WO2002096574A1

WO2002096574A1 - Intelligent pig

Info

Publication number: WO2002096574A1
Application number: PCT/GB2002/002277
Authority: WO
Inventors: Les Graves
Original assignee: Psl Technology Limited
Priority date: 2001-05-30
Filing date: 2002-05-30
Publication date: 2002-12-05
Also published as: GB0113006D0

Abstract

An apparatus in the form of a pipeline pig (10) for the efficient removal or treatment of water in pipelines (12) is described. The pig (10) includes one or more slugs (14,16,18) of a hydrate inhibiting material to remove the water and a sensor (24) to determine the degree of water content removal or treatment in the pipeline (12). In an embodiment, the sensor (24) measures water content in a rearmost slug (18) and transmits a signal (52) of the measurement to a remote location. The apparatus therefore finds application in subsea pipelines for the oil and gas industry.

Description

Intelligent pig

The present invention relates to techniques for the removal or treatment of water in pipelines used m the oil and gas industry and, in particular, although not exclusively, to an intelligent pig for determining the degree of such water content removal or treatment in a pipeline.

In a gas pipeline the accumulation of water or condensates causes an increase in the density of the transported gas which results in a reduced pipeline flow efficiency. The combination of water and gas can result in hydrate formation which if left untreated builds up as a scale on the walls of the pipeline and eventually blocks the pipeline. Hydrate formation is a major problem to the oil and gas industry due to the number and remote locations of pipelines used.

To prevent hydrate formation the inside of the pipeline needs to be kept dry or the residual water treated. A common process to dry or treat a pipeline is to perform a pigging operation. Such pigging operations require a pig ^λtrain' containing a slug or slugs of a hydrate- inhibiting compound to be passed through the pipeline. The slug causes a water removal and treating action as the hydrate-inhibitors absorb water as they pass through the pipeline. Any remaining water is also then treated by mixing with the compound. To achieve reliable drying of a pipeline typically requires the use of a pig train comprised of a number of slugs of hydrate-inhibitor passed through the pipeline. However once the pig train has passed through a pipeline, the effectiveness of the water content removal or treatment generally needs to be determined.

Currently, over land based or platform to platform pipelines a standard pig train is used and once passed through the pipeline the last slug on the pig is analysed to determine its water content level. Ideally the last slug in the pig should have hardly any, if any, water content on the basis that the earlier or foremost slugs in the pig had absorbed the remaining water in the pipeline. In the situation where the rearmost slug has a high water content, it would be appropriate to run a further pig train, to accomplish a more complete process.

The ability to determine whether a pipeline has been treated or dried in a subsea situation is far more difficult as it is extremely difficult and costly if not, impossible to recover the last slug for analysis. For this reason, it is usual in a subsea pipeline to run a pig train containing up to three times as much hydrate- inhibitor as one would expect is necessary. The addition of this safety feature has a detrimental cost implication, while also having a disadvantage in respect of environmental considerations, given that three times as much inhibitor may be discharged into the sea.

It is an object of the present invention to provide apparatus with the ability to determine the water content m-situ of a slug once the apparatus has passed through a pipeline.

Such apparatus may be referred to as an intelligent or a smart pig.

It is a further object of at least one embodiment of the present invention to provide an apparatus which when it has gathered the data on the water content level in the slug, can transmit the data to an operator in a remote location.

According to a first aspect of the present invention, there is provided apparatus to determine the degree of water content removal through a pipeline, the apparatus comprising one or more hydrate-inhibiting slugs and a sensor for determining water content in a slug.

The apparatus may be referred to as an intelligent pig or a smart pig.

Typically, the pipeline is a subsea pipeline.

Preferably the slug in which the water content is determined is the rearmost slug.

Preferably, the hydrate-inhibiting slugs are comprised of one or more materials being hydrate-inhibitmg compounds selected from a group comprising: salts, alcohols and glycols.

Preferably, the one or more hydrate-inhibiting slugs comprise a foremost slug, a rearmost slug and one or more slugs mounted there between. The foremost slug will contact the pipeline first, as the apparatus is moved through the pipeline. In a preferred embodiment,^' there are three slugs.

Preferably the sensor is located in proximity to the rearmost slug.

Preferably, the sensor is located forward of the rearmost slug.

Alternatively, the sensor is located behind the rearmost slug.

More preferably, the sensor abuts the rearmost slug. In this manner, the sensor is preferably in contact with the material of the slug.

It is known that as slugs within pigs pass through pipelines, there is a degree of turbulence caused within the slug material. This turbulence allows the slug mixture to remain reasonably homogenous, such that the sensor positioned at any point within, against or adjacent to the rearmost slug may provide a consistent measurement of water content.

The sensor may comprise one or more sensing elements contacting the material of the rearmost slug. The output of the sensor may then comprise the combined outputs of the sensing elements.

Preferably the sensor determines water content directly.

Alternatively the sensor measures electrical conductivity to determine the water content.

More preferably, the sensor measures specific gravity to determine the water content.

Preferably the apparatus further includes a data logger to store one or more water-content measurements. In this way if the apparatus is retrieved from the pipeline the water-content measurements may be downloaded.

More preferably the apparatus further includes means to transmit a signal representative of the water content.

Preferably, a transmitter is arranged to transmit a wireless signal to a receiver at a position remote from the apparatus.

Alternatively the transmitter may transmit a sonic or ultrasonic signal.

The apparatus may further include a power source. The power source may be a battery. Where the means to transmit a signal is via an umbilical, the power source may be positioned remotely and power may be supplied to the apparatus through the umbilical. The apparatus may include additional sensors to determine other parameters, such as pressure, temperature, acceleration, distance travelled and vibration of the apparatus within the pipeline. These additional sensors may be positioned at any point along the apparatus.

The apparatus may further include means for propulsion. The means for propulsion may move the apparatus along the pipeline. In this way the apparatus is not dependent on gas or fluid pressure within the pipeline to transport it through the pipeline. Preferably the means for propulsion is from gas such as natural gas or compressed gas. Alternatively the means for propulsion may be a motorised carriage.

According to a second aspect of the present invention, there is provided a method for determining the degree of water removal in a pipeline, the method comprising the steps:

(a) launching into the pipeline, apparatus including a moisture-absorbing material;

(b) propelling the apparatus along the pipeline to absorb moisture;

(c) performing an in-situ measurement of the water content in the material; and

(d) determining the degree of water removal by a comparison of the water-content measurement to a value of maximum acceptable water content. Preferably, the apparatus is propelled through the pipeline by gas pressure. Alternatively the apparatus is propelled by onboard propulsion means.

Preferably, the method includes the step of transmitting a signal representative of the water-content measurement. Preferably the signal is transmitted to a remote operator station.

Alternatively, the water-content measurement may be stored in an onboard data logger.

The method may further comprise the step of disposing of the apparatus in a pig trap.

A further step in the method may be in the deployment of a second apparatus, if the degree of water content removal is unsatisfactory in showing a water-content measurement higher than the maximum acceptable water content.

Thus, the present invention may provide real-time measurements of water content, as the pipeline is being dried off by the material of the slugs.

Embodiments of the present invention will now be described by way of example only, with reference to the following Figures, in which:

Figure 1 is a part cross-sectional view of an apparatus according to a first embodiment of the present invention, located within a section of pipeline; Figure 2 is a schematic diagram of a signal transmission system for the apparatus of Figure 1 in a subsea environment; and

Figure 3 is a second embodiment of the present invention presented in a similar manner to Figure 1.

Reference is initially made to Figure 1 of the drawings which depicts an apparatus in accordance with a first embodiment of the present invention. The apparatus is referred to as an intelligent pig and is indicated by reference numeral 10 in the Figure. Intelligent pig 10 is located within pipeline 12, being propelled along the pipeline in the direction X by the action of compressed gas.

Intelligent pig 10 comprises three slugs 14, 16, 18 and a sensor 24. The components of the intelligent pig 10 are arranged, such that there is a foremost slug 14, a divider 22b, an intermediary slug 16, a divider 22a, a rearmost slug 18 and sensor 24. The dividers 22a, b provide separation between each of the slugs 14, 16, 18. Each of the slugs 14, 16, 18 is made of a material which is a combination of glycol and methanol . There may be additional materials to hold the glycol and methanol in position to provide a slug which is of a gel-like consistency, alternatively the slugs 14, 16, 18 may be of a liquid type material. The slugs 14,16,18 may be formed of differing materials, but m all cases the materials will predominantly comprise hydrate-inhibiting compounds. As the slugs 14, 16, 18 pass through the pipeline 12, they will clear the pipeline 12 of water by absorption and will provide a cleaning action on the wall 20 of the pipeline 12.

Adjacent to the rearmost slug 18 is sensor 24. The front face 26 of sensor 24 abuts rear face 28 of rearmost slug 18. Mounted on the front face 26 of sensor 24 is sensing element 30. Sensing element 30 is an electrical conductivity sensor, which by a measurement of the electrical conductivity through the material of slug 18 can provide an indication of water content in slug 18. Data collected by the sensing element 30 is transmitted to a signal processing unit 32, where the signal is processed into an exact water-content measurement. The water-content measurement from signal processing unit 32 is transferred to a transmitter 34, where the signal is transmitted from the intelligent pig 10 to a remote location (not shown). In this embodiment, transmitter 34 is an acoustic transmitter, providing an acoustic signal capable of passing through the wall 20 of pipeline 12.

