Surface Service Equipment
Surface Service Equipment When a wireline crew and the wireline
equipment arrive at a well location to perform wireline service,
there are numerous pieces of equipment that must be assembled
before wireline operations begin. A typical wireline rigup is
illustrated in Figure 1 .
Figure 1
First, the connection on the wellhead must be adapted to the
connections used on the lubricator. This is accomplished by
screwing a tree connection into the tree, or in some cases by
flanging to the tree an adapter that will accept the connection on
the lubricator assembly.
The lubricator must be assembled, and both It and the wireline
valve must be lifted and placed on top of the wellhead. This can be
accomplished with a crane, a mast truck, an A-frame, or some other
type of winch assembly. If none of these devices is available or
practical, a gin pole must then be used to lift the lubricator
stack onto the wellhead. The gin pole usually consists of three
eight-foot sections of telescoping pipe. The gin pole must be
chained to the wellhead in a vertical position and secured to the
tree. Rope falls (block and tackle) are hooked to the top section
of the gin pole. The gin pole must be manually extended to its full
height (about 20 feet) by scoping each section and pinning it to
the next section through aligning holes.
With the gin pole in position, the wireline valve may be lifted
and placed in position on top of the tree connection where it is
"made up" to the tree connection. In a situation that requires the
well to be closed at the surface while wireline is in the well, the
wireline valve may be closed without damaging the wireline. The
lubricator sections are laid out and assembled next to the
wellhead. The tool string is assembled and slid into the top of the
lubricator, leaving about 1 ft (0.3 m) sticking out of the top of
the lubricator. The wireline is threaded through the stuffing box
and attached to the wireline socket by tying a knot in the
wireline. The wireline socket is screwed onto the tool string and
the completed tool string is pushed completely into the lubricator.
Now the stuffing box can be attached to the top of the lubricator
sections to complete the lubricator assembly. The stuffing box
seals off around the wireline to contain the well pressure in the
lubricator stack.
Before the lubricator can be lifted into position on the
well-head, the tool string must be secured in the lubricator so it
cannot fall out while the lubricator is being lifted. The wire is
clamped to the lubricator with a wireline clamp (also called a
Chicago clamp). Next, the lubricator is lifted into position above
the wellhead with the rope falls. A sheave is attached to the tree
and the wireline is threaded through this sheave. The slack left in
the wireline is reeled onto the reel of the wireline unit and the
clamp is removed from the wire. The tool string may now be lowered
out of the open lower end of the lubricator and the proper tool
attached to the bottom of the tool string. After attaching the
proper tool, the depth indicator is zeroed with the tool level with
the tubing hanger. The tool string is then pulled up into the
lubricator and the lubricator attached to the wireline valve.
Before opening the valve on the tree to begin wireline
operations, the entire lubricator stack should be tested. If an
external pressure source is available, the stack may be tested from
that source. If not, the stack is normally tested as follows:
First, the crown valve of the well is slowly opened and well
pressure is allowed to enter the lubricator stack gradually. The
person opening the valve should observe the lubricator stack for
leaks. If no leaks are detected, the valve may be opened fully.
Next, the wireline valve is closed. Once the wireline valve has
been closed, the pressure is bled from the lubricator above the
wireline valve. It no leaks are detected, the needle valve on the
lubricator is closed and pressure is equalized across the wireline
valve. This is accomplished by opening the equalizing valve built
into the wireline valve for this purpose. Once the pressure has
been equalized, the rams of the wireline valve are opened fully,
the equalizing valve is closed, and wireline operations may
begin.
If any leak is detected during the test procedure, wireline
operations should not be begun until the source of the leak is
identified and corrected.
Wirelines Wirelines are available in a variety of sizes and
materials. Wireline sizes are commonly stated in inches in
diameter. The most common wire sizes are .082, .092, .105, 108, and
.125. The diameter of the wireline relates directly to its minimum
breaking strength; the larger the wire size, the greater the
strength of the wireline.
The other factor that affects the strength of the wireline is
the type of material of which it is constructed. The most common
material from which wireline is made is improved plow steel, a type
of carbon steel. This is also sometimes called bright line.
Although the strength of wireline varies somewhat from manufacturer
to manufacturer, the approximate minimum breaking strengths of the
various sizes of plow steel line are shown in Figure 1 .
