CGE654_Lect 5_Wellhead & X-mass

Wellhead and X-mas Tree

Faculty of Chemical Engineering

CGE 654

Well

Completion


Wellhead and Christmas Tree


Purpose of Wellhead

Suspends casing and tubing string

Contains and isolate the pressure of the tubular strings

Provides interface with BOP, Xmas tree and tie back


Wellhead Configuration

A typical well head assembly for a 3-string casing consist of:

Xmas Tree

Section C Tubing Head

Section B Casing Head Spool

Section A Casing Head


A. Casing Head

Attached to the top of the surface casing (screwed or welded onto the surface casing

It accept the next string of casing either protective string or production casing depend on the needs of the well

The casing head is the lowest part of the wellhead assembly and is almost always connected to the surface casing.

It support BOP while the hole is drilled for the intermediate section and provides suspending and pack-off the next casing (intermediate casing)


Surface Casing

Protect fresh water aquifer

1st string that BOP can be setprovide primary pressure control

Cemented to surface/seabed to case-off unconsolidated or lost circulation area / support subsequent casing strings

@ wellhead

Common size 20,16,

13 3/8, 9 5/8


Intermediate Casing

Separates hole into workable sections

No. of intermediate casing set depends on:

Fracture last shoe

Hole problems (lost circulation, differential

sticking)

Common size 13 3/8,

10 3/4, 9 5/8


Production Casing

Final string to be run for production

/testing

Primary purpose to isolate the

production zones thus allowing proper control of reservoir

Cementing very important

to prevent communication in the annulus

Common size 7, 7 5/8,

9 5/8


Casing Head on Surface Casing


Casing Hanger

FunctionSuspends intermediate or production casing stringSeals off the casing annulusCenters of the casing string in

the head (or spool)

Slip Type Casing HangerWrap around casing slips with sealing capabilitySeal energized by casing weight


Casing Hanger

Slip Type Casing Hanger

Automatic hangers have seals which are energized by casing weight

Non-automatichangers have seals which require means other than casing weight to be energized

Non-automatic hangers - Typically used when insufficient casing load is available or when cementing back to the surface

Slip-type casing hangers transfer the weight or tension load of a casing string to a casing head or spool


B. Casing Head Spool


Casing Head Spool

Casing spool has a top bowl to accommodate the casing hanger and has a bottom bowl with a packoff seal and a flange / clamp hub for mounting it on top of a casing head or previous spool

Outlets are provided for annular access

Multiple casing spools may be stacked to hang intermediate and production casing strings

During production, the well temp. increase and the fluids in between the casing expand the outlets in the casing spools allow the bleed-off preventing uncontrolled pressure increase and casing damage


Casing Head Spool

FunctionsSeals off around surface casing string

Provide support for the next casing with hanger

Provides support for well control equipment (BOP Stack)

Sealing the wellbore from the atmosphere

Controlling access to the wellborePressure controlFluid returns


Casing Head Spool


Casing series & casing heads / spool


C. Tubing Head


Tubing Head

Primary functions of Tubing Head:Suspend tubing with hangerProvide hydraulic seal between tubing and annulusProvide access ports to the annulusProvide mounting for the x-mass tree

The tubing head is the top spool on a surface wellhead assembly. It is installed after the last casing string to provide a load shoulder to support the tubing hanger or production casing/tubing annulus seal. When the well is completed, the tree is installed on top of the tubing head with a tubing head adapter.