The sensing element 30, signal processing unit 32 and transmitter 34 are powered from a power supply 36. Power supply 36 is a long-life lithium battery capable of providing power to the intelligent pig 10 for hundreds of hours. Power supply 36 also provides power to a further sensor 38 mounted on the rear surface 40 of the sensor 24. Sensor 38 provides a dual measurement of pressure and temperature at the location of the intelligent pig 10 in the pipeline 12. It will be appreciated by those in the art that sensor 38 could include or be replaced by a sensor providing information on the location or acceleration of the intelligent pig 10 within the pipeline 12. An optional feature shown in Figure 1 is the presence of a data logger 42 mounted in relation to the signal processing unit 32. Data logger 42 records all measurements from the sensing element 30 and the water content determined data from the signal-processing unit 32. Data within the data logger 42 can be downloaded if the intelligent pig 10 is retrieved from the pipeline 12.

Reference is now made to Figure 2 of the drawings, which illustrates a signal transmission system for an intelligent pig, the pig being described hereinbefore with reference to Figure 1.

In Figure 2, intelligent pig 10A is located within pipeline 12A. Pipeline 12A is a subsea pipeline mounted on the seabed 44 by means of supports 46. The intelligent pig 10A is as described hereinbefore. The intelligent pig 10A has been launched into pipeline 12A from a pig launcher 48 located on pipeline 12A. Downstream of the pig launcher 48 is a pig trap 50, where the intelligent pig 10A is disposed of. Pig launcher 48 and pig trap 50 are as known in the art. As described hereinbefore, intelligent pig 10A travels in direction X through pipeline 12A, providing a drying process of the pipeline 12A. As it dries the pipeline 12A, a sensor within the intelligent pig 10A determines the water content within a rearmost slug 18 of the intelligent pig 10A. A transmitter within the intelligent pig 10A transmits a signal representative of the water-content measurement acoustically from the rear of the intelligent pig 10A. Acoustic signal 52 travels through the pipeline wall 20 and the sea 54 to an acoustic receiver 56 located from a ship 60 acting as a remote operating station.

In the Figure shown, further signals 62a, b and c demonstrate that the water-content measurement data can be onwardly transmitted by satellite to other locations 64a, b. Such additional transmission allows an operating signal to be transmitted, giving the instruction as to whether a further intelligent pig requires to be deployed into pipeline 12A if the degree of the water removal by the initial intelligent pig 10A is not satisfactory.

Reference is now made to Figure 3 of the drawings which depicts an intelligent pig 10B, according to a second embodiment of the present invention. Like parts to those of Figure 1 have been given the same reference numeral, but are suffixed "B".

Like the intelligent pig 10 of the first embodiment, intelligent pig 10B of the second embodiment is located within a pipeline 12B and is propelled in the direction marked by the arrow and X on the Figure.

Intelligent pig 10B comprises a foremost slug 14B and a rearmost slug 18B. These slugs 14B, 18B are composed of identical materials to those of the intelligent pig 10. Between the slugs 14B, 18B is mounted a sensor 24B. Sensor 24B comprises five sensing elements 30A to 30E, which project back from the rear surface 70 of sensor 24B into the rearmost slug 18B. Sensing elements 30A to 30E measure specific gravity within the rearmost slug 18B and transmit the signal to a signal-processing unit 32B, which averages the measurement across each of the sensing elements 30A to 30E. From signal processor 32B, a water- content measurement is determined from the specific gravity and the water-content measurement is stored in data logger 42B.

To the rear of the rearmost slug 18B is a propulsion unit 62. Propulsion unit 62 comprises a front face 74 which abuts the rear of the rearmost slug 18B and drives the rearmost slug forward and with it the intelligent pig 10B. Propulsion unit 62 is drive from a motor 64, and the unit propels the pig 10B from the motor driven wheels 66A,B. It will be appreciated that although only two wheels are shown 66A, B, there may be any number of wheels or other traction-bearing components in the intelligent pig 10B.

Connected to the rear of the propulsion unit 62 is an umbilical 68. Umbilical 68 carries power to the motor 64 and to the sensor 24B from a remote point down the pipeline 12B. In a further embodiment, the umbilical may transport signals from a remote location, not shown, to the intelligent pig and water-content measurements from the intelligent pig back to the remote station. In the second embodiment illustrated, the intelligent pig 10B is designed to be deployed into a pipeline 12B to project along the pipeline by means of the propulsion unit 62 and when the drying operation is complete, the intelligent pig 10B is retrieved by withdrawal of the umbilical 68, which pulls the pig 10B back out of the pipeline 12B. Once retrieved, the water-content measurement can be determined from the data logger 42B by downloading the water content information that is stored. In use, the intelligent pig is launched into a pipeline via a pig launcher. The pig is projected along the pipeline either by the fluid or gas pressure in the pipeline or by a projection unit on the intelligent pig. As the pig passes down the pipeline, the hydrate- inhibiting material in the slugs absorbs moisture and water through the pipeline, providing a drying process within the pipeline.

