WO2016145540A1

WO2016145540A1 - Sliding sleeve sub and method and apparatus for wellbore fluid treatment

Info

Publication number: WO2016145540A1
Application number: PCT/CA2016/050316
Authority: WO
Inventors: Ronald Van Petegem; Kevin O. Trahan; Fernando Olguin; Gustavo MENDOZA; John Lee Emerson; Ryan Michael ASHMORE; Mitchell MUELLER; Craig Willis Clark
Original assignee: Packers Plus Energy Services Inc.
Priority date: 2015-03-19
Filing date: 2016-03-18
Publication date: 2016-09-22

Abstract

A sliding sleeve sub including: a flexible ball seat configured to respond to a parameter of an actuating device moving through the ball seat to either (a) maintain the seat as flexible to allow the actuating device to be pushed through the ball seat without actuating the tool or (b) to reconfigure the seat to an inflexible condition to stop the actuating device from passing through the ball seat, to thereby allow actuation of the sliding sleeve sub.

Description

Sliding Sleeve Sub and Method and Apparatus for Wellbore Fluid Treatment

Field of the Invention

The invention relates to a method and apparatus for wellbore fluid treatment and, in particular, to a method and apparatus for selective communication to a wellbore for fluid treatment.

Background of the Invention

US Patents 6,907,936 and 7,108,067 to Packers Plus Energy Services Inc. (the assignee of the present application) describe wellbore treatment apparatus including a treatment string for staged well treatment, The wellbore treatment string is useful to create a plurality of isolated zones within a well and includes an openable port system that allows selected access to each such isolated zone. The treatment string includes a tubular string carrying a plurality of packers that can be set in the hole to create isolated zones therebetween about the annulus of the tubing string. Openable ports through the tubing string are positioned between at least some packers. The ports are selectively openable and include a sleeve thereover with a sealable seat formed in the inner diameter of the sleeve. By launching a ball, the ball can seal against the seat and pressure can be increased behind the ball to drive the sleeve through the tubing string, such driving acting to open the port in one zone. The seat in each sleeve can be formed to accept a ball of a selected diameter but to allow balls of lower diameters to pass.

Sometimes there are limitations with respect to the inner diameter of wellbore tubulars, for example due to the inner diameter of the well itself, such that a wellbore treatment system with graduated seat sizing may tend to be limited in the number of zones that may be accessed. For example, if the well diameter dictates that the largest sleeve in a well can at most accept a 3¾" ball, then the well treatment string will generally be limited to approximately 1 1 sleeves with different sized seats.

Summary of the Invention

In accordance with an aspect of the present invention, there is provided a sliding sleeve sub comprising: a housing; a sleeve valve axially slidable along the housing; and a ball seat on the sleeve valve, the ball seat being flexible and configured to respond to a length of time an actuating device resides in the ball seat to either (a) maintain the seat as flexible to allow the actuating device to be pushed through the ball seat without actuating the tool or (b) to reconfigure the seat to an inflexible condition to stop the actuating device from passing through the ball seat, to thereby allow actuation of the sliding sleeve sub by the actuating device..

In accordance with another aspect of the invention, there is provided a method for actuating a downhole tool, the method comprising: modifying a pumping condition driving the actuating device against the tool such that a tool component is signaled that the actuating device is to be retained by the tool, thereby actuating the downhole tool.

In one embodiment, there is provided a wellbore tubular string comprising: a first sliding sleeve sub including: a tubular housing including an inner bore defined by an inner wall; a sleeve installed in the inner bore and axially slidable therein at least from a first position to a final position, the sleeve including an inner diameter, an outer diameter facing the tubular inner wall, a ball seat installed on the sleeve in the inner diameter, the ball seat normally having a flexible condition wherein the ball seat is flexible to allow passage of an actuating device axially through the ball seat in a normal period of time and the ball seat being reconfigurable into an inflexible condition configured to stop the actuating device and to transfer an actuating force to the sleeve to move it to the final position; and a regulator to resist reconfiguration of the ball seat to the inflexible condition until the actuating device is retained in the ball seat for a selected minimum period of time greater than the normal period of time; and a second sliding sleeve sub axially spaced from the first sliding sleeve sub, the second sliding sleeve sub including: a normally flexible ball seat also being reconfigurable to an inflexible conditioned by a second actuating device of substantially the same size as the actuating device and being reconfigurable based on the residence time of the second actuating device in the normally flexible ball seat.