Figure 1
These strengths are the published minimum breaking strengths of
the wireline when new from the manufacturer. However, there are
other factors that affect the strength of the wireline. Wireline
must make a number of bends as it comes off the reel and is run
into the well. This bending of the wireline tends to cause the
wireline to become work hardened over time, so wire that has been
worked is not as strong as wire that is new. Also the well
environment has some effect on the strength of the wire. Salt water
and hydrogen sulfide are particularly damaging. At any point in
time, it is impossible to know the exact condition of the wireline
or exactly what the line is capable of pulling. Most wireline
specialists try to stay well below the published breaking strengths
of wireline when pulling on the wire. As a rule of thumb, 80% of
the minimum breaking strength is generally considered as the
maximum working strength of the wireline. But even that safety
factor is no guarantee that the wireline will not break at a lower
pull. Wireline, like a chain, is only as strong as its weakest
point.
Research in this area has focused on developing wirelines that
are more resistant to corrosive fluids. Stainless and alloy
wirelines are now available for use in hostile subsurface
environments. These wirelines are resistant to H2S and corrosive
fluids, but have a lower breaking strength than improved plow steel
(5% to l5%, depending on diameter) . Improved plow steel may be
used with a chemical inhibitor when high loads must be pulled for a
short time in a hostile environment.
Multistrand (braided) wireline is used for jobs requiring very
high pulling forces. The most common 3/16-in. (0.476-cm) cable is
made up of seven inner wires and nine thicker outer wires. The
breaking strength is 5062 lb (22,500 N), four times the strength of
0.082 single-strand wireline. Dyform cable, a product of British
Ropes, has a single-strand core surrounded by nine inner wires,
overlain by nine thicker, beveled outer wires. This cable has a
breaking strength of 6300 lb (28,000 N).
Reel Systems (Wireline Units)
Wireline units come in a variety of types and sizes and are
available from many manufacturers. They may be mounted on trucks or
trailers for land locations, boats for inland waters and shallow
offshore locations, or may be self-contained, compact units for use
offshore ( Figure1 and Figure2 ).
Figure 1
Some may weigh several thousand pounds and require cranes to
move them about, whereas some may be small and lightweight enough
for transport by helicopter to offshore or extremely remote
locations.
Figure 2
However, they are all designed for one purpose: to allow the
tools and wireline to be lowered into and to be retrieved from the
wellbore. This is an oversimplification, but basically that is all
a wireline unit does.
The reel systems used on wireline units must have a power
supply, which may be a diesel or gasoline engine, or an electric
motor. Regardless of what type of power supply is used, it always
performs the same function in the wireline unit: the power supply
provides the torque that either runs the wireline reel directly
through a transmission or runs a hydraulic pump. The pump supplies
hydraulic fluid under pressure to a hydraulic motor on the reel
system, which in turn provides the torque necessary to turn the
wireline reel. Since most modern wire-line units use these
hydraulically operated reel systems, a quick look at a typical
system is in order.
Figure3 shows a schematic for a typical hydraulic system.
Figure 3
The hydraulic fluid is supplied to the pump from the hydraulic
tank. From the pump, the fluid is pumped through a line to a system
relief valve. This valve is set to the maximum operating pressure
of the system and acts as a system safety valve. The return line
from the relief valve ties back into the main return line for the
system.
Immediately downstream of the relief valve on the pump output
line, another smaller line tees off and runs to an adjustable
bypass valve (a two-way valve). This valve is mounted on the
control panel of the wireline unit. By adjusting this valve, the
wireline specialist can control the speed of the reel and also the
amount of pull the reel can put on the wireline. When the bypass is
closed, all the hydraulic fluid is allowed to go to the hydraulic
motor for maximum speed and pull. When open, almost all the fluid
is bypassed to the return line of the hydraulic system. A hydraulic
pressure gauge is mounted on the panel of the wireline unit so the
specialist can see how much pressure is being delivered to the
hydraulic motor to turn the reel.
The handle that controls a four-way valve is also mounted on the
control panel of the wireline unit. This valve is used by the
wireline specialist to control the direction that the reel turns.
When the control handle is in the center position, both lines going
to the hydraulic motor are closed and the valve leading to the
return line is open. This delivers no hydraulic fluid to the motor
and the reel does not move in either direction. When the handle is
pulled back toward the operator of the wireline unit, the return
line is closed and the line to the motor is opened, causing the
reel to turn toward the operator. This action reels the wireline
onto the reel, retrieving the wire and tools from the well. When
the handle is pushed forward, the other valve outlet is opened,
which delivers the hydraulic fluid to the motor in the opposite
direction. This causes the reel to turn away from the operator,
dispensing wire off the reel to lower the tools into the wellbore.
