The present invention relates to a downhole tool, such as a circulating sub, for cleaning a borehole, comprising a housing defining a longitudinal direction, a first fluid conduit extending from an opening in a first end of the housing to an opening in a second end of the housing, and an activation mechanism configured to at least activate the downhole tool, the housing further has an outer side surface facing an inner wall of the borehole, when positioned in the borehole, and an inner side surface facing the first fluid conduit, the first fluid conduit is configured to lead a drilling fluid from the first end to the second end, the housing further has at least a second fluid conduit extending from at least a first opening connected to the first fluid conduit to a second opening arranged in the outer surface, the at least second fluid conduit is configured to lead a part of a drilling fluid from the first fluid conduit to an annulus between the downhole tool and the inner wall of the borehole, when the downhole tool is activated, and at least a first nozzle is arranged at the second opening of the at least second fluid conduit.

The present invention also relates to a drill string for positioning in a borehole, comprising at least two downhole tools as described above. Background of the Invention

It is well known that circulating subs comprises an activation mechanism for activating the circulating sub, wherein this activation causes one or more fluid conduits to open, thereby enabling a part of the drilling fluid to bypass the central fluid conduit and to enter the annulus between the circulating sub and the inner wall of the bore- hole. Some activation mechanisms are also able to close the fluid conduits again without having to retrieve the circulating sub and reset the activation mechanism. The activation mechanism can be triggered by dropping a ball into the drilling fluid at ground level where the ball is caught by a ball retainer in the circulating sub. It is also known to trigger the activation mechanism by dropping a RFID chip into the drilling fluid where a RFID antenna detects the presence of the RFID chips and a control unit activates the movement of a sleeve. It is known that the circulating sub comprises a central valve sleeve that is moved axi- ally along the housing. When activated, an opening in the sleeve is moved into alignment with a fluid conduit in the housing so that a part of the drilling fluid can exit through this fluid conduit, such as disclosed in EP 0787888 A2.

The bypassed drilling fluid in these solutions exits the fluid conduit with a low velocity and at an angle of 90° relative to the longitudinal direction of the circulating sub. This slowly flowing bypass fluid contributes to lowering the equivalent circulating density (ECD) and increasing the annular flow and velocity thereof. However, this solution has a very limited cleaning effect and lifting effect on the solid particles transported in the drilling fluid returning to ground level. Further, some of the bypass fluid follows a Vortex generated below the opening and, thus, flows back towards to the drill bit as confirmed by simulations. This Vortex increases the risk of solid particles, such as cuttings or swarf, accumulating and thus causing a packoff.

Some circulating subs have a nozzle arranged at the outer opening of this fluid conduit, wherein the fluid conduit is placed at a perpendicular angle relative to the longitudinal direction of the circulating sub. This nozzle increases the velocity of the exiting bypass fluid which, in turn, contributes to lowering the ECD and increasing the annular flow and velocity thereof. This accelerated bypass flow directly hits the inner wall, thereby generating a jet impact effect which contributes to erosion of any filter cakes formed on the inner wall. It also generates a strong Vortex above and below the nozzle which means that some of the bypass fluid will flow back towards the drill bit, thereby increasing the risk of solid particles accumulating and thus causing a packoff. This negative effect of the Vortex is confirmed by simulations and is illustrated in fig. 5.

In other circulating subs, such as in US 2013/0284424 Al, the fluid conduit is placed in a relatively small acute angle so that the outer opening is facing substantially towards the drill bit. However, in this fluid conduit a removable barrier is provided at the outer opening to initially prevent drilling fluid from exiting the fluid conduit. No details about the angle of the fluid conduit are provided, nor is it suggested if the bypassed drilling fluid has a cleaning effect or not. Until now the circulating sub industry has mainly been concerned with lowering the ECD and improving the borehole cleaning effect by increasing the annular flow and velocity of the returning drilling fluid. It has not previously been proposed to use directional nozzles to improve the cleaning effect and transport effect in a borehole. Secondly, simulations have not previously been used in the circulating sub industry to verify the performance of existing circulating subs.

Until now directional nozzles have only been proposed in bit nozzle systems where the jet impact effect generated by these nozzles is used to erode the underground for- mation. In such systems, as disclosed in US 4479558 A, the directional nozzles are situated just behind the drill bit and are placed in an acute angle so the nozzles face away from the drill bit. As stated, the bypass fluid exits the nozzles at a high velocity, thereby the bypass fluid provides a whirling effect which creates a strong Vortex below the opening. As further stated, this Vortex is necessary in order to lower the fluid pressure at the drill bit and, thus, improve the cutting process.

An alternative bit nozzle system is disclosed in US 4475603 A which uses a cyclone separator to divide the drilling fluid into a more dense portion and a less dense portion. The less dense portion is lead to the drill bit while the denser portion is lead into the annulus via nozzles placed in an acute angle. As stated, the dense fluid exits the nozzle at a high velocity, thereby reducing the hydrostatic pressure at the drill bit and improving the drilling process. As mentioned in relation to US 4479558 Al, this creates a Vortex below the opening which is necessary in order to lower the fluid pressure.

