WO2017009591A1

WO2017009591A1 - Pipeline plunger

Info

Publication number: WO2017009591A1
Application number: PCT/GB2015/052038
Authority: WO
Inventors: Torstein Vinge; Harald Kallevik; Geir HEGGUM
Original assignee: Statoil Petroleum As; Stevens, Jason
Priority date: 2015-07-15
Filing date: 2015-07-15
Publication date: 2017-01-19

Abstract

A plunger (10) located in a pipeline (20), which can be used as a pump or for pigging but which allows the pipeline (20) to be used as a normal pipeline when the plunger (10) is not in use includes an axial passage (12) extending in the same direction as the pipeline (20), wherein the axial passage (12) includes a valve (16) which can be used to open or close the passage (12) through the plunger (10). Means are provided to move the plunger (10) along the pipeline (20), and these may take the form of a magnet (14) in the plunger (10) and an electrical stator (22) in the pipeline (20), such that supply of electrical power to the stator (22) can be controlled to control the speed and direction of movement of the plunger (10). Stops (24, 26) may be provided to limit the range of movement of the plunger (10) in the pipeline (20), and one of these stops (24, 26) may be associated with a one-way valve.

Description

PIPELINE PLUNGER

The invention relates to a plunger located in a pipeline, and more particularly to a plunger which can be used a pump or for pigging, but which allows the pipeline to be used as a normal pipeline when the plunger is not in use.

In the oil production industry, there are many situations where a plunger must be moved along a pipeline. For example, if the inside of a pipeline needs to be cleaned (perhaps to remove solid hydrocarbon deposits such as wax), a pig is passed along the pipeline to scrape any such deposits from the pipe.

One field where the use of a pig or similar device to remove deposits from the inner wall of a pipe is particularly useful is for pipelines using the so-called "cold flow" principle. This is used for pipelines where the fluid flowing in the pipe includes a large amount of wax.

The idea behind the "cold flow" principle is to allow a relatively short section of the pipeline to be exposed to a cold medium (conveniently, for underwater pipelines, the surrounding seawater). As a result, this shorter section of pipeline is at a lower temperature than the rest of the pipeline, and so wax will tend to be deposited on this cooler shorter section, rather than on the warmer remainder of the pipe.

If the pipe is then to be cleaned to remove the wax deposits, it is only necessary to clean this relatively short section. Further, the removed wax will form small solid particles, which will be transported along the pipe with the rest of the downstream flow, and these small particles will have less tendency to be redeposited downstream.

The "cold flow" principle thus makes it easier to clean wax deposits from the inner wall of a pipe, as it is only necessary to clean a relatively short section.

However, in order to do this, it is necessary to introduce the pig into the pipeline at one end, and then remove the pig after it has passed along the pipeline (either at the other end of the pipeline, or by returning it to the point where it was introduced). Even if only a relatively short section of pipeline is to be cleaned, it is still necessary to introduce the pig into the pipeline at one end of the relatively short section. Since access to the pipeline may be difficult, it would be desirable if the pig could remain in the pipe when not in use. A similar need for a plunger to be moved along a pipeline occurs in so- called "plunger lifting". This process is used to remove liquids such as water and condensates from gas wells (so-called "dewatering" or "deliquification").

When natural gas flows to the surface in a gas well, the gas tends to carry some liquid with it. These liquids will tend to accumulate in the well, and this can slow or even stop gas production. Various methods of removing the liquid have been proposed, such as pumping.

Plunger lifting uses a plunger which has an opening that can be selectively opened and closed. The plunger is normally held at the top of the well, with the opening in its open position so that gas can flow through the plunger and out of the well. When it is necessary to remove liquid from the well, the flow from the well is closed off, and the plunger is allowed to fall to the bottom of the well, through the liquid. Once the plunger is below the liquid, the opening is closed. Gas pressure builds up beneath the plunger, and eventually this pressure is sufficient to lift the plunger and the liquid above it up the well. At this point, the well is opened again, and the liquid is removed at the top of the well. The opening in the plunger is reopened when the plunger reaches the top of the well, so that gas can again flow out of the well.

However, lifting the plunger and the liquid relies on gas pressure. The pressure may reduce during the lifetime of the well, and more mature wells may have insufficient pressure to provide the necessary lifting effect. It is possible to pump gas down the well to below the plunger to lift it (so-called "gas lift" pumping), but this increases costs.

