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.