The Vortex effect generated in both US 4479558 A and US 4475603 A is undesired further up the drill string since it significantly reduced the borehole cleaning effect and can potentially damage the inner wall. Such bit nozzle systems can therefore only be used next to the drill bit.

An alternative downhole tool is disclosed in US 6543532 B2 which solves the same problem as disclosed in both US 4479558 A and US 4475603 A. An electrical motor and control means in this circulating sub are connected to electrical cables extending to ground levels for receiving power and control signals. These electrical cables are likely to get damaged or otherwise will fail due to distance between ground level and the position of the circulating sub. The electrical motor activates the movement of a valve sleeve which, in the open position, completely closes off the axial fluid conduit so that all the drilling fluid is lead out of the bypass conduits through nozzles to pro- vide a cleaning effect. However, this solution cannot be used simultaneously with operating the drill bit since the downwardly flow is closed off when the circulating sub is activated. This limits the functionality of the circulating sub.

US 6543532 B2 states that the nozzles are placed in an inclined angle so they create a whirling effect in the returning flow. This indicates that the drilling fluid exits the nozzles at a high velocity due to the increased volume being lead out through the nozzles, thus generating a Vortex below the nozzles similar to that of US 4479558 A and US 4475603 A. This solution is therefore unsuitable for positions further up the drilling string. Secondly, US 6543532 B2 does not provide any further details about the angle of the nozzles.

Object of the Invention

An object of the invention is to provide a downhole tool that solves the above- mentioned problems. Another object of the invention is to provide a downhole tool that provides an improved cleaning effect, particularly during drilling operations.

Yet another object of the invention is to provide a downhole tool that provides an improved transport effect while reducing the risk of packoffs.

An object of the invention is to provide a drill string that enables solid particles to be transported to ground level while reducing the risk of the solid particles accumulating in the annulus.

Description of the Invention

An object of the invention is achieved by a downhole tool, such as a circulating sub or a cleaning tool, for cleaning a borehole, comprising a housing defining a longitudinal direction, a first fluid conduit extending from an opening in a first end of the housing to an opening in a second end of the housing, and an activation mechanism configured to at least activate the downhole tool, the housing further has an outer side surface facing an inner wall of the borehole, when positioned in the borehole, and an inner side surface facing the first fluid conduit, the first fluid conduit is configured to lead a drilling fluid from the first end to the second end when the downhole tool is not acti- vated, the housing further has at least a second fluid conduit extending from at least a first opening connected to the first fluid conduit to a second opening arranged in the outer surface, at least a first nozzle is arranged at the second opening of the at least second fluid conduit, characterised in that, the at least second fluid conduit is placed in a first acute angle relative to at least the longitudinal direction so that the at least sec- ond fluid conduit substantially extends towards one of the first and second ends, and wherein at least a third fluid conduit extends from a third opening connected to the first fluid conduit to a fourth opening arranged in the outer surface and at least a second nozzle is arranged at the fourth opening of the at least third fluid conduit, wherein the at least third fluid conduit is placed in a second acute angle of relative to at least the longitudinal direction so that the at least third fluid conduit substantially extends towards one of the first and second ends and wherein said first and second acute angle is between 30° and 65°.

This provides a downhole tool with an improved cleaning effect and improved transport effect compared to conventional downhole tools. This configuration utilizes a nozzle system, preferably a jet nozzle system, to lead some of the drilling fluid back into the annulus. The present configuration eliminates the formation of Vortexes around the nozzles by directing the bypassed drilling fluid into the annulus at a predetermined acute angle, thereby reducing the risk of solid particles accumulating and thereby causing a packoff. Secondly, the present configuration eliminates the risk of the bypassed drilling fluid causing an erosion of the inner wall of the borehole, thus all the energy of the bypassed drilling fluid is used to clean the annulus and to lift cuttings, swarf or other solid particles towards ground level. Unlike conventional techniques used in the circulating sub industry, simulations have been used to verify the effects of the present invention.

The simulations have shown that the optimal cleaning effect is achieved by placing the outer openings of the fluid conduits, i.e. the second and optional third fluid conduits, and thus their respective nozzles in an acute angle between 15° and 65°, in par- ticular between 30° and 65°, relative to the longitudinal direction of the downhole tool. The present configuration enables the fluid conduit to be angled so that it substantially faces towards the first or second end depending on the desired application. The present downhole tool can be used in any application in a borehole or wellbore in which a cleaning effect is desired, such as when drilling, milling, polishing, sidetracking, and other suitable applications.

The downhole tool comprises a housing having a first end and a second end, wherein each end is outfitted with suitable coupling means, such as a male or female threaded coupling, for mounting to other components of a drill string. Other suitable coupling means may also be used, such as a locking coupling. This enables the downhole tool to be connected to other components of the drill string, such as milling tools, sidetracking tools, Whipstocks, pipe sections, packers, line hangers or other downhole tools.

The housing has one or more first fluid conduits extending from the first end of the housing to the second end of the housing for leading a drilling fluid, e.g. mud, through the downhole tool and further towards the bottom hole assembly (BHA). The housing further has one or more inner side surfaces that define the inner walls of the first fluid conduits and an outer side surface which faces the inner wall of the borehole, when inserted into the borehole. This allows the drilling fluid to flow through the downhole tool when the downhole tool is not activated.

