Patent Description:
Downhole actuators are well known for use in controlling downhole devices. Our earlier <CIT> discloses a previous design of actuator for a valve, in which a fluid passageway is opened and closed by the action of a centrifugal force on a retaining member typically in the form of a ball. The present invention represents an improvement over our earlier design, with improved consistency of performance in deviated wellbores. <CIT>, <CIT>, <CIT>, <CIT>, and <CIT> disclose other actuators useful for understanding the invention.

According to the present invention, there is provided a downhole device according to claim <NUM>.

Typically the device comprises a valve, and typically has an inlet and a primary outlet, and optionally a secondary outlet. Typically actuation of the device diverts fluid normally flowing from the inlet to the primary outlet into an alternate fluid pathway, in which the fluid flows from the inlet to the alternate outlet. Typically, the closure device is capable of closing the bore and preventing or substantially preventing the flow of fluid past the closure device and through the bore. Typically, the closure device diverts fluid flowing through the bore to the flow path leading to the alternate outlet. In one aspect, the downhole device is embodied in a circulation sub, and the closure device diverts fluid normally flowing past the closure device within the bore into a circulation pathway, which typically passes through the body of the device.

In certain aspects, the closure device can be adapted to restrict the passage of fluid through the bore, but to allow a reduced flow through the bore without closing the bore entirely. Optionally, the closure device has a port allowing passage of some fluid through the closure device when the closure device is in the closed position, while the remainder of the fluid is diverted by the closure device into the alternate pathway (e.g. the circulation port).

Typically, the counterweight devices are moved between the first and second positions by centrifugal force created by rotation of the body. Optionally, the body is incorporated in a string, such as a drillstring, and the rotation of the body is typically caused by rotation of the string as a whole, typically from the surface, and typically during rotary drilling operations.

The counterweights are typically circumferentially spaced around the body, and typically the centrifugal force is balanced around the circumference. This is typically achieved by spacing the counterweights at equal distances around the circumference of the body, but in certain circumstances the spacing between adjacent counterweights can be different. Optionally the arrangement of counterweight devices around the body can be symmetrical around the axis of the body. In some cases, the circumferential arrangement of counterweights around the body can be non-symmetrical. Even or odd numbers of counterweights can be provided, typically spaced equi-distantly around the circumference of the body.

The masses of the counterweights can be the same, or in some aspects can be different between each respective counterweight, but in each arrangement, it is typically the case that the centrifugal force applied by any particular counterweight is balanced by at least one or more other counterweight, so that the centrifugal force is balanced around the circumference of the body and is not eccentric.

The movement of the counterweight devices between the first and second radial positions results in radial outward movement of the counterweight devices from a first radially retracted position in which the counterweight devices are retracted close to the axis of rotation of the body (typically the axis of the body is co-axial with the axis of rotation of the body) to a second radially extended position in which the counterweight devices have moved radially outwards (typically in opposite directions) away from the axis of rotation of the body. In the first position, the counterweight devices are typically aligned with the axis of rotation of the body, and in the second position, the counterweight devices are typically also aligned with the axis of rotation of the body, but radially spaced further from the axis than in the first position. The orientation of the counterweight devices is typically maintained by the link arms as the counterweight devices move between the first and second positions.

The counterweight devices are typically connected at axially spaced apart locations (for example at or near their upper and lower ends) to upper and lower sleeves. Typically the sleeves interconnect the counterweight devices. Typically the counterweight devices are spaced on different sides of the axis of rotation of the body, and are typically spaced at <NUM> degrees with respect to one another around that axis.

Typically, the upper and lower sleeves surround the bore and generally can have circular cross-sections, and typically the counterweight devices are circumferentially spaced equi-distantly in relation to one another around the sleeves The relative axial movement of the sleeves as a result of the radial movement of the counterweight devices typically triggers the actuator, typically resulting in activation of the closure device, typically by changing the configuration of a linkage mechanism operatively connected between one of the sleeves and the closure device.

The upper and lower sleeves typically surround a central axial tubular member forming the bore of the device. Typically, the sleeve devices slide axially along the outer surface of the tubular. Typically, the closure device closes the tubular member, and is typically mounted on the upper end of the tubular member to close the inlet of the tubular member at the upper end thereof.

Typically, the closure member can be locked in its open or in its closed configuration. Typically the locking is effected by a locking piston, typically located adjacent the closure device, typically at the upper end of the bore. Typically, the locking piston is in the form of a piston sleeve adapted to move relative to the tubular member, which typically constitutes the bore between an unlocked position and a locked position, in which the locking piston restricts the actuation of the closure device, typically by physically engaging it and preventing or restricting its movement to close or restrict the bore. Typically, the locking piston moves between the unlocked and locked positions as a result of fluid pressure acting on the locking piston to move it relative to the tubular.

