Mudline suspension system

From a historic point of view, as jackup (/Jackups) drilling vessels drilled in deeper water (/Deepwater_drilling), the needto transfer the weight of the well to the seabed and provide a disconnect-and-reconnect capability became clearlybeneficial. This series of hangers, called mudline suspension equipment, provides landing rings and shoulders to transferthe weight of each casing string to the conductor and the sea bed.

Contents

1 Mudline hanger system1.1 Mudline hangers

2 Temporarily abandoning the well3 Reconnecting to the well4 References

5 See also6 Noteworthy papers in OnePetro

7 External links

Mudline hanger system

The mudline hanger system (shown in Fig. 1) consists of the following components:

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Fig. 1—Illustration of a typical mudline

suspension system showing running tools on the

left side and tieback tools on the right side.

Butt-weld subShoulder hangers

Split-ring hangers

Mudline hanger running toolsTemporary abandonment caps and running toolTieback tools

Cleanout tools.

Mudline hangers

Each mudline hanger landing shoulder and landing ring centralizes the hanger body, and establishes concentricity aroundthe center line of the well. Concentricity is important when tying the well back to the surface. In addition, each hangerbody stacks down relative to the previously installed hanger for washout efficiency. Washout efficiency is necessary toclean the annulus area of the previously run mudline hanger and running tool (Fig. 2). This ensures that cement and debriscannot hinder disconnect and retrieval of each casing riser to the rig floor upon abandonment of the well.

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Fig. 2—All mudline hangers should stack down to

provide washout efficiency. Washout efficiency is

supplied by a series of wash ports located in the

running tool that (when opened for washing out)

are positioned below the running tool attached to

the previously run mudline hanger.

As each hole section is drilled and each casing string (/Casing_and_tubing#Casing_strings) and mudline hanger is run, thehanger is positioned in the casing string to land on a landing shoulder inside the mudline hanger that was installed with theprevious casing string. Each of the mudline hangers have casing and a mudline hanger running tool made up to it. Theserunning tools are released through right-hand rotation to allow disconnect from the well. The threads on the mudlinehanger used by the running tool can be used to install temporary abandonment caps (Fig. 3) into selected hangers totemporarily “suspend” drilling operations at the conclusion of the well.

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Fig. 3—Illustration of a mudline suspension

system with temporary abandonment caps

installed after the well is drilled.

The main difference between the wellheads used in the land drilling application and the jackup drilling application (withmudline) is the slip-and-seal assembly (Fig. 4). Because the weight of the well now sits at the seabed, a weight-set slip-and-seal assembly is not used. Instead, a mechanical set (energizing the seal by hand) is used, in which cap screws aremade up with a wrench against an upper compression plate on the slip-and-seal assembly to energize the elastomeric seal.

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Fig. 4—Illustration of a mechanical-set slip-and-

seal assembly.

Temporarily abandoning the well

The mudline suspension system also allows the well to be temporarily abandoned (disconnected) when total depth (TD) isachieved (when drilling is finished at total depth). When this occurs, the conductor is normally cut approximately 5 to 6 ftabove the mudline, and retrieved to the surface. After each casing string is disconnected from the mudline suspensionhanger and retrieved to the rig floor in the reverse order of the drilling process, threaded temporary abandonment caps or

stab-in temporary abandonment caps (both of which makeup into the threaded running profile of the mudline hanger; seeFig. 3) are installed in selected mudline hangers before the drilling vessel finishes and leaves the location. The temporaryabandonment caps can be retrieved with the same tool that installed them.

Reconnecting to the well

A mudline suspension system also incorporates tieback tools to reconnect the mudline hanger to the surface for re-entryand/or completion. These tieback tools can be of two types: threaded and stab-in (see Fig. 5). The tieback tools aredifferent from the running tools in that they makeup into their own dedicated right-hand makeup threaded profile. Thestab-in tieback tool offers a simple, weight-set, rotation-lock design that provides an easy way to tie the well back to thesurface. A surface wellhead system (/Wellhead_systems_for_land_drilling) is installed, and the well is completed similarlyto the method used on land drilling operations.

The mudline suspension system has been designed to accommodate tying the well back to the surface for surfacecompletion, and it also can be adapted for a subsea production tree. A tieback tubing(/Casing_and_tubing#Tieback_string) head can be installed to the mudline suspension system at the seabed, and a subseatree can be installed on this tubing head.

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Fig. 5—Illustration of a mudline suspension

system with threaded tieback tools installed (left)

and “stab-in” tieback tools installed (right) in

each hanger body.

References

See also

Wellhead systems (/Wellhead_systems)

PEH:Introduction to Wellhead Systems (/PEH%3AIntroduction_to_Wellhead_Systems)

Noteworthy papers in OnePetro

External links