GB2633640A

GB2633640A - A circulation tool

Info

Publication number: GB2633640A
Application number: GB2315437.0A
Authority: GB
Inventors: Mcgarian Bruce
Original assignee: Odfjell Tech Invest Ltd
Current assignee: Odfjell Technology Invest Ltd
Priority date: 2023-09-05
Filing date: 2023-10-09
Publication date: 2025-03-19
Also published as: GB2633548A; GB202313515D0

Abstract

A tool comprising a body 6 having an internal passage and a flow port 7. A control piston 8 with a central bore 9 is positioned within the body and is biased 24 towards a first end of the body. The control piston can move axially and a control arrangement limits movement of the control piston towards the first end and is switchable between a first configuration where the control piston can move a first maximum distance where the flow path is closed, and a second configuration in which the control piston can move a second maximum distance and fluid may flow between the central bore of the control piston and the flow port. The control mechanism may be a track based indexing mechanism (17, Fig 4a). A method is also defined which comprises attaching the tool to a drill string and operating the control arrangement to move from the first configuration to the second configuration.

Description

A CIRCULATION TOOL

FIELD

This invention relates to a circulation tool, and the particular concerns a tool to be included in a drill string to allow the selective delivery of solid material to the exterior of the drill string.

BACKGROUND

When drilling, for example for oil or gas, it is often the case that a significant quantity of drilling fluid is lost to the formation around the wellbore, in what are called "lost circulation zones". It is important to be able to control these losses, so that drilling can continue effectively.

Some losses can be controlled by varying mud weights, so that there is not a significant over-pressure on the formation being drilled. However, it is sometimes necessary to add solids to the drilling mud to fill or plug gaps in the formation. Solids of this type that are introduced into the drilling mud are referred to as "lost circulation material" (LCM). A wide variety of materials can be used as the LCM, and the materials generally fall into the categories of fibres, flakes and granules. Examples of different types of LCM can be seen in section 5.7.5.11 of Applied Well Cementing Engineering (DeBruijn and Whitton) 2021.

There are several components that might appear in a drill string through which solids of this type cannot be pumped, for instance a measurement while drilling (MWD) tool.

In known systems, a circulation tool is positioned above an MWD or other sensitive tool. When LCM is to be introduced, the circulation tool is set so that a main flow bore passing through the tool is blocked, for instance by the dropping of an obstruction such as a dart or ball. Ports to the annulus are opened, and the LCM can be then be pumped into the drill string, and into the annulus and surrounding formation through the ports of the circulation tool, without passing further through the drill string to sensitive components below.

One example of a circulation tool of this kind is shown in US9617812.

It is an object of the invention to provide an improved circulation tool of this type.

Accordingly, one aspect of the present invention provides a tool according to claim 1.

Another aspect of the of the present invention provides a method according to claim 25.

Preferred features of the invention are set out in the dependent claims.

In order that the invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figures 1, 2 and 3 show a tool embodying the invention in a first configuration; Figures 4a, 4b and 4c show a control piston of the tool of figures 1, 2 and 3; Figure 5 shows a track of the control piston; Figures 6 to 9 show stages in the operation of the tool; Figure 10 shows the lower end of an alternative tool embodying the invention; Figures 11 to 13 show an upper part of a further tool embodying the invention; and Figures 14 to 16 show a lower part of another tool embodying the invention.

With reference first to figures 1 to 3, major components of a circulation tool 1 embodying the present invention are shown.

The tool 1 is generally elongate, and has a top sub 2 at its upper end, and a bottom sub 3 at its lower end. The top sub 2 has a top connection 4 (not visible in figure 1), such as a threaded bore, for connection to another component in the drill string which is immediately above the circulation tool 1.

Similarly, the bottom sub 3 has a bottom connection 5, such as a threaded protrusion, for connection to a component immediately below the circulation sub 1 in the drill string.

The top and bottom subs 2, 3, and their connections 4, 5 can take any suitable form.

An outer tool body 6 extends between the top sub 2 and the bottom sub 3, and in the embodiment shown defines an outer surface of the tool between the top sub 2 and bottom sub 3. The outer tool body 6 is hollow, and various components are disposed within the outer tool body 6, as will be discussed below.

Two flow ports 7 are formed through the outer tool body 6. In this example the flow ports 7 are formed on opposite sides of the outer tool body 6, although this is not essential.

A control piston 8 is positioned within the outer tool body 6. The control piston 8 may slide axially with respect to the outer tool body 6, as will be described in more detail below. The control piston 8 has a flow bore 9 formed therethrough, allowing fluid from a top end 10 to a bottom end 11 thereof.

Overall, as can be seen most clearly in figure 2, both the top and bottom subs 2, 3 have flow bores formed therethrough, and in an initial configuration (as shown in figures 2 and 3) fluid may flow into the top sub 2, through the control piston 8, and then through the bottom sub 3 and out of the tool 1 into a lower component.

