Fixed-point packoff element with primary seal test capability

1. A fixed-point packoff element of a full-bore wellhead isolation tool, comprising:

a hollow body with a continuous sidewall and a central passage that is at least as large as a diameter of a production tubing supported by a tubing head spool of a wellhead isolated by the full-bore wellhead isolation tool, the hollow body having a cylindrical top end and a cylindrical bottom end, the cylindrical top end of the hollow body being adapted to be received in a seal bore above a side port of the tubing head spool and the cylindrical bottom end is adapted to be received in another seal bore below the side port of the tubing head spool;

at least one O-ring groove adapted to receive an O-ring that provides a primary seal between the cylindrical bottom end and the other seal bore below the side port of the tubing head spool;

at least one O-ring groove adapted to receive an O-ring that provides a test seal between the cylindrical top end and the seal bore above the side port of the tubing head spool; and

an O-ring groove in a bevel on the cylindrical bottom end that mates with a bit guide of the tubing head spool, the O-ring groove receiving an O-ring that inhibits well stimulation fluid from migrating between the bevel and the bit guide.

2. The fixed-point packoff element as claimed in claim 1 comprising three O-ring grooves respectively adapted to receive O-rings that provide the primary seal.

3. The fixed-point packoff element as claimed in claim 1 comprising four O-ring grooves respectively adapted to receive O-rings that provide the primary seal.

4. The fixed-point packoff element as claimed in claim 1 comprising two O-ring grooves respectively adapted to receive O-rings that provide the test seal.

5. The fixed-point packoff element as claimed in claim 1 further comprising a test fluid groove machined into the continuous sidewall of the hollow body between the cylindrical bottom end and the cylindrical top end.

6. The fixed-point packoff element as claimed in claim 1 wherein the cylindrical top end comprises a pin thread that cooperates with a box thread of a high-pressure mandrel of the full-bore wellhead isolation tool to connect the fixed-point packoff element to the high-pressure mandrel.

7. The fixed-point packoff element as claimed in claim 6 further comprising a seal pin above the pin thread, the seal pin cooperating with an O-ring received in an O-ring groove above the box thread of the high-pressure mandrel to provide a seal to inhibit well stimulation fluid from migrating into the pin thread and the box thread.

8. A fixed-point packoff element for a high-pressure mandrel of a full-bore wellhead isolation tool, comprising:

a hollow body with a continuous sidewall having a cylindrical top end and a cylindrical bottom end and a central passage at least as large as an internal diameter of a casing supported by a wellhead that is pressure isolated by the full-bore wellhead isolation tool, the central passage extending from the cylindrical top end to the cylindrical bottom end, the cylindrical top end of the hollow body being adapted to be received in a seal bore above a side port of a tubing head spool of the wellhead and having a larger outer diameter than an outer diameter of the cylindrical bottom end, which is adapted to be received in a seal bore below the side port of the tubing head spool;

at least one O-ring groove in an outer periphery of the cylindrical bottom end of the hollow body, the at least one O-ring groove being adapted to receive an O-ring that provides a primary seal between the cylindrical bottom end and the seal bore below the side port of the tubing head spool;

at least one O-ring groove in the outer periphery of the cylindrical top end of the hollow body, the at least one O-ring groove being adapted to receive an O-ring that provides a test seal in the seal bore above the side port of the tubing head spool; and

an O-ring groove in a bevel on the cylindrical bottom end that mates with a bit guide of the tubing head spool, the O-ring groove receiving an O-ring that inhibits well stimulation fluid from migrating between the bevel and the bit guide.

9. The fixed-point packoff element as claimed in claim 8 comprising 3 O-ring grooves for respectively receiving O-ring seals for providing the primary seal.

10. The fixed-point packoff element as claimed in claim 8 comprising 4 O-ring grooves for respectively receiving O-ring seals for providing the primary seal.

11. The fixed-point packoff element as claimed in claim 8 comprising 2 O-ring grooves for respectively receiving O-ring seals for providing the test seal.

12. A fixed-point packoff element for a high-pressure mandrel of a full-bore wellhead isolation tool, comprising:

a hollow body having a continuous sidewall with an outer diameter that increases from a first diameter to a second, larger diameter to respectively conform to an inner diameter of a lower seal bore below a side port of a tubing head spool and a larger upper seal bore above the side port of the tubing head spool into which the fixed-point packoff element is inserted, the hollow body comprising a cylindrical top end received in the upper seal bore, the cylindrical top end including a thread for connection to a high-pressure mandrel of the full-bore wellhead isolation tool, a cylindrical bottom adapted to be received in the lower seal bore, the cylindrical bottom end including a bevel adapted to mate with a bit guide in the tubing head spool, and a central passage that extends from the cylindrical top end to the cylindrical bottom end in fluid communication with the high-pressure mandrel;

a plurality of O-ring grooves in an outer periphery of the cylindrical bottom end, respectively adapted to receive O-rings that provide a primary seal between the cylindrical bottom end and the lower seal bore of the tubing head spool;

at least one O-ring groove in the outer periphery of the hollow cylindrical top end, adapted to receive an O-ring that provides a test seal between the cylindrical top end and the upper seal bore of the tubing head spool; and

an O-ring groove in the bevel adapted to receive an O-ring for providing a fluid seal between the bevel and the bit guide when the fixed-point packoff element is seated on the bit guide.

13. The fixed-point packoff element as claimed in claim 12 further comprising a test fluid groove in an outer periphery of the hollow body between the cylindrical top end and the cylindrical bottom end.