compensator chamber and actuation chamber. When the actuation chamber is filled with wellbore fluid, a setting piston is moved by the pressure of the fluid to set the packer device. Pressure charging of the pressure compensator reservoir allows for the tool to be operated at greater depths and to remain operable under higher external pressures than possible if the actuation chamber was at atmospheric pressure. 
     Alternative embodiments are described which incorporate different actuation or setting chamber designs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, wherein like reference numerals designate like or similar elements throughout the several figures of the drawings and wherein: 
         FIGS. 1A ,  1 B,  1 C,  1 D and  1 E are a side, partial cross-sectional view of an exemplary packer device constructed in accordance with the present invention. 
         FIG. 2  is a side, cross-sectional view of portions of an alternative packer device constructed in accordance with the present invention and in a run-in, unactuated position. 
         FIG. 3  is a side, cross-sectional view of the packer device shown in  FIG. 2 , now in an actuated position. 
         FIG. 4  is a side, cross-sectional view of a further alternative device constructed in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1A ,  1 B,  1 C,  1 D and  1 E depict an exemplary packer device  10  constructed in accordance with the present invention. The packer device  10  includes a central mandrel  12  having a threaded connection  14  at its upper axial end  16 . The central mandrel  12  is formed of an upper central mandrel portion  18 , middle central mandrel portion  20 , and lower central mandrel portion  22 , and a lower sub  24 , which are interconnected with one another by threaded connections, in a manner known in the art. The lower sub  24  presents a lower threaded connection  26  at its lower axial end. The threaded connections  14 ,  26  are used for interconnection of the packer device  10  into a wellbore production or injection string (not shown), as is known in the art. The central mandrel  12  defines a central flowbore  28  along its length. 
     Beginning at the upper end  16  of the tool  10  and working downwardly, the packer device  10  generally features a debris barrier  30 , a set of upper anchoring slips  32 , an elastomeric packer assembly  34 , and a set of lower anchoring slips  36 . The slip assemblies  32 ,  36  are set using axial compression of the assemblies with respect to the central mandrel  12  so as to cause the slip elements  38  of the slip assemblies  32 ,  36  to be urged radially outward, as is known in the art. As the construction and operation of such devices is well known, they will not be further described herein. A setting collar  42  and body lock ring assembly  44  are located axially below the lower slip assembly  36 . The packer assembly  34  is set by axial compression as well so as to cause the elastomeric packer elements  40  to be extruded radially outward. Axial compression of the packer assembly  34  and slip assemblies  32 ,  36  is caused by upward axial movement of the setting collar  42  with respect to the central mandrel  12 . 
     The lower portion of the packer device  10  includes a hydraulic setting section, generally shown at  46  and a hydrostatic setting assembly, generally shown at  48 , which are used to generate the axial force to set the slip assemblies  32 ,  36  and the packer assembly  34 . 
     The hydraulic backup setting piston  50  is moveably retained within a setting piston chamber  52  which is defined radially between the central mandrel  12  and an outer sleeve  54 . The backup setting piston  50  includes a compression end  56 , which abuts the compression collar  42 . In addition, the piston  50  includes an enlarged sealing portion  58  with fluid seals  60  to provide fluid sealing against both the central mandrel  12  and the outer sleeve  54 . The enlarged portion  58  presents a fluid pressure receiving surface  62 . It is noted that an upper setting piston chamber  52  is in fluid communication with the annulus  53  surrounding the tool  10  via a port  15  while a lower setting piston chamber  52 ′ is in fluid communication with the flowbore  28  via a radial port  64  disposed through the central mandrel  12 . Pressurized fluid may enter the lower setting piston chamber  52 ′ via the port  64  and be applied against the surface  62 . In the event that the absolute pressure setting technique, which will be described shortly, fails, the backup setting piston may be used to set the packer assembly  34  and slip assemblies  32 ,  36 . To do this, the flowbore  28  is pressurized at the surface of the well to exude pressure upon the surface  62  of the backup setting piston  50 . The backup setting piston  50  is axially moved to cause the compression end  56  of the piston  50  to urge the setting collar  42  against the lower slip assembly  36 . As pressurized fluid enters the lower chamber  52 ′ through port  64 , and the piston  50  moved, fluid is expelled from the upper chamber  52  into the annulus  53  through port  15 . Setting force is retained in slips  32 ,  36  and packer  34  by body lock ring assembly  44 . 