The result is that the four-way valve gives the wireline specialist
total control of the direction in which the reel is allowed to
turn.
The remainder of the system is less important from a basic
functional standpoint. The return line carries the circulated
hydraulic fluid back to the tank through a filter. There may also
be a heat exchanger, which keeps the hydraulic fluid cool to
prevent fluid breakdown. On any hydraulically operated system, the
location of the valves might be slightly different but the
operating principle will be the same. This system gives the
wireline specialist the precise control needed to perform sensitive
wireline operations.
There are a few other devices that are normally considered to be
part of a wireline unit but that really have nothing to do with the
reel system itself. These devices provide the wire-line specialist
with information about what the tools are doing in the well.
Depth Measuring Devices
The conventional depth measuring device used on the wireline
unit is the counter wheel connected to a Veeder-Root counter, which
measures the wireline as it is run in the wellbore. This allows the
wireline specialist to read the measured depth of the tools
attached to the end of the wireline simply by reading the depth
registering on the on the counter. Since there are two separate
parts of this device (the counter wheel assembly and the
Veeder-Root counter) , each shall be discussed separately.
Immediately after leaving the wireline reel the wireline is
looped around the counter wheel. The wireline wraps completely
around the counter wheel, which means that it must make a complete
loop at this point. This is significant because this is the only
location where the wireline must make such a bend. Because of the
fatiguing effect such a bend has on the wire-line, this is the most
common place for the wireline to break when pulling heavy loads on
the wire or working the wire continuously in the well at the same
depth. The counter wheel is precision machined so that when the
wireline is wrapped around it, the circumference of the circle
measured to the center of the wireline is exactly two feet. (This
dimension is different for metric counters and counters made for
large-diameter wire-lines. Be sure to check the counter to
determine whether measurement is in feet or meters.) This is
important to remember for two reasons. First, if the counter wheel
becomes worn, then the counter will not measure to the center of
the wireline and the wireline measurements read on the counter will
be in error. At greater depths this error can be significant. This
may not be critical when doing most wireline operations, but it can
become important when performing operations that require the best
possible accuracy, such as bottomhole pressure surveys in very deep
wells, or tubing caliper surveys. In such situations, a depth
inaccuracy could result in misleading data.
The second Important point about the counter wheel is that
because the counter wheel must measure to the center of the wire,
wherever the size of wire is changed on the wireline reel, the
counter must also be changed to match the wire. There are counter
wheels machined for each size of wire. Care should be taken to
ensure that the correct wheel has been installed for the line size
in use.
In addition to the counter wheel, there are two pressure wheels
on the counter assembly. One is mounted above the counter wheel and
one below. These pressure wheels keep the wire in place around the
counter wheel and minimize slippage of the wire, which could lead
to inaccurate measurements. They also serve to balance the force
exerted on the bearing of the counter wheel when excessive strains
are being pulled on the wireline.
The Veeder-Root counter is attached to the shaft of the counter
wheel either directly or via a cable that is quite similar to an
automobile speedometer cable. (The counter itself is similar to the
odometer of an automobile.) It is typically geared so that each
revolution of the counter wheel counts off two feet on the counter
(also available in 3 and 4 ft circumference; metric wheels and
counters measure meters.) The counter has a key that allows the
wireline specialist to zero the counter before lowering the tools
in the well. This is normally done with the tools suspended within
the lubricator and the bottom of the tool string even with the
tubing hanger of the well. This means that wireline measurements
read directly from the counter will only correspond to pipe
measurements if the elevation from the tubing hanger to the rig
floor is added to the wireline measurement. If a tubing hanger is
not in place, the bottom flange, rotary table, or drill floor is
used as a point of reference.
Weight Indicators
The weight indicator tells the wire-line specialist the
"weight," or tensorial force, being pulled on the wireline. This
information is used in many ways by the specialist to know what is
happening to the tools in the well.
This weight indicator consists of a load cell ( Figure1 and
Figure2 ),
Figure 1
which is secured to the wellhead or some other equally secure
location as close as possible to the tree.