In preferred embodiments a relatively wide flow bore is formed along the length of the circulation tool 1 in this initial configuration. For example, in an embodiment the circumference of the flow bore may be at least 25% of the circumference of the outer diameter of the tool 1, at all points along the length of the tool 1. In another embodiment, the circumference of the flow bore may be at least 20% of the circumference of the outer diameter of the tool 1, at all points along the length of the tool 1.

In other embodiments, the overall flow area through the tool 1, in the initial configuration, is at least 5% of the total cross-sectional area of the outer tool body 6, at all points along the length of the tool 1. In another embodiment, the overall flow area through the tool 1, in the initial configuration, is at least 4% of the total cross-sectional area of the outer tool body 6, at all points along the length of the tool 1.

In embodiments the flow bore of the tool 1 is positioned on a central longitudinal axis of the tool 1, at all or substantially all points along its length.

In one particular example the tool 1 may have an outer diameter of 21cm (8.25 inches), and the circumference of the flow bore is 5.4cm (2.125 inches).

At its upper end the control piston 8 has a top chamber 13, which is open at its top end. The top chamber 13 has a pair of flow apertures 14 (which in the example shown are generally radial) which provide communication between the top chamber 13 and the exterior of the control piston 8. These flow apertures 14 are radially aligned with the flow ports 7 of the outer tool body 6.

However, in the initial configuration shown in figures 2 and 3 the flow apertures 14 of the control piston 8 are axially displaced with respect to the flow ports 7 of the control piston 8.

Axial movement of the control piston 8 within the outer tool body 6 is controlled by an indexing mechanism. The control piston 8 is shown in isolation in figures 4a, 4b and 4c. As can be seen in these figures, at its upper end the control piston 8 has a widened section 15, which contains the top chamber 13, and through which the flow ports 7 are formed. A mid section 16 of the control piston 8 extends from the lower end of the widened section 15, and is narrower in cross section. The mid section 16 is generally cylindrical in shape.

A lower section 12 protrudes from the lower end of the mid section 16. The lower section preferably takes the form of a tube, which in the example shown is narrower in outer cross section than the mid section 16.

A bottom end of the lower section 12 is received in a bore 36 in the bottom sub 3, and so can deliver fluid to the bottom sub. As will be explained below the control piston 8 may move axially with respect to the outer tool body 6 and bottom sub 3. The bore 36 in the bottom sub 3 is long enough to accommodate this movement without the lower section 12 leaving the bore 36. In the example shown the bottom end of the lower section 12 is not sealed within the bore 36, and pressure within the bore 36 may be communicated to the surrounding region within the outer tool body 6.

A track 17 is formed on the outer surface of the control piston 8. The track 17 preferably takes the form of a groove. In the example shown the track 17 is formed on the outer surface of the mid section 16.

Figure 5 shows a schematic view of the track 17 that is formed around the perimeter of the control piston 8. The track 17 is of a similar shape to the one shown in W02022/079423 for which the inventor is the same as for this application, and the track 17 will not be described in great detail herein. The track 17 has a repeating pattern including a number of peaks 18, which lie closer to the top end 10 of the control piston 8, and a series of troughs 19a, 19b, which lie closer to the bottom end 11 of the control piston 8. A timing ring 21 is provided around the control piston 8, and is rotatable with respect to the control piston 8. The timing ring 21 has an inwardly-protruding pin (not shown) which is received in the track 17, and may travel within the track 17.

Inclined surfaces 20 are formed in sections of the track 17 between the peaks 18 and troughs 19a, 19b so that, if the pin is received in a first peak 18, and the track 17 is driven directly upwardly with respect to the pin, the pin will be guided (through rotation of the timing ring 21) to a first trough 19a, 19b, which is most directly to the left of the first peak 18. If the track 17 is then driven directly downwardly with respect to the pin, the pin will be guided to a second peak 18, which is one to the left of the first peak 18. If the track 17 is then again driven directly upwardly with respect to the pin, the pin will be guided to a second trough 19a, 19b, which is one to the left of the first trough 19a, 19b, and so on.

The skilled reader will therefore understand that repeatedly driving the track 17 directly upwardly and downwardly with respect to the pin will lead to the pin being guided successively leftward with respect to the track 17.

In this example, while the inclined surfaces 20 of the track 17 will guide the pin to the left during successive movements, in alternative embodiments the track could equally be configured to guide the pin in a rightward direction.

Returning to figure 5, in the example shown in this figure each peak 18 is at the same level.

However, the troughs are not all at the same level. Two of the troughs 19a extends downwardly by relatively great distance with respect to the remainder of the track 17. The remaining four troughs 19b all extend downwardly with respect to the track 17 by the same, lesser amount. For brevity hereafter the troughs 19a that extends downwardly by relatively long distance will be referred to as "long troughs", with the other troughs 19b being referred to as "short troughs".

As can be seen most clearly in figure 3, within the interior of the outer tool body 6 there is a first upward-facing shoulder 22 on which the timing ring 21 rests.