It is to be understood that other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein various embodiments of the invention are shown and described by way of illustration. As will be realized, the invention is capable for other and different embodiments and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present invention. Accordingly the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.

Brief Description of the Drawings

A further, detailed, description of the invention, briefly described above, will follow by reference to the following drawings of specific embodiments of the invention, These drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. In the drawings:

Figures 1 A to ID are sequential sectional views through a wellbore having positioned therein a wellbore tubing string; and

Figures 2A to 2C are sequential sectional views through a sleeve valve sub. Detailed Description of Various Embodiments

The description that follows and the embodiments described therein, are provided by way of illustration of an example, or examples, of particular embodiments of the principles of various aspects of the present invention. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the invention in its various aspects. In the description, similar parts are marked throughout the specification and the drawings with the same respective reference numerals. The drawings are not necessarily to scale and in some instances proportions may have been exaggerated in order more clearly to depict certain features.

A downhole tool is provided for the purpose of formation fluid treatment such as stimulation by fracturing (also known as fracing or fracking), acidizing, etc. The tool is actuated by an actuating device, such as an actuating ball or dart, such as one that is untethered and moved by fluid pressure. The tool may, for example, be a sliding sleeve sub that includes a sleeve valve that is axially moveable to open a port over which it is positioned. The sleeve valve may include a seat for stopping an actuating device, such as an actuating ball or dart, such that a force can be generated by the actuating device sealing against the seat, to generate a pressure differential across the actuating device/seat to move the sleeve valve to the lower pressure side and open the port to access the formation.

The sliding sleeve sub employs a ball seat that is flexible, but is configured to be made inflexible. It is noted that a flexible seat is sometimes referred to as an expandable, collapsible or passable seat. When the ball seat is flexible the actuating device can pass through, for example be pushed by fluid pressure through, the ball seat. When the ball seat is configured to an inflexible condition, the actuating device cannot pass through the ball seat.

When the ball seat is inflexible, a force can be applied through the ball seat to actuate a component of the downhole tool. The actuation of the downhole tool can be by hydraulic pressure force and/or mechanical force. Generally, such actuation results in the opening of ports in the tool, to generate a flow path from the inner bore of the tool to an outer surface of the tool, which is to the formation.

The sliding sleeve sub is configured to respond to the conditions of how the actuating device moves through the ball seat to either (a) maintain the seat as flexible to allow the actuating device to be pushed (for example, by pumping) through the ball seat without actuating the tool or (b) to reconfigure the seat to an inflexible condition to stop the actuating device from passing through, such that the actuating device thereby actuates the tool. The conditions of how the actuating device moves through the ball seat may include (i) a sufficient force, (ii) a force applied over a sufficient time, etc. These conditions may be controlled by pump control of the fluids in the tubing string surrounding the actuating device and, therefore, applying pressure against and moving the actuating device. In one embodiment, the conditions are controlled to force the actuating device against the ball seat with a pressure less than a pass through pressure for the ball seat and to maintain the force against the ball seat for a time longer than the set time.

A component of the sliding sleeve sub tool may be responsive to pump control effects on the actuating device such as the rate or the force at which the actuating device is moved against the seat.

A method of actuating the tool may include modifying the pumping conditions driving the actuating device against a ball seat of the tool such that a tool component is signaled that the actuating device is to be retained by the tool for actuation thereof.

