COLLIS, Sarah, Lai-Yue (105 Charlock Way, BurphamGuildford, Surrey GU1 1XY, GB)
BP CORPORATION NORTH AMERICA INC. (4101 Winfield Road, Warrenville, IL, 60555, US)
MAKOGON, Taras, Yurievich (11774 Duart Drive, Hedwig VillageHouston, TX, 77024, US)
COLLIS, Sarah, Lai-Yue (105 Charlock Way, BurphamGuildford, Surrey GU1 1XY, GB)
| Claims 1. A method of disintegrating, removing or reducing a blockage in a flowline using a remotely controlled tool, wherein there is a fluid in situ within the flowline adjacent or in the vicinity of the blockage and wherein the remotely controlled tool comprises a fluid intake means in fluid communication with a jet formation means, the method comprising: actuating the fluid intake means to draw at least a portion of the in situ fluid into the tool; and actuating the jet formation means to expel one or more jets comprising the fluid from the tool such that the or each jet is incident upon the blockage. 2. A method according to claim 1, wherein the pressure in the flowline is controlled so that hydrates present in the flowline are stable. 3. A remotely controlled tool for disintegrating, removing or reducing a blockage in a flowline, in which there is a fluid in situ within the flowline adjacent or in the vicinity of the blockage, the tool comprising: an actuatable fluid intake means adapted to draw at least a portion of the in situ fluid into the tool; and an actuatable jet formation means in fluid communication with the fluid intake means, the jet formation means being adapted to produce one or more jets comprising the fluid, the or each jet being incident upon the blockage, in use. 4. A tool according to claim 3, wherein the jet formation means comprises a nozzle head having one or more outlets. 5. A tool according to claim 4, wherein the nozzle head is mounted on a steering means. 6. A tool according to any one of claims 3 to 5, wherein the jet formation means is rotatable. 7. A tool according to any one of claims 3 to 6, wherein the fluid intake means comprises at least one inlet and a pump or compressor unit, the or each inlet being in fluid communication with the pump or compressor unit and the pump or compressor unit being in fluid communication with the jet formation means. 8. A tool according to any one of claims 3 to 7, further comprising a propulsion system. 9. A tool according to any one of claims 3 to 8, further comprising on-board power supply means. 10. A tool according to claim 9, wherein the on-board power supply means comprises electrochemical power supply means. 11. A tool according to any one of claims 3 to 10, having connected thereto a cable for one or more of: providing power to the tool and providing for the transmission of data, instructions or information between the tool and a control facility. 12. A tool according to claim 11, wherein the cable is self-retracting. 13. A train of two or more separate cars or units, each of which has its own propulsion system and a spool for a self-retracting cable, in which the frontmost car or unit comprises a tool according to any one of claims 3 to 12. |
FLOWLINE
This invention relates to a method and apparatus for re-starting the flow of a fluid through a flowline when the flowline has become blocked with a solid material such as gas hydrates, wax, mineral scale, asphaltenes or corrosion products. In particular, this invention relates to a method and apparatus for re-starting the flow of a fluid through a subsea flowline.
Subsea flowlines may be used in the oil industry for transporting produced fluids from a wellhead to a riser through which the produced fluid passes to a surface separation facility. The surface separation facility may be on a platform or a Floating Production Storage and Offloading (FPSO) vessel. Subsea flowlines may also be used for transporting gaseous streams comprising natural gas (gas export flowlines or gas injection flowlines). A problem may arise when a subsea flowline is used for transporting a multiphase fluid that comprises crude oil and/or gas condensate, produced water and produced gas in that the flowline may become blocked " with gas hydrate, owing to the temperature at the seabed being below the temperature at which gas hydrates are formed at typical flowline pressures, for example, the temperature external of the flowline may be in the range of from 4 to 7°C. Similarly, gas hydrates may form in a subsea flowline that is used for transporting a gaseous stream that comprises natural gas and produced water. Gas hydrates may also form in a land flowline when the ambient temperature is below the hydrate formation temperature at the flowline pressure. A problem may also arise when a subsea flowline or land flowline is used for transporting a heavy crude oil in that wax and/or asphaltene components of the crude oil may deposit onto the walls of the flowline. Similarly, mineral scale may deposit onto the walls of a flowline from the aqueous phase of a multiphase fluid. Finally, corrosion of the flowline may lead to corrosion products accumulating in the flowline. These deposits may restrict or prevent flow of the multiphase fluid.