Where the widened section 15 of the control piston 8 meets the lower section 16, there is a first downward-facing shoulder 23.

A spring 24, which in the example shown takes the form of a compression spring, is positioned between a top side of the timing ring 21 and the first downward-facing shoulder 23.

In the example shown, bearings 38 are provided above and below the timing ring 21, allowing the timing ring 21 to rotate freely with respect to the first upward-facing shoulder 22 and with respect to the spring 24.

It will be understood that the effect of the spring 24 is to bias the control piston 8 upwardly with respect to the inner tool body 6.

In the initial configuration shown in figures 1-3, the pin of the timing ring 21 is positioned at or near the bottom of one of the long troughs 19a of the track 17. With reference to figure 5, the pin is initially received in the leftmost one of the two long troughs 19a (which is shown in two halves in figure 5, and it should be understood that these two halves will meet where the track 17 is "wrapped" around the exterior of the control piston 8). The spring 24 biases the control piston 8 upwardly.

At the limit of its upward motion, the top end 10 of the control piston 8 contacts an upper stop ring 37 which is provided within the outer tool body 6. The upper stop ring 37 may, for instance, be held in place by a circlip, and a suitable taper in the internal bore of the outer tool body 6 (as can be seen in figure 6, for example), and/or by an extended part of the top sub 2 that protrudes into the outer tool body 6. In the example shown, this contact takes place before the pin reaches the bottom of the long trough 19a. The pin therefore serves to guide the timing ring 21, in this position, but does not bear the load of preventing further motion of the control piston 8 within the outer tool body 6. Excessive forces on the pin of the timing ring 21 are therefore avoided at this stage.

The upward motion of the control piston 8 can be halted by any suitable stop feature, and an upper stop ring 37 as described above is not essential. However, it is preferred that a stop feature is provided, to halt upward motion of the control piston 8 before the pin of the timing ring reaches the bottom end of the long trough 19a.

As can be seen most clearly in figure 3, a recess 25 is formed on the inner surface of the outer tool body 6, which is in fluid communication with the flow ports 7, and extends upwardly therefrom by a certain distance. In some embodiments the recess 25 may be annular, extending around the circumference of the outer tool body 6. In other embodiments a single recess 25 may be provided in communication with each flow port 7, with the recesses 25 being isolated from each other.

In the initial configuration, the flow apertures 14 of the control piston 8 lie above the recess 25. The outer ends of the flow apertures 24 are therefore fully or substantially fully blocked by the inner surface of the outer tool body 6.

In the initial configuration, fluid that is introduced into the top sub 2 of the circulation tool 1 will flow through the control piston 8, to the bottom sub 3 and out of the lower end of the circulation tool 1.

In the initial configuration, therefore, the circulation tool 1 does not present any significant obstruction to the flow of fluid therethrough, and this configuration fluid may be pumped through the drill string during, for example, a drilling operation. Circulating pumps may be started and stopped multiple times in this configuration and the tool 1 will not interfere with, or be materially affected, by this.

As discussed above, at certain times during the drilling operation it may be necessary to introduce LCM into the drill string, to be delivered to the annulus.

Wth reference firstly to figure 6, at a bottom end of the top chamber 13 of the control piston 8 a ball seat 26 is formed. A ball 27 is introduced into the drill string, and comes to rest in the ball seat 26. The ball 27 forms a complete or substantially complete obstruction in the control piston 8.

In embodiments the ball seat 26 may incorporate a ring, to prevent the ball 27 from floating off the seat 26, for instance in the event of back flow.

As the ball 27 is received in the ball seat 26, an increase in pressure may be detected at the surface, thus allowing operators to determine that the ball 27 has correctly landed.

Fluid continues to be pumped into the drill string, and since the ball 27 obstructs the flow of fluid through the control piston 8, the pressure of fluid above the ball 27 will drive the control piston 8 downwardly, against the biasing force of the spring 24.

As the control piston 8 is driven downwardly the pin of the timing ring 21 will be driven into one of the peaks 18 of the track. This position is shown in figure 6.

Where the mid section 16 of the control piston 8 meets the bottom section 12 thereof, a second downward-facing shoulder 40 is formed, as can be seen in figures 3 and 4a. At the limit of the downward motion of the control piston 8, this second downward-facing shoulder 40 contacts a second upward-facing shoulder 39 that is formed within the outer tool body 6. This second upward-facing shoulder 39 can be seen in figures 2 and 3.

This contact occurs before the pin of the timing ring 21 reaches the end of any one of the peaks 18 of the track 17. Therefore, in this position excessive forces on the pin are avoided.

Once again, any suitable stop feature can be provided, to halt the downward motion of the control piston before the pin of the timing ring reaches the end of a peak 18 in the track 17.

As can be seen in figure 6, at the limit of the downward motion the flow apertures 14 of the control piston 8 are aligned or substantially aligned with the flow ports 7 of the outer tool body 6.