Figure 2
A sheave called a hay pulley is attached to the other end of the
load cell. The wireline from the wireline unit is strung through
the hay pulley and continues up the side of the lubricator to the
sheave on the stuffing box and on through the stuffing box to the
wireline socket of the tool string. Inside the load cell is a
fluid-filled diaphragm that communicates through a port on the side
of the load cell with a high-pressure hydraulic hose. When a load
is placed on the wireline, the fluid inside the diaphragm of the
load cell is compressed and the fluid is pressurized. The hose,
which is also filled with fluid, transmits the pressure to a gauge
which is usually mounted on the panel of the wireline unit. The
gauge consists of a bourdon tube attached to a needle. This gauge
functions as a pressure gauge. When the pressurized fluid is forced
into the bourdon tube of the gauge, it causes the needle to deflect
on a dial face, which gives the specialist a reading of the weight
being pulled on the wireline.
Electronic weight indicators, which offer greater accuracy and
precision than mechanical indicators, are also available. They are
generally not as durable, however, and are more difficult to repair
on site.
Lubricators and Stuffing Boxes
In order to perform wireline operations on a well, it is
necessary to be able to gain access to the wellbore and contain the
well pressure while the tools are being run in the wellbore. This
is the function of the lubricator sections and the stuffing
box.
Lubricators
Lubricator sections come in a variety of sizes and pressure
ratings. The sizes of lubricators range from 2-in. (5-cm) sections
to 7-in. (18-cm) sections. The size of the sections used on a given
well is determined by the size of the equipment being run in the
well and the size of the tool string being used. The tool string
must have enough clearance to move freely in and out of the
lubricator. The lubricator must also have a large enough ID to
permit the communication of well pressure around the tools when the
valve on the tree is opened. If the clearance is too small, the
pressure entering the lubricator pushes the tools up against the
stuffing box at the top of the sections. If this happens, the
wireline could be damaged or broken, resulting in a fishing
job.
Lubricator sections are about 8 ft long for ease of handling and
transportation. The lower lubricator section is normally larger
than the upper sections to allow space for the larger diameter
equipment that will be attached below the operating tool string.
The lower sections of lubricator must have ports for valves to
allow the pressure to be released from the lubricator when the
lubricator stack is to be lifted off the wellhead. This valve port
is often used to monitor the well pressure with a gauge while
wireline operations are taking place. The number of lubricator
sections needed is determined by the length of the tool string
being run into the well and by the operation to be performed in the
well. The length of the tool string includes the extended jars,
plus the length of the devices attached or to be retrieved.
Lubricator sections come with pressure ratings of 5000 psi,
10,000 psi, 15,000 psi, and 20,000 psi (34.5, 69, 103.5, and 138
MPa). Lubricators also are rated for sweet or sour (hydrogen
sulfide) service. Special lubricator sections are also needed for
subzero arctic conditions. The proper pressure rating and service
rating must be matched to the well pressure and environment for
safe operation.
Quick Union Connections
The lubricator, stuffing box, and wireline valve normally have
quick union connections for ease of assembly. The quick unions are
either threaded or welded (in high-pressure lubricators) onto the
proper size pipe to Construct a lubricator section, or onto the
body of the wire-line valve to adapt it to the lubricator and tree
connection. The stuffing box also has a quick union pin and collar
for attaching it to the top section of lubricator. The quick union
has three parts: the box, the pin, and the collar. Figure1 shows
the three parts of the quick union assembled as they would be in a
lubricator stack on the well.
Figure 1
There are two basic quick union designs: the Otis and the Bowen.
The Otis union has a knurled collar, whereas the Bowen has holes
for a special spanning wrench. Their internal angles also differ
slightly. To assemble the quick union, the pin with the 0-ring seal
is slipped into the box end of the quick union until the shoulder
of the pin rests against the top of the box. Then the collar is
slid down over the pin and threaded onto the box end of the quick
union. The connection is designed to be "made up" by hand and
should not be tightened with a wrench or hammered upon. The collar
is fully threaded onto the box when all threads of the box are
covered. The collar is then "backed off" about 1/4 turn to prevent
the collar from sticking and making removal difficult.
When the pressure is admitted into the lubricator stack, the
seal on the pin is forced against the wall of the box, preventing
the pressure from escaping. (When stabbing the pin into the
wireline valve, care should be taken to avoid damaging this seal.)