The housing further comprises at least one set of second fluid conduits for leading the drilling fluid into the annulus located between the downhole tool and the inner wall of the borehole. Each set comprises at least one, e.g. two, three, four or more, individual second fluid conduits distributed along the circumference of the housing. Each second fluid conduit has an inner opening arranged in the inner side surface and an outer opening arranged in the outer side surface. The second fluid conduits may be config- ured to be closed off, when the downhole tool is not activated or deactivated, and to be opened, when the downhole tool is activated, as described later. This allows a part of the drilling fluid to bypass the opening in the second end and instead flow directly into the annulus. A nozzle is arranged at all or some of the outer openings of the second fluid conduits. The nozzle may be formed as part of the housing, i.e. integrated into the housing, or be mounted to the housing during assembly of the downhole tool. The nozzle may be configured to increase the velocity of the drilling fluid exiting the second fluid conduit for improving the cleaning effect and the lifting effect of the downhole tool.

According to one embodiment, the at least second fluid conduit is configured to lead a part of a drilling fluid from the first fluid conduit to an annulus between the downhole tool and the inner wall of the borehole, when the downhole tool is activated, while the remaining drilling fluid is lead through the downhole tool via the first fluid conduit.

The present downhole tool does not completely block of the first fluid conduit as in US 6543532 B2, instead the present downhole tool ensures that drilling fluid is continuously lead through the downhole tool even when it is activated. This allows the present downhole tool to be used during drilling and in combination with other down- hole tools, such as drill bits, rotary steering systems and motors which require a continuous flow in order to function properly. This increases the functionality of the present downhole tool. According to one embodiment, the downhole tool further comprises at least a third fluid conduit extending from a third opening connected to the first fluid conduit to a fourth opening arranged in the outer surface, at least a second nozzle is arranged at the fourth opening of the at least third fluid conduit, wherein the at least third fluid conduit is placed in a second acute angle relative to at least the longitudinal direction so that the at least third fluid conduit substantially extends towards one of the first and second ends.

The housing may further comprise at least one set of third fluid conduits also for leading the drilling fluid into the annulus. Each set comprises at least one, e.g. two, three, four or more, individual third fluid conduits distributed along the circumference of the housing. Each third fluid conduit has an inner opening arranged in the inner side surface and an outer opening arranged in the outer side surface. The third fluid conduits may be configured to be closed off, when the downhole tool is not activated or deactivated, and to be opened, when the downhole tool is activated, as described later. This further allows a part of the drilling fluid to bypass the opening in the second end and instead flow directly into the annulus.

The downhole tool may comprise at least two sets of fluid conduits, e.g. second and third fluid conduits, arranged relative to each other along the circumference of the housing.

In example, the second fluid conduits may be aligned with or offset from the third fluid conduits in a longitudinal direction. This allows for a more optimal cleaning ef- feet as the bypassed drilling fluid is distributed over a plurality of fluid conduits.

The size and orientation of each second fluid conduit and/or third fluid conduit of each respective set may be optimised to reduce annular friction factor which, in turn, reduces the ECD.

According to a special embodiment, the second fluid conduit and the at least third fluid conduit substantially extend towards opposite ends or towards the same end.

The second or third fluid conduits may be orientated so that they and their correspond- ing nozzle substantially face towards the first or second end. Alternatively, one group of second or third fluid conduits may substantially face towards the first end, while one other group of second or third fluid conduits may substantially face towards the second end. This enables one group to be used for cleaning while the other group can be used for transporting the solid particles towards ground level.

Alternatively, the second fluid conduits may be orientated so that they and their corresponding nozzle substantially face towards the first end while the third fluid conduits may be orientated so that they and their corresponding nozzle substantially face towards the second end, or vice versa. This enables one set of fluid conduit to be used for cleaning, while the other set of fluid conduits can be used for transporting the solid particles towards ground level.

Preferably, the downhole tool further comprises one or more fourth fluid conduits each extending from a fifth opening connected to the first fluid conduit to a sixth opening arranged in the outer surface, at least a third nozzle is arranged at the sixth opening of the at least fourth fluid conduits. The at least fourth fluid conduit is preferably placed in a third acute angle relative to at least the longitudinal direction so that the at least third fluid conduit relative to the longitudinal direction of the down hole tool and substantially extends towards the drill bit end, i.e. in downhole direction, of the down hole tool.

This configuration is particularly useful for removing chips that are drilled off by the drill bit, e.g. when drilling out an existing steel tubing in a down hole. The chips that are cut off during drilling are removed from the drilling area substantially immediately after being cut away. Then they are carried away from the drilling area by means of the fluid flow from the fourth fluid conduits. The fluid flow is led upwards in the an- nulus. When the chips are removed from the drilling area, they are not aggregating in the drilling area, which may cause that they are subjected to disintegration by the drilling tool. The larger drilled off chips are more easily transported in up-hole direction than disintegrated chips that have been caught by the drill bit and thus have a smaller average particle size.