     The primary setting assembly  48  includes a setting sleeve  66  which is attached by one or more set screws  68  to the compression collar  42 . The lower end of the setting sleeve  66  is secured to outer sleeve  54 . A pressure chamber  55  is formed radially between the lower sleeve  72  and the central mandrel  12  (see  FIG. 1D ). The chamber  55  is pressurized to a level above wellbore hydrostatic pressure. The lower end of the outer sleeve  54  is secured by securing ring  70  to lower sleeve  72 . Annular fluid seals  57  ensure pressure integrity of the pressure chamber  55 . A body lock ring assembly  74 , of a type known in the art for ensuring one-way relative axial movement between components, is incorporated between the outer sleeve  54  and the central mandrel  12 , as depicted in  FIG. 1D . The lower end of the lower sleeve  72  is affixed by a threaded connection  74  to an interlock assembly housing  76 . The interlock assembly housing  76  overlies the lower sub  24  without being affixed to it. Seals  80  provide fluid sealing between the interlock assembly housing  76  and the lower sub  24 . 
     A setting chamber  82  and an interlock assembly, generally indicated at  84 , are retained radially between the interlock assembly housing  76  and the central mandrel  12 . A number of features of the interlock assembly  84  are described in U.S. Pat. No. 6,779,600 entitled “Labyrinth Lock Seal for Hydrostatically Set Packer” issued to King et al. That patent is owned by the assignee of the present application and is hereby incorporated by reference in its entirety. The interlock assembly  84  includes a lock sleeve  86  that is moveably disposed within the setting chamber  82 . The lock sleeve  86  is affixed by shear pin  88  to an interlock piston  90 . The interlock piston  90  is secured by a locking dog  92  to the lower central mandrel portion  22 . 
     A fluid pressure compensator reservoir  94  is defined within the lower sub  24 . In a currently preferred embodiment, the fluid pressure compensator reservoir  94  contains pressurized nitrogen. A fluid communication passage  96  extends between the reservoir  94  and the setting chamber  82 . A fluid communication port  98  (see  FIG. 1E ) is disposed through the interlock assembly housing  76  to permit fluid communication from the exterior annulus  100  into the setting chamber  82 . The port  98  is initially closed off by a frangible rupture disc  102 . 
     Prior to running the packer device into a wellbore, the reservoir  94  is filled with pressurized nitrogen or another pressurized fluid. The reservoir  94  is pressurized to a pressure that is greater than atmospheric pressure. The level of pressure within the reservoir  94  is set based upon the external wellbore pressure that the tool  10  is expected to be exposed to. In a presently preferred embodiment, the reservoir  94  is pressurized to a level that approximates the expected exterior pressure. Therefore, the tool  10  may be actuated by increasing pressure within the annulus by an amount approximately equal to the burst rating of the rupture disc  102 . A fill port  104  is disposed through the exterior wall of the lower sub  24  to permit fluid to be communicated into the reservoir  94 . The fill port  104  is closed off with a removable plug. The pressure within the reservoir  94  will be communicated to the setting chamber  82  via the passage  96 . One advantage of pressurizing the setting chamber  82  is that, at great depths, outer housing components, including the interlock assembly housing  76  will not be deformed or deflected radially inwardly, or very minimally so, by the significant hydrostatic wellbore pressure, so that the operational movement of members within the setting chamber  82  is not impeded by this deformation. 
     In operation, the fluid pressure compensator reservoir  94  is filled with pressurized fluid at the surface prior to running the tool  10  into a wellbore. The packer device  10  is incorporated into a production tubing string in a manner known in the art. The production tubing string and packer device  10  are then disposed into a wellbore and lowered to a desired depth. 
     When the desired depth of setting is reached in the wellbore, the annulus  100  is sufficiently pressurized at the surface of the wellbore so that the rupture disc  102  will burst and allow high pressure wellbore fluid to flow from the annulus  100  into the setting chamber  82 . As the wellbore fluid enters the setting chamber  82 , it urges the lock sleeve  86  axially upwardly within the chamber  82 . Movement of the lock sleeve  86  causes shear member  88  to rupture and releases the locking dog  92  from engagement with the central mandrel  12 . Once the locking dog  92  is released, the interlock assembly housing  76  and lower sleeve  72  are free to move axially with respect to the central mandrel  12 . 
     Increased fluid pressure within the annulus  100  will also cause the packer device  10  to be set. The increased fluid pressure will bear upon the lower end  106  of the interlock assembly housing  76  and urge the interlock assembly housing  76 , the affixed lower sleeve  72 , outer sleeve  54  and setting sleeve  66  and compression collar  64  axially upwardly with respect to the central mandrel  12 . The interlock assembly housing  76 , lower sleeve  72 , outer sleeve  54 , and setting sleeve  66  serve as a primary setting piston for setting of the packer device  10 . Because the locking dog  92  has been released, the primary setting piston may now move freely with respect to the central mandrel  12 . The compression collar  64  is urged against the lower slip assembly  36  causing the slip assemblies  32 ,  36  and the packer assembly  34  to be set. The chamber  55  collapses. 
     Pressurization of the compensator reservoir  94  provides an increase in internal pressure for the setting chamber  82 . This allows the packer device  10  to be run to deeper depths and resulting higher hydrostatic pressures before actuation occurs. The amount of external fluid pressure required to destroy the rupture disc  102  is determined by adding the internal pressure of the compensator reservoir  94  to the burst rating of the rupture disc  102 . For example, if the rupture disc  102  is designed to rupture at approximately 10,000 psi, and the compensation reservoir  94  contains fluid that is pressurized to 2,000 psi, the absolute external pressure applied to the tool  10  must exceed 12,000 psi in order to rupture the disc  102  and actuate the tool  10 . 
     Referring now to  FIGS. 2 and 3 , there is depicted an alternative packer assembly  200  wherein there is a single piston with balanced or nearly balanced atmospheric chambers which urge the piston up and down more or less equivalently. The upper portions (not shown) of the packer assembly  200  may have the identical construction as the packer device  10  described previously. The packer assembly  200  includes a central mandrel  202  and a bottom sub  204 . A setting cylinder  206  surrounds the central mandrel  202  above the bottom sub  204 . The setting cylinder  206  presents a radially-inwardly projecting piston  208  which contacts the outer radial surface  210  of the mandrel  202 . O-ring seals  212  provide fluid sealing across the piston  208 . The setting cylinder  206  is initially affixed to the bottom sub  204  by frangible shear pins  214 . 
     A first setting chamber, indicated generally at  216 , is defined below the piston  208  and radially between the central mandrel  202  and the bottom sub  204 . The lower end of the first setting chamber  216  is closed off by fluid seals  218 . A fluid port  220  is disposed through the lower sub  204  to provide fluid communication between the first setting chamber  216  and the surrounding annulus  222 . The port  22  is initially closed off by a frangible rupture disc  224 . 
     A second setting chamber  226  is located above the piston  208  and defined radially between the setting cylinder  206  and the mandrel  202 . The upper end of the second setting chamber  226  is closed off by a radial projection  228  from the central mandrel  202  and fluid seals  230 . The second setting chamber  226  is in fluid communication with the first setting chamber  216  via a weep hole  232  or other restrictive fluid path, which is disposed through the piston  208 . 