Although the pressure tends to push the box and pin ends apart, the
collar threaded onto the box prevents the box and pin from
separating. The spreading action locks the collar so that as long
as there is pressure in the lubricator stack sufficient to keep the
collar locked, the collar cannot be unthreaded from the box. For
safety reasons, the collar should never be hammered upon and a
wrench should never be put on the collar if it does not unthread
easily. An inspection should be made to be certain that there is no
pressure still trapped inside the lubricator before any further
attempt is made to remove the collar of the quick union.
Stuffing Box
The stuffing box seals around the wireline and allows the tools
to be run into the well with no loss of well fluids. The body of
the stuffing box has a quick union pin machined on the lower end
for attaching it to the lubricator ( Figure2 ).
Figure 2
Over the body is mounted a sheave staff that has bearings
mounted between the body and the staff to allow the staff to swivel
around the body. This keeps the sheave mounted to the staff in line
with the hay pulley so the wireline tracks around the sheaves in a
straight line on its way to the stuffing box. Inside the stuffing
box, the packing is held in place by two glands, one below the
packing and one above. The gland below the packing is threaded into
the body of the stuffing box and fixed. The gland above the packing
is held in place by the packing nut. The packing nut is adjustable
so that the packing can be compressed to expand it against the wire
as the packing becomes worn by the wire. The glands also serve to
guide the wire through the packing to prevent excessive wearing of
the packing. The packing segments are small cylindrical pieces of
rubber or some other elastomer with a hole through the middle. The
required number of packing segments varies, but is normally about
seven. Immediately below the lower gland is a plunger, which is
also made of resilient material. This plunger is held in place by a
plunger stop, which is threaded onto the lower end of the stuffing
box. If something should happen to the packing that would cause a
stuffing box to leak severely, the flow coming around the plunger
pushes it against the lower gland and seals off on the wireline.
The glands, the packing, and the plunger in a stuffing box are
subject to severe wear from the wireline passing through them on
its way into and out of the well. They must be inspected and
changed frequently to maintain the stuffing box in good operating
condition. Stainless steel wirelines require glands made from a
special material (ampcoloy or bronze) to prevent the glands from
damaging the softer stainless wireline.
Wireline Valves
The wireline valve is a very important piece of equipment for
performing wireline operations. There is always a possibility that
the well may have to be shut-in while wireline is in the well. The
wireline valve allows the specialist to do this without damage to
the wireline. The capability to do this successfully is especially
important when fishing broken pieces of wireline from a well under
pressure.
The wireline valve consists of a body, a set of opposing rams,
ram stems, ram caps, and an equalizing assembly ( Figure1 ).
Figure 1
The body either has the proper quick union box machined on the
upper end or is threaded to accept a quick union box. The lower end
of the body is also threaded to accept a quick union pin and collar
or some other appropriate connection to allow mounting the wireline
valve to the wellhead. The ram assemblies have rubber seals that
seal around the wireline to contain the well pressure. The rams
also seal in the body of the wireline valve to prevent well
pressure from escaping around the ram when the valve is in the
closed position. The rams are connected to the ram stems, which are
threaded through the ram caps. The ram caps are threaded into the
body of the wireline valve. The rams can be closed or opened by
turning the ram stems. The wireline valve is designed in such a way
that when the valve is closed and pressure is released above the
rams of the valve, the well pressure trapped below the rams holds
them in a closed position. To reopen the valve, pressure must be
equalized across the rams. This is done by opening the equalizing
valve and allowing the pressure below the valve into the lubricator
above the valve. Once the pressure has been equalized, the rams may
be opened to allow the wireline and tools to pass through the
valve. The ram stems and ram caps all have seals to contain the
well pressure within the body of the wireline valve whether the
rams are opened or closed.
Wireline valves are available in a variety of designs. The
design described here is a manual design that is quite commonly
used. However, wireline valves that are hydraulically operated are
also available. Some designs allow either hydraulic or manual
operation. Wireline valves are available in sizes ranging from
2-in. bore to 7-in. bore and pressure ratings from 5000 psi to
20,000 psi, just like lubricators.
These valves hold pressure in one direction only. It is vitally
important that the valve be installed right-side-up to avoid
problems. Wireline valves should be transported and stored with the
rams closed and the stem handles removed. Routine shop testing is
necessary to ensure proper operation.
Dual wireline valves are made primarily for use with braided
line. This component has a single valve body with two sets of rams
placed one above the other. Two single valves can be installed, one
above the other, as a less convenient alternative in high-pressure
situations.
In very high pressure gas wells, a third BOP may be installed.
In this case, the lowest set of rams are installed upside down to
hold pressure from above.