In yet another alternative, the second and third fluid conduits may be orientated so that they and their corresponding nozzle substantially face towards the same end, e.g. the first or second end. This enables the second and third fluid conduits to be used for cleaning the borehole and transporting the solid particles towards ground level.

By orienting the fourth conduits, or a group thereof, towards the second end, e.g. in the opposite direction of the returning flow in the annulus, these fluid conduits can be used to clean indentations, pockets or other inaccessible areas which normally cannot be cleaned by the returning flow in the annulus. This is particularly suited for milling and sidetracking applications. According to another special embodiment, the first acute angle differs from the at least second acute angle.

Each of the second and third fluid conduits extends in a direction defined by their respective inner and outer openings. The second fluid conduit may be placed in a first angle, e.g. a first acute angle, measured relative to the longitudinal direction of the downhole tool. The third fluid conduit may be placed in a second angle, e.g. a second acute angle, also measured relative to the longitudinal direction of the downhole tool. The first and second acute angles may be measured in the same axial direction or in opposite axial directions.

The first acute angle of the second fluid conduit may be greater than the second acute angle of the third fluid conduit, or vice versa. This allows the second and third fluid conduits to cover and, thus, clean a greater total area. The first and second acute an- gles may be selected depending on the intended application, the operating parameters of the drilling fluid, and/or the desired size and configuration of the downhole tool.

Alternatively, the first acute angle of the second fluid conduit may be equal to the second acute angle of the third fluid conduit. This allows the second and third fluid con- duits to concentrate the cleaning over a smaller area.

If the second or third fluid conduits are divided into groups, as described earlier, one group may be placed in a third angle, e.g. a third acute angle, while another group may be placed in a fourth angle, e.g. a fourth acute angle. The third and fourth acute angles may be measured relative to the longitudinal direction of the downhole tool. This also allows the second or third fluid conduits to cover and thus clean a greater total area.

According to yet another special embodiment, the at least second fluid conduit is placed in a first acute angle between 30° to 50°, and the at least third fluid conduit is placed in a second acute angle between 50° to 65°.

The second fluid conduit may be placed in a first acute angle between 30° to 50°, while the third fluid conduit may be placed in a second acute angle between 50° to 65°. The second and third fluid conduits may substantially face in the same direction. This configuration provides the best cleaning effect which has been verified by simulations. In example, but not limited to, the second fluid conduit may be placed in a first acute angle of between 30° and 65°, or between 30° and 60°, or 40° to 50°, e.g. 45°, while the third fluid conduit may be placed in a second acute angle between 55° to 65°, e.g. 60°. If the second and third fluid conduits substantially face in opposite directions, then the acute angle of the fluid conduit substantially facing towards the second end may be between 30° and 50°, while the acute angle of the other fluid conduit substantially facing towards the first end may be between 50° and 65° This provides the best cleaning effect and transport effect which also have been verified by simulations.

Preferably, the lower most third fluid conduits (when seen in downhole direction ) are angled at a larger acute angle than the uppermost second fluid conduits relative to the longitudinal direction of the downhole tool. Alternatively, the second and third fluid conduits have the same acute angle relative to the longitudinal direction of the down- hole tool.

The best configurations have been found to be a solution having second fluid conduits and third fluid conduits provided at angles of 45° and 60° respectively or at 45° and 45° respectively, and with both fluid conduits directed in uphole direction. This allows for an increased upflow of the drilling fluid and may lead to a flow of 150% or more flow can be pumped through the drill pipe without exceeding a generalized ECD.

The results from several simulations show the third fluid conduits at the 60°, which is preferably arranged at a lower level (when seen in downhole direction ) than the sec- ond fluid conduit, which provided at an angle of 45° helps the upper flow coming from the 45° fluid conduit (upper fluid conduits) to be diverted upstream and increasing the velocity, while the upper nozzle in the second fluid conduits allow a higher mud flow to be exerted through the annulus, whereby both also improve aspects of hole cleaning.

According to a further special embodiment, the first nozzle and the at least second nozzle have different sizes. The nozzle may have a fixed size, e.g. a nozzle diameter, or an adjustable nozzle size which can be adjusted during assembly or during operating of the downhole tool. The nozzle size may be selected dependent on the intended application, the operating parameters of the drilling fluid, and/or the desired size and configuration of the down- hole tool. The nozzle size should be selected to prevent the formation of Vortexes and/or erosion of the inner wall of the borehole.

According to one embodiment, the housing further defines a circumferential direction, wherein at least one of the second and third fluid conduits is placed in a combined first or second acute angle relative to the longitudinal direction and the circumferential direction.

The second and/or third fluid conduit may substantially be arranged in an axial, i.e. longitudinal, plane so that the fluid conduit substantially extends in an axial direction. The inner and outer openings of that fluid conduit may thus be located in the same radial plane. This enables the nozzles to generate a flow parallel to the longitudinal direction of the downhole tool which is transformed into a rotational flow, i.e. a spiral shaped flow, as the drill string rotates, thereby cleaning the borehole. The second and/or third fluid conduit may substantially be arranged in a plane defined by a chord of the downhole tool so that the fluid conduit substantially extends in a combined axial and circumferential direction. In this arrangement, the inner opening of that fluid conduit may be located in a first radial direction while the outer opening of that fluid conduit may be located in a second radial direction. This enables the noz- zles to generate a rotational flow around the downhole tool, thereby cleaning the borehole even if the drill string is not rotating.

