Wellhead Sealing System and Method

Abstract

A system for sealing a wellhead. The system includes a setting frame, a driver cylinder selectively applying an axial motion, an adaptor attached to the wellhead, and a power mandrel operatively attached to the driver cylinder. The system may also include a setting sleeve attached to the power mandrel, with the setting sleeve having a packer element, wherein the setting sleeve is responsive to a pressure applicator and retractor device so that the packer element is expanded within the master valve. A method of isolating a wellbore is also disclosed.

Description

BACKGROUND OF THE INVENTION

This invention relates to a packer assembly and method. More particularly, but not by way of limitation, this invention relates to a packer assembly used with a wellhead and a method of sealing a wellhead.

In the drilling and production of hydrocarbons, various valves are used to control the flow of subterranean liquids and gas. A wellhead is used to isolate a wellbore from the surface, as readily understood by those of ordinary skill in the art. The wellbore may be in communication with a subterranean reservoir. The wellhead may contain several valves arranged to flow the well, shut-in the well, as well as kill the well if required.

Various components may be placed into an inner portion of a wellhead. For instance, a tubing hanger may be placed in the wellhead for attaching a tubing string that extends from the wellhead to the subterranean reservoir. Operators may conduct test during the life of a well to ensure that the valves associated with the wellhead are functioning properly. Due to the high pressure, flammability and toxicity of hydrocarbons, operators may perform many types of test to ensure proper operability of the wellhead and associated components. Valves will be tested for proper sealing. If a valve and/or seal is found to be leaking, remedial action is required in a timely fashion.

SUMMARY OF THE INVENTION

An apparatus for sealing a surface wellhead containing a master valve. In one embodiment, the apparatus comprises a driver cylinder for selectively applying an axial motion, an adaptor, operatively attached to the wellhead, with the adaptor having an inner bore in communication with an inner portion of the wellhead, and a setting frame operatively attached to the adaptor. This embodiment further includes a packing stack member operatively attached to the adaptor, with the packing stack member having a seal unit, a power mandrel operatively attached to the driver cylinder, a setting sleeve operatively attached with the power mandrel, with the setting sleeve having a packer element and wherein the setting sleeve is adapted to sealingly engage said seal unit, and pressure applicator and retractor means, operatively attached to the power mandrel, for transferring an applied rotational force to the setting sleeve so that the packer element is expanded within an inner bore of the master valve. In this embodiment, the wellhead may contain a tubing hanger that has a tubing string hanging therefrom, and the apparatus further comprises internal engaging means, operatively attached to the power mandrel, for selectively engaging the inner bore of the wellhead. In one embodiment, the internal engaging means includes a distal mandrel attached to the power mandrel and a protrusion rotatably attached to the distal mandrel, with the protrusion having a radial position and an axial position, wherein in the radial position, the protrusion engages an inner portion of the tubing hanger. In another embodiment, the internal engaging means includes a grapple-spear assembly for anchoring into the internal portion of the master valve.

In one embodiment, the pressure applicator and retractor means comprises an external thread means located on the power mandrel, a nut member disposed about the setting sleeve, with the nut member having an internal thread means operatively associated with the external thread means on the power mandrel, a shell member engaging the nut member, a set screw for attaching the shell to the setting sleeve, and wherein rotation of the nut member moves the setting sleeve relative to the power mandrel.

A method of isolating a wellbore having a master valve is also disclosed. The method comprises closing the master valve so that the wellbore is isolated, and attaching a master valve adaptor to the wellhead and installing a packer assembly to the master valve adaptor. In one embodiment, the packer assembly comprises: a setting frame; a setting sleeve operatively associated with a power mandrel, with the setting sleeve having a packer element, a pressure applicator and retractor device, threadedly connected to the power mandrel, for providing a rotational force transferred to the setting sleeve, wherein the setting sleeve is responsive to the transferred rotational force so that the packer element is expanded within an inner bore of the master valve. The method includes forming a seal with the setting sleeve engaging a packing stack on the master valve adaptor, opening the master valve and retaining a pressure from the wellbore at the packing stack. The method may also include placing a downward force on the power mandrel so that the power mandrel and the setting sleeve are pushed down into the wellhead and applying a rotational force with the pressure applicator and retractor device and transferring the rotational force to the setting sleeve so that the setting sleeve is moved downward and the packer element is compressed and expanded within an inner bore of the master valve. The method may also include opening a vent valve in the adaptor, testing whether the packer element is sealing pressure and removing the setting frame from the packer assembly. Next, the master valve can be removed from the wellhead.

In one embodiment, the method may include observing a rise in the pressure from the wellhead and reattaching the master valve adaptor to the wellhead. In one preferred embodiment, the packer assembly further comprises internal engaging means, operatively attached to the power mandrel, for selectively engaging the internal portion of the master valve. In one embodiment, the method may include mounting a driver cylinder to the packer assembly, attaching the driver cylinder to the power mandrel, creating an upward force so that a set of shear dogs engage a tubing hanger, shearing the shear dogs and pulling the power mandrel and the setting sleeve from the master valve. In another embodiment, the method would include mounting a driver cylinder to the packer assembly, attaching the driver cylinder to the power mandrel, rotating the power mandrel in order to set the internal engaging means which includes a grapple-spear assembly, pulling up on the power mandrel in order to cause the grapple-spear assembly to anchor the packer assembly in the internal portion of the master valve.

A system for sealing a wellhead is also disclosed. This system may include an adaptor, operatively attached to the wellhead, with the adaptor having an inner bore in communication with an inner portion of the wellhead, a driver cylinder for selectively applying an axial motion, with the driver cylinder being operatively associated with the adaptor, a power mandrel operatively attached to the driver cylinder, and a setting sleeve operatively attached with the power mandrel, the setting sleeve having a packer element, and wherein the setting sleeve is adapted to sealingly engage the seal unit. The system may also include a pressure applicator and retractor means, operatively attached to the power mandrel, for transferring an applied rotational force to the setting sleeve, wherein the setting sleeve being responsive to the rotation force so that the packer element is expanded within an inner bore of the master valve, and an internal engaging means, operatively attached to the power mandrel, for selectively engaging an internal portion of the wellhead. In one embodiment, the internal engaging means comprises a distal mandrel attached to the packer mandrel and a protrusion pivotly attached to the distal mandrel, the protrusion having a radial position and an axial position, wherein in the radial position, the protrusion engages an inner portion of a tubing hanger. In this embodiment, the packer mandrel may be operatively associated with a shear member for shearing the packer mandrel from the distal mandrel. In another embodiment, the internal engaging means may comprise a grapple having an outer profile and an inner profile; and a spear having an outer spiral, the outer spiral of the spear operatively engaged with the inner profile of the grapple in order to selectively engage and disengage the grapple with the internal portion of the wellhead.

In yet another embodiment a method of isolating a wellbore having a master valve is disclosed. In this embodiment, the includes closing the master valve so that the wellbore is isolated, attaching an adaptor to the master valve, installing a packer assembly to the adaptor, with the packer assembly containing a setting sleeve and a power mandrel, forming a seal by engaging a packing stack member within the adaptor with the setting sleeve, opening the master valve, retaining a pressure from the wellbore at the packing stack member and placing a downward force on the power mandrel and the setting sleeve of the packer assembly so that the power mandrel is pushed down into the wellhead. This method further includes applying a rotational force to a pressure applicator and retractor device and transferring the rotational force to the setting sleeve and creating a downward force on a packer element on the packer assembly thereby compressing and expanding the packer element in the inner portion of the master valve. The method may then include setting a grapple-spear assembly in the inner portion of the master valve. The grapple-spear assembly contains an inner spear mandrel operatively associated with an outer grapple member. The method may also include opening a vent valve in the adapter and testing whether the packer element is sealing pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of the first embodiment of the packer assembly.

FIG. 2 is a partial cross-sectional view of the packer assembly seen in FIG. 1 attached to a wellhead.

FIG. 3 is an enlarged cross-sectional view of the pressure applicator and retractor means seen in area “A” in FIG. 1.

FIG. 4 is a sequential view of the packer assembly seen in FIG. 2 engaging a tubing hanger.

FIG. 5 is a sequential view of the packer assembly seen in FIG. 3 sheared-off at the tubing hanger.

FIG. 6 is a partial cross-sectional view of a second embodiment of the internal engaging means shown in the run-in hole (RIH) position.

FIG. 7 is a sequential partial cross-sectional view of the internal engaging means embodiment of FIG. 6 in the set position.

FIG. 8 is a sequential partial cross-sectional view of the internal engaging means embodiment of FIG. 7 with the packer element being set.

FIG. 9 is a schematic view of a prior art wellbore associated with a wellhead.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a partial cross-sectional view of the first embodiment of the packer assembly 2. The packer assembly 2 includes an adaptor 4 that has an outer surface 6 and an inner surface 8. The outer surface 6 contains a first end 10 that will connect (via thread means in one embodiment) to the surface wellhead (not seen in this view). The outer surface 6 extends to a second end 12 that extends to radial surface 13 and then inward to the inner surface 8. As seen in FIG. 1, the second end 12 contains a packing stack member 14. In one embodiment, the packing stack member 14 is threadedly engaged with the adaptor 4. At a first end 16 of the packing stack member 14 there is disposed a packing stack 18, wherein the packing stack 18 is sometimes referred to as seal unit 18. The packing stack 18 is placed within an inner bore portion of the adaptor 4. In one embodiment, the seal unit 18 comprises a series of packing seals commercially available from Knight Oil Tools, Inc. under the name Chevron Packing Seals Also, the packing stack member 14 has a shoulder 20 that cooperates with the radial surface 13. The packing stack member 14 contains an inner bore 22.

The packer assembly 2 further includes a polished setting sleeve 24 wherein the outer surface 26 of the polished setting sleeve 24 will cooperate with and engage the seal unit 18. The setting sleeve 24 contains a recess 25, sometimes referred to as a profile 25. The packer assembly 2 also includes the packer mandrel 28, sometimes referred to as the power mandrel 28, wherein the power mandrel 28 contains the outer thread means 29. As FIG. 1 depicts, the power mandrel 28 may have a first portion 32 and a second portion 34. The polished setting sleeve 24 includes a setting sleeve radial surface 35 that abuts to and cooperates with the packer rubber 36, also referred to as the packer element 36. The packer element 36 will compress and expand as the power mandrel 28 and setting sleeve 24 are moved axially and rotated, as will be more fully explained later in the specification. FIG. 1 also depicts the shoulder 38 of the power mandrel 28 that abuts and cooperates with the packer element 36.

FIG. 1 further illustrates one embodiment of the internal engaging means, seen generally at 40, for selectively engaging (i.e. anchoring) an internal portion of the wellhead. The internal engaging means 40, which is attached to the power mandrel 28, generally includes a distal mandrel 42 attached to the power mandrel 28 and a protrusion 44 (seen in the retracted position) pivotly attached to the distal mandrel 42. Note that the protrusion 44 has a radial position and an axial position (axial position shown in FIG. 1), wherein in the radial position, the protrusion 44 can engage an inner portion of a tubing hanger as will be described later. Also provided is the shear ring member 46 wherein once a shear pin (not shown) is sheared, the shear ring 46 moves axially along the distal mandrel 42 allowing the protrusions 44 to collapse back into a retracted position so that the power mandrel 28 can be pulled out of the wellhead. A vent valve 49 is included in the adaptor 4, wherein the vent valve 49 allows the venting of pressure from the inner bore 8 to the outer portion of the adaptor 4. The vent valve 49 can be a ball valve with a manual open and closed position. Other types of valves are possible.

FIG. 1 further illustrates the setting frame 48 that is attached to the adaptor 4, and wherein the setting frame 48 is further attached to hydraulic cylinder 50, which is referred to as a driver cylinder 50 for moving (i.e. pushing and pulling force) the power mandrel 28 and setting sleeve 24 in an axial direction with the extendable piston 52, as will be more fully described later. The driver cylinder 50 is connected to the power mandrel 28 via conventional means, such as by a clevis pin. Also, the setting frame 48 may be constructed of conventional means such as flat bar. A pressure applicator and retractor means, seen generally at 53, for applying pressure to the packer element 36 to expand the packer element 36 as well as retracting the packer element 36 is shown. The pressure applicator and retractor means 53 will be described in more detail in the description of FIG. 3.

FIG. 2 is a partial cross-sectional view of the first embodiment of the packer assembly 2 seen in FIG. 1 operatively associated with a master valve 54, wherein the master valve 54 may be a valve component of a wellhead. It should be noted that like numbers appearing in the various figures refer to like components. As those of ordinary skill in the art will appreciate, a wellhead may comprise a series of valves that control flow into a wellbore as well as out of a wellbore, as depicted in FIG. 9. Returning to FIG. 2, the master valve 54 has an inner throat portion 56 that in turn extends to an inner bore 58, wherein the inner bore 58 contains a tubing hanger 60, with the inner bore 58 being in communication with the wellbore. The tubing hanger 60 can be used to hang a tubing string (such as a production string) therefrom. In the view of FIG. 2, the master valve 54 has been opened, and the power mandrel 28 and setting sleeve 24 have been driven downward via the driver cylinder 50 so that the protrusions 44 of the internal engaging means 40 are within the inner bore 58 but above the tubing hanger 60.

FIG. 3 is an enlarged cross-sectional view of the pressure applicator and retractor means 53 seen in area “A” of FIG. 1. More specifically, pressure applicator and retractor means 53 comprises a nut top portion 70 that is attached, such as by welding, to a plate 72. The nut top portion 70 contains an inner portion having internal thread means 74 and an outer portion 76, which in one embodiment is hexagonal, which can cooperate with a wrench tool for applying a rotational force. The internal thread means 74 engage and cooperate with the outer thread means 29. The plate 72 has a top surface 78 and a bottom surface 80. The applicator and retractor means 53 further includes a shell member 82 which contain a top ledge 84 that extends to a circular wall 86. As shown in FIG. 3, the top ledge 84 abuts the plate 72. The pressure applicator and retractor means 53 also contains bearing means 88a, 88b for allowing rotation of plate 72 relative to the setting sleeve 24 as well as transferring the rotational force. The bearing means 88a, 88b may be ball bearings made of various materials such as stainless steel, plastic etc, or the bearing means may be a radial sheet to facilitate rotation. Also, brass set screws 90a, 90b are depicted which cooperate with the profile 25 formed on the setting sleeve 24, with the brass set screws 90a, 90b holding the shell member 82 in place while allowing axial movement of the setting sleeve 24 relative to the power mandrel 28 when engaging the thread means 29, 74 for rotational movement. One of the functions of the shell member 82 is to hold the bearings 88a, 88b in place as lifting and lowering the setting sleeve 24 when a rotational force is applied to the nut 70. Hence, in operation, if the nut 70 is turned, the setting sleeve 24 and radial shoulder 35 moves downward and compresses the packer element 36 which in turn forms a seal with the inner bore. Another aspect of the shell member 82, as part of the pressure applicator and retractor means 53, is the ability to move the setting sleeve 24 down as well as to move the setting sleeve 24 up.

Referring now to FIG. 4, a sequential view of the first embodiment of the packer assembly 2 seen in FIG. 2 engaging a tubing hanger 60 will now be described. The power mandrel 28 and setting sleeve 24 has been driven downward via the driver cylinder 50, so that the protrusions 44 of the internal engaging means 40 have been allowed to collapse through the tubing hanger 60 and then axially extend outward as seen in FIG. 4. In the event that the operator believes it is now necessary to set the packer element 36 with the first embodiment, the operator would place a downward force on the setting sleeve 24 and in particular radial surface 35 via turning of the nut 70 as previously mentioned. As noted earlier with reference to FIG. 3, the threads 74 are engaged with threads 29. The turning of the nut 70 can be accomplished manually (such as a wrench) or with power tool means.

Returning to FIG. 4, since the protrusions 44 are engaged with the tubing hanger 60, this applied torque from the top nut portion 70 will cause the radial surface 35 to lower which in turn causes the packer element 36 to expand and set, resulting in a seal within the inner bore 58. FIG. 5 is a sequential view of the packer assembly 2 seen in FIG. 4 which depicts the protrusions 44 being sheared-off from the tubing hanger 60. In order to release the seal 36, the nut 70 is backed-off thereby moving the setting sleeve 24 to move upwards since the plate 72 is moved up which in turn moves the shell 82 and sleeve 24 (as well as radial surface 35). This upwards movement will deflate the packer seal 36. Next, the operator can pull the packer assembly 2 from the master valve 54 by pulling up on the power mandrel 28 (via driver cylinder 50) if needed by the operator. In other words, the operator causes the extendable piston 52 to transmit an upward force to the power mandrel 28 which will engage the protrusions 44 with the tubing hanger 60. Due to the disclosed design, as the extendable piston 52 is pulled-up, the power mandrel 28 and threadedly attached setting sleeve 24 will also be driven up. Once a predetermined force is reached, the shear member will shear thereby allowing the protuberance to retract.

In accordance with the first embodiment and referring collectively to FIGS. 1, 2, 3, 4 and 5, a method of isolating a wellbore having a master valve 54 includes closing the master valve 54 so that the wellbore is isolated, attaching the adaptor 4 to the master valve 54 and installing the packer assembly 2 to the adaptor 4. The method includes forming a seal by engaging the packing stack 18 in the adaptor 4 with the setting sleeve 24. The master valve 54 can be opened and a pressure from the wellbore is retained at the packing stack 18. The method includes placing a downward force on a power mandrel 28 and setting sleeve 24 so that the power mandrel 28 and setting sleeve 24 is pushed down into the wellhead engaging the protuberance 44 with the tubing hanger 60, and rotating (turning) the nut 70 which causes the setting sleeve 24 to move the sleeve radial surface 35 down so that the packer element 36 on the packer assembly 2 is compressed and expanded in the inner portion 58 of the master valve 54. The method may further comprise opening the vent valve 49 in the adaptor 4 and test whether the packer element 36 is sealing pressure. If the test shows the seals holding pressure, the adaptor 4 can be removed from the wellhead. If a rise in the pressure from the wellhead is observed, the operator can measure the torque on the setting sleeve 24. As noted earlier, if deemed appropriate, the operator can create an upward predetermined force via the drive cylinder 50 so that the protrusion 44 engages the tubing hanger 60, which will in turn shear after exerting the predetermined pulling force on the power mandrel 28.

FIG. 6 is a partial cross-sectional view of the second embodiment of the internal engaging means 100 in a run in the hole (RIH) position. The internal engaging means 100 is connected to the distal end of the power mandrel 28 (and more specifically to the second portion 34), and in the second embodiment, takes the place of the internal engaging means 40 depicted in FIGS. 1-5, and therefore, the remaining part of the packer assembly 2 remains unchanged and will not be shown. With the embodiment seen in FIG. 6, the internal engaging means 100 includes a flush type grapple-spear assembly, with the grapple-spear assembly being commercially available from Logan Oil Tools under the name Standard Releasing Spear (hereinafter “grapple-spear assembly 100”). The setting and releasing procedure of a typical grapple-spear assembly 100 can be found at www.loganoiltools.com and is incorporated herein by reference. The grapple-spear assembly 100 can be set within the inner bore 58 of the master valve 54. The grapple-spear assembly 100 contains an outer grapple 102 and an inner spiral mandrel 104. The outer grapple 102 contains a series of ridges that will engage the inner bore 58 and the inner spiral mandrel 104 contains an outer spiral profile that engages a receptacle inner spiral profile of the outer grapple 104. The inner spiral mandrel 104 is threadedly connected to the power mandrel 28. Reference is now made to FIG. 7 which is a sequential partial cross-sectional view of the internal engaging means 100 embodiment of FIG. 6 in the set position wherein the grapple-spear assembly 104 has contacted the inner portion of the grapple 102 and expanded the grapple 102 into a set position with the inner portion i.e. the series of ridges of grapple 102 engages the inner portion 58. Hence, by rotating the mandrel 104, the grapple 102 is engaged, then pulling up on the power mandrel 28 causes the outer spiral profile 105a on mandrel 104 to engage the inner grapple 102 and to expand the grapple 102 so that the grapple 102 engages the inner bore 58. It should be noted that to disengage the grapple 102, a set down weight on the mandrel 28 is applied by the operator, then the mandrel 28 is rotated to the right, and then a straight pull up on the mandrel 28 allows the grapple 102 to release i.e. the grapple 102 is no longer engaged with the inner portion 58

In operation, the grapple-spear assembly 100 is set (i.e. outer ridges of grapple engaging inner bore 58) so that the grapple-spear 100 is anchored in the inner portion 58, the setting sleeve 24 is moved downward (via rotation of nut top portion 70 as previously described) which in turn sets the packer element 36. Reference is now made to FIG. 8. FIG. 8 is a sequential partial cross-sectional view of the internal engaging means 100 embodiment of FIG. 7 depicting the packer element 36 being set.

FIG. 9 is a schematic view of a prior art wellbore 110 associated with a wellhead 112. The wellbore 110 is completed to a subterranean reservoir 114. The wellhead 112 has the tubing hanger 60 with a tubing string 116 extending therefrom. As is well understood by those of ordinary skill in the art, the wellhead 112 is sometimes referred to as a Christmas tree, and the wellhead 112 has the master valve 54 along with valves 118, 120 which can be used for instance for flowing liquids and gas from the wellbore 110 or for pumping fluids into the wellbore 110.

Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.

Claims

1. An apparatus for sealing a surface wellhead, wherein said wellhead contains a master valve, the apparatus comprising:

a driver cylinder for selectively applying an axial motion;

an adaptor, operatively attached to the wellhead, said adaptor having an inner bore in communication with an inner portion of the wellhead;

a setting frame operatively attached to said adaptor;

a packing stack member operatively attached to said adaptor, said packing stack member having a seal unit;

a power mandrel operatively attached to said driver cylinder;

a setting sleeve operatively attached with said power mandrel, said setting sleeve having a packer element and wherein said setting sleeve is adapted to sealingly engage said seal unit,

pressure applicator and retractor means, operatively attached to said power mandrel, for transferring an applied rotational force to said setting sleeve so that said packer element is expanded within an inner bore of the master valve.

2. The apparatus of claim 1 wherein the wellhead further contains a tubing hanger that has a tubing string hanging therefrom, the apparatus further comprising:

internal engaging means, operatively attached to said power mandrel, for selectively engaging the inner bore of the wellhead.

3. The apparatus of claim 2 wherein the internal engaging means comprising:

a distal mandrel attached to said power mandrel;

a protrusion rotatably attached to said distal mandrel, said protrusion having a radial position and an axial position, wherein in the radial position, said protrusion engages an inner portion of the tubing hanger.

4. The apparatus of claim 2 wherein said internal engaging means comprises a grapple-spear assembly for anchoring into the internal portion of the master valve.

5. The apparatus of claim 2 wherein said pressure applicator and retractor means comprises:

an external thread means located on said power mandrel;

a nut member disposed about said setting sleeve, said nut member having an internal thread means operatively associated with the external thread means on said power mandrel;

a shell member engaging said nut member;

a set screw for attaching said shell member to said setting sleeve;

and wherein rotation of said nut member moves said setting sleeve relative to said power mandrel.

6. A method of isolating a wellbore having a master valve, the method comprising:

closing the master valve so that the wellbore is isolated;

attaching a master valve adaptor to the wellhead;

installing a packer assembly to the master valve adaptor, wherein said packer assembly comprises: a setting frame; a setting sleeve operatively associated with a power mandrel, said setting sleeve having a packer element; a pressure applicator and retractor device, threadedly connected to said power mandrel, for providing a rotational force transferred to said setting sleeve, wherein said setting sleeve being responsive to the transferred rotational force so that said packer element is expanded within an inner bore of the master valve;

forming a seal with said setting sleeve engaging a packing stack on said master valve adaptor;

opening the master valve;

retaining a pressure from the wellbore at the packing stack;

placing a downward force on said power mandrel so that said power mandrel and said setting sleeve are pushed down into the wellhead;

applying a rotational force with said pressure applicator and retractor device and transferring the rotational force to said setting sleeve so that said setting sleeve is moved downward and said packer element is compressed and expanded within an inner bore of said master valve.

7. The method of claim 6 further comprising:

opening a vent valve in said adaptor;

testing whether said packer element is sealing pressure.

8. The method of claim 7 further comprising:

removing the setting frame from the packer assembly.

9. The method of claim 8 further comprising:

removing said master valve adaptor from the wellhead.

10. The method of claim 9 further comprising:

observing a rise in the pressure from the wellhead;

reattaching the master valve adaptor to the wellhead.

11. The method of claim 6 wherein the packer assembly further comprises internal engaging means, operatively attached to said power mandrel, for selectively engaging the internal portion of the master valve, and the method further comprises:

mounting a driver cylinder to said packer assembly;

attaching the driver cylinder to said power mandrel;

creating an upward force so that a set of shear dogs engage a tubing hanger;

shearing said shear dogs;

pulling said power mandrel and said setting sleeve from said master valve.

12. The method of claim 6 wherein the packer assembly further comprises a grapple-spear assembly, operatively attached to said power mandrel, for selectively anchoring to the internal portion of the master valve, and the method further comprises:

mounting a driver cylinder to said packer assembly;

attaching the driver cylinder to said power mandrel;

rotating the power mandrel in order to set the grapple-spear assembly;

pulling up on the power mandrel in order to cause the grapple-spear assembly to anchor said packer assembly in the internal portion of the master valve.

13. A system for sealing a wellhead, said wellhead containing a tubing hanger therein, the system comprising:

an adaptor, operatively attached to said wellhead, said adaptor having an inner bore in communication with an inner portion of the wellhead;

a driver cylinder for selectively applying an axial motion, said driver cylinder being operatively associated with said adaptor;

a power mandrel operatively attached to said driver cylinder;

a setting sleeve operatively attached with said power mandrel, said setting sleeve having a packer element, and wherein said setting sleeve is adapted to sealingly engage said seal unit;

pressure applicator and retractor means, operatively attached to said power mandrel, for transferring an applied rotational force to said setting sleeve, wherein said setting sleeve being responsive to the rotation force so that said packer element is expanded within an inner bore of the master valve;

internal engaging means, operatively attached to said power mandrel, for selectively engaging an internal portion of the wellhead.

14. The apparatus of claim 13 wherein the internal engaging means comprising:

a distal mandrel attached to said packer mandrel;

a protrusion pivotly attached to said distal mandrel, said protrusion having a radial position and an axial position, wherein in the radial position, said protrusion engages an inner portion of said tubing hanger.

15. The apparatus of claim 14 further comprising:

a shear member operatively attached to said packer mandrel for shearing the packer mandrel from said distal mandrel.

16. The apparatus of claim 13 wherein the internal engaging means comprise:

a grapple having an outer profile and an inner profile;

a spear having an outer spiral, said outer spiral of said spear operatively engaged with the inner profile of the grapple in order to selectively engage and disengage the grapple with the internal portion of the wellhead.

17. A method of isolating a wellbore having a master valve, the master valve having an inner portion in communication with the wellbore, the method comprising:

closing the master valve so that the wellbore is isolated;

attaching an adaptor to the master valve;

installing a packer assembly to the adaptor, said packer assembly containing a setting sleeve and a power mandrel;

forming a seal by engaging a packing stack member within said adaptor with said setting sleeve;

opening the master valve;

retaining a pressure from the wellbore at the packing stack member;

placing a downward force on said power mandrel and said setting sleeve of said packer assembly so that the power mandrel is pushed down into the wellhead;

applying a rotational force to a pressure applicator and retractor device and transferring the rotational force to said setting sleeve and creating a downward force on a packer element on said packer assembly thereby compressing and expanding the packer element in the inner portion of the master valve

setting a grapple-spear assembly in the inner portion of the master valve.

18. The method of claim 17 further comprising:

opening a vent valve in said adapter;

testing whether said packer element is sealing pressure.

19. The method of claim 18 further comprising:

removing said adaptor from the wellhead.

20. The method of claim 17 further comprising:

observing a rise in the pressure from the wellhead;

reattaching the adaptor to the master valve.

21. The method of claim 17 wherein the grapple-spear assembly includes an inner spear mandrel operatively associated with an outer grapple member.