In one embodiment, the sliding sleeve sub employs a flexible ball seat and the sliding sleeve sub is configured to respond to the length of time the actuating device resides in the ball seat to either (a) maintain the seat as flexible to allow the actuating device to be pushed through the ball seat without actuating the tool to, for example, open the sleeve valve or (b) to reconfigure the seat to an inflexible condition to stop the actuating device from passing through, to thereby permit a force to be applied through the seated actuating device against the seat, to thereby apply a force to the sliding sleeve to actuate the tool. The size of the actuating device does not determine which of the two operations, (a) or (b), result, but instead one operation or the other is selected based on the time that the actuating device remains in the seat. For example, a first actuating device can be landed on the ball seat and can be allowed to pass through without actuating the sliding sleeve of the sub by limiting the amount of time that the ball remains on the ball seat before moving through and, thereafter, a second actuating device of the same diameter as the first actuating device, can be landed on the ball seat and retained to actuate the sliding sleeve sub, for example, to move the sliding sleeve valve of the sub to the port open position, simply retaining the actuating device in the ball seat for an amount of time sufficient to permit reconfiguration of the ball seat to its inflexible condition. The amount of time that the actuating device resides in the ball seat may be determined by controlling the pressure at which the actuating device is pumped against the ball seat.

In one embodiment, the sliding sleeve sub is configured with a ball seat that is flexible and reconfigurable to an inflexible condition and the ball seat has a pass through pressure rating, which is the pressure differential at which the flexible ball seat is expanded to allow an actuating device to push through. At pressures below the pass through pressure, an actuating device landed against the seat remains in the seat and cannot pass through. The sliding sleeve sub is further configured with a time delay mechanism such that only if the actuating device remains in the ball seat longer than a set time will the ball seat reconfigure to an inflexible state and thereby permit opening of the ports. If the actuating device pushes through before the set time lapses, the ball seat remains in the inflexible state and the ports remain closed.

The sliding sleeve sub may be configured to sense when an actuating device lands against the ball seat and any fluid pressure in excess of 0 psi is applied against the actuating device. In one embodiment, the sliding sleeve valve of the sliding sleeve sub is configured to move axially when an actuating device is landed against the ball seat.

Sensing may include the sleeve beginning to move axially. The sleeve may have a stroke length through which it maintains the seat as flexible. If the actuating device passes through the seat before the end of the stroke length is reached, the ball seat remains flexible. If, on the other hand, the actuating device remains in the ball seat without being pushed through when the sleeve reaches the end of its stroke length, the ball seat is reconfigured to its inflexible state and the actuating device cannot pass through. As such, keeping the actuating device in the ball seat a time long enough to allow the sleeve valve to moves along its entire stroke length, the ball seat reconfigure to the inflexible state to permit opening of the ports. The actuating device may be retained in a ball seat without passing through by ensuring that the fluid pressure applied against the ball does not exceed the ball seat's pass through pressure, because when an actuating device is landed against the ball seat in its flexible condition, substantially as soon as the fluid pressure applied against the actuating device exceeds the ball seat's pass through pressure, the actuating device will pass through and the force applied by the actuating device against the ball seat will be removed so that the sleeve valve stops stroking.

A plurality of the tools may be employed in a well to permit selected fluid treatment such as staged fluid treatment in the well. For example, a wellbore treatment tubing string 8, as shown in Figures 1 A to ID, may include a plurality of downhole tools 10a, 10b, 10c each with a ball seat 12a, 12b, 12c. The ball seats may all be similar, or even identical, with each having a similar inner diameter across the seat, each having an initial resiliently flexible configuration, each being capable of activation to an inflexible condition and each when inflexible being capable of generating a force to actuate another component, such as a sliding sleeve valve 14a, 14b, 14c, of the downhole tool. The seats are resiliently flexible and each seat has a neutral inner diameter D, each has the capability of responding to a force applied to expand from its neutral condition to an expanded condition with a seat inner diameter greater than diameter D, and each is resilient such that once the force is removed, the seat reforms to have a neutral inner diameter of D. Also, when the seats are flexible and when they are inflexible, they have the same seat diameter D. The force that is needed to be applied to expand a ball seat from its neutral condition to an expanded condition is called the pass through pressure. Each ball seat 12a, 12b, 12c is configured to only expand when an actuating device has landed against it and a pressure is applied against the ball seat that is greater than the seat's pass through pressure. The pass through pressure for the seats may each be substantially similar or may vary, as will be described below. The pass through pressure may be determined by material resiliency properties, seat geometry, a frictional device, interference angles, springs, etc.

The ball seat is reconfigurable from the flexible condition to the inflexible condition if the residence time of an actuating device 18, such as a ball (as shown) or dart, in the ball seat is greater than a specified time. A regulator 16a, 16b, 16c may assist with the reconfiguration, by ensuring that the ball seat is reconfigured from the flexible condition to the inflexible condition only after a specified period of time.

Because all tools in this portion of string 8 have a similar inner diameter across their seats 12a, 12b, 12c, they are all actuated by the same size actuating device 18. One actuating device 18 could be used to actuate any one of the tools 10a- 10b. Device 18 can be passed through all or some of the plurality of tools and, if desired, that one actuating device 18 can also be used to land on a ball seat of any one of the tools and actuate that one tool.

For example, in this illustrated string, there is a sliding sleeve valve 20, here illustrated with a fixed seat 22, which is positioned downhole of the tools 10a - 10c. Valve 20 requires a ball to be landed its seat 22 for actuation of the valve, for example, to open ports 24. Thus, a device such as device 18 can be pumped, arrows P (Figure 1A), through all of tools 10a - 10c without actuation thereof to reach seat 22 to open ports 24 (Figure IB). While seats 12a- 12c of the tools each has an inner diameter to stop device 18, the seats each are flexible and if operator suitably controls the operation, the seats each remain flexible and allow device 18 to be pumped through without actuation of the tools 10a - 10c. When seat 22 is reached, the device 18 will be stopped, pressure can be increased uphole of the device and of seat 22 to shear the sleeve 20 and move it axially to open ports 24 (Figure IB). Seats 12a- 12c are resiliency flexible, such that once they are flexed to allow passage of device 18, they regain their form and their neutral inner diameter D and can be acted upon again by an actuating device similar in size to device 18, which just passed. The seats each, however, have a mechanism through which they can be reconfigured from the resiliently flexible to an inflexible condition, also with inner diameter D,

Thereafter (Figure 1C), a further actuating device 26 of the same size as device 18 may be pumped through the string. If the operator wants to actuate one of the tools 10a - 10c, the process is controlled to ensure the device remains long enough in the seat of the target tool, such as seat 12c in tool 10c, to reconfigure the seat of the target tool to an inflexible condition such that device 26 cannot pass the seat and instead actuates the tool 10c (Figure ID).

Whether actuating device 26 (or 18) remains in a ball seat long enough to reconfigure the ball seat to an inflexible condition generally depends on the whether or not the actuating device is driven against the seat at a pressure greater than the pass through pressure.

Regulators 16a, 16b, 16c are provided for each seat and are employed to regulate the set time after which the seat is capable of reconfiguring to the inflexible condition.

Regulators 16a, 16b, 16c determine the residence time that the actuating device must remain in the ball seat before the seat reconfigures from flexible to inflexible. The regulator may take many forms such as including one more of: a timer, a stroke length mechanism, a flow restrictor metering device, a biasing mechanism, a mechanical spacing, etc. In one embodiment, for example, the regulator includes a timer. When the actuating device lands on the ball seat, the timer is commenced and provided the pressure pushing the actuating device against the ball seat never exceeds the pass through pressure, the ball seat reconfigures to an inflexible condition once the set time of the timer lapses. In another embodiment, for example, the regulator operates based on a stroke length of sliding sleeve valve 14a, 14b, 14c. In such a configuration, the sliding sleeve valve is configured to begin sliding axially as soon as an actuating device lands with some pressure against the ball seat. Provided the pressure pushing the actuating device against the ball seat never exceeds the pass through pressure, the ball seat reconfigures to an inflexible condition if the actuating device 26 is retained in the seat for at least the amount of time sufficient to move the sleeve to the end of its stroke length. In another embodiment, for example, the regulator is a flow restricting metering device that only permits a ball seat to reconfigure to an inflexible condition if the actuating device 26 is retained in the seat for at least a set amount of time sufficient to permit the flow restricting metering device to complete its metering operation.

In some embodiments, the ball seat and the regulator for each tool 10a to 10c may be similar or the same, but it is the rate and force, for example as determined by fluid pressure, at which an actuating device moves against the seat that determines whether the actuating device 26 is retained in the seat for the selected amount of time. For example, the regulator may delay, by resistance or by spacing, the reconfiguration of the seat to dictate whether or not the force applied by the ball against the seat is sustained for a long enough time to reconfigure the seat to the inflexible state.

If it is desired to reconfigure the seat in one of the tools, for example 10c, to an inflexible condition, the pumping characteristics for the ball can be controlled to ensure that the suitable force is applied against the correct, targeted tool, such as tool 10c to retain the actuating device in the ball seat for long enough that the set time lapses. For example, if it is desired to reconfigure the seat of tool 10c, to an inflexible condition, so that the inflexible seat can be employed to open the tools ports and fracture the formation through the ports, the pumping characteristics moving the actuating device 26 can be controlled to ensure that the actuating device applies a force against the seat but that the pressure is maintained less than the pass through pressure to thereby retain the actuating device in the ball seat for long enough that the set time lapses and the ball seat reconfigures into the inflexible condition.

Because the pump pressure is adjusted to control actuation of a tool, the location of the actuating device is monitored. The passage of the actuation device through a string, including through a plurality of downhole tools with ball seats, can be monitored such as by surface indication such as by one or more of acoustic, digital, analog or hydraulic indications (for example by any of fluid pressure, sound monitoring, release of tracers, etc.) In one embodiment, some tools have output different signals so that the progress for example, depth, of the actuating device may be followed. By surface monitoring, therefore, the location of the actuating device 26 can be determined and pump conditions can be adjusted when it is determined that the actuating device is approaching the tool of interest, such as tool 10c.

Pump conditions P' (Figure 1 C) can be controlled such that when device 26 lands on seat 12c of the tool, a suitable force is applied by ball as determined by fluid pressure P', as sensed by the ball seat and controlled by regulator 16c to allow the seat to be

reconfigured to an inflexible condition 12c'. In this inflexible condition, actuating device 26 cannot pass seat 12c' and therefore applies a force against the seat that is transferred into sleeve 14c. This force causes sleeve 14c to move axially to expose ports 28 to inner bore such that fluid may be communicated through ports 28 into contact with the formation at wellbore wall W. Device 26 remains in seat 12c' to divert fluid through ports 28.

Thereafter, if desired, another device, not shown, may be launched, pumped through seat 12a, as may be confirmed by surface indications, and landed at seat 12b. The pump pressure may be controlled to ensure that a suitable pressure is applied to be sensed by regulator 16b to reconfigure seat 12b to an inflexible condition, so that the actuator device is retained and force is applied to sleeve 14b to move it to open the ports in that tool 10b.

Thereafter, if desired, another actuating device may be launched and pumped to land in seat 12a. The pump pressure may be controlled to ensure that seat 12a is reconfigured to an inflexible condition to cause the sleeve 14a to open.

If a sleeve fails to open due to the actuating device pushing through a seat before the seat can reconfigure into an inflexible condition, another similarly sized actuating device may be launched, movement monitored, fluid pressure controlled to again attempt to retain the actuating device in the ball seat long enough to reconfigure the seat and open the sleeve.

The string 8 can include any number of tools similar to tools 10a - 10c. In particular, while three tools are shown in Figure 1 A, there may be fewer or more such tools installed in the string. Since all the tools are similar, the string does not require a lot of pre- engineering as may be required with sleeves of graduating sized seats or indexing mechanisms.

If desired, however, some tools with larger diameter seats, but similarly regulated configurable seats may be installed between the upper end of the string and tool 10a or some tools with smaller diameter, but similarly regulated configurable, seats may be installed between tool 10a and the distal end of the string.

There may be one or more packers 30 installed along string 8 to isolate the annulus communicated through ports 28 from the annular area communicated through other ports, such as ports 24, so that a staged treatment may be effected. Alternately, clusters of tools may be provided in an annular zone.