The second and/or third fluid conduit and thus the nozzle thereof may be placed in a third acute angle between 15° and 65°, preferably between 30° and 65°, or between 30° and 60° e.g. between 30° and 50°, relative to the longitudinal direction. The second and/or third fluid conduit and thus the nozzle thereof may further be placed in a fourth acute angle between 15° and 65°, e.g. between 20° and 40°, relative to the circumferential direction. The fourth angle is measured between the first and second radial directions. According to one embodiment, the activation mechanism comprises at least one movable valve element connected to at least one actuator unit controlled by a control unit, the at least one actuator unit is configured to move, e.g. repeatedly, the at least one valve element relative to at least the second fluid conduit or the at least third fluid conduit between an open position and a closed position.

The downhole tool further comprises an activation mechanism configured to at least activate the downhole tool, e.g. a single-use mechanism. Alternatively, the activation mechanism may be a multi-use mechanism configured to repeatedly activate and deactivate the downhole tool. The downhole tool may be activated, and optionally deactivated, upon receiving one or more suitable control signals or detecting a certain event, e.g. the operating flow rate or fluid pressure exceeding a threshold value. Any suitable activation mechanism may be arranged in the downhole tool for activating the downhole tool.

In example, but not limited to, the activation mechanism may comprise at least one valve element configured to move relative to at least one of the second and third fluid conduits. A common activation element may be used to open or close a second fluid conduit and a third fluid conduit. Alternatively, individual valve elements may be used to open or close the respective second and third fluid conduits. A drive unit may be connected to the valve element for moving it between a closed position, where the respective fluid conduit is closed, and an open position, where the respective fluid conduit is open. The drive unit may comprise a linear actuator, e.g. powered by a bat- tery, a motor, a solenoid configured to inductively move the valve element, or another suitable drive unit. A control unit, e.g. a microprocessor, control logics, or another suitable electronic circuit, may be connected to the drive unit for controlling the movement of the valve element. The control unit may be connected to a pressure sensor configured to detect the fluid pressure of the drilling fluid in the first fluid conduit. Optionally, another pressure sensor may be connected to the control unit and configured to detect the fluid pressure of the drilling fluid in the annulus. The control unit may trigger the movement of the valve element when the internal fluid pressure or the differential pressure exceeds or drops below the threshold. Alternatively, the control unit may be connected to a RFID antenna or electrical cables which, in turn, are used to receive the control signals. Mud pulses may alternatively be used to activate or deactivate the downhole tool. The activation mechanism may be arranged within a cavity formed in the outer side surface of the housing. Optionally, at least the drive unit and the control unit may be arranged within another protective housing where the valve element may extend at least partly out of this protective housing. The cavity may be closed off by a removable cover configured to seal off the cavity in a water tight manner.

An object of the invention is also achieved by a drill string for positioning in a borehole, comprising at least two downhole tools as described above, wherein a first downhole tool is placed at a first position and at least a second downhole tool is placed at a second position relative to the first downhole tool along the length of the drill string.

The present downhole tool may be used in combination with other components or downhole tools arranged in a drill string. This enables the downhole tool to be used as a cleaning tool capable of cleaning the borehole and transporting solid particles, such as cuttings or swarf, to ground level. This provides an improved cleaning effect and transport effect in the annulus along the drill string.

According to one embodiment, a lowermost downhole tool is positioned at least lOmetres from a drill bit of the drill string.

Multiple downhole tools may be distributed along the length of the drill string at predetermined intervals to ensure a continuous flow in the annulus towards ground level. The drill string may comprise a lowermost downhole tool and an uppermost downhole tool and a number of intermediate downhole tools arranged there between. The low- ermost downhole tool may be positioned at least 10 metres from the drill bit so that it is not influenced by any bit nozzle systems arranged adjacent to the drill bit. This allows each downhole tool to act as a boosting station for lifting the solid particles and returning the drilling fluid up to ground level. The downhole tool may in example, but not limited to, be used to clean the transition area between two different sized casings, to remove the free flowing material from the milling tool, or to clean indentations, pockets, sidetracks and other areas which normally cannot be cleaned by the flow of the returning drilling fluid.

The individual downhole tools may be configured to be operated either independently or synchronously depending on the desired application. The individual downhole tools may be configured to be activated or deactivated in the same manner, alternatively a common controller may be used to control the operation of the downhole tools.

The invention is not limited to the embodiments described herein, and thus the described embodiments can be combined in any manner without deviating from the objections of the invention.

Description of the Drawing

The invention is described by example only and with reference to the drawings, wherein:

Fig. 1 shows a downhole tool having a conventional arrangement of a second fluid conduit,

Fig. 2 shows an exemplary embodiment of a protective housing of an activation mechanism,

Fig. 3 shows an exemplary embodiment of the activation mechanism,

Fig. 4 shows a cross sectional view of the downhole tool shown in fig. 1 and the activation mechanism shown in figs. 2 and 3,

Fig. 5 shows a flow diagram of a drilling fluid passing through a drill string comprising the downhole tool of fig. 1,

Fig. 6 shows a first exemplary embodiment of the downhole tool according to the invention,

Fig. 7 shows a cross sectional view of the downhole tool shown in fig. 6,

Fig. 8 shows a flow diagram of a drilling fluid passing through a drill string comprising the downhole tool of fig. 6,

Fig. 9 shows a second exemplary embodiment of the downhole tool according to the invention, Fig. 10 shows a cross sectional view of the downhole tool shown in fig. 9,

Fig. 11 shows a flow diagram of a drilling fluid passing through a drill string comprising the downhole tool of fig. 9,

Fig. 12 shows a flow diagram of a drilling fluid passing through a drill string com- prising a third exemplary embodiment of the downhole tool according to the invention,

Fig. 13 shows a flow diagram of a drilling fluid passing through a drill string comprising a fourth exemplary embodiment of the downhole tool according to the invention, and

Figs. 14-16 illustrates the flow in the annulus with a downhole tool having second and and/or third fluid conduit at different angles.

In the following text, the figures will be described one by one, and the different parts and positions seen in the figures will be numbered with the same numbers in the different figures. Not all parts and positions indicated in a specific figure will necessarily be discussed together with that figure.

Position number list

1. Downhole tool

2. Housing

3. First end

4. Second end

5. First fluid conduit

6. Inner side surface

7. Outer side surface

8. Second fluid conduit

9. Cavity

10. Housing

11. Activation mechanism

12. Valve element

13. Drive unit 14. Control unit

15. Sensor unit

16. First nozzle

17. Drilling fluid

18. Drill string

19. Borehole

20. Inner wall

21. Drill bit

22. Flow towards the drill bit caused by Vortex

23. Annulus

24. Third fluid conduit

25. Second nozzle

26. Casings

α First acute angle β Second acute angle

Detailed Description of the Invention

Fig. 1 shows an exemplary embodiment of a downhole tool 1 having a housing 2 with a first end 3 and a second end 4. The housing 2 defines a longitudinal direction of the downhole tool 1. A first fluid conduit 5 extends from an opening in the first end 3 to an opening in the second end 4. The housing 2 has an inner side surface 6 facing the first fluid conduit 5 and an outer side surface 7 facing an inner wall of the borehole (shown in fig. 5). The housing 2 further comprises at least a second fluid conduit 8 extending from an inner opening connected to the first fluid conduit 5 to an outer opening in the outer side surface 7. Here, two second fluid conduits 8 are arranged in opposite side surfaces 7 as shown in fig. 1. The second fluid conduit 8 defines a second longitudinal direction. A cavity 9 is formed in the outer side surface 7 and configured to receive an activation mechanism (shown in fig. 3) and a protective housing thereof (shown in fig. 2). The activation mechanism is closed to activate the downhole tool 1 so that the second fluid conduit 8 is open, thus allowing a part of a drilling fluid (shown in fig. 5) to bypass the first fluid conduit 5.

Fig. 2 shows an exemplary embodiment of a protective housing 10 shaped to receive the activation mechanism (shown in fig. 3). The housing 10 is configured to seal of the electrical components of the activation mechanism so they are not damaged by the drilling fluid (shown in fig. 5). The housing 10 is configured to partly receive a moveable valve element as shown in fig. 3.

Fig. 3 shows an exemplary embodiment of the activation mechanism 11 comprising a moveable valve element 12 configured to move relative to the housing 10. The valve element 12 has a free end configured to be brought into contact with a valve seat arranged relative to the second fluid conduit 8.

The valve element 12 is connected to a drive unit 13 configured to move the valve element 12 between a closed position (shown in fig. 4) and an open position (shown in fig. 5). Here, the drive unit 13 is shown as a solenoid configured to inductively move the valve element 12.

The drive unit 13 is further connected to a control unit 14 configured to control the operation and, thus, the activation and deactivation of the downhole tool 1. The control unit 14 is further connected to a sensor unit 15 in the form of a pressure sensor. The control unit 14 is configured to control the operation of the downhole tool 1 as function of the fluid pressure of the drilling fluid in the first fluid conduit 5.

Fig. 4 shows a cross sectional view of the downhole tool 1 and the activation mechanism 11. Here the valve element 12 is shown in the closed position where the free end is resting on the valve seat so that the second fluid conduit 8 is closed off. The drilling fluid is then lead through the downhole tool 1 via the first fluid conduit 5. A first nozzle 16 is arranged at the outer opening of the second fluid conduit 8. The second fluid 8 and thus the first nozzle 16 are placed at a perpendicular angle relative to the longitudinal direction of the downhole tool 1 as illustrated in fig. 4. The downhole tool 1 comprises two activation mechanisms 11 configured to be arranged in the corresponding cavities 9 in the housing 2. The activation mechanisms 11 are controlled individually or synchronously dependent on the desired application.