Typically, the locking piston is biased by resilient device such as a spring into the unlocked configuration. Typically, the locking piston occludes the alternate pathway in its unlocked configuration.

Typically, the device has a balancing mechanism adapted to balance the volume of hydraulic fluid within the body of the device between the first and second positions of the counterweight devices. The balancing mechanism typically comprises a piston sealed within an annulus between the bore and the body in fluid communication with the radial chamber adjacent to the counterweight devices, whereby changes in the volume of the radial space adjacent to the counterweight devices as a result of the movement of the counterweight devices between the first and second positions can be accommodated by the balancing mechanism, optionally by sliding movement of the piston within the annulus. While an annular piston is a useful configuration for the balancing mechanism, a piston housed within a bore is suitable for certain examples of the invention. Typically the balancing piston is typically connected to the upper sleeve, and typically moves linearly with the upper sleeve.

Examples of the invention can optionally be utilised to activate other devices apart from valves, and to change the activation state of various devices, typically by physical connection between the counterweight devices, typically in the form of the control rods etc. and link arms, but in certain other examples, change of the activation status can be transmitted by non-physical mechanisms, for example electronic transmission without requiring a physical connection between the counterweight devices and the element being actuated. Typically the element being actuated can be a closure device, but could also be a signal device initiating a signal to a different part of the string or to another tool within the string in order to signal or power the transition of that tool from one configuration to another. In one aspect of the invention, the actuator changes its activation state by rotation of the string and as a result activates a different tool in the string, for example, a latching or hanger device, or a cutting tool such as a reamer etc. Typically the other tool activated by the actuator is below the actuator in the string, and the axial translation of the sleeve in the actuator pushes or pulls a component in the actuated device between different configurations corresponding to different states of activation of the actuated device. For example, the actuator can push or pull cutters on a reamer device below the actuator up and down ramps or around pivot points, in order to change their activation status.

The body has a fluid flowpath, and permits passage of fluid through the body in at least one of the configurations. Typically changes in activation status results in changes in fluid flow through the body, for example, re-routing of the fluid through the body from a first flowpath to a second flowpath. One typical example of this is diversion of the fluid through a port, typically in the side wall of the body, but other in aspects the activation status of the body changes without resulting in re-routing of fluids through the body. Optionally changes in activation status results in choking or reduction of fluid flow through the flowpath. Typically changes in the activation status are maintained by fluid pressure acting on the closure member.

The various aspects of the present invention can be practiced alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one aspect or example can typically be combined alone or together with other features in different aspects or examples of the invention.

Various examples will now be described in detail with reference to the accompanying figures.

Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes.

Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention.

In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting essentially of", "consisting", "selected from the group of consisting of", "including", or "is" preceding the recitation of the composition, element or group of elements and vice versa.

All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa. References to positional descriptions such as "upper" and "lower" and directions such as "up", "down" etc in relation to the well are to be interpreted by a skilled reader in the context of the examples described and are not to be interpreted as limiting the invention to the literal interpretation of the term, but instead should be as understood by the skilled addressee, particularly noting that "up" with reference to a well refers to a direction towards the surface, and "down" refers to a direction deeper into the well, and includes the typical situation where a rig is above a wellhead, and the well extends down from the wellhead into the formation, but also horizontal wells where the formation may not necessarily be below the wellhead.

Referring now to <FIG>, a downhole device is typically in the form of a circulation sub <NUM> incorporating a valve with a body <NUM> in the form of a tubular having a central axis and having an axial bore <NUM> and box and pin connections at either end of the bore enabling the body <NUM> to be incorporated within a string of tubulars for deployment in an oil or gas well as is known in the art. The bore <NUM> has a central portion <NUM>, a throat <NUM> located above the central portion <NUM>, and an expansion chamber <NUM> located within the central portion <NUM>.

The bore <NUM> typically houses a tubular member in the form of a tubular <NUM> extending co-axially with the bore <NUM>, and typically having a narrower diameter than the central portion <NUM> of the bore, and a flange 10f spacing the tubular <NUM> from the inner surface of the central portion of the bore <NUM>, thereby forming an annulus 8a between the inner surface of the central portion of the bore <NUM> and the outer surface of the tubular <NUM> and a similar annulus 9a between the tubular <NUM> and the expansion chamber <NUM>. The tubular <NUM> typically provides an inner bore 10b passing substantially from the throat <NUM> at the upper end to the lower end of the valve body <NUM>. The inner diameter of the bore 10b of the tubular <NUM> can be relatively wide, allowing a large bore conduit between the upper and lower ends of the valve <NUM>, and allowing high volumes of fluid to pass at high speed through the valve when the valve is open. The large diameter central bore 10b of the tubular <NUM> typically enables normal wireline and coil tubing operations through the centre of the circulation device, without occlusion of the bore 10b. Typically the flange 10f is secured to the inner surface of the bore <NUM> in the body <NUM>, restricting axial movement of the tubular <NUM> in the body <NUM>, typically by shear pins, or by a ledge, or by other securing mechanism. Typically the expansion chamber <NUM> can be sealed to prevent debris entering, and can therefore have a sealed volume of clean hydraulic fluid enabling reduced service requirements.

The upper end of the tubular <NUM> is provided with a closure device typically in the form of a flapper <NUM>, although other forms of closure device can be used with alternate examples of the invention. In this example, the flapper <NUM> is pivotally mounted to an upper edge of the side wall of the tubular <NUM>, and can pivotally move around the mounting from the open position shown in <FIG>, where the flapper <NUM> does not occlude the bore 10b of the tubular <NUM>, to the closed position shown in <FIG>, where the flapper <NUM> has pivoted into a closed position, in which it occludes the bore 10b of the tubular <NUM>.

Above the upper end of the tubular <NUM> the valve <NUM> is provided with a control piston <NUM> which is typically in the form of a sleeve that is sealed within the central portion of the bore <NUM> and is axially slidable therein, relative to the tubular <NUM>. The upper end of the control piston <NUM> has an inlet to admit fluid which is typically no smaller than the throat <NUM>, so that fluid can pass substantially unhindered from the throat <NUM> and through the control piston <NUM>. Adjacent to the opening of the upper end of the control piston <NUM>, the lower surface of the control piston typically has a recess <NUM> adapted to receive a portion of the flapper <NUM> in order to lock it in position. The control piston <NUM> is typically adapted to slide within the bore between the position in <FIG>, where the flapper <NUM> is clear of the recess <NUM> and is unobstructed by the piston <NUM>, to the position shown in <FIG>, where the piston <NUM> has moved axially down the central portion of the bore <NUM>, to engage the flapper <NUM> within the recess <NUM> and restrict its movement around its pivotal mounting, preventing it from closing the bore 10b of the tubular <NUM>.

The tubular <NUM> is typically centralised within the bore <NUM> of the body <NUM> by the flange 10f at the lower end and by a sliding spacer ring <NUM> at the upper end. Typically, the sliding spacer ring <NUM> is sealed against the outer surface of the tubular <NUM>, and is typically secured to the upper end of a balancing piston <NUM>, which is typically in the form of a sleeve sealed between the outer surface of the tubular <NUM> and the inner surface of the body <NUM>. The lower end of the balancing piston <NUM> has flange that is sealed within the central portion of the bore <NUM> across the annulus 8a. The upper end of the balancing piston <NUM> is typically secured, for example by screwing or fixing such as bolts, to the sliding spacer ring <NUM>, so that the sliding spacer ring <NUM> and balancing piston <NUM> move as a unitary component. The sliding spacer ring <NUM> and balancing piston <NUM> are subjected to a biasing force by a resilient device typically in the form of a control piston spring <NUM>, which is held in compression between the sliding spacer ring <NUM> and a fixed block <NUM> which is secured to the inner surface of the central portion of the bore <NUM>. The control piston spring <NUM> is typically held in compression, and urges the sliding spacer ring <NUM> and balancing piston <NUM> axially upwards, to push the control piston <NUM> up the bore <NUM> towards the throat <NUM> at the upper end of the body <NUM>.

The valve <NUM> has an actuator in the form of a counterweight assembly V to control the state of activation of the flapper <NUM>. The counterweight assembly V comprises first and second counterweight devices as will now be described.

In this example, the counterweight devices comprise four plates <NUM>, arranged in opposed pairs at equi-distant spacings around the circumference of the tubular <NUM>.

The plates <NUM> typically all have the same mass and dimensions, and their equi-distant spacing in relation to the axis of the valve and in relation to one another around the circumference of the valve body <NUM> enables a useful characteristic described below.

The plates <NUM> are connected to the valve by a linkage mechanism typically in the form of link arms <NUM>. The link arms <NUM> are typically provided at the upper and lower ends of each plate <NUM>, and are typically pivotally connected to the plate allowing pivotal movement between the link arms <NUM> and the plate <NUM>. Typically, each plate <NUM> has four link arms <NUM>, two connected at its lower end, and two connected at its upper end. Typically, one end of each link arm <NUM> is pivotally connected to the plate, and the other end of each link arm <NUM> is pivotally connected to either one of an upper and lower sleeve provided at opposite ends of the actuator V. Therefore, at the lower end of the plates <NUM>, each pair of link arms <NUM> pivotally connects to a fixed sleeve <NUM>. Typically, the fixed sleeve <NUM> is secured to the inner surface of the central portion of the bore <NUM>, optionally by bolts or pins or other fixings, so that it is axially fixed in position within the bore <NUM>.

At the upper end of each plate <NUM>, the plate <NUM> is typically connected by a respective pair of link arms <NUM> to a sliding sleeve <NUM> in the same way. The sliding sleeve <NUM> is free to move axially within the bore <NUM>. Typically, the pivotal connections between the plate <NUM> and the link arms <NUM> are axially spaced from the upper and lower ends of the plate <NUM>, as best shown in <FIG>. Typically the pivotal connections between the plate <NUM> and the link arms <NUM> are spaced circumferentially around the plate. Typically the link arms <NUM> connecting the plates <NUM> with the collars <NUM>, <NUM>, are adapted to resist rotation of the plates <NUM>. This can typically be achieved by providing at least two link arms <NUM> at each radially spaced location (respective upper and lower ends) of each plate, and connecting the link arms at circumferentially spaced pivot points between the plate <NUM> and the link arms <NUM>, thereby resisting rotation of the plate around the long axis, and maintaining stability of the plate <NUM> as the plate transitions between the first and second configurations.

Therefore, each plate <NUM> is connected by link arms <NUM> between a single lower fixed sleeve <NUM> and a single upper sliding sleeve <NUM>. The link arms <NUM> guide and restrict the movement of the plates <NUM> in a radial direction within the annulus 9a of the expansion chamber <NUM>. All plates <NUM> typically move simultaneously as a result of the link arms <NUM> and the sleeves <NUM>, <NUM>. Therefore, all four plates <NUM> are constrained to move radially outwardly from the radially retracted position shown in <FIG> to the radially extended position shown in <FIG> in concert with one another, so that, at any particular point, each plate <NUM> is the same radial distance away from the outer surface of the tubular <NUM>, and has the same orientation, i.e. parallel to the axis of the tubular <NUM>. Radially outward movement of the plates <NUM> in this manner therefore draws the sliding sleeve <NUM> towards the fixed sleeve <NUM>, which cannot move axially within the body <NUM>, so radial extension of the plates causes the sliding sleeve <NUM> to slide axially within the central section of the bore <NUM> down towards the fixed sleeve <NUM>. The force generated from the axial rotation can typically vary with the mass of the plates (which can be varied by adjusting their length, number and circumferential dimensions). In the typical example described with four plates the typical force generated is approximately <NUM> kgf (<NUM> lbft) at <NUM> rpm. Other examples can be devised having a larger number of plates <NUM>, with a reduced radial travel, and optionally a larger radial dimension of the initial radially retracted first position. Because of the increased centrifugal force resulting from a greater radius of the rotated mass, this enables an increase in the internal dimensions of the bore 10b in the tubular <NUM>, while maintaining a high force from the governor mechanism surrounding the tubular <NUM>, and represents a significant advantage to certain examples of the invention.

As best seen in <FIG>, a control rod <NUM> connects the sliding sleeve <NUM> with a pivot mechanism operatively connected to the flapper <NUM>. When the sliding sleeve <NUM> is in the uppermost position as best shown in <FIG>, with the plates <NUM> in their radially retracted position, the control rod <NUM> typically pushes the flapper up away from the inlet of the tubular <NUM>, to open the bore of the tubular <NUM>. This is the position adopted in <FIG>. When the sliding sleeve <NUM> moves axially downwards as a result of radial displacement of the plates <NUM>, as best shown in <FIG>, the control rod <NUM> causes the flapper <NUM> to move to the closed position where it occludes the opening of the upper end of the tubular <NUM>, preventing or at least reducing fluid flow through the tubular <NUM>. In the present example, the control rod <NUM> typically comprises a pair of rods or bars extending axially generally parallel to the axis of the tubular <NUM>, along its outer surface, but in other examples, the control rod or other actuator transmitting the motive force or signals from the actuator to the closure device can take other forms.

Typically the control rod <NUM> moves down to rotate the flapper down to a closed position around a pivot point between the flapper <NUM> and the upper end of the tubular <NUM>. However, in certain other examples, the flapper <NUM> and control rod <NUM> could move in opposite directions, or the flapper <NUM> could be closed by fluid pressure, and could optionally have a spring mechanism to open it against the force of the fluid pressure.

In use, the circulation sub <NUM> is run into the hole in the configuration shown in <FIG>, with the plates <NUM> in the radially retracted position, close to the axis of the tubular <NUM>. In this configuration, the sliding sleeve <NUM> is urged upwardly within the bore <NUM>, so the control rod <NUM> keeps the flapper <NUM> open as shown in <FIG> and <FIG>. The sliding sleeve <NUM> adopts an axial position close to the fixed block <NUM>, as best shown in <FIG> and <FIG>. The plates <NUM> are radially collapsed, close to the axis of the sub <NUM>.

The spring <NUM> is held in compression between the fixed block <NUM>, and the sliding spacer ring <NUM>, thereby pushing the control piston <NUM> towards the top of the bore <NUM>, adjacent to the throat <NUM>. In this position, the flapper <NUM> is urged upwards clear of the recess <NUM> and is held in the open position by the control rod <NUM>. Fluid can pass through the bore 10b in either direction allowing efficient running in. The circulation sub <NUM> can act as a fluid conduit for supplying drilling fluid or other wellbore fluids to tools situated lower down in the string, beneath the circulation sub <NUM>. Typically, the circulation sub <NUM> is set relatively high in the string, above the drill bit, and typically above scraping and other cleaning tools, which typically generate particulate debris and cuttings from their drilling, cleaning and scraping operations.

The fluid conduit position is shown in <FIG>. In the flowing position shown in <FIG>, the plates <NUM> are in the radially retracted position as shown in <FIG>, the flapper <NUM> remains open by virtue of the action of the control rod <NUM>. The only difference between <FIG> and <FIG> configurations is that the control piston <NUM> has slid axially down the bore, away from the throat, to butt against the sliding spacer ring <NUM>, and to compress the spring <NUM>. The control piston <NUM> slides as a result of the pressure differential across it within the bore <NUM>. Downward movement of the control piston <NUM> as shown in the transition from <FIG> moves the recess <NUM> over the upper edge of the flapper <NUM>, thereby preventing closure of the flapper <NUM> across the opening to the tubular <NUM>. The balancing piston <NUM> typically compensates for any volume changes as a result of the movement of the control piston <NUM>.

In this configuration shown in <FIG>, the circulation sub <NUM> behaves as a simple flow conduit allowing passage of fluid from above the circulation sub <NUM> through the bore <NUM>, in order to reach various tools located below the circulation sub <NUM> in the string. For example, in drilling operations, drilling fluid can be pumped at high volumes and high speeds through the circulation sub <NUM> while in the <FIG> locked configuration, without radial movement of the plates <NUM>, which remain radially collapsed, and without closure of the locked flapper <NUM>, allowing substantially full bore flow through the large bore tubular <NUM>. Activation of the flapper <NUM> to close the primary flow path through the bore 10b of the tubular <NUM> is not possible while the control piston <NUM> is in the <FIG> position, so the valve body <NUM> can be rotated at high speeds, for example when conducting rotary drilling operations, at the same time as pumping drilling fluids through the bore <NUM> at high pressures, volumes and flow rates, or separately, without activating the valve <NUM>. The control piston <NUM> is maintained in the locked position axially displaced downwards from the throat <NUM> as shown in <FIG> by the pressure differential applied across the piston <NUM>. While in the locked position, the linkage between the flapper <NUM> and the sliding sleeve <NUM> effected by the control rods <NUM>, typically pulls the sliding sleeve <NUM> upwards in the central portion of the bore <NUM>, thereby keeping the plates <NUM> in their radially retracted linear position shown in <FIG> and <FIG>, so even with high speed rotation of the drill string and the body <NUM>, the plates <NUM> remain radially close to the axis of the body <NUM>, and the tool remains in the <FIG> retracted configuration.

The downward sliding of the control piston <NUM> pushes the sliding spacer ring <NUM> downwards through the central portion <NUM> of the bore <NUM>, to compress the spring <NUM> against the fixed spacer <NUM>. This also pushes the optional balancing piston <NUM> down the bore, as it is secured to the sliding spacer ring <NUM>.

When the circulation sub <NUM> is to be activated, the pressure across the control piston <NUM> is reduced until the force of the spring <NUM> overcomes the force on the piston <NUM> exerted by the pressure differential, and the spring <NUM> then returns the piston <NUM> to the upper position shown in <FIG>, butted against the downwardly facing shoulder <NUM> of the central portion of the bore <NUM>, adjacent to the throat <NUM>. In this configuration, the flapper <NUM> is free from the recess <NUM> in the control piston <NUM>, as best shown in <FIG>, and is free to move. The fixed and sliding sleeves <NUM> and <NUM> are biased apart by a counterweight spring <NUM>, which is held in compression between the fixed and sliding sleeves <NUM>, <NUM>, and which maintains the counterweight assembly V in the linear retracted configuration shown in <FIG> in the absence of any other force. However, when the circulation sub <NUM> is to be activated in order to divert fluids passing through the bore <NUM> to tools situated below the circulation sub <NUM>, and instead pump that fluid out through the wall of the body <NUM> in order to maintain circulation of particulates within the annulus outside the body <NUM>, the body <NUM> is rotated from the surface, typically at normal drilling speeds of around <NUM>-<NUM> rpm, and the centrifugal force acting on the plates <NUM> as a result of the rotation causes them to move radially outwards into the annulus 9a of the expansion chamber <NUM>. Because the control piston <NUM> has moved up, and the flapper <NUM> is clear of the recess <NUM>, the plates <NUM> are free to move radially outwards within the annulus 9a, against the force of the spring <NUM>, which is compressed further between the fixed and sliding sleeves <NUM>, <NUM>, which move axially together as best shown in the transition between the <FIG> and <FIG>. The radial outward movement of the plates <NUM> effectively pulls the sliding sleeve <NUM> axially down the bore <NUM>, towards the fixed sleeve <NUM>, which is fixed immovably to the body <NUM>, as a result of the link arms <NUM>. As the sliding sleeve <NUM> is operatively linked to the flapper <NUM> by virtue of the control rod <NUM>, the radial outward movement of the plates <NUM> under the centrifugal force resulting from the rotation therefore pulls the control rod <NUM> axially down the bore <NUM> in order to close the flapper <NUM> over the inlet at the upper end of the tubular <NUM>, thereby closing the bore <NUM> through the body <NUM> as best shown in <FIG>. The flapper <NUM> is thereby locked in the closed position by the sleeve above it. The closed flapper position also helps to maintain the radially outward configuration of the plates <NUM>. The inner counterweight assembly V inside the body <NUM> is then in the configuration shown in <FIG>.

With the circulation sub <NUM> still rotating, the fluid pressure above the closed flapper <NUM> then increases, causing the control piston <NUM> to move down the central portion of the bore <NUM> from the position shown in <FIG> to the position shown in <FIG>. Typically the control piston <NUM> has seals above and below circulation ports 5p in the body <NUM>, so that in the running in configuration shown in <FIG>, the circulation ports 5p are sealed off (typically by double seals) from the bore <NUM> of the circulation sub <NUM>. The downward movement of the piston <NUM> exposes circulation ports 5p passing through the wall of the body <NUM> and connecting the bore <NUM> with the annulus outside the body <NUM>, and allowing the high pressure fluid to be jetted radially out through the ports 5p when the counterweight assembly V is in the configuration shown in <FIG>. In that configuration, the shoulder <NUM> on the downward facing surface of the control piston <NUM> presses downwards on the top of the flapper <NUM>, keeping it sealed over the inlet to the bore 10b of the tubular <NUM>, and thereby preventing fluid flow through the bore 10b of the tubular <NUM>, so that substantially all of the fluid passing through the throat <NUM> is diverted through the circulation ports 5p, and is available to jet radially outwards into the annulus, and wash particulates and other debris in the annulus towards the surface. Keeping the flapper <NUM> pressed down against the inlet at the upper end of the tubular <NUM> also keeps the sliding sleeve <NUM> urged axially downwards towards the fixed sleeve <NUM>, thereby keeping the plates <NUM> in their radially expanded configuration shown in <FIG>, even in the absence of sufficient rotation to generate the central centrifugal force to overcome the force of the spring <NUM>. Typically the flapper <NUM> has a bypass port (not shown) to allow partial flow through the bore <NUM> in order to provide some reduced flow to tools below the circulation sub if required. This is an optional feature and is not required in all examples. The balance piston <NUM> typically compensates for the volume changes in the system arising from the movement of the components in this phase.

Once the flapper <NUM> is closed and the plates <NUM> have swung out to the radially extended position within the chamber <NUM>, the fluid pressure acting on the piston <NUM> is generally sufficient to keep the control piston <NUM> pressed down against the top of the flapper <NUM>, keeping the flapper <NUM> closed and retaining the seal on the tubular <NUM>, and maintaining the circulating position, even in the absence of rotation. Therefore, when circulating with the control piston <NUM> in its axially downward position exposing the circulation ports, rotation is not necessary, but can be conducted without affecting the circulation operations.

When the circulation operation is completed, and the circulation ports 5p are to be closed, the pressure on the piston <NUM> (typically from surface pumps) is reduced until the force of the spring <NUM> returns the sliding spacer ring <NUM> and piston <NUM> to the <FIG> position. In this configuration, the flapper <NUM> can still remain closed, with the plates <NUM> and the radially extended configuration shown in <FIG> if the body <NUM> is still subject to sufficient rotation to generate the required centrifugal force to maintain the plates <NUM> in their radially extended configuration. Therefore, operation of the flapper <NUM> can optionally be independent of the movement of the control piston <NUM>. However, in most situations, the rotation of the body <NUM> at this point will be reduced to reduce the centrifugal force acting on the plates <NUM>, and allow the spring <NUM> to urge the sliding sleeve <NUM> axially back up the central portion of the bore <NUM>, and open the flapper <NUM>, so that the configuration of the circulation sub returns to the <FIG> and <FIG> positions, again allowing fluid flow at high velocity and high pressure through the bore <NUM> across substantially the full bore of the tubular <NUM>.