At the end of a run, a sensor within the pig has determined the water content m-situ in the rearmost slug of the pig. A signal representative of this water content is transmitted to an operator via either an umbilical attached to the back of the pig or by some remote sensing means, for example acoustic or radio- frequency signalling from the pig to a receiver positioned remotely from the pipeline. The water content measured is compared to a maximum acceptable water content and if the water content is above the maximum acceptable, a further pig can be run within the pipeline and the process repeated until an acceptable water content is reached. Once the pig has completed its run, it may either be retrieved back along the pipeline by use of the umbilical, if attached, or it may be released from the pipeline into a pig trap.

The principal advantage of the present invention is that it provides an m-situ determination of water content level, and thus the degree of water content removal from a pipeline. This advantage means a reduction in both costs and impact on the environment, as an optimum number and volume of slugs can be used to dry or treat the pipeline. A further advantage of the present invention is that by the in-situ measurement of water-content removal within a pipeline, a continuous measure of water content can be determined through a pipeline also.

Various modifications may be made to the present invention without departing from the scope thereof. For example, the remote transmitting means by which the signal representative of the water content is transmitted to a receiver, may in fact be done by a telemetry signal passed back or forward along the pipeline. Additionally, any number of slugs may be positioned in the intelligent pig to form a larger pig train, particularly if it is felt that there is a significant amount of water or moisture to be removed from the pipeline.

Advantageously, this technique could also be applied to the removal of other liquids of particulates found in pipelines which are amenable to the process of attaching themselves to a chemical compound which can be injected or propelled through the pipeline.

Claims

1. Apparatus to remove and determine the degree of water content removal through a pipeline, the apparatus comprising one or more hydrate-inhibitmg slugs to remove the water and a sensor for determining water content in a slug.

2. Apparatus as claimed in Claim 1 wherein the one or more slugs are arranged substantially m a train for passing through the pipeline, the train including a foremost slug and a rearmost slug.

3. Apparatus as claimed m Claim 2 wherein the sensor determines water content in the rearmost slug.

4. Apparatus as claimed in Claim 2 or Claim 3 wherein the sensor is located in proximity to the rearmost slug.

5. Apparatus as claimed in any preceding claim wherein the one or more hydrate-inhibitmg slugs include one or more materials being hydrate-inhibiting compounds selected from a group comprising: salts, alcohols and glycols.

6. Apparatus as claimed in Claim 5 wherein the sensor comprises one or more sensing elements contacting the material of the slug.

7. Apparatus as claimed in any preceding Claim wherein the sensor measures electrical conductivity to determine the water content.

8. Apparatus as claimed in any preceding Claim wherein the sensor measures specific gravity to determine the water content.

9. Apparatus as claimed in any preceding Claim wherein the apparatus further includes a data logger to store one or more water-content measurements.

10. Apparatus as claimed in any preceding Claim wherein the apparatus further includes means to transmit a signal representative of the water content.

11. Apparatus as claimed in Claim 10 wherein the means to transmit a signal is a wireless transmitter.

12. Apparatus as claimed in any preceding Claim wherein the apparatus further includes a power source.

13. Apparatus as claimed in any preceding Claim wherein the apparatus includes additional sensors to determine parameters other than water content.

14. Apparatus as claimed in any preceding Claim wherein the apparatus further includes propulsion means to move the apparatus through the pipeline.

15. A method to remove and determine the degree of water content removal through a pipeline, the method comprising the steps:

(e) launching into the pipeline, apparatus including a moisture-absorbing material;

(f) propelling the apparatus along the pipeline to absorb moisture;

(g) performing an in-situ measurement of the water content in the material; and

(h) determining the degree of water removal by a comparison of the water-content measurement to a value of maximum acceptable water content.

16. A method as claimed in Claim 15 wherein the method includes the step of transmitting a signal representative of the water-content measurement.

17. A method as claimed in Claim 15 wherein the method includes the step of storing the water-content measurement in an onboard data logger.

18. A method as claimed in any one of Claims 15 to 17 wherein the method further comprises the step of disposing of the apparatus in a pig trap.

9. A method as claimed in any one of Claims 15 to 18 wherein the method further comprises the step of deploying a second apparatus when the water-content measurement is higher than the maximum acceptable water content.