Fig. 5 shows a flow diagram of the drilling fluid 17 passing through a drill string 18 comprising the downhole tool 1. When the control unit 14 activates the downhole 1, the valve element 12 is moved from the closed position shown in fig. 4 to the open position shown in fig. 5. In the open position, a part of the drilling 17 is lead through the second fluid conduit 8 while the remaining drilling 17 is lead through the first fluid conduit 5.

The drill string 18 is positioned in a borehole 19 comprising an inner wall 20. The downhole tool 1 is positioned at a distance from a drill bit 21 of the drill string 18 as shown in fig. 5. As indicated by the arrows, the bypassed drilling fluid 17 is lead directly into the inner wall 20 at an angle of 90°, this generates a Vortex below the outer opening of the second fluid conduit 8. The Vortex causes part of the drilling fluid 17 and thus the solid particles to flow back towards to drill bit 21 as indicated by arrows 22. The Vortex has a significantly negative effect on the cleaning effect of the downhole tool 1, thereby increasing the risk of the solid particles accumulating in the annulus 23 (at areas having the lowest velocity).

Fig. 6 shows a first exemplary embodiment of the downhole tool according to the invention. Here the downhole tool is shaped as a circulating sub.

For illustrative purposes, the housing 2, the first fluid conduit 5 and the cavities 9 have the same configuration as shown in fig. 1. The activation mechanism 11 shown in figs. 2 and 3 can be used to operate the downhole . In this embodiment, the downhole tool comprises a second fluid conduit 8' and a third fluid conduit 24. The third fluid conduit 24 extends from an inner opening connected to the first fluid conduit 5 to an outer opening in the outer side surface 7. Here two third fluid conduits 24 are arranged in opposite side surfaces 7 as shown in fig. 7. The third fluid conduit 24 defines a third longitudinal direction. A second nozzle 25 is arranged at the outer opening of the third fluid conduit 24.

Fig. 7 shows a cross sectional view of the downhole tool where the activation mechanism 11 has been removed for illustrative purposes.

The second fluid conduit 8' is placed in a first acute angle a relative to the longitudinal direction of the downhole tool 1 ' . The third fluid conduit 24 is placed in a second acute angle β relative to the longitudinal direction of the downhole tool 1 ' . The second fluid conduit 8' is placed in a first acute angle a between 30° and 50°. The third fluid conduit 24 is placed in a second acute angle a between 50° and 65°. This provides the best cleaning effect as confirmed by simulations.

Fig. 8 shows a flow diagram of the drilling fluid 17 passing through the drill string 18' comprising the downhole tool , wherein the valve element 12 is used to open and close both the second and third fluid conduits 8', 24.

When activated as describe above, the valve element 12 is placed in the open position as shown in fig. 8. In the open position, a part of the drilling 17 is lead through the second fluid conduit 8' and the third fluid conduit 24 while the remaining drilling 17 is lead through the first fluid conduit 5.

As indicated by the arrows, the bypassed drilling fluid 17 is lead into the annulus 23 at an acute angle towards the first end 3 due to the orientation of the second and third fluid conduits 8', 24. No Vortex is generated above or below the outer openings of the second and third fluid conduits 8', 24, thus all the bypassed drilling fluid 17 is lead towards the first end 3 as indicated by the arrows. This provides the best cleaning effect and transport effect that lifts the solid particles towards ground level (not shown). Fig. 9 shows a second exemplary embodiment of the downhole tool 1" according to the invention. Here the downhole tool 1" is shaped as a circulating sub.

For illustrative purposes, the housing 2, the first fluid conduit 5 and the cavities 9 have the same configuration as shown in fig. 1. The activation mechanism 11 shown in figs. 2 and 3 can be used to operate the downhole 1" .

In this embodiment, the downhole tool 1" comprises a second fluid conduit 8" placed in a different first acute angle α'.

The second fluid conduit 8" extends in the longitudinal direction so that the bypassed drilling fluid 17 is lead towards the first end 3 substantially parallel to the longitudinal direction. Fig. 10 shows a cross sectional view of the downhole tool 1" where the activation mechanism 11 has been removed for illustrative purposes. In this embodiment, the second fluid conduit 8" is placed in a first acute angle a between 15° and 65°. This provides an optimal cleaning effect compared to the downhole tool 1 as confirmed by simulations.

Fig. 11 shows a flow diagram of the drilling fluid 17 passing through the drill string 18" comprising the downhole tool 1", wherein the valve element 12 is used to open and close the second fluid conduit 8" . When activated as describe above, the valve element 12 is placed in the open position as shown in fig. 11. In the open position, a part of the drilling 17 is lead through the second fluid conduit 8" while the remaining drilling 17 is lead through the first fluid conduit 5. As indicated by the arrows, the bypassed drilling fluid 17 is lead into the annulus 23 at an acute angle towards the first end 3 due to the orientation of the second fluid conduit 8'. No Vortex is generated above or below the outer opening of the second fluid conduit 8', thus the bypassed drilling fluid 17 is substantially lead towards the first end 3 as indicated by the arrows. This provides an improved cleaning effect and transport effect compared to the flow of the downhole tool 1 as shown in fig. 5.