As the control piston 8 moves to this position, an increasingly wide flow path to the annulus will be established, and so the fluid pressure will decrease. When the flow apertures 14 are fully aligned with the flow ports 7, the pressure will stop decreasing, and operators will be able to tell that the downward motion of the control piston 8 is complete, for a given flow rate.

With the control piston 8 in this position, LCM can be introduced into the drill string. The LCM will flow into the top chamber 13 of the control piston 8, and out into the annulus through the flow apertures 14 of the control piston 8 and the flow ports 7 of the outer tool body 6.

In this configuration, the position of the control piston 8 will not be affected by relatively high fluid flow/pressure, since the control piston 8 is already at the limit of its downward motion. In some circulation tools, such as that shown in W02019/063985, the tool has a position in which fluid may flow out of the tool through ports to the annulus, but above a certain limit fluid flow will drive a valve element downwardly within the tool, such that the ports to the annulus are closed. Flow to the annulus is therefore only possible at relatively low pressures or flow rates. This can be disadvantageous when pumping LCM through the tool, or when raising the tool out of the wellbore (which is discussed in more detail below).

When the circulation of LCM has finished, the pumping of fluid into the drill string is stopped (or reduced), such that the spring 24 drives the control piston 8 upwardly. This motion will occur until the pin of the timing ring 21 reaches the end of one of the short troughs 19b.

This position is shown in figure 7.

It should be noted that, in this position, fluid may flow out of the flow apertures 14 of the control piston 8, into the recess 25 formed in the inner circumference of the outer tool body 6, and out through the flow ports 7 of the outer tool body 6 to the annulus. Therefore, when the pin of the timing ring 21 is received in one of the short troughs 19b, fluid may still flow into the top end of the circulation tool 1 and out through the flow ports 7 of the outer tool body 6 to annulus.

In this example fluid initially flows into a first part of the recess 25, which is not axially aligned with the flow ports 7 (in this case, is axially above the flow ports 7), and then flows along the recess 25 to reach the ports 7.

Fluid pressure in this position will, in preferred embodiments, be intermediate between the pressures when the bore is fully blocked (i.e. when the ball 27 first lands on the seat 26) and when the flow apertures 14 and flow ports 7 are fully aligned (i.e. the position shown in figure 6).

In the position of figure 7 the ball 27 is still received in the ball seat 26, and prevents or substantially prevents fluid from passing all the way through the control piston 8.

As a next step fluid is once again pumped into the drill string, which will drive the control piston 8 downwardly with respect to the outer tool body 6 against the biasing force of the spring 24, so that the pin of the timing ring 21 is guided, by axial movement of the control piston 8 and rotation of the timing ring 21, into one of the peaks 18. The circulation tool 1 will then once again be in the configuration shown in figure 6.

The pumping of fluid is then once again stopped or reduced such that the spring 24 returns the control piston 8 upwardly, until the pin of the timing ring 21 reaches another one of the short troughs 19b.

Cycling is continued in this manner, with the control piston 8 travelling axially within the outer tool body 6 so that the pin of the timing ring 21 moving between peaks 18 and short troughs 19b of the track 17. The provision of a number of short troughs 19b allows the pumps to be activated and deactivated a number of times, which may be desirable depending on the operations that are being carried out at this stage, and during this cycling fluid may at all times flow into the top end of the circulation tool 1 and out into the annulus through the flow ports 7 of the outer tool body 6.

This cycling continues until the pin of the timing ring 21 reaches the peak 18 immediately before the first one of the long troughs 19a (i.e. the one that crosses over the left and right hand sides of figure 5).

Pumping of fluid into the drill string is stopped or reduced, and two further balls 28 are introduced into the drill string. The pumps are switched on, and these further balls 28 will arrive in the top chamber 13 of the control piston 8, and block the flow apertures 14 of the control piston 8. At this stage the pin of the timing ring 21 will be guided into the first one of the long troughs 19a. This situation is shown in figure 8.

Pressurised fluid continues to be pumped into the drill string. Due to the presence of the further balls 28 blocking the flow apertures 14, the pressurised fluid will not be able to escape to the annulus. The resilience of the ball 27, and its size with respect to the ball seat 26, are chosen so that, when an appropriate fluid pressure is applied, the ball will pass through the ball seat 26, and subsequently along the main flow bore of the circulation tool 1, and out of the bottom of the circulation tool 1. The ball 27 may be sheared, or otherwise broken, in this process, or may be deformed and extruded through the flow bore.

The two further balls 28 will also be carried through the ball seat 26 and out of the bottom of the circulation tool 1 (these further balls 28 are, in preferred embodiments, smaller than the ball 27).

As the skilled reader will understand, the balls 27, 28 may be caught by a ball catcher or similar arrangement.

Once this has occurred, and the pumps have been deactivated, the spring 24 will drive the control piston 8 upwardly with respect to the outer tool body 6, until the pin of the timing ring 21 is guided into the second of the long troughs 19a. The tool 1 has now returned to the initial configuration, which is shown in figures 1-3. Fluid may now be pumped through the circulation tool 1.

