The present disclosure is directed to a coiled piston assembly per se, and to a coiled piston assembly for use in a wellhead system which includes a tubing hanger that is landed and locked in a wellhead positioned at the upper end of a well bore. In particular, the coiled piston assembly is mounted on the tubing hanger and is used to adjust the vertical position of the tubing hanger load shoulder so that the vertical distance between the load shoulder and the tubing hanger lockdown mechanism is the same as the vertical distance between the seat on which the load shoulder is landed and the locking profile in the bore of the wellhead which the lockdown mechanism is configured to engage. The present disclosure is also directed to a coiled piston assembly for use in securing an inner member to an outer member which surrounds at least a portion of the inner member.

BACKGROUND OF THE DISCLOSURE

Subsea hydrocarbon production systems typically include a wellhead which is positioned at the upper end of a well bore. The wellhead comprises a central bore within which a number of casing hangers are landed. Each casing hanger is connected to the top of a corresponding one of a number of concentric, successively smaller casing strings which extend into the well bore, with the uppermost casing hanger being connected to the innermost casing string. After the innermost casing string is installed, a tubing string is run into the well bore. The top of the tubing string is connected to a tubing hanger having a downward facing circumferential load shoulder which lands on a seat formed at the top of the uppermost casing hanger. In certain tubing hangers, the load shoulder is formed on a load nut which is threadedly connected to the tubing hanger body.

The tubing hanger is usually secured to the wellhead using a lockdown mechanism, such as a lock ring or a number of locking dogs, both of which comprise a number of axially spaced, circumferential locking ridges. The locking dogs are supported on the tubing hanger body and are expandable radially outwardly into a locking profile formed in the bore of the wellhead, such as a number of axially spaced, circumferential locking grooves, each of which is configured to receive a corresponding locking ridge. In order to ensure that the tubing hanger is properly locked to the wellhead, the vertical distance between the load shoulder and the locking dogs must be the same as the vertical distance between the seat and the locking profile, which is commonly referred to as the wellhead space-out. In this regard, the term “the same as” should be interpreted to mean that the vertical distance between the seat and the locking profile is such that the locking ridges can fully engage their corresponding locking grooves. In tubing hangers in which the load shoulder is formed on a load nut that is threadedly connected to the tubing hanger body, the vertical distance between the load shoulder and the locking dogs can be adjusted by rotating the load nut relative to the tubing hanger body. Thus, once the wellhead space-out is determined, the load nut can be rotated until the vertical distance between the load shoulder and the locking dogs is the same as the wellhead space-out.

In the prior art, a lead impression tool (LIT) is sometimes used to measure the wellhead space-out. In subsea wellheads, the LIT is lowered on a drill string and landed on the seat. The LIT is then hydraulically actuated to press typically three circumferentially spaced lead impression pads into the locking profile. After the impressions are taken, the LIT is retrieved to the surface and mounted on a storage/test stand, which is then manually adjusted to match the lead impression tool. The tubing hanger is then mounted on the storage/test stand and the load nut is adjusted until the vertical distance between the load shoulder and the locking dogs is the same as the wellhead space-out.

Although the LIT provides a useful means for determining the wellhead space-out, the time required to run and retrieve the LIT can be relatively long, especially in deep water. Also, setting the tubing hanger on the storage/test stand and adjusting the load nut can be a time consuming process and is dependent on human interpretation.

SUMMARY OF THE DISCLOSURE

In accordance with one embodiment of the present disclosure, a tubing hanger assembly is provided which includes a body which comprises an annular outer surface; a lockdown feature which is located on the body; a load nut which is threadedly connected to the body, the load nut comprising a downward facing load shoulder; and a piston assembly. This piston assembly includes an elongated cylinder which is positioned circumferentially around the outer surface of the body axially adjacent the load nut, the cylinder comprising a first cylinder end which is connected to the body and an open second cylinder end; an elongated piston which is slidably received in the cylinder, the piston comprising a first piston end which is oriented toward the first cylinder end and a second piston end which is configured to extend through the second cylinder end and engage the load nut such that extension of the piston causes the load nut to rotate relative to the body; and a seal which is positioned between the piston and the cylinder to thereby define a piston chamber between the first cylinder end and the first piston end, the piston chamber being connectable to a source of fluid pressure. In operation of the piston assembly, the piston rotates the load nut to thereby move the load nut axially relative to the body. In this manner, an axial distance between the load shoulder and the lockdown feature is adjustable.

In accordance with one aspect of the disclosure, the piston and the cylinder may each comprise a helical configuration. In addition, the piston may comprise at least two winds.

In accordance with another aspect of the disclosure, the body may include a first outer surface portion comprising a first diameter and an axially adjacent second outer surface portion comprising a second diameter which is less than the first diameter, and the piston assembly may be positioned around the second outer surface portion. For example, the piston assembly may be positioned between the first outer surface portion and the load nut.

In accordance with a further aspect of the disclosure, the load nut may comprise an end surface located opposite the load shoulder and a contact surface which extends generally axially from the end surface, and the second piston end may be configured to engage the contact surface.

In accordance with an additional aspect of the disclosure, the first outer surface portion may comprise a recess which defines a radially extending mounting surface to which the first cylinder end is connected.

In accordance with another aspect of the disclosure, the body may include a fluid conduit which is connectable to the source of fluid pressure and comprises a first conduit end that terminates at the mounting surface, and the first cylinder end may be connected to the first conduit end via a fluid coupling.

In accordance with a further aspect of the disclosure, the tubing hanger assembly may be configured to be installed in a wellhead which comprises a central bore in which a casing hanger is positioned, and the load shoulder may be configured to land on a seat which is formed on the casing hanger to thereby support the tubing hanger in the wellhead.