It would be desirable to provide some means for the plunger to be moved along the pipeline without relying on gas pressure.

According to a first embodiment of the invention, there is provided an arrangement of a plunger in a pipeline, wherein the plunger includes an axial passage extending in the same direction as the pipeline, the axial passage including a valve which can be used to open or close the passage, and wherein means are provided to move the plunger along the pipeline.

In one preferred form, means are provided to control the open or closed state of the valve.

In an alternative preferred form, the valve is a one-way valve. By controlling the movement of the plunger along the pipeline and the open or closed state of the valve (which, if the valve is a one-way valve, can be controlled as a result of the movement of the plunger), the plunger can serve a number of different purposes.

For example, if the valve remains open and the plunger is moved along the pipe, the plunger can act as a pig to remove deposits from the inner wall of the pipe while still allowing flow through the pipe. If the valve is closed and the plunger is moved along the pipe, then the plunger will act as a piston, with the pipeline acting as a cylinder, and may be used to pump fluids.

Any suitable means can be used for moving the plunger. In a preferred arrangement, the plunger comprises at least one magnet, and the pipeline includes an electrical stator, such that supply of electrical power to the stator can be controlled to control the speed and direction of movement of the plunger.

Using an electrical stator and a magnetic plunger means that there is no need for any material to pass through the wall of the pipeline in order to cause the plunger to move. Thus, the integrity of the pipeline is unaffected. Further, the use of electrical power is preferred as this allows the arrangement to be used at considerable depths.

In a preferred form, stops are provided in the pipeline to limit the range of movement of the plunger. Even if the valve in the passage of the plunger is open, fluid flow can exert a force on the plunger which will tend to move the plunger along the pipeline. The provision of stops will prevent the plunger from being moved by the fluid flow to unwanted positions in the pipeline.

In a further preferred form, the stops are located at the ends of the stator. With this arrangement, it is possible to ensure that the plunger will always be within the section of pipeline provided with the stator, and thus will be capable of being moved by the stator.

Preferably, at least one of the stops is associated with a check valve disposed in the pipeline.

The provision of a check valve in combination with the plunger allows the plunger to be used as a positive displacement pump. By closing the valve in the plunger and then moving the plunger towards the check valve, fluid in the pipeline will be forced through the check valve. The valve in the plunger can then be opened and the plunger moved away from the check valve, allowing fluid to flow through the plunger toward the check valve. This fluid can then be forced through the check valve by again closing the valve in the plunger and moving the plunger towards the check valve. This process can be repeated as necessary to move fluid through the pipeline.

In a preferred form, if the valve in the plunger is a one-way valve, the check valve and the one-way valve both allow flow in the same direction along the pipeline. The open and closed state of the valve in the plunger as described above then arises automatically from the motion of the plunger.

Preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figures 1 and 2 are highly schematic views illustrating the principle behind the invention.

As shown in Figure 1 , a plunger 10 is disposed within a pipeline 20, and has a passage 12 extending therethrough in the same direction as the axis of the pipeline 20. The passage 12 through the plunger 10 is shown as being relatively narrow; however, it will be appreciated that this is solely for the purpose of illustration, and that in practice, the passage 12 through the plunger 10 will have a sufficient size to allow flow through the pipeline 20 to continue relatively unimpeded.

Electrical drive means are provided allowing the plunger 10 to be moved along the pipeline 20. As shown in Figures 1 and 2, an electrical stator 22 is provided on the outside of the pipeline 20, and may take the form of coils wound around the pipeline 20. Further, the plunger 10 is provided with magnets 14, preferably permanent magnets, as this simplifies the construction of the plunger 10. When electrical power is supplied to the stator 22, the interaction between the electrical and magnetic fields will push the plunger 10 along inside the pipeline 12. The speed and direction of motion of the plunger 10 can be varied and controlled by suitable control of the electrical power supplied to the stator 22.