Should the operation required to introduce a further LCM into the annulus, the cycle can repeated.

As a variation to the sequence described above, operators of the tool 1 may choose to introduce the further balls 28 into the drill string at an earlier stage, before the pin of the timing ring 21 reaches the long troughs 19a. As discussed above, this will lead to the ball 27 being sheared or extruded through the ball seat 26, and passing out of the bottom of the tool 1. The spring 24 will then return the control piston 8 upwardly, until the pin reaches the end of one of the short troughs 19b. This position is shown in figure 9.

As the skilled reader will understand, in this configuration the main flow bore through the tool 1 is unobstructed, and fluid may flow through the tool and out of the bottom sub 3. However, fluid may also flow out through the flow apertures 14 of the control piston, through the recess 25, and out the flow ports 7 of the outer tool body 6. The tool 1 is therefore in a "split flow" configuration, which may be useful for certain operations involving the tool.

The tool 1 can be cycled out of the split flow configuration, if needed, by introducing a further ball 27 into the drill string, so that it is received in the ball seat 26. The steps described above can then be resumed.

Overall the indexing system is moved through one discrete step for every suitable pressure/flow cycle that is applied at the surface when the ball 27 is received in the ball seat 26. Any alternative control system that allows the axial movement range of the control piston to be controlled in a similar manner may also be used, and the invention is not limited to the indexing system shown in the figures.

Wth reference to figure 1, in the example shown a guide pin 29 protrudes inwardly with respect to the outer tool body 6, and is received in the guide slot 30 formed in the control piston 8. This prevents the control piston 8 from rotating with respect to the outer tool body 6. One effect of this will be to maintain the rotational alignment of the flow ports 7 and the flow apertures 14.

In another embodiment, a rotating sleeve can be positioned around the control piston, with the rotating sleeve having the indexing track formed on its outer surface. A fixed pin can protrude inwardly from an inner surface of the outer tool body 6. In this way a similar result can be achieved to that described above.

It is also not necessary to have four short troughs and two long troughs. Any suitable arrangement of peaks and troughs can be used in an indexing track.

The skilled person will be aware of other configurations and variations that could be used.

Wth reference to figure 2, the lower section 12 of the control piston 8 passes through a narrowed section 31 of the outer tool body 6, and into a wider section 32 which is below the narrowed section 31. A floating piston 33 surrounds the lower section 12 within the wider section 32, and has inner and outer seals which seal against the lower section 12 and against the inner wall of the outer tool body 6. In the example shown the floating piston 33 is generally annular in shape, The first seal 34 is provided between the control ring 8 and the inner surface of the outer tool body 6, below the level of the flow ports 7.

In the embodiment shown, the region within the outer tool body 6 that is between the floating piston 33 and the first seal 34 is filled with oil or another fluid. This oil surrounds the control piston 8. This feature ensures that this region is kept "clean", and is not in contact with drilling fluid or mud. The fact that the floating piston 33 may move up and down with respect to the control piston 8 allows movement of the control piston 8, with the fixed volume of oil being contained between the floating piston 33 and the first seal 34.

A fill port 35 and a bleed port 42 allow oil to be introduced into this region. Oil can be pumped into the fill port 35 and out through the bleed port 42. A partial vacuum can also be applied to the bleed port 42 to exhaust any air or other gas entrained in the oil and/or chamber during the fill process. During servicing both the fill and bleed ports 35, 42 could be opened, with oil draining from the fill port 35 and air entering through the bleed port 42 (or vice versa depending on the orientation of the tool 1).

The skilled reader will appreciate that this arrangement allows simple control of the circulation sub, to cycle between different positions which will be useful in various stages of a drilling operation.

One advantage of the tool 1 relates to the retrieval of the drill string from the wellbore. When a drill string is removed from a wellbore, fluid within the string must be able to drain from the tool. Some components, such as an MWD, motor (i.e. PDM) or rotary steerable assembly, may have relatively small ports and hence not allow fluid to drain from the drill string at a sufficiently high rate.

Wth the tool 1 in the configuration shown in figure 8, fluid is blocked from flowing through the main bore of the tool 1 (and hence will not flow down the drill string to a component such as a drilling head), but instead may drain to the annulus through the flow apertures 14 and flow ports 7.

By contrast, in a tool such as the one shown in US9617812, the tool can be placed either in a fully open position, or in a blocked position in which flow is diverted to the annulus. However, the blocked position can only be maintained by the flow of pressurised fluid from the surface, which cannot practically be achieved while retrieving the drill string from the wellbore. In use of the tool 1 described above, the control piston 8 is maintained in the appropriate position by the spring and indexing system, and no fluid flow or pressure is required to maintain this configuration.