     A fluid pressure compensator reservoir  234  is defined within the bottom sub  204 . The reservoir  234  is similar in structure and function to the fluid pressure compensator reservoir  94  described earlier. In a currently preferred embodiment, the fluid pressure compensator reservoir  234  contains pressurized nitrogen. A fluid communication passage  236  extends between the reservoir  234  and the first setting chamber  216 . A chamber fill port  238  is preferably provided for readily filling the reservoir  234 . Prior to running the packer device  200  into a wellbore, the reservoir  234  is charged with fluid that is pressurized greater than atmospheric pressure, thereby enabling the packer assembly  200  to be run in deeper wells containing greater hydrostatic pressure. The greater-than-atmospheric pressure from the reservoir  234  is transmitted through the passage  236  to the first setting chamber  216  and through the weep hole  232  to the second setting chamber  226 . 
     To activate the packer assembly  200 , the annulus  222  is pressurized to rupture the rupture disc  224 . Fluid from the annulus  222  will pass through the port  220  and enter the first setting chamber  216 . The increased fluid pressure will bear against the lower side  238  of the piston  208  and cause the shear pins  214  to shear. When the pins  214  are sheared, the setting cylinder  206  is released and moves upwardly with respect to the central mandrel  202 . The second setting chamber  226  is collapsed, and the setting cylinder  206  will set the associated packer and slip elements (not shown) in the manner described previously with regard to packer device  10 . 
       FIG. 4  illustrates an exemplary alternative packer device  300  incorporating an improved setting assembly in accordance with the present invention. In the depicted device  300 , the packer element  302  is located above the setting assembly  304  while a slip anchoring assembly  306  is located below the setting assembly  304 . The setting assembly  304  includes an upper setting cylinder  308  and a lower setting sleeve  310 . An upper setting chamber  312  is defined radially between the central mandrel  314  and the upper setting cylinder  308 . The upper setting chamber  312  is bounded on its lower end by shoulder  316  and at its upper end by setting piston  318 . A charging port  320  is disposed through the setting cylinder  308  to permit the upper setting chamber  312  to be charged with a fluid. The charging port  320  is closed off by a plug, as is known in the art. 
     A lower setting chamber  322  is defined radially between the central mandrel  314  and the lower setting sleeve  310 . The lower setting chamber  322  is bounded at its upper end by a fluid seal  324  between the lower setting sleeve  310  and the central mandrel  314 . At its lower end, the lower setting chamber  322  is bounded by a lower setting piston  326 . A fluid port  328  is disposed through the lower setting piston  310  to permit the lower setting chamber  322  to be charged with a fluid. The fluid port  328  is closed off by a closure plug, as is known in the art. A shear screw  330  secures the lower setting sleeve  326  to the upper setting sleeve  308 . 
     Prior to running the packer device  300  into a wellbore, the upper and lower setting chambers  312 ,  322  are charged with a fluid at a pressure that exceeds atmospheric pressure. This permits the packer device  300  to be run to deeper depths with higher hydrostatics within a wellbore. In this embodiment, the fluid pressure compensation reservoir is integrated into the setting chambers  312 ,  322 . However, the packer device  300  might also be constructed so as to have one or more separate fluid compensation reservoirs which is/are maintained separately from the setting chambers  312 ,  322 . 
     When it is desired to set the packer device  300 , the annulus surrounding the packer device  300  is pressurized from the surface to a predetermined level. The increased fluid pressure acts upon the outer radial surfaces of the upper setting cylinder  308  and the lower setting sleeve  310  and particularly at the point  332  where the cylinder  308  and sleeve  310  meet and causes the shear screw  330  to rupture, thereby releasing the cylinder  308  from the sleeve  310 . The increased annular fluid pressure then causes the upper and lower setting chambers  312 ,  322  to collapse. As the chambers  312 ,  322  collapse, the upper setting cylinder  308  is moved axially upwardly with respect to the central mandrel  314 , thereby setting the packer element  302 . The lower setting sleeve  310  is moved axially downwardly with respect to the central mandrel  314 , thereby setting the slip anchoring assembly  306 . Body lock ring  332  maintains the axial compression force in packer element  302  and slip anchoring assembly  306 . 
     Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof.