Ball seat assembly for a downhole tool

Abstract

A ball seat assembly (2) for a downhole tool comprises a collet (6) having a collet shank (8) with an inner collet shank wall (36) and an outer collet shank wall, and collet fingers (10) arranged around a central axis (12) of the collet shank (8) and 5 attached to an uphole end (14) of the collet shank (8); an inner sleeve (34) configured to be axially movable along the inner collet shank wall (36), the inner sleeve (34) having a ball seat (40) and a central flow channel (42) extending through the ball seat (40); wherein the collet fingers (10) have a neutral position creating an uphole opening (26) having a first diameter (D1) and are expandable to 10 a second diameter (D2) larger than the first diameter (D1); wherein in a run-in state of the downhole tool, the inner sleeve (34) is in a first axial position relative to the collet shank (8), in which first position the inner sleeve (34) urges the collet fingers (10) to expand to the second diameter (D2) to allow a ball (44) having a ball diameter (d) less than the second diameter (D2) and larger than the first diameter 15 (D1) to pass through the uphole opening (26) of the collet (6); wherein the inner sleeve (34) is configured to move into a second axial position upon a fluid pressure applied uphole and acting against the ball (44) covering the ball seat (40) and the central flow channel (42), and wherein the ball seat assembly (2) is configured to let the collet fingers (10) snap back into the neutral position, thereby preventing the 20 ball (44) from leaving the collet (6).

Description

[0001] Ball seat assembly for a downhole tool

[0002] Field of the invention

[0003] The invention relates to a ball seat assembly for a downhole tool, a downhole tool, and a method of operating a component in a downhole tool.

[0004] Background

[0005] Exploration and production of hydrocarbons, such as oil and gas, involve complex drilling operations that require the deployment of various downhole tools. These tools perform a variety of functions, including borehole enlargement, fluid control, and pressure management, among others. In some downhole operations a reliable activation and control of downhole tools after they have been deployed in the borehole is required. Over the years, numerous mechanisms have been developed to address this challenge, including wireline activation, hydraulic actuation using shear pins, and electronically controlled systems. However, ball-operated mechanisms have emerged as a particularly effective solution due to their simplicity and reliability.

[0006] Ball-operated mechanisms are widely used in downhole tools for activation and control purposes. These mechanisms typically involve dropping or pumping a ball through wellbore tubulars, where it eventually lands on a designated ball seat within the downhole tool. Once the ball engages the ball seat, it restricts or closes a flow passage through the downhole tool, such that hydraulic pressure can build up above the ball. The pressure is then used to actuate the downhole tool, such as expanding reamer blades, opening sliding sleeves or the like. This method of activation is mechanically simple and does not require complex electric or electronic systems.

[0007] A primary application of ball-operated mechanisms may be the control of underreamers, i.e., downhole tools designed to enlarge the diameter of a borehole. In drilling operations, an initial borehole, known as the pilot hole, may need to be expanded to accommodate additional casing or to improve the flow of hydrocarbons. Under-reamers are typically run in a retracted state and must be activated at a specific depth, often after passing beyond existing casing. Balloperated mechanisms provide an efficient means of activating the under-reamer, allowing blades or other components to extend and enlarge the borehole as needed. This method not only enhances the efficiency of drilling operations but also reduces the time and cost associated with alternative activation methods.

[0008] Summary of the invention

[0009] An object of at least the preferred embodiments of the invention is to propose a reliable and mechanically simple ball seat assembly that allows to retain a ball in a downhole tool.

