This disclosure relates in general to connections in well assemblies, such as wellhead assemblies and other connection points such as the upper mandrel on a blowout preventer (BOP) stack, among others. In particular, the disclosure relates to a mating profile that provides increased fatigue resistance.
Subsea well systems typically include a tubular wellhead located at the sea floor. During drilling operations, a riser extends from a vessel at the surface down to the wellhead. A wellhead connector connects the lower end of the riser, or a lower marine riser package (LMRP) and BOP, to the wellhead. After the drilling operation, to prepare for production, the riser is disconnected and a similar wellhead connector may be used to connect the subsea production tree to the wellhead. Additionally, a production or workover riser may be connected from a floating vessel. In either setup, the wellhead connector mates with the wellhead via an interface between the two. In some cases, the wellhead connector has a housing which slides over the wellhead to securely mate with the wellhead. The wellhead connector may include a plurality of dogs that surround the wellhead profile and a cam ring which may urge the dogs inward onto the wellhead, thereby engaging and locking the wellhead connector onto the wellhead.
Subsea systems may be subject to various forces, which cause stress and fatigue to the connection between the wellhead and the wellhead connector. Over time, such stress and fatigue may cause the connection to fail.
Applicant recognized the problems noted above and conceived and developed embodiments for wellhead profiles with increased fatigue resistance.
In an example embodiment, a wellhead includes a wellhead body and a cylindrical locking end coupled to the wellhead body for locking onto a wellhead connector. The locking end includes an exterior surface comprising an exterior locking profile. The exterior locking profile comprising an exterior groove formed between exterior stab and load flanks on the exterior surface. The locking end also includes an interior surface comprising an interior locking profile. The interior locking profile comprising an interior groove formed between interior stab and load flanks on the interior surface. At least one of the exterior groove or the interior groove is a relief groove that undercuts at least one of the respective stab or load flank.
In certain such embodiments, the exterior groove includes the relief groove that undercuts the load flank on the exterior surface. In some embodiments, the interior groove includes the relief groove that undercuts the load flank on the interior surface. In some embodiments, the relief groove corresponds to a portion of the contour of an ellipse intersecting at least a portion of the respective stab or load flank. In some embodiments, an axis of the ellipse is aligned with an axis of the wellhead. In some embodiments, an axis of the ellipse is at an angle with respect an axis of the wellhead. In some embodiments, the relief groove includes 10% to 50% of the contour of the ellipse.
In accordance with another example embodiment, a wellhead includes a wellhead body and a locking end coupled to the wellhead body for locking onto a wellhead connector. The locking end includes a cylindrical surface includes a locking profile. The locking profile includes a stab flank, a load flank, and a groove formed between the stab flank and the load flank on the cylindrical surface, in which the groove undercuts at least one of the stab flank or load flank.
In certain such embodiments, the groove corresponds to a portion of the contour of an ellipse intersecting at least a portion of the stab flank or load flank. In some embodiments, an axis of the ellipse is aligned with an axis of the wellhead. In some embodiments, an axis of the ellipse is at a tilted angle with respect an axis of the wellhead. In some embodiments, the groove includes 10% to 50% of the contour of the ellipse. In some embodiments, the groove is a first groove and the ellipse is a first ellipse, and wherein the locking profile further comprises a second groove adjacent the first groove, wherein the second groove corresponds to a portion of the contour of the second ellipse, the second ellipse overlapping with the first ellipse.
In accordance with another example embodiment, a wellhead system includes a wellhead connector comprising a plurality of dogs with grooves formed on an interior surface, and a wellhead comprising a locking end for locking onto the wellhead connector. The locking end includes a cylindrical surface having a locking profile for engaging with the grooves in the wellhead connector. The locking profile includes relief grooves formed between stab flanks and the load flanks on the cylindrical surface, in which the relief grooves undercut at least one of a neighboring stab flank or load flank.
In certain such embodiments, the relief grooves correspond to respective ellipses intersecting respective neighboring stab flanks or load flanks. In some embodiments, at least a portion of the ellipses have different sizes, angles, or positions relative to the wellhead. In some embodiments, an axis of at least one of the ellipses is aligned with an axis of the wellhead. In some embodiments, an axis of at least one of the ellipses is at a tilted angle with respect to an axis of the wellhead. In some embodiments, the relief grooves include 10% to 50% of the contour of the corresponding ellipses. In some embodiments, two of the relief grooves are adjacent and the ellipses corresponding to the two relief grooves overlap each other.
