Wellhead basics

Wellheads and Trees
• Simple to complex
• Seal Points and Control Points
• Basic use and intervention
3/14/2009 1George E. King Engineering

Dual master valve tree – flow path
is through wing valve. Swab valve is
removed for a wireline run.
Operations on a tree with a dual
master valve use the top valve. If a
leak develops, a plug can be set in
the profile at the tubing hanger and
the lower master closed to give two
barriers while the upper master
valve is repaired.

Simple, older
wellhead on a
low pressure gas
well allowing
flow from tubing
or annulus.
Ken Hall – Canadian well3/14/2009 3George E. King Engineering

Remote actuated valve additions
to an older tree.

A high pressure well head on a dry gas well

Casing Hangers
• Transfers part of the load of the casing string
(any tubular string) to the wellhead. The
actual weight is transferred to the string on
which the wellhead flange is mounted.
• Two Types
– Slip type
– Mandrel type

Hangers
• Slip Type:
– Used to suspend the casing in the slip bowl
– The hanger may also incorporate seals to casing
and annulus.
• Mandrel type thread to the casing

Casing Head
• Other names:
– “A” section
– Casing head
– Starting head
– Lower-most housing
– Braden head

Welded, hydraulically formed
or screwed to casing.
Centralizing and lock
down screws.
Annular access port.
Flange plate connection
to upper spools.

Casing Head
• The first piece of wellhead equipment
installed.
• Most likely affixed to most outside, fully
cemented casing string.
• Designed for universal use on all types and
depths of wells.

Spools showing annular access ports
and lockdown screws.

The wellhead flange attaches to the first cemented surface casing string designed to hold
pressure.

Well flange attachment to the casing may be by welding, forming, threaded connection or set
screws.

The second string of casing is run and the hanger is landed in the bowl.

Lock down screws
engaged
Hanger set in the
casing spool
Annular access port

The tubing spool follows.

The tubing is landed in the spool.

Lock down pins are
engaged and the seal
activated.

One or two full opening
master valves come next.

Followed by the flow T or
Cross.

The tree before adding
control valves.

Completed Wellhead with choke
and partly built left side of flow
cross.

Wellhead with surface safety valve
above the mechanical master valve and
below the flow T.

Tubing hanger.
Note the lockdown screw and small seal
isolating the tubing from the annulus.
Other seals are above the hanger.
Note that the top part of the hanger is
threaded to allow pickup of the tubing
string.

Seal Assembly in the Wellhead
Slips
Ring Gasket
Seals

Energizer ring with shoulder
Seal block
Slips
Lower seal and shoulder
Casing hanger assembly

Example of the base of a
coiled tubing wellhead,
showing flange groove.

Ring gasket still on master valve.
Carbide blast joint for annular frac.

Ring and groove types
Sealing rings are single use
items. The metal-to-metal
seal depends on deforming
metal to the sealing surface of
the spool groove.

A hanger flange showing:
alignment/lockdown pins,
slip bowl,
annular access port
seal elements
“leak” investigation ports.
Cutaway of a tubing
hanger spool

Lockdown screws and a tubing “donut”

Pressure Tests
• Before testing wellhead or BOP’s, consider the
condition of the casing. Many older wells with
low grade or poor quality casing can be
damaged by a pressure test on a new
wellhead.

Tubing hanger with
pass thru for electric
cable.

Hanger with a lock mechanism for subsea well.

Basic hanger, with tubing seal, lockdown,
annular access and casing seal. The
master valve is just above this unit.
Leak test port
Annular
Valve
Lockdown
screw
Casing
Tubing3/14/2009 37George E. King Engineering

Tubing hanger spool with annular access valves
3/14/2009 George E. King Engineering 38

Develop One Side Only?
Valve instead of a blind flange on
the left side would give better
repair opportunities.

Develop both sides?
In high rate, high pressure,
sensitive wells, or H2S wells, the
second side may be a well saver!