In accordance with an additional aspect of the disclosure, the central bore may comprise a locking profile and the lockdown feature may comprise a number of locking dogs which are supported on the body and are expandable into the locking profile to thereby secure the tubing hanger assembly to the wellhead. In operation of the piston assembly, for example, the piston rotates the load nut until a distance between the load shoulder and the locking dogs is the same as a distance between the seat and the locking profile.

The present disclosure is also directed to a method for installing a tubing hanger in a wellhead, the wellhead comprising a first tubing hanger lockdown feature and a central bore in which a casing hanger is positioned, and the tubing hanger comprising a second tubing hanger lockdown feature which is configured to engage the first tubing hanger lockdown feature, an annular body, and a load nut which is threadedly connected to the body, the load nut comprising a downward facing load shoulder which is configured to land on a seat that is formed on the casing hanger. The method comprises the steps of lowering the tubing hanger into the wellhead; and then adjusting the axial position of the load nut until an axial distance between the load shoulder and the second tubing hanger lockdown feature is the same as a second axial distance between the seat and the first tubing hanger lockdown feature.

In accordance with another aspect of the disclosure, the method may also comprise the step of engaging the first and second tubing hanger lockdown features to thereby secure the tubing hanger to the wellhead.

In accordance with a further aspect of the disclosure, the step of engaging the first tubing hanger lockdown feature with the second tubing hanger lockdown feature may be performed prior to the step of adjusting the axial position of the load nut.

In accordance with yet another aspect of the disclosure, the tubing hanger further comprises a piston assembly which is positioned circumferentially around the body, the piston assembly comprising an elongated cylinder which is connected to the body and an elongated piston which is slidably received in the cylinder and is configured to extend from the cylinder and engage the load nut such that extension of the piston causes the load nut to rotate relative to the body. In addition, the step of adjusting the axial position of the load nut is performed by operating the piston assembly.

The present disclosure is also directed to a piston assembly which includes a helical cylinder which comprises first and second cylinder ends; a helical piston which is slidably received in the cylinder, the piston comprising a first piston end which is oriented toward the first cylinder end and a second piston end which is configured to extend through the second cylinder end; and a seal which is positioned between the piston and the cylinder to thereby define a piston chamber between the first cylinder end and the first piston end; wherein in operation of the piston assembly, pressurization of the piston chamber forces the piston to extend from the cylinder.

The present disclosure is further directed to a piston assembly for use in securing an inner member to an outer member which surrounds at least a portion of the inner member, the inner member comprising first and second axially spaced inner features and the outer member comprising first and second axially spaced outer features which are configured to engage the first and second inner features, respectively, to secure the inner member to the outer member, one of the first inner feature and the first outer feature being formed on a load nut which is threadedly connected to one of the inner member and the outer member such that rotation of the load nut relative to said one of the inner member and the outer member moves the load nut axially relative to said one of the inner member and the outer member. In this embodiment, the piston assembly comprises a helical cylinder which is positioned around said one of the inner member and the outer member to which the load nut is connected, the cylinder comprising first and second cylinder ends, the first cylinder end being connected to said one of the inner member and the outer member to which the load nut is connected; and a helical piston which is slidably received in the cylinder, the piston comprising a first piston end which is oriented toward the first cylinder end and a second piston end which is configured to extend through the second cylinder end and engage the load nut wherein with the second inner feature engaged with the second outer feature, the piston assembly is operable to rotate the load nut to thereby move the first inner feature into engagement with the first outer feature to thereby secure the inner member to the outer member.

In accordance with another aspect of the disclosure, the piston assembly further comprises a piston chamber which is formed between the first cylinder end and the first piston end; wherein the piston chamber is selectively connected to a source of fluid pressure to thereby operate the piston assembly.

The present disclosure is also directed to a method for securing an inner member to an outer member which surrounds at least a portion of the inner member, the inner member comprising first and second axially spaced inner features and the outer member comprising first and second axially spaced outer features which are configured to engage the first and second inner features, respectively, to secure the inner member to the outer member, one of the first inner feature and the first outer feature being formed on a load nut which is threadedly connected to one of the inner member and the outer member such that rotation of the load nut relative to said one of the inner member and the outer member moves the load nut axially relative to said one of the inner member and the outer member. In this embodiment, the method comprises the steps of providing a piston assembly which comprises a helical cylinder which is positioned around said one of the inner member and the outer member to which the load nut is connected, the cylinder comprising first and second cylinder ends, the first cylinder end being connected to said one of the inner member and the outer member to which the load nut is connected; and a helical piston which is slidably received in the cylinder, the piston comprising a first piston end which is oriented toward the first cylinder end and a second piston end which is configured to extend through the second cylinder end and engage the load nut; inserting the inner member into the outer member until the second inner feature engages the second outer feature; and operating the piston assembly to rotate the load nut to thereby move the first inner feature into engagement with the first outer feature to thereby secure the inner member to the outer member.

In accordance with an aspect of the disclosure, prior to the step of operating the piston assembly to rotate the load nut to thereby move the first inner feature into engagement with the first outer feature, the method may also comprise the step of applying a preload force on the inner member in a direction opposite to a direction in which the inner member is inserted into the outer member.

Thus, in one illustrative embodiment of the disclosure, the tubing hanger and coiled piston assembly enables the vertical spacing between the load shoulder and the locking dogs to be adjusted in real time as the tubing hanger is landed and locked in the wellhead. As a result, the need to measure the wellhead space-out and adjust the position of the load nut before the tubing hanger is run into the wellhead is eliminated, which greatly reduces the time required to install the tubing hanger.

These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings. In the drawings, the same reference numbers may be used to denote similar components in the various embodiments.