The present technology will be better understood on reading the following detailed description of non-limiting embodiments thereof, and on examining the accompanying drawings, in which:
The foregoing aspects, features and advantages of the present technology will be further appreciated when considered with reference to the following description of preferred embodiments and accompanying drawings, wherein like reference numerals represent like elements. In describing the preferred embodiments of the technology illustrated in the appended drawings, specific terminology will be used for the sake of clarity. The present technology, however, is not intended to be limited to the specific terms used, and it is to be understood that each specific term includes equivalents that operate in a similar manner to accomplish a similar purpose. For example, the term “ellipse” may be used herein to describe generally various curvatures of the relief groove profile, and is not limited to curvatures that follow a perfect elliptical shape. For example, an “elliptical” profile, shape, or curvature may be used to describe any type of curvature, including but not limited to that of a circle, and those not defined by a geometric shape.
When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Any examples of operating parameters and/or environmental conditions are not exclusive of other parameters/conditions of the disclosed embodiments. Additionally, it should be understood that references to “one embodiment”, “an embodiment”, “certain embodiments,” or “other embodiments” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Furthermore, reference to terms such as “above,” “below,” “upper”, “lower”, “side”, “front,” “back,” or other terms regarding orientation are made with reference to the illustrated embodiments and are not intended to be limiting or exclude other orientations.
Subsea systems may be subject to various forces. For example, tides may pull on a riser, which may pull on the connection at the wellhead connector. This may cause stress and fatigue to the connection between the wellhead and the wellhead connector. Over time, such stress and fatigue may cause the connection to fail. The present disclosure provides a wellhead locking profile between the wellhead and the wellhead connector that is more fatigue resistant and robust than the conventional profile.
In contrast, the elliptical relief grooves of the enhanced profile cuts into sides of where the conventional grooves would be to create a smoother and more gradual curvature transition. As illustrated, the elliptical relief grooves are wider and/or deeper than the conventional grooves. This gradual curvature transition reduces the peak stress and which makes the wellhead profile more fatigue resistant. In some embodiments, as shown by relief groove type one 58 (formed by ellipse 54) in
The enhanced wellhead profile includes one or more relief grooves formed therein, in which the existing root radii of the natural groove is replaced with elliptical relief grooves 58, 60 that extend into and undercut the load and stab flanks 62, 64 and thereby provide for reduced fatigue stress. The ellipses 54, 56 by which the relief grooves 58, 60 are formed are illustrated in
In various embodiments, the elliptical relief grooves 58, 60 may be shaped according to the contour of various different ellipse configurations, including ellipses of different sizes, height to width ratios, and tilt angles.
In certain such embodiments, the first relief groove 78a corresponds to a portion of the contour of a first ellipse 80a intersecting at least a portion of the respective stab flank 74a or load flank 76a, or both. Similarly, the second relief groove 78a corresponds to a portion of the contour of a second ellipse 80a intersecting at least a portion of the respective stab flank 74a or load flank 76a, or both. As illustrated, the first ellipse 80a, from which the first relief groove 78a is formed, has an axis aligned with an axis of the wellhead. Thus, the first ellipse 80a is positioned upright with respect to the axis of the wellhead. The second ellipse 80b, from which the second relief groove 78b is formed, has an axis at an angle with respect to the axis of the wellhead. Thus, the second ellipse 80b is positioned at a tilted angle with respect to the axis of the wellhead. In some embodiments, the relief grooves may include 10% to 50% of the contour of the ellipse. In some other embodiments, a relief groove may include more or less of the contour of an ellipse. In some embodiments, some of the ellipses may have various different sizes, angles, or positions relative to the wellhead. In some embodiments, not all of the grooves on a wellhead profile are the relief grooves provided herein, and there may be a mix of the relief grooves and conventional grooves.
In some embodiments, the relief grooves formed from the ellipses may be able to achieve 10%-20% reduction of the fatigue inducing stress with minimal impact on the structural behavior. The stress gradient along the grooves is lowered, and the peak stress is reduced by 10%-20% depending on the individual connectors mated to the wellhead profile. Because of the subtlety of the angled relief grooves, the structural behavior impact may be minimal, including but not limited to the preload, system stiffness, and the load bearing capacities at the interface. The elliptical profile may be retrofitted to existing wellheads and does not change the interface with existing wellhead connectors.
In some embodiments, the first and second relief grooves 102, 104 have the same configuration, such as having the same ellipse size and orientation. In some embodiments, the first and second ellipse relief grooves 102, 104 may have different configurations, such having different ellipse sizes, different tilt angles, and/or different amounts of the ellipse contour. In some embodiments, more than two adjacent elliptical relief grooves may be used. The number of elliptical relief grooves, and size and orientation of the elliptical relief grooves may be selected based on the parameters of the wellhead and wellhead assembly among other contribution design factors. The elliptical relief grooves described herein may be used in both the external wellhead profile and/or the internal wellhead profile.
Although the technology herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present technology. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present technology as defined by the appended claims.
This application claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 62/695,660 filed Jul. 9, 2018 titled “WELLHEAD PROFILE WITH INCREASED FATIGUE RESISTANT” the full disclosure of which is hereby incorporated herein by reference in its entirety for all purposes.
Number | Date | Country | |
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62695660 | Jul 2018 | US |