[0010] The present invention is defined by the appended claims and in the following:

[0011] In a first aspect, the invention relates to a ball seat assembly for a downhole tool, comprising a collet having a collet shank with an inner collet shank wall and an outer collet shank wall, and collet fingers arranged around a central axis of the collet shank and attached to an uphole end of the collet shank; an inner sleeve configured to be axially movable along the inner collet shank wall, the inner sleeve having a ball seat and a central flow channel extending through the ball seat; wherein the collet fingers have a neutral position creating an uphole opening having a first diameter and are expandable to a second diameter larger than the first diameter; wherein in a run-in state of the downhole tool, the inner sleeve is in a first axial position relative to the collet shank, in which first position the inner sleeve urges the collet fingers to expand to the second diameter to allow a ball having a ball diameter less than the second diameter and larger than the first diameter to pass through the uphole opening of the collet; wherein the inner sleeve is configured to move into a second axial position upon a fluid pressure applied uphole and acting against the ball when the ball is, in use, covering the ball seat and the flow channel, and wherein the ball seat assembly is configured to let the inner sleeve snap back into the second position in the collet, thereby preventing the ball from leaving the collet.

[0012] By the use of this ball seat assembly it is ensured that after a ball is dropped and initially engages with the ball seat then the ball cannot move fully away from the ball seat. For example it may be retained in place such that it can only move at most short distance (e.g. less than twice the ball diameter, or less than 1.5 times the ball diameter) away from the ball seat. Thus, the ball seat assembly addresses a problem that the ball may fall out of the seat, which may in turn compromise operation of other parts of the tool. The inventors have found that in prior art designs the ball can be dislodged when the fluid pressure above it is released, especially where the tool may encounter highly inclined or horizontal well bores. Advantageously the ball seat assembly may permit some movement of the ball when the inner sleeve is in the second position (such as uphole movement of more than half the ball diameter or more than one diameter of the ball), for example in order to permit fluid to flow upward whilst always reliably stopping downward flow of fluid. Retainment of the ball whist permitting some motion may be achieved by setting a suitably large distance between the uphole opening and the ball seat when the inner sleeve is in the second axial position.

[0013] The collet in the ball seat assembly includes a collet shank. The collet shank may be understood as an end section of the collet that is opposite to free ends of the collet fingers. The collet shank has an inner collet shank wall and an outer collet shank wall. The inner collet shank wall may comprise a substantially cylindrical shape at least in a section. Thus, the inner sleeve may slide along the inner collet shank wall if it has a cylindrical outer wall with a corresponding diameter.

[0014] The collet may be manufactured in the form of a single component. For example, it may be made from a cylindrical or frusto-conical metallic sleeve that is slitted along a part of its axial length. The sections between two consecutive slits may form the collet fingers. The remaining part that is not slitted may be referred to as the collet shank. Alternatively, the collet fingers and the collet shank may be manufactured separately, and the collet fingers may be attached to the collet shank, e.g., by welding. Other variants are not ruled out herein.

[0015] When used herein, the term “uphole” refers to the direction or end of the borehole that leads back towards the surface when the downhole tool is in operation. This is in contrast to “downhole”, which refers to the direction towards the downhole tool and deeper into the earth. “Uphole” describes the orientation away from the downhole tool.

[0016] An uphole end of the collet has an uphole opening, which is formed and delimited by free ends of the collet fingers. The free ends of the collet fingers face away from the collet shank. The collet fingers can be expanded and contracted in that the free ends of the collet fingers are radially moved outwards or inwards, thereby changing the size of the uphole opening. When the uphole opening is sufficiently large, a correspondingly shaped and sized ball can pass through the uphole opening to enter an interior space of the collet, where the inner sleeve is arranged. When the uphole opening is smaller than the ball, the ball cannot pass it and hence is prevented from entering the collet or is trapped inside the collet.

[0017] The inner sleeve is designed to be axially movable along the inner collet shank wall. Preferably, the inner sleeve may be of a hollow-cylindrical shape. For achieving an axial movability the inner sleeve may have a sliding section with a constant outer diameter. At least a part of the inner collet shank wall may in turn have a constant inner diameter. It may be preferred that the inner sleeve and the collet shank have a sliding fit, such that the inner sleeve may easily slide along the inner collet shank wall. The inner sleeve comprises a ball seat. The ball seat may at least approximately have the shape of a ball segment. The ball segment may be based on a ball radius that corresponds to or exceeds the radius of the ball that is used in the downhole tool. In an alternative, the ball seat may have a frusto-conical shape. The ball seat may be arranged symmetrically around the longitudinal axis of the inner sleeve. The central flow channel may symmetrically extend along the longitudinal axis and through the ball seat. The central flow channel allows for passage of a fluid when the ball seat is unobstructed. When the ball is placed on the ball seat, the central flow channel is obstructed and a fluid flow through the central flow channel is at least partially interrupted, thereby increasing the fluid pressure at the ball seat assembly.

[0018] The collet fingers have free ends facing away from the collet shank. The free ends define an uphole opening. In a neutral, unbiased, state of the collet fingers, the uphole opening has a first diameter. The term “neutral” is to be understood as a state in which no external forces act onto the collet fingers. By applying a bending or biasing force, the free ends of the collet fingers may move in a radial outwards direction, such that the collet fingers are biased outwards. In this state, the uphole opening reaches the second diameter, which is larger than the first diameter. The expandability is important for allowing a ball with a diameter less than the second diameter but larger than the first diameter to pass through the uphole opening to reach the ball seat.

[0019] In the run-in state of the downhole tool, to which the ball seat assembly is attached, the inner sleeve is in a first axial position relative to the collet shank, thereby urging the collet fingers to expand to the second diameter. This may be achieved by a selective biasing of the collet fingers through geometric features arranged at an outer surface of the inner sleeve and / or an inner surface of the collet fingers. For example, the collet fingers may comprise protrusions arranged on their radial inner side. When the axial positions of the protrusions overlap with the axial position of the inner sleeve, the protrusions rest on the outer surface of the inner sleeve and the collet fingers are biased outwards. However, also the inner sleeve may comprise such protrusions, which urge the collet fingers in a radial outward position in the first axial position of the inner sleeve. Other elements or mechanisms may be used in addition or as an alternative. Urging the collet fingers to expand allows the ball to pass through the uphole opening of the collet, thereby facilitating the initial passage of the ball through the collet.

[0020] The inner sleeve is configured to move into the second axial position upon the application of an elevated fluid pressure uphole, acting against the ball that covers the ball seat and, resultantly, the flow channel. When the ball is placed on the ball seat, the fluid flow is at least partially blocked. The fluid pressure uphole acts along the longitudinal axis of the ball seat assembly onto a surface area perpendicular to the longitudinal axis, which includes the projection area of the ball onto the inner sleeve and the part of the inner sleeve that radially protrudes beyond the ball. As a result, a pressing force is created, which presses the inner sleeve in a direction away from the collet fingers. With a sufficient pressure uphole, the inner sleeve is moved from its first position to its second position.

[0021] The ball seat assembly is configured to let the inner sleeve snap back into the neutral position, thereby preventing the ball from leaving the collet. In the second axial position the inner sleeve does not urge the collet fingers into an expanded state. For example, if above-mentioned protrusions are arranged on an inner side of the collet fingers, they may slide along an outer surface of the inner sleeve and pass an end face of the inner sleeve, such that the collet fingers snap back into their neutral state. However, other mechanisms are not ruled out.

[0022] The collet fingers may comprise a first engagement element, the inner sleeve may comprise a second engagement element, and the first engagement element and the second engagement element may engage in the second position of the inner sleeve to latch the inner sleeve in the second position. The first engagement element may be arranged on an inner side of the collet fingers and may, for example, comprise radial protrusions or radial grooves. The second engagement element may be arranged on an exterior of the inner sleeve and may, for example, comprise an end face of the inner sleeve, a shoulder on the end face of the inner sleeve, a radial groove extending into the inner sleeve or radial protrusions radially extending away from the inner sleeve. The first engagement element may be selected to be complementary to the second engagement element and may, for example, comprise radial protrusions or radial grooves. In the second position, the first engagement element may, for example, snap into or onto the second engagement element. This engagement mechanism ensures that the inner sleeve is securely latched in the second position, thereby preventing a return into the first position. Consequently, the collet fingers remain in their neutral state and prevent the ball from escaping the collet.

[0023] One of the first engagement element and the second engagement element may be a radial protrusion, and the other one of the first engagement element and the second engagement element may be a radial groove, a step, or a section with a reduced diameter complementary to the radial protrusion. This complementary engagement mechanism ensures a secure and reliable latching of the inner sleeve in the second position. The mechanism is particularly simple and reliable, thereby providing a robust and reliable latching function.

[0024] The ball seat assembly may comprise a resilient element arranged at a downhole end of the inner sleeve, wherein the resilient element may be configured to be compressed upon axial movement of the inner sleeve towards the second position. This resilient element ensures that the inner sleeve is held in the first position during normal or initial operation of the downhole tool. It may preferably be designed and dimensioned to avoid inadvertent movement into the second position before a ball is placed into the downhole tool. A spring coefficient of the resilient element may be chosen to let the resilient element only be compressed when a ball closes the central flow channel to move the inner sleeve in a downhole direction.

[0025] Alternatively, or additionally, a shear pin may be arranged at a downhole end of the inner sleeve, wherein the shear pin may be configured to break when a predetermined pressure is applied or exceeded uphole. This may further simplify the design and setup of the ball seat assembly.

[0026] The ball seat assembly may comprise a radial seal between the uphole end and the downhole end of the inner sleeve, wherein the radial seal may be configured to seal against the collet shank. The radial seal prevents a fluid leakage between the inner sleeve and the collet shank to improve the performance of the ball seat assembly.

[0027] The ball seat assembly may be configured to be installable at an end of a downhole tool. For example, it allows to be attached to a downhole opening of the downhole tool by screwing the collet shank into an internal thread of the downhole opening. This configuration allows for easy installation and integration of the ball seat assembly into existing downhole tools.

[0028] The ball seat assembly may comprise a retainer ring, wherein the retainer ring may be configured to allow a downhole end portion of the inner sleeve to pass through in an axial direction. The retainer ring may be attached to a downhole end of the collet shank. The downhole end portion of the inner sleeve may have a smaller diameter than the remaining part of the inner sleeve. Hence, the inner sleeve may comprise a stepped outer surface, which forms a shoulder at the transition between the downhole end portion and the remaining part of the inner sleeve. The retainer ring may in turn have a bore, which has a larger diameter than the downhole end portion of the inner sleeve. The downhole end portion of the inner sleeve may thus pass through the bore of the retainer ring. The uphole part of the inner sleeve may be dimensioned to have a larger diameter than the bore of the retainer ring, such that the retainer ring reliably prevents the inner sleeve from leaving the collet when the resilient element fails or when the shear pin is broken. The resilient element mentioned above may be placed in a space between the shoulder of the inner sleeve and the retainer ring.

[0029] The resilient element may comprise a disk spring assembly. The disk spring assembly provides a comparably high spring force in a small installation space and thus enhances the compactness of the ball seat assembly. It is further proposed a downhole tool comprising the ball seat assembly according to the above. The downhole tool may be a well tool configured to perform well operations within a liner of a wellbore. The downhole tool may include underreamers, sliding sleeves, fracturing tools, plugging tools, cement fundaments or any other tool that may benefit from using a ball seat assembly to control its operation.

[0030] The invention may include use of the ball seat assembly in a well operation using a downhole tool that incorporates the ball seat assembly.

[0031] It is also proposed a method of operating a component in a downhole tool, comprising providing a ball seat assembly according to the above, running the downhole tool into a wellbore with the inner sleeve in the first axial position, wherein the collet fingers are expanded to the second diameter; allowing a ball to pass through the uphole opening of the collet; and applying a fluid pressure uphole to move the inner sleeve to the second axial position whilst the ball blocks passage of fluid through the central flow channel, thereby allowing a subsequent increase in hydraulic pressure above the ball in order to operate the component.

[0032] This method may include use of a ball seat assembly with any of the optional features discussed above.

[0033] The method may include using the movement of the inner sleeve into the second position as a mechanism for driving a secondary component in the downhole tool. By placing the ball into the downhole tool, the secondary component provided in the downhole tool may be driven by the inner sleeve due to the pressure applied uphole. This may for example involve sufficient force for overcoming the resistance to movement of the inner sleeve that is provided by the spring and / or shear pin. In an alternative the motion of the inner sleeve may be used for driving the main component of the downhole tool, either in addition to hydraulic pressure or without separate use of the hydraulic pressure. Notably, the movement of the inner sleeve can be a one-shot actuation, which is not reversible and can involve a component being locked in place, whilst increased hydraulic pressure above the ball can be released and reapplied and hence used multiple times if required.

[0034] Brief description of the drawings

[0035] In the following description this invention will be further explained by way of exemplary embodiments shown in the drawings:

[0036] Fig. 1 shows a ball seat assembly in a sectional view in a run-in state with the inner sleeve in the first position and the collet fingers being expanded. Fig. 2 shows the ball seat assembly in a sectional view in the run-in state with the inner sleeve in the first position and a ball reaching the collet.

[0037] Fig. 3 shows the ball seat assembly in a sectional view with the inner sleeve in the second position and the collet fingers being in their neutral position.

[0038] Fig. 4 shows a ball seat assembly with a shear pin in a sectional view in a run-in state.

[0039] Detailed description of the invention

[0040] In the following, the terms “above”, “top”, “uppermost”, and “below”, “bottom”, “lowermost” are used to indicate a location of a component in the tool. “Above” refers to a location closer to an uphole end of the tool or the surface. “Top” and “uppermost” refer to an uppermost component, which is closest to the uphole end or the surface. “Below” instead refers to a location further away from the uphole end or the surface and closer to a downhole end of the tool. “Bottom” and “lowermost” refers to a location closest to the downhole end or furthest away from the surface. When using these terms, it is assumed that the tool is in use, i.e., inserted into a well casing.

[0041] Figs. 1 to 3 show a ball seat assembly 2 at a downhole end 4 of a downhole tool. The ball seat assembly 2 comprises a collet 6 having a collet shank 8 and collet fingers 10 arranged around a central axis 12 of the collet shank 8 and attached to or formed at an uphole end 14 of the collet shank 8. The collet 6 may be made of steel, in particular a spring steel.

[0042] The collet shank 8 exemplarily comprises an outer thread 16 engaging an internal thread 18 of the downhole tool. The downhole end 20 of the collet shank 8 exemplarily has a radial shoulder 22, which is clamped against the downhole end 4 of the downhole tool. Thus, the ball seat assembly 2 is rigidly attached to the downhole end 4 of the downhole tool.

[0043] The collet fingers 10 are flexible and their uphole ends can be moved in a radial direction. Exemplarily, some or each of the free ends of the collet fingers 10 comprise a radial constriction 24. The free ends of all collet fingers 10 define an uphole opening 26 having an opening diameter D. An uphole part of each of the constrictions 24 has a downwardly tapered, funnel-like shape.

[0044] Between a central region 28 and the radial constriction 24 at an inner side of the collet fingers 10, a first engagement element 30 in the form of several radial protrusions is provided. In the state of the ball seat assembly 2 as shown in Fig. 1, the first engagement element 30 rests on an outer surface 32 of an inner sleeve 34. Thereby, the collet fingers 10 are urged or biased radially outwards into an expanded position. The diameter D2 of the uphole opening 26 in this state may be referred to as “second diameter”, while in a neutral state of the collet fingers 10, in which the collet fingers 10 are not biased outwardly, the diameter Di may be referred to as “first diameter”, which is smaller than the second diameter.

[0045] The inner sleeve 34 has a substantially hollow-cylindrical shape and is configured to be axially movable along an inner collet shank wall 36. An uphole end of the inner sleeve 34 has an uphole end face 38, in which a ball seat 40 is integrated. The ball seat 40 may comprise a frusto-conical shape or the shape of a ball segment. A central flow channel 42 extends through the inner sleeve 34 and through the ball seat 40.

[0046] In the run-in state of the downhole tool, the inner sleeve 34 is in an axial position shown in Fig. 1. This is referred to as the “first axial position”. In this state, the uphole opening 26 is expanded to the second diameter D2. Fluid can flow through the central flow channel 42 along the central axis 12, which in this state is substantially unobstructed.

[0047] As shown in Fig. 2, a ball 44 has been inserted into the downhole tool and reaches the uphole opening 26 of the ball seat assembly 2. The ball 44 has a diameter d, which is smaller than the second diameter D2. Thus, the ball 44 is able to pass through the uphole opening 26 to reach an interior space between the constrictions 24 and the ball seat 40. The funnel-like shape of the uphole opening 26 assists in guiding the ball 44 to pass through the uphole opening 26.

[0048] When the ball 44 enters the ball seat 40 as depicted in Fig. 3, the central flow channel 42 will be substantially closed. Thus, a flow through the central flow channel 42 is obstructed and a pressure applied at an uphole end of the downhole tool acts onto the surface area of a combination of the ball 44 and the end face 38. This leads to generating a pressing force into the downhole direction along the central axis 12. The pressing force presses the ball 44 onto the ball seat 40 and the inner sleeve 34 moves along the central axis 12 until the end face 38 passes the first engagement elements 30.

[0049] Resultantly, the first engagement element 30 radially snaps back in a radial direction and the uphole ends of the collet fingers 10 reduce the size of the uphole opening 26. The uphole opening 26 then defines the size given by the first diameter Di, which is smaller than the diameter d of the ball 44. Hence, the ball 44 is trapped inside the collet 6. As the first engagement element 30 has snapped back in a radial direction and radially overlaps with the end face 38, the inner sleeve 34 is latched in the second position. In this state the ball 44 will block downward flow of fluid allowing for increased pressure above the ball 44, e.g. to actuate components of the downhole tool such as pistons or other hydraulic devices. However, if there is any upward flow of fluid then the ball 44 can lift off the ball seat 40 and fluid can flow around the ball 44 and through the openings in between the collet fingers 10. The ball 44 may for example be free to move upward by a distance of about one diameter of the ball 44, or more, as shown in the drawings. The ball seat assembly is therefore not a seal or isolation valve, but instead allows one-way circulation.

[0050] To avoid an inadvertent axial motion of the inner sleeve 34 before the ball 44 is been inserted, a resilient element 46 generates a pressing force onto the inner sleeve 34 into an uphole direction. The resilient element 46 is placed at a downhole portion 48 of the inner sleeve 34 and is clamped between the inner sleeve 34 and retainer ring 50 attached to a downhole end of the collet 6. In an alternative implementation a shear pin (not shown) may be used in place of or in addition to the resilient element 46. The shear pin can retain the inner sleeve 34 in place until a sufficiently large force is applied.

[0051] Exemplarily, the downhole portion 48 has a smaller diameter than the remaining part of the inner sleeve 34 and the resilient element is arranged to enclose the downhole portion 48. The retainer ring 50 has a bore 52, into which the downhole portion 48 can be moved when the inner sleeve 34 is pressed into the downhole direction. The resilient element 46 is exemplarily placed between the retainer ring 50 and a shoulder 54 of the inner sleeve 34, which separates the downhole portion 48 and the remaining part of the inner sleeve 34.

[0052] In the exemplary embodiment shown herein, the resilient element 46 is provided in the form of a disk spring assembly. It is dimensioned to require a minimum pressing force to let the inner sleeve 34 move from the first position into the second position, such that the inner sleeve 34 can be latched. Hence the ball seat assembly 2 reliably provides a control of a downhole tool with an insertable ball in a mechanical simple manner.

[0053] A seal 56 is arranged between the inner sleeve 34 and the collet shank 8 to reduce or eliminate an annular leakage flow, thereby improving the function of the ball seat assembly 2.

[0054] There may also be another mode of operation, as well as optionally a variation in the design, where the ball 44 is pre-loaded e.g. by insertion whilst the tool is topside. In that case the tool may always be in the final state when it is in use in the well bore, i.e. with the ball 44 retained close to the ball seat 40 but allowed to move upwardly to permit upward flow of fluid. That tool might be used absent a resilient member 46 (or shear pin), i.e. with a simple sliding of the inner sleeve 34 to retain the ball in place by shifting into the second position. Fig. 4 shows a ball seat assembly 58 at a downhole end 4 of a downhole tool. The ball seat assembly 58 has substantially the same general design as the ball seat assembly 2 from Figs. 1 to 3. Thus, it comprises the collet 6, which is exemplarily attached to the downhole tool through the threads 16 and 18.

[0055] In Fig. 4, the ball seat assembly 58 is in a run-in state and the first engagement element 30 rests on the outer surface 32 of the inner sleeve 34, urging the collet fingers 10 into the expanded position. In Fig. 4, the inner sleeve 34 is in the first axial position, in which it is held by shear pins 60 instead of the resilient element 46. The shear pins 60 radially extend from the downhole end 20 of the collet 6 into pin recesses 62 of the inner sleeve 34. They may be made from a material that differs from the material of the inner sleeve 34 or the collet 6.

[0056] When the ball 44 is placed on the ball seat 40, the central flow channel 42 will be substantially closed and a pressure applied at an uphole end of the downhole tool 58 acts onto the surface area of a combination of the ball 44 and the end face 38, thereby pressing the inner sleeve 34 towards in the downhole direction. The shear pins 60 are dimensioned to break if a predetermined minimum pressing force is reached. When the shear pins 60 break, the inner sleeve 34 can reach the second position, and the inner sleeve 34 can be latched. Hence the ball seat assembly 58 reliably provides a control of a downhole tool with an insertable ball in a mechanical simple manner.

[0057] Reference numerals

[0058] 2 ball seat assembly

[0059] 4 downhole end

[0060] 6 collet

[0061] 8 collet shank

[0062] 10 collet fingers

[0063] 12 central axis

[0064] 14 uphole end (of collet shank)