Figure 2 shows that stops 24, 26 are provided inside the pipeline 20 at each end of the electrical stator 22, and the plunger 10 cannot move past these stops. Thus, the range of motion of the plunger 10 is limited to the extent of the stator 22 along the pipeline 20, so that the plunger 10 can be prevented from moving away from the stator 22. If these stops were not provided, then it would be possible for the stator 22 to "shoot" the plunger 10 along the pipeline 20. This could lead to the plunger 10 moving so far away from the stator 22 that the stator 22 could no longer be used to move the plunger 10, which would result in the plunger 10 becoming "lost" in the pipeline 20. Of course, there may be situations where this "shooting" of the plunger is desirable. For example, a series of relatively short stators could be arranged along a considerable length of pipeline, and these could be used to pass the plunger from one stator to the next, avoiding the need for a single stator to extend the whole length of the pipeline.

Figure 2 also shows that the passage 12 through the plunger 10 is provided with a valve 16, which can selectively open or close the passage 14. When the valve 16 is open, fluid can flow through the pipeline 20 and the plunger 10 normally; further, when the plunger 10 is moved, it can move easily along the pipeline 20 through the fluid, as the passage 12 through the plunger 10 is open. However, when the valve 16 is closed, fluid flow through the pipeline 20 and the plunger 10 is largely prevented (although it may be possible for the flow to move the plunger 10 along the pipeline 20 if there is sufficient pressure). Further, if the plunger 10 is moved with the valve 16 closed, it will act as a piston, and will cause movement of the fluid in the pipeline 20.

The valve can be a simple one-way valve, allowing flow through the plunger in one direction but preventing flow in the other direction. With this arrangement, the plunger can be freely moved through the fluid in the pipeline in a first direction, with the fluid flowing through the valve and the plunger, but when the plunger is moved in a second direction (opposite to the first), it pushes the fluid along and acts as a piston.

Alternatively, means may be provided at the end stops for opening or closing the valve.

By controlling the supply of electrical power to the stator 22 and also controlling the open/closed status of the valve 16 in the passage 12 through the plunger 10, motion of the plunger 10 in the pipeline 20 and flow of fluid within the pipeline 20 can be controlled. Depending on the orientation of the pipeline 20 (generally horizontal or generally vertical), a number of different effects can be achieved.

In a generally horizontal pipe, the plunger can be used as a pig, for example for the removal of wax or other solid hydrocarbon deposits from the inner wall of the pipeline. Motion of the plunger can be achieved by supplying electrical power to the stator; alternatively or additionally, the valve in the passage through the plunger can be closed, and the flow of fluid in the pipeline can push the plunger along the pipeline. When not in use as a pig, the valve in the plunger can be opened, and it can be "parked" at the downstream stop. Positioning the plunger at the downstream stop means that any forces acting on the plunger as a result of fluid flow will be resisted by the stop. If the valve is a one-way valve, then the valve is arranged such that fluid can flow through the plunger while it is positioned at the downstream stop.

When pigging is required, electrical power is supplied to the stator to move the plunger upstream, against the flow of fluid in the pipe, to bring the pig to the upstream end of the stator. The valve in the plunger passage remains open during this travel, to reduce the power required to move the pig.

Once the plunger has reached the upstream end of the stator, it can be moved back to the downstream end using electrical power with the valve open; this allows the pipeline to be cleaned while still allowing fluid to flow through the pipeline. Alternatively, the valve can be closed, and the electrical power to the stator may be switched off, so that the plunger is moved downstream by the fluid flowing in the pipe.

It will be appreciated that this arrangement is particularly useful when the plunger is used as a pig in a "cold flow" section of the pipe. It is only necessary to provide the electrical stator along the relatively short section of pipe which is exposed to lower temperature, and thus means can be provided for removing wax from the inner surface of the pipe at relatively low cost.

In an alternative form, the plunger can be used as a seabed booster pump. In some subsea wells, the pressure produced by a well is insufficient to force the produced hydrocarbons to the surface of the sea, and it is necessary to install subsea pumps at or near the wellhead to allow the produced hydrocarbons to be pumped upwards.

The plunger can be used as a pump (specifically, a positive displacement pump) if one of the stops associated with the ends of the stator is combined with a check valve. The plunger can be then operated as a pump, by positioning the plunger at the stop with the check valve, and opening the valve in the passage in the plunger. Electrical power is then supplied to the stator to move the plunger to the other stop, and fluid can flow through the passage in the plunger as the plunger moves to the other stop. The valve in the passage through the plunger is then closed, so that the plunger will act as a piston. This effectively traps a section of fluid between the plunger and the check valve. Electrical power is then supplied to the stator to move the plunger back to the first stop (the one with the check valve). This motion will force the fluid between the plunger and the first stop through the check valve, and the check valve will prevent this fluid from flowing back. Once the plunger has reached the stop with the check valve, the valve in the passage through the plunger can be opened again, and the cycle repeated.