It is known to unblock a flowline by using a tool to cut or drill a borehole through a blockage formed therein. Remotely controlled tools for use in a flowline, e.g. drilling or cutting tools for removing blockages in the flowline, may be connected either directly or indirectly to a cable linking the tool to a surface facility. The cable may supply electrical power to the tool and/or provide a data link between the tool and a surface-based controller. It is often necessary for the tool to travel a significant distance through the flowline in order to reach its site-of-use. For instance, a drilling tool may often be required to travel in excess of 10 km along a flowline in order to reach the blockage it is intended to remove.
Dragging a significant length (e.g. in excess of 10000 m) of cable through a flowline may lead to problems with the flowline and/or the cable. For instance, dragging the length of cable over an area of the wall of the flowline may create a groove or the like within the area of the wall i.e., result in erosion of the wall. This may render the pipeline more susceptible to spot corrosion in the vicinity of the groove.
Also, it will be appreciated that friction between the wall of the flowline and the cable may damage an outer, e.g. insulating, layer of the cable. A first aspect of the invention provides a method of disintegrating, removing or reducing a blockage in a flowline using a remotely controlled tool wherein there is a fluid in situ within the flowline adjacent or in the vicinity of the blockage and wherein the remotely controlled tool comprises a fluid intake means in fluid communication with a jet formation means, the method comprising: actuating the fluid intake means to draw at least a portion of the in situ fluid into the tool; and actuating the jet formation means to expel one or more jets comprising the fluid from the tool such that the or each jet is incident upon the blockage.
Preferably, the in situ fluid may comprise a liquid phase. This may often be the case, as hydrates may typically form in low spots within a flowline, where liquids would also be likely to collect, for example, upstream and/or downstream of the blockage.
Typically, the flowline is used for transporting a multiphase produced fluid comprising crude oil and/or gas condensate, produced water and produced gas. Accordingly, the in situ fluid may comprise a two phase mixture comprising a liquid phase and a gaseous phase. Alternatively, the flowline may be used for transporting a gaseous stream comprising produced natural gas and produced water. Accordingly, the in situ fluid may comprise a gaseous phase. The flowline may be a land or subsea flowline.
The flowline may be either completely blocked such that there is a plug in the flowline or partially blocked such that the flowline has a substantially reduced flow channel or bore, for example, a layer of gas hydrate, wax, asphaltene or mineral scale may be present on the inner walls of the flowline.
Where the flowline is completely blocked, the tool typically is used to create a borehole through the blockage. There may be a single blockage or a plurality of blockages in the flowline. Where there is a plurality of blockages in the flowline, pressure communication is achieved once a borehole has been created through all of the blockages. The person skilled in the art will understand that "pressure communication" is achieved when the pressure downstream of the blockage(s), is equal to the pressure upstream of the blockage(s) as a result of a borehole being created through the blockage(s) (where upstream and downstream refer to the direction of flow of fluids through the flowline prior to a complete blockage forming in the flowline). Pressure sensors in the flowline or at a surface separation facility may be used to determine if pressure communication has been achieved through removal of the blockage in the flowline. The pressure of the fluid upstream of a complete blockage (plug) or a plurality of blockages (plugs) is typically at least 100 bar, for example, 150 to 300 bar.
Where the flowline is partially blocked, the drilling or cutting tool may be used to remove deposits from the wall of the flowline thereby increasing the available flow channel or bore through the flowline. The tool may be deployed into the flowline and approach the blockage from either the upstream or downstream direction (where upstream and downstream are defined as above). Where the tool is deployed from a platform, the tool will approach the blockage from the downstream direction. However, where the tool is deployed via a subsea entry point, the tool may approach the blockage from either the upstream or downstream direction.
A second aspect of the invention provides a remotely controlled tool for disintegrating, removing or reducing a blockage in a flowline, in which there is a fluid in situ within the flowline adjacent or in the vicinity of the blockage, the tool comprising: an actuatable fluid intake means adapted to draw at least a portion of the in situ fluid into the tool; and a jet formation means in fluid communication with the fluid intake means, the jet formation means being adapted to produce one or more jets comprising the fluid, the or each jet being incident upon the blockage, in use. Preferably, the jet formation means may comprise a nozzle head having one or more outlets. Accordingly, the tool may expel one or more jets comprising the fluid, in use. Preferably, the nozzle head may comprise up to 50, more preferably up to 20, outlets. For instance, the nozzle head may comprise between 2 and 15 outlets. Typically, the outlets are arranged such that the jets are incident upon the blockage at a plurality of different locations and at a plurality of different angles.
In one embodiment, the nozzle head may comprise a central outlet for emitting a central forward jet and a plurality, say from 4 to 12, further outlets arranged, preferably regularly-spaced, around the central outlet. Each of the further outlets may be adapted to emit a jet which diverges, converges or is parallel with the central forward jet.
The or each outlet may be operable individually, e.g. one or more of the outlets may be closed while others are open, in use.
The nozzle head may be mounted on a steering means, preferably an electrically actuatable steering means, to allow adjustment of the orientation of the nozzle head. The steering means may comprise a steerable joint. Preferably, the steering means may be comprise a continuously variable bent-sub or a continuously rotary steerable system that is capable of adjusting the orientation of the nozzle head relative to the longitudinal axis through the tool by from 0 to 10°, for example, from 0 to 5°.
Preferably, the jet formation means, e.g. nozzle head, is rotatable. Preferably, the fluid intake means may comprise at least one inlet in fluid communication with a pump or compressor unit, which is then in fluid communication with the jet formation means, e.g. nozzle head. The pump or compressor unit is adapted to provide a relatively high pressure stream to the jet formation means. The pump or compressor unit may comprise a single stage or multistage pump or compressor. Accordingly, if the in-situ fluid is primarily liquid, a pump can be used, whereas if the in- situ fluid is primarily gas, a compressor can be used. Preferably, the pump unit will be tolerant of multiphase fluids.
Typically, the tool further comprises a propulsion system. The propulsion system may comprise a traction means, in particular, an electrically operated traction means. Suitable traction means include a wheeled tractor, bristle-brush tractor, gripper tractor or push-pull tractor.
The tool may further comprise on-board power supply means, e.g. to provide electrical power to one or more of the fluid intake means and/or the or a propulsion system and/or the or a steering means. Accordingly, the tool may be autonomously powered and/or propelled.
Preferably, the on-board power supply means may comprise an electrochemical power supply means such as a battery and/or a fuel cell. Alternatively or additionally, the on-board electrical power supply means may comprise an atomic battery. Typically, the on-board electrical power supply means should have a high power to weight ratio.
A suitable electrochemical battery may be of the type generally known as traction batteries. For instance, a lithium ion battery, a lithium polymer battery or a lithium thionyl chloride battery may be suitable.
A preferred fuel cell may be a proton exchange membrane (PEM) fuel cell. Preferably, the fuel may comprise methanol, e.g. a methanol/water mix. Alternatively, the fuel may comprise propane. Accordingly, the tool may be provided with a tank for the fuel. The provision of on-board electrical power supply means gives certain advantages.
For instance, a tool having on-board power supply means can be introduced into a flowline from an unmodified pig launcher. In contrast, when the tool is deployed by wireline, i.e. on a cable, typically it is necessary to provide additional components such as a blow-out preventer, a winch system for lowering and raising the tool into and out of the flow line, and a wireline stuffing box and a grease seal, the wireline stuffing box and grease seal being provided to assure passage of the cable into the flowline without loss of flowline fluids into the environment. A further advantage over cable- or wireline-deployed tools is that a tool having on-board power supply means may exit the flowline via a different path from the one it took to get to the blockage. Nevertheless, the tool may be deployed on a cable, e.g. an electrical cable for providing power to the tool. The cable may further provide for the transmission of data, instructions or information between the tool and a control facility. Advantageously* a tool may be able to operate for longer periods within a flowline when it is powered via a cable rather than its own on-board power supply means. Alternatively, the tool may be deployed on tubing, e.g. coiled tubing. If the tool is deployed on tubing, then the pump unit may be powered mechanically at least in part by fluid circulation through the tubing. It is also envisaged that fluid that is circulated through the coiled tubing may be used as part of the intake for the jet formation means. Thus, the fluid that is circulated through the coiled tubing may be mixed with the in situ fluid and the resulting mixture may be fed to the jet formation means. Where the fluid that is circulated through the coiled tubing is fed to the jet formation means, it is preferred that this fluid is capable of dissolving the blockage.
It is also envisaged that when the tool is not deployed on tubing, it may be provided with a reservoir or tank for a treatment chemical that is capable of dissolving the blockage and that this treatment chemical may be mixed with the in situ fluid to assist in removal of the blockage. The pump unit may be autonomously or remotely powered by means of chemical, mechanical, electrical, gravitational or magnetic energy, or a combination thereof. When the tool is cable- or wireline-deployed, it may further comprise a self- retractable cable. The self-retractable cable may be provided on a spool provided in or on the tool. In-use, the self-retractable cable may unwind from the spool as the tool travels towards the blockage. Preferably, the self-retractable cable may be wound back on to the spool as the tool is being retrieved from the flowline.
The tool may comprise a train of two or more, e.g. from 3 to 10, separate cars or units, each of which has its own housing and propulsion system and each of which further comprises a spool for a self-retracting cable. A single self-retracting cable may pass along the entire train from one spool to the next. Alternatively, a series of shorter self-retracting cables may be provided. For instance, a discrete self-retracting cable may be provided between each pair of adjacent cars or units. Thus, the cars are joined together via either the single self-retracting cable or the series of shorter self-retracting cables. Components of the tool may be distributed between the cars. For example, the nozzle head and steering means may be provided on a first car, the pump unit and fluid intake means on a second car, and where the tool is provided with an on-board power supply means, this power supply means may be provided on a third car. Where the components of the tool are located on different cars, where necessary, electrical communication means (typically, an electrical cable) and/or fluid communication means (typically, a flexible conduit) may be provided between the cars. It is therefore envisaged that the self-retracting cable may be an electrical cable and/or may be provided with a fluid conduit (an internal channel or bore). Suitably, the tool may be provided with sensors that are in communication with recording equipment at the surface. This communication may be achieved wirelessly, e.g. by radio or acoustic communication and/or through a wire or cable, e.g. via an electrical or fibre optic cable. Suitably, the sensors are located in proximity to the jet formation means, e.g. close to the nozzle head. However, it is also envisaged that sensors may extend along the length of the tool, for example, there may be sensors for each of the separate cars. These sensors may monitor the temperature and pressure at the jet formation means or the level of in situ fluid and the precise location of the tool in the flowline (determined using internal sensors). Data may be continuously or intermittently sent to the surface, thereby allowing the tool, and hence the unblocking operation, to be controlled in real-time. Thus, the signals received at the surface may be monitored and instructions may be sent to the tool, e.g. to the jet formation means, fluid intake means or the or a steering means, in response to these signals. Preferably, the signals that are transmitted between the surface and the tool are controlled by a telemetry unit that is located within the housing of the tool. Alternatively, the tool may be provided with programmable control means in communication with the or each sensor, which may be pre-programmed so that the tool "knows" how to react when certain conditions or situations (as indicated by the measurements or data received from the or each sensor) are encountered. For instance, the control means may be programmed so as to cause the fluid intake means to stop working when the level of in situ fluid falls below a critical level. By providing programmable control means onboard the tool, there may be no need for real-time communication between the tool and the surface. Also, the control means may be programmed to suit the characteristics of a given flowline in which the tool is to be deployed.
According to another aspect of the invention there is provided a tool for use in a flowline, the tool or a part thereof being connected directly or indirectly to an electrical cable, the cable connecting the tool, in use, with a structure or facility outside the flowline, wherein at least a portion of the cable is self-retracting.
