Flow Head: Drill Stem Testing Christmas Tree
Flow Head: Drill Stem Testing Christmas Tree
Flow Head: Drill Stem Testing Christmas Tree
Introduction
The "Surface Test Equipment" figure shows where the flowhead is
located in relationship to the other surface testing equipment. The
flowhead is located directly on top of the well and is the first piece of
equipment that fluid from the well flows through. Its principal function
is to control the fluid flow in and out of the well.
The flowhead can be used to provide temporary shut off at the surface for:
pre-completion testing
drill stem testing (DST)
post-completion testing (carried out without the use of a christmas tree)
After the well is tested and completed, a permanent assembly of surface equipment
(referred to as the christmas tree) replaces the flowhead and will provide shut off
services.
a master valve that allows isolation of the surface equipment from the
downhole test string.
a swab valve that permits introduction and retrieval of wireline tools.
a flow line valve to allow fluid to flow from the well. This valve is usually
operated with a hydraulic actuator, allowing remote and automatic closure.
a kill line valve used to pump fluid into the well.
an optional swivel allowing the test string suspended from the flowhead to be
rotated independently of the main flowhead block.
an elevator sub used to handle the flowhead with the rig elevators.
a threaded connection on top of the elevator sub used to attach pressure
equipment.
The only alternative to the flowhead is the christmas tree, which is a permanent head
installed after the well is completed. The christmas tree accommodates a completion
string. Because the flowhead facilitates testing that occurs before a well is completed,
in contrast to the christmas tree, it is designed to accommodate a temporary test string.
The threaded connection on the bottom sub allows easy connection and disconnection
of the temporary test string.
Applications
The flowhead is used to provide temporary shut off at the surface for the following:
pre-completion testing
drill stem testing
post-completion testing
Objectives
Upon completion of this package, you should be able to:
Upon completion of the practical exercises for the Flowhead, you should be able to:
List the specifications for the flowhead that you are working on.
Document the procedures for pressure testing a flowhead and swivel, both at
the shop and at the well site.
Using the flowhead provided, study the complete fast inspection tool (FIT)
and tool review and inspection monthly (TRIM) as described in the
maintenance manual for the flowhead, and study the Field Operating
Handbook (FOH) for Surface Well Testing.
Principles of Operation
The following list describes the elements of a flowhead from the bottom up:
Bottom sub
Master valve
The swivel is designed to allow rotation of the subsurface string while supporting the
weight of the whole subsurface string. Roller bearings are used to support the
significant weight of the test string and the downhole tools. Ball bearings are used to
support the lighter weight of the flowhead and the equipment above the flowhead.
The swivel should not be rotated under pressure which means that it is not designed to
hold the pressure when submitted to a continuous rotating movement like in drilling
operations. The most common applications (as mentioned earlier) are done with the
pressure close or equal to zero at a very low rotating speed . During a well test, the
pressure can be close to the swivel working pressure but the swivel either does not
move (onshore) or oscillates a little due to the heave (offshore).
Wing valves
Hydraulic actuator
The hydraulic actuator is a safety device that operates the flowhead outlet wing valve.
The valve is normally closed. Pressure needs to be applied to the actuator to compress
the spring and open the valve.
The pressure needed to keep the valve open can be provided with a simple hand pump
which, in an emergency, is bled off on the rig floor. However, a more sophisticated
system called an emergency shut down (ESD) is recommended because it allows the
actuator to be activated remotely.
Wing union connection
Both wing valves are equipped with wing unions connections. They allow
quick connection or disconnection of pipe work using a sledge hammer.
Swab valve
Lifting sub
Elevator
Elevators are used for many drilling-related operations; for the flowhead, the elevator
latches onto the flowhead to raise and lower the entire test string in and out of the
hole.
Pressure equipment
A set of equipment that is temporarily placed above the swab valve on top of the
flowhead. It is used to run tools into a well under pressure without having to close the
well.
Equipment
Flowheads are available in working pressure ratings of 3,000; 5,000; 10,000; and
15,000 psi. The biggest difference between flowheads are the gate valves.
Schlumberger uses gate valves from several manufacturers: Malbranque, McEvoy,
and Worldwide Oilfield Machine (WOM) Inc. The wide range of flowheads available
makes it possible to select a flowhead to accommodate all types of well tests, without
having to use equipment that is larger, more complicated, or expensive than the
overall project requires.
These drawings show examples of several types of flowheads and a swivel. For each
drawing, specifications are provided. If you would like to have a printed version of
these tool specifications, please use the PDF's provided in the original graphics.
A minimum of two primary pressure barriers must be used in the flow path:
the master valve and the flow line valve.
The valves must be rated at least 1.2 times the maximum expected shut-in
wellhead pressure.
The maximum pressure that can be used to test the flowhead at the well site is
the working pressure.
When the surface equipment includes a swivel, it must always be located
downstream of the master valve.
Flowhead Identification
The flowhead can be identified by its working pressure (WP) rating and service type.
The information can be on: a metal plate, a permanently attached metal ring, or a dot
that is stamped on a noncritical area of the flowhead. It is also typical to use colored
bands (painted or taped) on the flowhead for quick visual identification of flowhead
pressure and service type.
Safety
The following is a list of key safety considerations for flowheads:
Comment: This animation shows how to prepare the flowhead for installation, how
to move it to the rig floor, and how to connect it to the test string. If followed, this
procedure minimizes safety risks and protects equipment from accidental damage, as
well as ensuring that the flowhead is properly installed.
Maintenance
For information about flowhead preparation and functional checks, see the
recommended steps in the Field Operating Handbook (FOH) for Surface Well Testing.
For infomation about equipment maintenance, see the maintenance manuals for the
flowhead and the Field Operating Handbook (FOH) for Surface Well Testing.
Summary
In this training page, we have discussed:
Typical Flowhead
Hydraulic Actuator
Swivel
Valve Settings for Common Operations
Basic to the operation of the flowhead is the opening and closing of valves in a
particular sequence or order depending on what operation needs to be done. The
following list describes several common operations and provides figures that show the
typical status of the valves for these operations. The valve settings may change
depending on whether other operations must be performed simultaneously.
Description
The flowhead supports the drill string and allows the flowhead:
Specifications
Connections
Top 4 1/2 in.- 4 stub ACME box
Bottom 3 1/2 in. IF pin
Kill line 2 in. Fig. 1502 female
Flow line 2 in. Fig. 1502 male
Reference
FHL-F P-779617
Weight and dimensions
Height 3m
Width 0.8 m
Diameter max 0.14 m
Weight 600 kg
Accessories (optional)
Flow line valve actuator P-780092
Flow head:
Description
The flowhead supports the drill string and allows the flowhead: