RELATED APPLICATION

[0001] This patent application claims the benefit of U.S. Provisional Patent Application No. 62/830,169 filed on April 5, 2019, incorporated herein by reference.

FIELD

[0002] The present disclosure relates to oil and gas well drilling and production, and in particular, to an internal lock-down mechanism for a tubing hanger.

BACKGROUND

[0003] Oil rigs are used to drive and rotate a drill string with a drilling bit attached at its end to create a well in the ground. The same rig is also used for a second purpose to place casing in the well to provide a conduit from the surface to the producing formation. After a well bore has been drilled and lined with casing, the usual practice is to cement the casing in place to protect ground water and the integrity and stability of the well. Conventional cementing techniques involve displacing cement slurry down through the bore of the casing and out a shoe on the bottom thereof so that the cement fills the annulus between the casing and the well bore wall. Typically, three to four casing strings are cemented in the wellbore, and a production tubing is installed that will become the fluid conduit with the target formation underground.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1 is a simplified block diagram illustrating a hydrocarbon production system according to the teachings of the present disclosure; and

[0005] FIG. 2 is a cross-sectional view of an exemplary embodiment of an internal lock-down mechanism for a production tubing hanger according to the teachings of the present disclosure. DETAILED DESCRIPTION

[0006] Generally, the well is lined with steel pipes or casings to allow unobstructed access to the target reservoir deep in the ground. Up to four casing strings may be installed and each string is cemented in place to structurally support the wellbore and hydraulically isolate the target reservoir from ground water sources and other formations. In a well, the tubing string is the main conductor that brings reservoir fluid to the surface or injects fluid from the surface into the target formation. The tubing string is supported from the wellhead and is hung, anchored or sealed against the cemented casing string by the tubing hanger. The tubing hanger is threaded onto the top of a tubing string and is designed to sit on top of and seal in the tubing head. The top of a conventional tubing hanger provides a profile to enable the use of external lock screws (also called lock-down screws) to secure the hanger in the tubing head. These lock down screws are used to hold down and energize the seals on a tubing hanger. The lock screw is threaded into the tubing head and the thread is located between the wellbore and the packing. The use of these lock screws exposes the wellbore to the atmosphere and the threaded screw bore becomes a potential leak path. The screw thread is also exposed to wellbore fluids that can impede the function of the lock screw. Further, installation of the lock screws is more prone to error, due to incorrect positioning, under- or over-application of torque, improper order of engagement or backing out, and other issues.

[0007] FIG. 1 is a simplified block diagram illustrating a hydrocarbon production system 10. As illustrated, the system 10 includes a wellhead 12 coupled to a mineral deposit 14 via a well 16, wherein the well 16 includes a wellhead hub 18 and a wellbore 20. The wellhead hub 18 generally includes a large diameter hub that is disposed at the termination of the wellbore 20. The wellhead hub 18 provides for the connection of the wellhead 12 to the well 16. The wellhead 12 typically includes many components that control and regulate activities and conditions associated with the well 16. For example, the wellhead 12 generally includes bodies, valves and seals that route produced hydrocarbons from the mineral deposit, provide for regulating pressure in the well, and provide for the injection of chemicals into the wellbore 20. In the illustrated embodiment, the wellhead 12 includes a production tree 22, a tubing spool 24, a casing spool 26, and a tubing hanger 28. A blowout preventer (BOP) 30 may be used, either as a part of the tree 22 or as a separate device. The BOP 30 may consist of a variety of valves, fittings and controls to prevent oil, gas, or other fluid from exiting the well in the event of an unintentional release of pressure or an overpressure condition.

[0008] Instead of using external lock screws to secure the tubing hanger 28, an inward- biased lock ring 40 and an energizing ring 42 are used to provide an internal locking mechanism to secure the tubing hanger 28. The energizing ring 42 is contoured with an inward facing locking flange 43 so that it engages a circumferential groove 44 formed in the tubing hanger 28 above the shoulder 45. The lock ring 40 is disposed about the energizing ring 42. A plurality of annual seals 47 are disposed at the interface between the tubing hanger 28 and tubing head 46.

[0009] In operation, the tubing head 46 is secured to a casing spool 26 or another structure already in place over the wellbore. The tubing hanger 28 with the lock ring 40 and energizing ring 42 are then inserted into the tubing head 46 using a running tool 48 to install the tubing hanger 28. The running tool 48 pushes on a circumferential flange 50 in the energizing ring 42 and advance it downward to urge the lock ring 40 into a circumferential groove 52 formed in the inner wall of the tubing head 46. The lock ring is thus biased inward to maintains the position of the tubing hanger 28 within the tubing head 46. The running tool 48 includes a longitudinal flange 54 having one or more circumferential internal peaks and valleys that function to exert downward forces on a circumferential longitudinal flange 56 of the tubing hanger 28 with external peaks and valleys to position the tubing hanger in place. The locking ring 40 and energizing ring 42 sit on a circumferential shoulder 45 of the tubing hanger 28, and the longitudinal flange 54 of the running tool 48 also exert forces on the energizing ring 42 to urge it into place. The lock ring 40, wedged in the groove 52 of the tubing head 46, prevents any upward movement of the tubing hanger 28 and energizing ring 42. The use of an internal lock-down mechanism (including the lock ring 40 and energizing ring 42) means that external lock screws are no longer needed to secure the tubing portion of the completion. This internal lock-down mechanism (including the lock ring 40 and energizing ring 42) is able to withstand the high internal pressure (15,000 psi) of the wellbore.

[0010] The lock ring 40 and energizing ring 42 may be fabricated from any suitable elastomer material and/or metal now known or to be developed. The running tool 48 has a threaded coupling 58 at its top end to facilitate its retrieval. The use of the internal lock ring 40 and energizing ring 42 eliminates a potential leak path from the wellbore and thus provides additional safeguards to the wellhead.

[0011] The features of the present invention which are believed to be novel are set forth below with particularity in the appended claims. However, modifications, variations, and changes to the exemplary embodiments described above will be apparent to those skilled in the art, and the internal lock-down mechanism for a tubing hanger described herein thus encompasses such modifications, variations, and changes and are not limited to the specific embodiments described herein.