In preferred embodiments of the tool, the surface area that is presented at the upper end of the control piston 8, perpendicular to the longitudinal axis of the tool 1, is the same or substantially the same as the surface area that is presented at the upper end of the control piston 8, perpendicular to the longitudinal axis of the tool 1. As the skilled reader will understand, this will mean that the tool is pressure balanced within the outer tool body 6, and will not (if no ball is received in the ball seat 26) be driven upwardly or downwardly by pressure within the drill string.

In the examples shown, the control piston 8 has two flow apertures 14, which are on opposite sides of the control piston 8, and the outer tool body 6 similarly has two flow ports 7, which are on opposite sides of the outer tool body 6. However, this is not essential, and there may be any suitable number and arrangement of flow apertures and flow pods.

In embodiments one or more liners may be positioned within the outer tool body 6, to provide a non-corrosive surface. Liners can be placed in any suitable position(s), such as within the upper bore that contains the indexing track 17, adjacent the flow apertures 14 of the control piston 8, and the lower bore in which the floating piston 33 is received.

It is envisaged that, in some embodiments, the control piston may not have flow apertures. Instead, the flow pods in the outer tool body may be covered by part of the control piston in some positions, and uncovered when the control piston moves to other positions. These embodiments are not currently preferred, however, as seals would need travel over the flow ports, leading to a high risk of damage to the seals.

If the upward force generated by the spring 24 is not sufficient, it may be desirable to introduce a second spring into the tool. With reference to figure 10, a view of the lower end of an alternative tool is shown. The alternative tool includes a second spring 41. The lower end of the second spring 41 is received by the bottom sub 3, and the top end of the second spring 41 bears against (or otherwise engages) the lower section 12 of the control piston 8, to bias the control piston 8 upwardly with respect to the bottom sub 3.

During use of the tool 1 it may be desirable to bypass the flow apertures 14 and flow ports 7, and ensure that all flow into the tool 1 is diverted along the main flow bore. To achieve this a guide element such as a dart may be introduced into the drill string. The guide element may include a conduit that is received in the control piston, and which prevents fluid from entering the flow apertures of the control piston. For example, the guide element may take the form of a dart which has a central tube, surrounded by outwardly-protruding support elements such as fins (which may, for example, be formed from rubber). A nose of the tube may be received in the ball seat, or in any other suitable location below the level of the flow apertures. When the guide element is received in the control piston in this way, an upper end of the tube is above the level of the flow apertures, and substantially fills the main flow bore.

While the discussion above focuses on drilling operations, the tool 1 may be used in many different applications and is not limited to this. The tool 1 may be useful in any scenario in which circulation is required to boost flow down hole, through ports which are positioned partway along the drill string. An example of this is wellbore clean up.

It is envisaged that, due to the relatively wide bore of the tool in its initial configuration (i.e. with no ball or other obstruction on the seat), it will be possible to displace cement or similar substances through the tool 1.

With reference to figures 11 to 13, a further embodiment of the invention is shown. This embodiment has many features in common with those shown above, and where this is the case the same reference numerals are used as in previous figures. The description below focuses on the features that are different with respect to previous embodiments.

Turning firstly to figure 11, an upper sleeve 43 is positioned within the outer tool body 6. In the example shown the outer sleeve 43 is fixed in place with respect to the outer tool body 6. The upper sleeve 43 covers the region of the flow ports 7 that are formed in the outer tool body 6. The upper sleeve 43 has flow openings 44 formed therethrough, which are aligned with respective flow ports 7 of the outer tool body. In this example the cross-sectional area of the flow openings 44 is the same or substantially the same as that of the flow ports 7. The presence of the upper sleeve 43 therefore preferably does not impede or obstruct the flow of fluid though the flow ports 7.

The upper sleeve is held in place with respect to the outer tool body 6 by a circlip 46, which is received in a recess within the inner bore of the outer tool body 6, but any other suitable retaining arrangement can be used.

In the example shown in figures 1-9, a recess 25 is formed on the inner side of the outer tool body 6. In the embodiment shown in figure 11, instead a recess 45 is formed on the inner side of the upper sleeve 43. The features of this recess 45 are similar to those of the recess 25 shown in figures 1-9. The recess 34 is in fluid communication with the flow openings 44, and extends upwardly therefrom by a certain distance.

In this embodiment the top end 10 of the control piston 8 is received within the upper sleeve 43. The outer diameter of the top end 10 is reduced, compared to the embodiment shown in figures 1- 9. To account for the fact that the upper sleeve 43 is positioned within the outer tool body 43.

The upper sleeve 43 extends between a top end 47 and a bottom end 48. The length and positioning of the upper sleeve 43 is such that, throughout the full range of motion of the control piston 8, the flow apertures 14 of the control piston are within the length of the upper sleeve 43, i.e. between the top and bottom ends 47, 48 thereof In figure 11, the control piston 8 is shown in the initial configuration, corresponding to the position shown in figures 2 and 3. In this position, the flow apertures 14 of the control piston 8 are above, and not or substantially not, in fluid contact with the flow openings 44 of the upper sleeve 43. It should be understood that the flow apertures 14 of the control piston 8 are also above the top end of the recess 45 that is formed in the upper sleeve 43.