Fig. 12 shows a flow diagram of the drilling fluid 17 passing through the drill string 18" ' comprising a third exemplary embodiment of the downhole tool Γ ". Here the downhole tool Γ " is shaped as a circulating sub.

For illustrative purposes, the housing 2 and the first fluid conduit 5 have the same configuration as shown in fig. 1. The cavity 9 and the activation mechanism 11 shown in figs. 2 and 3 can be used to operate the downhole 1 ' " .

In this embodiment, the downhole tool Γ" comprises a second fluid conduit 8' " facing towards the first end 3 and a third fluid conduit 24' facing towards the second end 4. The second fluid conduit 8" ' is placed in a first acute angle a" between 30° and 50° relative to the longitudinal direction of the downhole tool " . The third fluid conduit 24' is placed in a second acute angle β' between 50 ° and 65 ° relative to the longitudinal direction of the downhole tool 1 " ' .

When activated as describe above, the valve element 12 is placed in the open position. A part of the drilling 17 is lead through the second fluid conduit 8' " and the third fluid conduit 24' while the remaining drilling 17 is lead through the first fluid conduit 5 as shown in fig. 12.

As indicated by the flow lines, a first part of the bypassed drilling fluid 17 is lead into the annulus 23 at an acute angle towards the first end 3 due to the orientation of the second fluid conduit 8" ' . This provides a transport effect that lifts the solid particles towards ground level (not shown).

As further indicated by the flow lines, a second part of the bypassed drilling fluid 17 is lead into the annulus 23 at an acute angle towards the second end 4 due to the orientation of the third fluid conduit 24'. This provides a cleaning effect that is used to clean inaccessible areas which normally cannot be cleaned by the returning flow in the annulus 23. Here the downhole tool " is used to clean the transition area between two different sized casings 26. Fig. 13 shows a flow diagram of the drilling fluid 17 passing through the drill string 18" " comprising a fourth exemplary embodiment of the downhole tool 1"" . Here the downhole tool 1" " is shaped as a circulating sub.

For illustrative purposes, the housing 2 and the first fluid conduit 5 have the same configuration as shown in fig. 1. The cavity 9 and the activation mechanism 11 shown in figs. 2 and 3 can be used to operate the downhole 1"". The second fluid conduit 8" " differs from the second fluid conduit 8' shown in fig. 9 as it extends in a combined longitudinal direction and circumferential direction. The second fluid conduit 8" " faces towards the first end 3 and is placed in a third angle relative to the longitudinal direction and in a fourth angle relative to the circumferential direction of the downhole tool 1" " . By placing the second fluid conduit 8" " in a combined angle relative to the longitudinal and circumference directions, the bypassed drilling fluid 17 is lead into the annulus 23 in a rotational direction causing it to rotate along the drill string 18" " as shown in fig. 13 even if the drill string 18"" is not rotating. In this embodiment, the second fluid conduit 8" " is placed in a third angle between 30° and 50° relative to the longitudinal direction and in a fourth angle between 20° and 40° relative to the circumferential direction.

Figs. 14-16 illustrate the flow in the annulus with a downhole tool having second and/or third fluid conduits at different angles using simulation software. Pressure losses are calculated taking in account not only the non-Newtonian nature of the fluid, but the solid content on it. In order to do so, particle laden flow is integrated which accounts the friction of the particles. In figs. 14-16, the arrows show the flow direction while the lines show the flow velocity in m/s as indicated by the scale on each draw- ing. On figs. 14-16, the drill bit end, i.e. downhole direction is towards the bottom on the drawing, and the top of figs. 14-16 is the upflow direction from downhole to the surface. The flow in the center of figs. 14-16 is the first fluid conduit 5 inside the downhole tool 1. The thin gap 23 is the annulus flow.

All fluid conduits and corresponding nozzles in figs. 14-16 are angled towards the upflow direction.

In fig. 14, the second fluid conduit 8 is angled at 60° while the third fluid conduit 24 is angled at 45° relative to the longitudinal axis of the downhole tool. Thus, the corresponding nozzles (not shown in figs 14-16) are directed into the annulus 9 in upflow direction.

The simulation indicates that an excess of a 150% more flow can be pumped through the drillpipe without exceeding a generalized ECD configuration with the second and third fluid conduits having the above mentioned angles. Fig. 15 shows simulation with the second conduit (two conduits are shown) 8 angled 20° relative to the longitudinal axis of the downhole tool.

Here, the angle is too low for having the above-mentioned effect and the flow velocity in the annulus is lower than in fig. 14. This also reduces the self-cleaning effect which can be obtained by a high flow velocity and efficient distribution of the flow across the annulus.

Fig. 15 shows simulation with the second conduit (two conduits are shown) 8, which are perpendicular to the longitudinal axis of the downhole tool. This causes reversed flow in the annulus 23 as indicated by the arrows. This reversed flow increases the turbulence, which results in higher pressure drops and, thus, lower flow velocity. Thus, providing the second fluid conduit perpendicularly to the longitudinal axis of the downhole tool significantly reduces the flow in the annulus 23. This also signifi- cantly reduces the self-cleaning effect because of low flow velocities and a poor distribution of the flow in the annulus 23.