It will be appreciated that if the plunger valve is a one-way valve, then the one-way valve and the check valve must both be arranged to allow flow in the same direction.

In view of the relatively large piston travel, it will in some circumstances be possible for the piston to be used as a pump even without the check valve. It is often desirable to avoid having check valves (or indeed valves in general) present in a pipeline, as this can disrupt the smooth internal surface of the piping and cause obstructions or changes in the pipe diameter. With a long stroke (as here), the piston can create a good pumping effect even in the absence of a check valve.

The advantage of using the plunger as a pump is that the pump can remain entirely passive until it is required. As long as the valve in the passage through the plunger remains open, the flow of fluid in the pipeline is generally unaffected.

However, should the pressure in the fluid drop for any reason, the pump can be activated to maintain a desired level of flow (for example, to ensure that the flow rate is such that unwanted condensation or solidification does not take place).

Further, the plunger pump can have a long stroke and a relatively low piston speed.

If the pipeline is generally vertical, then the plunger can again be used as a pig or as a pump, in a similar manner that outlined above, and so these will not be discussed in detail again.

If the plunger is to be used as a pump, then it will be necessary for one of the stops to include a check valve. The plunger can be installed as a pump during the initial formation of the well, and can remain passive until the ageing of the well (and consequent reduction in well pressure) requires the use of the pump.

Further, the pump can be used for well dewatering, and can carry out "plunger lifting" as referred to in the introduction. In this case, the stator must extend down as far as the liquid to be removed from the well.

In order to carry out plunger lifting, the valve in the passage through the plunger is opened, and the plunger is moved down to the bottom of the stator. The plunger may be allowed to move under the force of gravity, or may be moved by supplying electrical power to the stator; in either case, the rate of descent can be controlled by controlling the power supply to the stator, to ensure that the plunger is not travelling too fast when it reaches the lower end of the stator.

Since the valve in the passage through the stator is open during the descent, the liquid can pass through the passage so that the plunger can reach the desired position. The valve is then closed, and power is supplied to the stator to lift the plunger back up the well. This valve closure will happen automatically if the plunger valve is a one-way valve. Since the valve in the passage through the plunger is closed, the plunger will act as a piston, and lifting the plunger will also lift the liquid above the plunger, so that the liquid can be brought to the top of the well and removed.

This procedure can be repeated as often as necessary, to remove the liquid from the well. Once a sufficient amount of liquid has been removed, the plunger can be "parked" in the well, with the valve in the passage through the plunger in its open state to allow fluid to flow through the plunger.

It will be appreciated that a plunger arrangement of this type can be installed wherever necessary during the initial installation of the plant, and only used when necessary (which may not be for some considerable time). After installation, the plunger can rest at its downstream position with the valve in the passage through the plunger in its open state, allowing free flow of fluid in the pipeline.

Claims

1 . An arrangement of a plunger in a pipeline, wherein the plunger includes an axial passage extending in the same direction as the pipeline, the axial passage including a valve which can be used to open or close the passage, and wherein means are provided to move the plunger along the pipeline.

2. An arrangement as claimed in claim 1 , wherein means are provided to control the open or closed state of the valve.

3. An arrangement as claimed in claim 1 , wherein the valve is a one-way valve.

4. An arrangement as claimed in any preceding claim, wherein the plunger comprises at least one magnet, and the pipeline includes an electrical stator, such that supply of electrical power to the stator can be controlled to control the speed and direction of movement of the plunger.

5. An arrangement as claimed in any preceding claim, wherein stops are provided in the pipeline to limit the range of movement of the plunger.

6. An arrangement as claimed in claim 5 when dependent on claim 4, wherein the stops are located at the ends of the stator.

7. An arrangement as claimed in claim 5 or claim 6, wherein at least one of the stops is associated with a check valve disposed in the pipeline.

8. An arrangement as claimed in claim 7 when dependent on claim 3, wherein the check valve and the one-way valve both allow flow in the same direction along the pipeline.