Wth reference to figure 12, a ball 27 is received in the ball seat 26 of the control piston 8. Fluid is pumped from the surface to drive the control piston 8 downwardly, to the lowest point of its motion, corresponding to the position shown in figure 6. In this position, the flow apertures 14 of the control piston 8 are aligned or substantially aligned with the flow openings 44 of the upper sleeve 43. Fluid can therefore flow through the flow apertures 14 and the flow openings 44, and then through the flow ports 7 of the outer tool body 6, to the annulus. In this position, preferably the flow apertures, flow openings 44 and flow ports are fully or substantially fully aligned with each other.

Turning to figure 13, the tool is shown in the position in which the pin of the timing ring 21 reaches the end of one of the short troughs 19b. This position corresponds to the one shown in figure 7. In this position the flow apertures 14 of the control piston 8 are spaced apart from the flow openings 44 of the upper sleeve 43. However, fluid within the control piston 8 may flow through the flow apertures 14 thereof, along the recess 45, and out of the tool through the flow openings 44 of the upper sleeve 43 and the flow ports 7 of the outer tool body 6.

The addition of the upper sleeve 43 allows the manufacturing of the tool to be simplified. It also allows higher flow rates through the tool, when no ball is received on the ball seat, because the outer diameter of the control piston 8 is smaller (and hence the cross-sectional area of the control piston 8 is reduced), and so a higher differential flow rate is required to offset the reduction in the piston area. Safety margins can therefore be increased under normal flow conditions.

Wth reference to figures 14 to 16, a lower part of a further tool embodying the invention is shown. In this embodiment a lower sleeve 49 is positioned within the wider section 32 that is formed within the outer tool body 6, below the narrowed section 31. In the example shown the lower sleeve 49 lies against the inner surface of the outer tool body 6. The floating piston 33 is positioned within the lower sleeve 49, and the inner and outer seals of the floating piston seal against the lower section 12 of the control piston 8, and against the inner side of the lower sleeve 49.

The positions of the control piston 8 in figures 14, 15 and 16 correspond to those shown in figures 11, 12 and 13, respectively.

As can be seen in figures 14-16, a second spring 41 is provided, as described above in relation to figure 10.

Where both an upper sleeve 43 and a lower sleeve 49 are used, in preferred embodiments the inner diameters of the upper and lower sleeves 43, 49 are equal or substantially equal.

The inclusion of the lower sleeve 49 allows the inner diameter of the chamber formed by the wider section 32 to be the same or substantially the same as that which surrounds the top end 10 of the control piston 8, when the upper sleeve 43 is in place. The lower section 12 of the control piston 8 can therefore act, along with the floating piston 33, as a balancing piston.

This helps to ensure that the fluid volume displacement does not need an excessively long chamber, and allows the spring sizes to be optimised to assist in the differential pressure required to displace the control piston upwardly if no ball is present on the seat.

Tools embodying the invention preferably include both an upper sleeve and a lower sleeve in conjunction. However, in other embodiments only an upper sleeve, or only a lower sleeve, is provided.

In this document references are made to the "top" and "bottom" of the tool, and of components of the tool and a drill string in which the tool is included. Similar terms such as "above" and "below" are also used. It should be understood that these terms refer to the normal position in which the tool will be used, and that a "top" part of the tool is positioned closer to the surface of a bore, and a "bottom" part of the tool is positioned further from the surface of the bore. This is not affected by the fact that, in use, the orientation of the bore at any particular point might mean that the bottom end is level with, or higher than, the top end.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The invention may also broadly consist in the parts, elements, steps, examples and/or features referred to or indicated in the specification individually or collectively in any and all combinations of two or more said parts, elements, steps, examples and/or features. In particular, one or more features in any of the embodiments described herein may be combined with one or more features from any other embodiment(s) described herein.

Protection may be sought for any features disclosed in any one or more published documents referenced herein in combination with the present disclosure.

Although certain example embodiments of the invention have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and/or to encompass equivalents.

