Wellhead hold-down apparatus and method

1. An apparatus to be mounted to a wellhead stack, the apparatus comprising:

a hold-down retainer affixed to a component of the wellhead stack, the hold-down retainer having a locking dogs profile;

a hold-down mandrel having locking dogs for engagement with the hold-down retainer;

a seal configured between a surface of the hold-down mandrel and a surface of the retainer to prevent the escape of well fluids;

an engagement profile configured to be retained by the locking dogs profile when the hold-down mandrel is in a locked position;

the engagement profile configured to be axially displaced with respect to said locking dogs profile when said hold-down mandrel is in an unlocked position; and

a lubricator assembly extending upward from said hold-down mandrel.

2. The apparatus of claim 1 wherein said locking dogs include inclined plane surfaces to facilitate engagement and disengagement of said engagement profile with said locking profile.

3. The apparatus of claim 1 further comprising a stinger attached to a distal end of said hold-down mandrel.

4. The apparatus of claim 3 wherein said stinger is configured to seal with a packing element of an annular blowout preventer.

5. The apparatus of claim 3 wherein said stinger is removably attached to said distal end of said hold-down mandrel.

6. The apparatus of claim 1 wherein said lubricator, hold-down mandrel, and hold-down retainer are configured to prevent fluids from the wellhead stack from escaping without assistance from a packing element of an annular blowout preventer.

7. The apparatus of claim 1 further comprising a removable bell nipple extending upward from said hold-down retainer.

8. An apparatus to be mounted to a wellhead stack, the apparatus comprising:

a hold-down retainer affixed to a component of the wellhead stack, said hold-down retainer having a locking profile in a longitudinal bore thereof;

a hold-down mandrel having an engagement profile on an exterior surface thereof;

a lubricator assembly extending upward from said hold-down mandrel;

the engagement profile comprising a plurality of radially spaced rotational elements disposed on a distal end of the hold-down mandrel and a plurality of axial rows of mandrel locking dogs, each row of mandrel locking dogs axially aligned with a rotational element; and

the locking profile comprising a plurality of radially spaced alignment elements disposed adjacent a proximal end of the longitudinal bore, a plurality of axial rows of retainer locking dogs to interlock with the plurality of axial rows of mandrel locking dogs, each row of retainer locking dogs axially aligned with an alignment element, and a plurality of radially spaced locking elements disposed at a distal end of the longitudinal bore axially offset from the retainer locking dogs to impart rotation to the hold-down mandrel to interlock the locking dogs of the mandrel and the retainer when the mandrel is axially displaced into the retainer.

9. The apparatus of claim 8 wherein the rotational element comprises an angled surface aligning the hold-down mandrel and the retainer into an engaging orientation when the angled surface is axially displaced into contact with an opposingly angled surface of the alignment element, and rotating the locking dogs of the hold-down mandrel and the retainer into an interlocking arrangement when the angled surface is axially displaced into contact with an opposingly angled surface of a locking element.

10. An apparatus to allow the insertion of tools through a wellhead stack, the apparatus comprising:

a hold-down retainer secured to the wellhead stack, the hold-down retainer includes a locking profile having locking dogs and said locking dogs include inclined plane surfaces;

a mandrel having an engagement profile having locking dogs and said locking dogs having inclined plane surfaces to facilitate engagement and disengagement of said engagement profile with said locking profile, wherein said engagement profile is configured to be retained by said locking profile when said mandrel is in a locked position;

said engagement profile configured to be removed from said locking profile when said mandrel is in an unlocked position; and

a lubricator assembly extending upward from said mandrel, said lubricator configured to house the tools to be inserted through the wellhead stack.

11. The apparatus of claim 10 wherein said wellhead stack includes an annular blowout preventer.

12. The apparatus of claim 11 further comprising a stinger attached to a distal end of said mandrel.

13. The apparatus of claim 12 wherein said stinger is configured to seal with a packing element of said annular blowout preventer.

14. The apparatus of claim 12 wherein said stinger is removably attached to said distal end of said mandrel.