Tubing Hanger Types

Threaded Hanger Flange Used in low pressure well

Boll Weevil TypeUnsuitable for completions under tension or compression

Ram Type Tubing HangerAllows free tubing manipulation to latch tension/compression before landing


Tubing Hanger and Packoffs

Production tubing is suspended from a tubing hanger

The hanger has an internal threaded section in its base to allow connection to the tubing

The hanger also allows installation of a plug or check valve to isolate the tubing pressure beneath the Xmass tree

In some wellhead configurations the hanger also has an extended neck which projects into the base of the Xmass tree

It uses this to provide a sealed flow path through the wellhead-Xmass tree interface


Compact Spool System

The great disadvantage of the conventional spooled wellhead is a separate spool must be install at each stage of the well (requiring the BOP to be removed)

This is potentially hazardous, particularly in the lower sections of the well where zones containing hydrocarbons may be encountered at high pressure, and time consuming

Many wellhead companies also offer a one piece spool system which provides the hang-off areas for the suspension of two or more casing strings (e.g. one intermediate casing string and the production casing string, as well as the production tubing string)


Compact Spool System


Completed Well


Xmass Tree


Xmass Tree

Functions:Primary flow control system for well once in productionFeatures and access requirementsOutflow from well productionInflow to well injection or killingVertical access to tubing wirelineAccess for electrical cable or hydraulic conduitse.g. ESP or safety valve


Xmass Tree Components

There are many designs and configuration of trees commonly in use. However, almost all will be assemble with the following components:

1. Pressure gauges allow well pressure to be monitored. Tubing head pressure, casing or annular pressure are generally monitored with permanent gauges fitted to the Xmass tree

2. Gauge flange / tree cap provides a seal for the top of the tree but is removed when access to the tubing is required (e.g slick line work)

3. Swab valve upper most valve of the tree, used to isolate pressure and allow access to the well for intervention tools such as wireline or coiled tubing



4. Production wing valve first valve on the production wing used to isolate the well for most routine operations (the easiest to replace in the event of damage or cutting out of the valve)

5. Kill wing valve enables connection of pumping equipment for treatment without interfering with the production wing.

6. Choke controls the rate of flow from the well (may be remotely controlled)



7. Master valves the main isolation valves for the well. The master valves are open for most of the wells life and used as little as possible since any fault would require an interruption in production. Two master valves are generally required (legislative requirement) Upper Master Valve often a hydraulically controlled valve

which is often linked to emergency production shutownsystems which used in preference to the Lower Master Valve due to ease of repair or replacement

Lower Master Valve commonly a manually operated valve and remains open in order not to wear it out. It is considered as back up for the Upper Master gate Valve


Monoblock Xmas Tree


Monoblock Xmas Tree

A monoblock tree comprises an inline or Y shaped of a single casting/forging. It has less external seal area than a flanged Xmas tree. The valves arrangement:

Lower valve a manual master gate valve Upper master valve a remotely controlled master valve Y piece or side outlet flange houses both choke and kill wing

valves. Normally the production flow wing is a remotely controlled valve. The kill wing valve is either manually or remotely operated

Uppermost valve manually operated swab valve


Multiple Completion

In cases where more than one completion string is installed, each string must be independently suspended and must independently or collectively seal off the tubing casing annulus

In addition, the control of fluid flow in each tubing string must be accomplished independently


Xmass Tree Selection


Flanges


Flanges

Flange sealing is commonly accomplished using metal ring joint gaskets

The flange face has a circular recess in which a ring gasket is installed. (gasket is compressed)

Gasket design and the dimensions of the ring groove are specified in API Specification 6A

Various type are available, depending principally on the pressure rating. (Gasket provides a pressure seal due to a combination of the make up load and the differential pressure across the gasket). API type R ring joint gasket are designed for low to moderate pressure service


Flanges


Flanges

They are primarily energized by the compressive force applied on make up of the flanges

The gasket can be oval or octagonal in shape

An alternative connection more commonly used in higher pressure application is the C clap or Grayloc connector. This type of connection uses a pair of clamps which act on the flange profiles to effect a high force on the seal ring gasket.


Gasket

API type R ring joint gaskets are designed for low to moderate pressure service. They are primarily energized by the compressive force applied on make up of the flanges. The gasket can be oval or octagonal in shape

The API BX gasket is designed for high pressures and for use with an API 6BX flange. The gasket is octagonal in cross-section

Both RC and BX gasket recesses have pressure relief holes for the release of trapped fluid behind the gasket

Documents

CGE654_Lect 5_Wellhead & X-mass