Claims

CLAIMS: 1. A tool, comprising: an outer tool body having a first and end an opposite second end, an internal passage and a flow port provided part way along the length of the outer tool body, the flow port forming a fluid path between the internal passage and an exterior of the inner tool body; a control piston positioned with the outer tool body and axially movable with respect to the outer tool body, the control piston having a central bore; a biasing arrangement biasing the control piston towards the first end of the outer tool body a control arrangement which limits movement of the control piston towards the first end of the outer tool body, wherein the control arrangement can be switched between a first configuration, in which the control piston can move to a first maximum distance towards the first end of the outer tool body, in which position there is no fluid path between the flow aperture of the control piston and the flow port of the outer tool body, and a second configuration, in which the control piston can move to a second maximum distance towards the first end of the outer tool body, in which position fluid may flow between the central bore of the control piston and the flow port of the outer tool body.
2. A tool according to claim 1, wherein: the control piston has a flow aperture providing a fluid path between the central bore and an exterior of the control piston; and in the second configuration, fluid may flow from the central bore of the control piston, through the flow aperture thereof to the flow port of the outer tool body.
3. A tool according to claim 1 or 2, wherein the control arrangement comprises first and second components, a first of the components being formed as part of, or held axially in place with respect to, the outer tool body, and a second of the components being formed as part of, or held axially in place with respect to, the control piston.
4. A tool according to claim 3, wherein the first component comprises an elongate track, and the second component comprises an element which is received in, and may travel along, the track.
5. A tool according to claim 3 or 4, wherein the control system is an indexing system.
6. A tool according to any preceding claim, further comprising a seat onto which an obstruction may be received to block or substantially block the flow of fluid through the control piston.
7. A tool according to claim 6 wherein when an obstruction is received on the seat, pressurised fluid may be introduced into the first end of the outer tool body to drive the control piston towards the second end of the outer tool body, against the biasing force of the biasing element.
8. A tool according to any preceding claim wherein the biasing arrangement comprises a spring.9. A tool according to any preceding claim, wherein the first maximum distance is greater than the second maximum distance.
9. A tool according to any preceding claim, wherein a recess is provided on an inner surface of the outer tool body, the recess being in communication with, and extending axially with respect to, the flow port.
10. A tool according to claim 9 wherein, in at least one position of the control piston, fluid may flow from the interior passage of the outer tool body, into a first part of the recess which is not axially aligned with the flow port, axially along the recess and out of the flow port.
11. A tool according to claim 10, when dependent upon claim 2, wherein in at least one position of the control piston the flow aperture of the control piston is axially aligned with the first part of the recess.
12. A tool according to claim 11 or 12 wherein a fluid path axially along the recess, from the first part of the recess to the flow port, is defined at least partly between the interior surface of the outer tool body and an exterior surface of the control piston.
13. A tool according to any preceding claim, wherein the control piston can move axially by a maximum distance within the outer tool body, towards the second end of the outer tool body.
14. A tool according to claim 13 wherein, when the control piston is at the limit of its axial motion towards the second end of the outer tool body, fluid may flow between the central bore of the control piston and the flow port of the outer tool body.
15. A tool according to any preceding claim 1 to 8, 13 or 14, further comprising an upper sleeve, positioned within the outer tool body and surrounding at least part of the control piston, wherein: the upper sleeve covers the flow port of the outer tool body; and the upper sleeve has a flow opening formed therethrough which is in fluid communication with the flow port.
16. A tool according to claim 15 wherein a recess is provided on an inner surface of the upper sleeve, the recess being in communication with, and extending axially with respect to, the flow opening.
17. A tool according to claim 16 wherein, in at least one position of the control piston, fluid may flow from the interior passage of the outer tool body, into a first part of the recess which is not axially aligned with the flow opening, axially along the recess and out of the flow opening.
18. A tool according to claim 17, when dependent upon claim 2, wherein in at least one position of the control piston the flow aperture of the control piston is axially aligned with the first part of the recess.
19. A tool according to claim 17 or 18 wherein a fluid path axially along the recess, from the first part of the recess to the flow port, is defined at least partly between the interior surface of the upper sleeve and an exterior surface of the control piston.
20. A tool according to any preceding claim, wherein a lower part of the control piston is received within a chamber formed in the outer tool body.
21. A tool according to claim 20, wherein a floating piston surrounds the lower part of the control piston, and is axially movable with respect to the lower part of the control piston.
22. A tool according to claim 21, wherein the floating piston has an inner seal which seals against the lower part of the control piston, and an outer seal which seals against an inner surface of the outer tool body.
23. A tool according to claim 20 or 21, wherein a lower sleeve is positioned within the chamber.
24. A tool according to claim 23, wherein the floating piston has an inner seal which seals against the lower part of the control piston, and an outer seal which seals against an inner surface of the lower sleeve.
25. A method comprising: providing a drill string incorporating a tool according to any preceding claim; introducing the drill string into a wellbore; and operating the control arrangement to move the control arrangement from the first configuration to the second configuration.
26. A method according to claim 25, wherein the tool is in accordance with claim 6 or any claim dependent thereon, and the method further comprises the step of introducing an obstruction into the drill string so that the obstruction is received on the seat; moving the control piston into a position in which the flow aperture thereof is aligned or substantially aligned with the flow port of the outer tool body; and pumping fluid carrying solid material into the first end of the tool, such that the fluid passes through the flow aperture and flow port, and to a region surrounding the exterior of the tool.
27. A method according to claim 25 or 26, wherein the tool is in accordance with claim 11, further comprising the step of cycling the tool, using the control arrangement, between (a) the second configuration and (b) the limit of the axial of the control piston towards the second end of the outer tool body.
28. A method according to any one of claims 25 to 27, further comprising the steps of: operating the control arrangement to place the control arrangement in the second configuration; and withdrawing the tool from the wellbore with the control arrangement in the second configuration.