In certain examples, one optional feature relates to the balancing piston <NUM>. Examples can be constructed without this component, but in the current example it performs a useful optional function, in that it permits equalisation of the volume of the expansion chamber <NUM> in the different modes of operation of the device. The balancing piston <NUM> is sealed within the annulus 8a at the lower end of the central portion of the bore <NUM>. Typically the chamber <NUM> is filled with hydraulic fluid, and is typically sealed. The radially outwards movement of the plates <NUM> and the downward sliding movement of the sliding sleeve <NUM> when the circulating sub transitions between the <FIG> and <FIG> positions can typically cause small volume changes in the chamber <NUM>. These can sometimes result in changes in hydraulic pressure of the fluid within the sealed chamber <NUM>, leading to hydraulic lock. These volume changes can optionally be accommodated by sliding of the balancing piston <NUM> in order to maintain the volume (and therefore the pressure) of the fluid within the chamber <NUM> within relatively constant ranges. The balancing piston <NUM> is connected at its upper end to the sliding spacer ring <NUM>, and is generally biased upwardly within the annulus <NUM> by the spring <NUM> acting in compression between the fixed spacer <NUM> and the sliding spacer ring <NUM>. Volumetric changes in the chamber <NUM> caused by transition of the plates <NUM> and downward sliding of the sliding sleeve <NUM> typically cause pressure changes within the hydraulic fluid in the chamber <NUM> which act on the sealed piston area of the balancing piston <NUM>. Typically the force of the spring <NUM> is such that the balancing piston <NUM> can typically cause it to compress slightly to pull the sliding spacer ring <NUM> axially down the body <NUM> in order to accommodate the slightly larger volume and increased pressure and balance out any hydraulic locks. The balancing piston <NUM> therefore accommodates changes in volume and pressure of the hydraulic fluid within the chamber <NUM>, and combats the sticking of the sliding sleeve <NUM> as a result of hydraulic lock. The details of the seals of the balancing piston <NUM> are best shown in <FIG>.

Optionally, the balancing piston <NUM> has a balance rod mechanism comprising a balance rod extending axially on one side of the bore, and terminating in a piston head 26p which is sealed within the enlarged lower flange of the balance piston <NUM> (the details of which are best shown in <FIG>). The upper end of the balance rod <NUM> is connected to the sliding sleeve <NUM>, so that downward movement of the sliding sleeve <NUM> in response to outward movement of the plates <NUM> in the chamber <NUM> causes concurrent downward movement of the piston head 26p sealed within the flange of the balance piston <NUM>. The linear movement of the balance rod <NUM> with the upper sliding sleeve <NUM> compensates for differences in volume as the sleeve moves and resists hydraulic locking.

A further optional feature that is useful in certain examples of the invention but is not required in others is an orientation compensating mechanism, shown in <FIG>, <FIG>.

Optionally, the compensating mechanism typically comprises a floating sleeve <NUM> freely movable around the outer surface of the spring <NUM>. The sleeve <NUM> is typically supported from beneath by cam devices <NUM> spaced equidistantly around the circumference of the sleeve, which are supported in pivot mountings on the upper surface of the fixed sleeve <NUM>, so that one inner end of the cam device <NUM> supports the lower surface of the sleeve <NUM>. An outer end of the cam device <NUM> typically supports a push rod <NUM> which extends between the cam device <NUM> and the opposing lower surface of the sliding sleeve <NUM>. When the body <NUM> is in a vertical orientation, as shown schematically in <FIG>, the sleeve <NUM> slides down under gravity to bear on the upper surface of the inner part of the cam device <NUM>, so that the weight of the sleeve <NUM> is borne by the cam devices <NUM>, which rotate about their pivot mountings in the fixed sleeve <NUM>, and push the outer ends of the cam devices <NUM> upwards, thereby urging the push rods <NUM> axially upwards, to push the sliding sleeve <NUM> axially away from the fixed sleeve <NUM>. This balancing action only takes effect when the body <NUM> is in the vertical position as shown in <FIG>, and the sleeve <NUM> is pulled under gravity to rest on the cam member <NUM>, and when the body <NUM> is in the horizontal position, the sleeve <NUM> is free to slide axially between the fixed and sliding sleeves <NUM>, <NUM>, and does not apply the same force to the cam devices <NUM>, which in turn, do not exert the same axial force on the push rods <NUM>. Therefore, the balancing mechanism shown in <FIG> typically provides additional axial force acting to spread the sleeves <NUM>, <NUM> apart from one another when the body <NUM> is in the vertical orientation. This is a useful feature which compensates for the weight of the plates <NUM>, which tend, in the vertical position, to fall radially outwards due to gravitational force. The plates <NUM> are maintained in their axially retracted position shown in <FIG> by the spring <NUM>, but the balancing action of the compensation mechanism shown in <FIG> means that when the body <NUM> is in the vertical orientation as shown in <FIG>, the weight of the sleeve <NUM> counteracts the tendency of the plates <NUM> to fall outwards, and the force applied by the spring <NUM> can therefore be reduced. Since the compensating mechanism shown in <FIG> only applies any force to the governor mechanism when the body <NUM> is in the vertical position, it selectively compensates the activation force between the horizontal and the vertical positions, leading to a more consistent operation of examples of the invention that utilise this feature.