Motor Operated
Master Valve
Manual Wing Valve
Motor Operated
Wing Valve
Choke to flow line

Motor Operated
Master Valve
Manual Master Valve
Motor Operated
Wing Valve Choke to flow line

TMB = Twin Monobore
Wellhead (Dual Wellhead)
Well 1 Well 2

Flanges
• Basic types
• Assembly and Inspection
• Seal types
Source: Woodco

Nominal
Size of
Flange
Casing
Size
Diameter
of Flange
Diameter
of Bolt
Circle
Number of
Bolts Ring Type
2-1/16 2-3/8 8-1/2 5-1/2 8 R-24
2-9/16 2-7/8 9-5/8 7-1/2 8 R-27
3-1/8 3-1/2 11 8-1/2 8 R-37
4-1/16 4-1/2 12-1/4 9-1/2 8 R-38
5-1/8 5-1/2 14-3/4 11-1/2 8 R-44
7-1/16 7 15-1/2 12-1/2 12 R-46
11 9-5/8 23 19 12 R-54
13-5/8 16 30-3/8 26-5/8 16 BX-160
Flanges with Ring Grooves, API Type 6B,
for 5000 psi working pressure

Flange Assembly
• Clean the Ring Grooves and inspect for damage.
• Select a new Ring Gasket of the specified size and type.
• Place lubricated bolts in place and install nuts, lubricated on their
back face, by hand.
• Tighten bolts by hand until nuts on both sides touch the backs of
their respective flanges and have equal engagement on their stud
bolts.
• Observe the stand-off between flanges for equal appearance all
around, make any adjustment necessary to equalize the stand-off all
around. Measure the standoff if visual inspection questionable.
• Tighten with proper wrenches to achieve equal stand-off.

Flange bolt tightening sequence – also check for equal gap.3/14/2009 49George E. King Engineering

Tightening
• Begin tightening by rotating nuts clockwise 1/2
turn, choosing one bolt first, then choosing the
bolt 180 opposite second. then one at 90 and
then the one 180 from that.
• Step over one nut from the first nut tightened
(consistent clockwise or counter-clockwise) and
continue the same pattern as with the first four.

6 BX Flanges
Those flanges for which API Spec. 6A specifies BX Ring Gaskets.
These flanges have raised faces that the design permits to meet or touch when the
connecting bolts have reached the required torque.
Made-up 6 BX Flanges -
6 BX flange raised faces
shown in contact after
assembly. In actual field
situations any small gap
present after achieving
specified torque should
appear uniform all around.

6 B Flanges
• Those flanges for which API Spec. 6A specifies
R or RX Ring Gaskets
• These flanges (usually without raised faces)
have designs that leave a stand-off (gap)
between the flanges after bolts have reached
the required torque. See illustration.
• Select flange size to display stand-off between
flanges using R and RX Gaskets in standard
Ring Grooves.

6 B flanges must always stand
apart after assembly.
Raised faces on 6 B flanges make
the stand-off (gap) space difficult
to measure accurately but field
construction of a simple feeler
gage will usually give a
satisfactory approximation of the
measurement.
This stand-off should appear
uniform all around

Drift Testing of Assembled
Equipment
For 6 B or 6 BX flanges that have
not been pulled fully face to face,
non-uniformity of stand-off may
prevent the passing of a Drift past
the connection. See the
exaggerated illustration:
Select full bore flange size to display
Drift major diameter and length.
If the equipment bore has the minimum I.D. and the stand-off does not appear
uniform (or the flange faces do not appear to run parallel), a passing drift may
contact the wall of the connected piece of equipment and "bind" or "stick"
instead of passing freely.3/14/2009 54George E. King Engineering

Assembly
• API Spec. 6A or Spec. 16A requires a drift test on each piece of
flange equipment.
• When separate units of equipment require field assembly, the
person(s) making the assembly may create an unexpected problem
by not keeping any stand-off between flanges uniform all around.
Rarely do field personnel have a drift gage available, so the best
insurance against a stuck working tool comes from careful make-up
of flange connections.
• Even if the job doesn't require close fitting tools, such tools may
come into play should a well emergency occur.

Flange Assembly Learnings
• BOP stacks frequently experience Kelly wear on
their I.D. because flange make-up lacked
uniformity all around and all or a portion of the
stack leaned from the vertical, allowing the Kelly
to rub against the side leaning in.
• If operators do anticipate the need for running
tools that have a small clearance with the I.D. of
the BOP or Trees, then having a Drift Gage
available and used at the make-up site will
provide cheap insurance against later downtime.

A lock-ring type connection attaching the head to the casing.
Attachment depends on the engagement of the bolts.

Never throttle with a gate valve! - washouts will ruin seal ability. Valves in series give
repair opportunities.

Wellhead basics

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Wellhead basics