Optionally, the pressure in the flowline is controlled so that hydrates in the flowline are stable. The relationship between pressure and temperature and their effect on the stability of hydrates is well known. As the temperature decreases and/or as the pressure is increased, hydrates are more likely to form. By keeping the pressure in the flowline high enough for the particular fluid temperature in the flowline so that hydrates are stable, the debris from drilling the blockage will stay in the form of individual particles which can be removed, for example when flow through the flowline is resumed. If the hydrate debris is allowed to dissociate, there is a risk that it may re-form, thereby creating a new hydrate blockage behind the tool. Preferably, the tool may comprise any of the tools described herein.
The invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 shows a part of a flowline in which a blockage has formed; Figure 2 shows a blockage being broken down using a tool according to the invention; and Figure 3 shows an embodiment of a cable-deployed tool according to the invention.
Referring to Figure 1, there is shown in cross section a part of a flowline 1. The flowline 1 is a multiphase flowline, through which fluid normally flows in the direction of the arrow A. The part of the flowline 1 shown in Figure 1 comprises a low point 5. In the region of the low point 5, a gas hydrate blockage 2 has formed. On the downstream side of the gas hydrate blockage 5, there has accumulated a body of liquid 3.
As shown in Figure 1 , a remote controlled tool 4 is approaching the gas hydrate blockage 5 from the downstream side of the gas hydrate blockage 5. The tool 4 is a self- propelled tool, i.e. it has onboard power supply means. Alternatively, the tool 4 could be a cable- or wireline-deployed tool. The tool 4 comprises a traction means 6. The traction means may comprise a wheeled tractor, a bristle-brush tractor, a gripper tractor or a push- pull tractor.
Figure 2 shows in cross section, looking down on the part of the flowline 1, the tool 4, in use. As can be seen in Figure 2, the tool 4 further comprises a nozzle head 7 having a plurality of outlets. Liquid 3 is drawn into the tool 4 by fluid intake means (not shown) and then expelled from the tool 4 via the nozzle head 7 towards the blockage 2 as a plurality of jets.
A single-phase centrifugal or a multi-phase gear pump of approximately 1 HP rating may be suitable for drawing fluid into the tool and subsequently circulating it at higher pressure to the jetting head. Preferably, the tool may be provided with a rotating or rotatable nozzle head so as to achieve more uniform jetting of a blockage. The nozzle head may be rotatable at speeds of from O to 10,000 rpm. Figure 3 shows a cable-deployed tool within a section of flowline 8. The tool is made up of a "train" comprising a front "car" 9 and a rear "car" 12. The front car 9 comprises a propulsion system 11. The front car 9 further comprises a spool 10 around which is wound a first self-retracting cable 15. The first self-retracting cable 15 connects the front car 9 to the rear car 12.
The rear car 12 comprises a propulsion system 14. The rear car 12 further comprises a spool 13 for a second self-retracting cable 16. As shown in Figure 3, the second self- retracting cable 16 is unwound from its spool. The second self-retracting cable 16 connects the second car to a further car (not shown) in the train or to a control facility (not shown).
The train may comprise any number of cars comprising one or more spools for a self- retracting cable. A single self-retracting cable may pass through the entire train, the single self-retracting cable being wound and unwound around the each of the spools in turn, as the tool moves forwards and backwards along a flowline. It is envisaged that as the tool makes its way along the flowline, initially a first spool will unwind until it can unwind no further, at which point a second spool will unwind until it can unwind no further and so on, the pattern taking place in reverse when the tool is being retrieved from the flowline.
Advantageously, if the first spool to unwind is at the rearmost spool within the train, the second spool to unwind is the next rearmost and so on, it will be appreciated that the cable(s) once unwound will essentially remain still within the flowline and will not be dragged any significant distance. Accordingly, cable friction and wear on the wall of the flow line may be substantially reduced.
Furthermore, a train of cable-linked cars may provide a tool which can negotiate relatively tight corners.
It is envisaged that any wireline- or cable-deployed tool for use in a flowline may benefit from being deployed in this way. For instance, the front car of a train could comprise any of the tools described herein. Also, a remotely controlled electrically operated drilling tool as disclosed in international patent application number PCT/GB2008/003888 could beneficially be deployed in this way, e.g. the front car of a train could comprise such a tool.