Examples can, of course, be constructed without necessarily requiring the compensation mechanism shown in <FIG>, but it has the advantage that the spring <NUM> can be reduced in strength, and the tool can be operated in a wider variety of operational situations.

Examples provide advantages over earlier systems, in that as the arrangement of counterweight devices is typically balanced around the axis of the body, rotation of the counterweight devices to move them between the first and second configurations is substantially unaffected by the orientation of the axis within the bore hole, enabling the actuator to be used in deviated wells with greater consistency of operation. Examples of the invention therefore facilitate operations at various different angles of deviated well in a consistent manner.

Examples typically permit easier activation at normal drill string speeds, for example actuation of the circulation sub described in the examples herein can be achieved at drill string rotation speeds of around <NUM> to <NUM> rpm, and in certain examples, the actuator can be maintained in the circulating position by continued flow, with or without continued rotation at the transition speed. The transition speed can typically be adjusted by adjusting the spring strengths and the weights of the plates to suit particular wellbore conditions and different string diameters. Certain examples can easily be reset to the original configuration by stopping flow through the valve with no rotation, or with rotation at speeds below the transition level. Again, this can be adjusted independently by selecting different spring tensions allowing additional adaptability of the device.

The circulation sub <NUM> can typically be locked in normal and circulating positions and reset any number of times to original configurations without reliance on dropped balls or other actuation mechanisms requiring reset or recovery of the string.

In certain examples of the invention, the plates <NUM> do not require symmetrical movement, and in one simplified example of the invention, the plates are directly linked at pivot points to the fixed collar <NUM>, and are linked by link arms <NUM> to the sliding collar <NUM>, so that only one end of the plates <NUM> (e.g. the upper end) moves radially outwards into the expansion chamber. However, the example shown in the figures with link arms at each end of the plates is advantageous, as it allows a longer travel of the sliding collar <NUM>.

Typically the tubular <NUM> is fixed within the bore <NUM>. Optionally, the tubular <NUM> can have a ball seat (not shown) for emergency operation in the event that the flapper <NUM> becomes stuck, allowing a ball to be dropped into the ball seat (not shown) to close the bore 10b of the tubular <NUM>, allowing pressure to build up above the tool to move the control piston <NUM> down and expose the circulation ports 5p as described above.

Examples permit increased bore diameter in circulating subs allowing operation of conventional tools through the bore, while at the same time permitting a decreased outer diameter and typically decreased total length. An increased centrifugal force is permitted at lower rotational speeds, and the balanced governor mechanism increases the stability of the tool and allows simplification of the design.

Claim 1:
A downhole device (<NUM>) having a body (<NUM>) with an axis, a bore with a fluid flowpath for permitting passage of fluid through the body (<NUM>), a closure device (<NUM>) for restricting passage of fluid through the fluid flowpath of the bore, and an actuator (V) for actuating the closure device; the actuator (V) comprising first and second counterweight devices (<NUM>) moveably mounted at different circumferential positions around the axis of the downhole device, wherein the counterweight devices (<NUM>) are radially movable relative to the body between first and second positions, wherein movement of the counterweight devices (<NUM>) between the first and second positions actuates the closure device (<NUM>) between different activation states, wherein each counterweight device (<NUM>) is supported by a number of link arms (<NUM>) adapted to guide the radial movement of each counterweight device (<NUM>) between the first and second positions, wherein the counterweight devices (<NUM>) are pivotally connected at axially spaced apart locations to upper and lower sleeves (<NUM>, <NUM>) by pivot links connected between the upper and lower sleeves (<NUM>, <NUM>) and the link arms (<NUM>), wherein the link arms (<NUM>) are adapted to transmit axial forces between the upper and lower sleeves (<NUM>, <NUM>), and are adapted to urge relative axial movement between the upper and lower sleeves (<NUM>, <NUM>) when the counterweight devices (<NUM>) move radially, wherein the counterweight devices (<NUM>) are movable from a first radially retracted position in which the counterweight devices (<NUM>) are retracted close to an axis of rotation of the body (<NUM>) to a second radially extended position in which the counterweight devices (<NUM>) have moved radially outwards away from the axis of rotation of the body (<NUM>), and characterised in that movement of the counterweight devices (<NUM>) from the first radially retracted position to the second radially extended position actuates the closure device (<NUM>) to restrict the fluid flowpath of the bore.