[0065] 16 outer thread

[0066] 18 internal thread

[0067] 20 downhole end

[0068] 22 radial shoulder

[0069] 24 radial constriction

[0070] 26 uphole opening

[0071] 28 central region

[0072] 30 first engagement element

[0073] 32 outer surface

[0074] 34 inner sleeve

[0075] 36 inner collet shank wall

[0076] 38 uphole end face

[0077] 40 ball seat

[0078] 42 central flow channel

[0079] 44 ball

[0080] 46 resilient element

[0081] 48 downhole end portion

[0082] 50 retainer ring

[0083] 52 bore

[0084] 54 shoulder

[0085] 56 seal

[0086] 58 ball seat assembly

[0087] 60 shear pin

[0088] 62 pin recess

[0089] Di first diameter

[0090] D2 second diameter d ball diameter

Claims

CLAIMS1. A ball seat assembly (2, 58) for a downhole tool, comprising: a collet (6) having a collet shank (8) with an inner collet shank wall (36) and an outer collet shank wall, and collet fingers (10) arranged around a central axis (12) of the collet shank (8) and attached to an uphole end (14) of the collet shank (8); an inner sleeve (34) configured to be axially movable along the inner collet shank wall (36), the inner sleeve (34) having a ball seat (40) and a central flow channel (42) extending through the ball seat (40); wherein the collet fingers (10) have a neutral position creating an uphole opening (26) having a first diameter (Di) and are expandable to a second diameter (D2) larger than the first diameter (Di); wherein in a run-in state of the downhole tool, the inner sleeve (34) is in a first axial position relative to the collet shank (8), in which first position the inner sleeve (34) urges the collet fingers (10) to expand to the second diameter (D2) to allow a ball (44) having a ball diameter (d) less than the second diameter (D2) and larger than the first diameter (Di) to pass through the uphole opening (26) of the collet (6); wherein the inner sleeve (34) is configured to move into a second axial position upon a fluid pressure applied uphole and acting against the ball (44) covering the ball seat (40) and the central flow channel (42), and wherein the ball seat assembly (2, 58) is configured to let the collet fingers (10) snap back into the neutral position, thereby preventing the ball (44) from leaving the collet (6).

2. The ball seat assembly (2, 58) of claim 1, wherein the ball seat assembly (2, 58) is configured to permit some movement of the ball (44) when the inner sleeve (34) is in the second position, for example in order to permit fluid to flow upward whilst always reliably stopping downward flow of fluid.

3. The ball seat assembly (2, 58) of claim 1 or 2, wherein the collet fingers (10) comprise a first engagement element (30), wherein the inner sleeve (34) comprises a second engagement element (38), and wherein the first engagement element (30) and the second engagement element (38) engage in the second position of the inner sleeve (34) to latch the inner sleeve (34) in the second position.

4. The ball seat assembly (2, 58) of claim 3,wherein one of the first engagement element (30) and the second engagement element (38) is a radial protrusion, and wherein the other one of the first engagement element (30) and the second engagement (38) is a radial groove, a step, or a section with a reduced diameter complementary to the radial protrusion.

5. The ball seat assembly (2, 58) of any of the preceding claims, comprising a resilient element (46) arranged at a downhole end of the inner sleeve (34), wherein the resilient element (46) is configured to be compressed upon axial movement of the inner sleeve (34) towards the second position.

6. The ball seat assembly (2, 58) of claim 5, wherein the resilient element (46) comprises a disk spring assembly.

7. The ball seat assembly (2, 58) of any of the preceding claims, wherein a shear pin (60) is arranged at a downhole end of the inner sleeve (34) to connect with the collet shank (8), and wherein the shear pin (60) is configured to break when a predetermined pressure is applied or exceeded uphole.

8. The ball seat assembly (2, 58) of any of the preceding claims, comprising a radial seal (56) between the uphole end and the downhole end of the inner sleeve (34), wherein the radial seal (56) is configured to seal against the collet shank (8).

9. The ball seat assembly (2, 58) of any of the preceding claims, wherein the ball seat assembly (2, 58) is configured to be installable at an end of a downhole tool.

10. The ball seat assembly (2, 58) of any of the preceding claims, comprising a retainer ring (50), wherein the retainer ring (50) is configured to allow a downhole end portion (48) of the inner sleeve (34) to pass through the retainer ring (50) in an axial direction.

11. A downhole tool comprising the ball seat assembly (2, 58) of any of claims 1 to 10,12. A downhole tool as claimed in claim 11, wherein the downhole tool is a well tool configured to perform well operations within a liner of a wellbore.

13. A method comprising use of the ball seat assembly (2, 58) of any of claims 1 to 10 during a well operation using a downhole tool comprising the ball seat assembly.

14. A method as claimed in claim 13 including operating a component in the downhole tool, the method comprising: providing a ball seat assembly (2, 58) according to any of claims 1 to 10; running the downhole tool into a wellbore with the inner sleeve (34) in the first axial position, wherein the collet fingers (10) are expanded to the second diameter (D2); allowing a ball (44) to pass through the uphole opening (26) of the collet(6); and applying a fluid pressure uphole to move the inner sleeve (34) to the second axial position whilst the ball (44) blocks passage of fluid through the central flow channel (42), thereby allowing a subsequent increase in hydraulic pressure above the ball in order to operate the component.

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