Due to the physical properties of the seat material or a seat collapse mechanism, an actuating device, such as a ball, applied with a suitable pressure, is able to resiliently deform the ball seat allowing the actuating device to be pushed, as by pumping, through. Neither the ball seat nor the tool in which it is installed needs indexing mechanism and may be formed without slots, segments, etc. such that debris contamination, as by rust, proppant, scale, sand, etc. is avoided. The ball seat allows the ball to be pumped through within a pre-set time and above a pressure/force limit. However, by use of a regulator, times/pressures less than the pre-set limits cause the ball seat to reconfigure to an inflexible condition, where it cannot expand to permit the ball to be pushed through. As such, in a string with a plurality of similar ball seats, spaced apart, the ball can be pumped through the ball seats, by ensuring that the pump through process is maintained at particular time or pressure limits. However, when the ball reaches a target seat, where it is desired that the ball stay on the seat and actuate the tool, the pressure moving the ball may be changed and maintained at a value that is lower than the value required to pump/push the ball through the flexible seat and for such a time that the ball seat can be reconfigured, as by movement of the seat or other components, to a condition that prevents the ball seat from flexing such that the ball cannot be pumped through. When the seat reconfigures to an inflexible condition, a force can be generated at the seat to operate other components, such as to axially slide, and/or to apply a greater force to, a sleeve on which the seat is installed. This movement of sleeve may expose ports so that a flow path may be opened between the tubing string bore and the formation, which contains a zone to be fluid treated such as for stimulation, fracturing, matrix treatment, sand control, etc. or a combination.

The location of the ball, as it moves through the string and approaches the target seat, may be determined by indications sensed at surface. For example, the ball's location may be indicated by one or more of acoustic, digital, analog or hydraulic indications. In one embodiment for example, pressure and/or acoustic spikes may be sensed when a ball is landed on a seat and pushed through the seat, when in the flexible condition. Since the seats can be used in a large numbers in a single string, it may be useful to employ a system where certain subs at regular intervals, such as every fifth sub, provide a different indication than a few others at least upstream of it when a ball passes. For example, in one embodiment, the tools can be installed in a string and the tools can be configured such that known tools in the string, such as every fifth or every tenth tool in series has a ball seat with a push through pressure that is different than the other four or nine in the series. Thus, as the ball passes through the string, a unique signature of pressure increases as the ball passes through the ball seats. For example, as the actuating device arrives at and passes through each seat, a pressure signature is generated that can be sensed at surface. Every firth or tenth seat would generate a different, for example, higher pressure pulse than what had been generated at the preceding four or nine seats passed. In one example, the tools can be installed in a string such that each set of five tools in series includes four tools with ball seat pass through pressures of about 2000 psi, while the fifth one of the set is 4000 psi. In a well with such a string installed, a distinct pressure feedback is generated to identify where the ball is along the string.

A sliding sleeve sub 1 10 with an embodiment of the above noted-ball seat 1 12 and regulator 1 16 is shown in Figures 2A to 2C. Ball seat 1 12 is mounted on a sleeve 1 14 that controls the closed and open condition of ports 128.

Ball seat 1 12 is initially flexible (Figure 2A) but can be reconfigured to an inflexible condition (Figures 2B and 2C) to drive movement of a sleeve 1 14 beyond an initial stroke length to open ports 128 (Figure 2C). While sleeve 1 14 is shown in two parts, a multipart construction is not necessary but facilitates installation and assembly of the sub.

The ends of the sub may be configured, as by threading ends of tubular housing 113 for example, to be assembled together with other tubulars for formation of a tubing string such as one shown in Figure 1 A. The sliding sleeve sub is run into a wellbore in a string. Initially the sliding sleeve sub is in the un-shifted position (Figure 2A) with the fracturing port openings 128 in the outer housing 1 13 of the sub isolated from the inner bore ID of the sub by sleeve 1 14. O-rings 115 are positioned to seal the interface between sleeve 114 and housing 1 13 on each uphole side and downhole side of the ports.

The sleeve is held in a port closed position within the outer housing by a releasable lock such as shear pins 117. To move sleeve 1 14 to a port open position, retracted to some degree from ports 128, the holding strength of shear pins 1 17 must be overcome.

While shear pins 1 17 can hold sleeve 1 14 rigidly against axial movement, in this embodiment some axial movement of sleeve 1 14 is permitted even while the sleeve remains in the port closed position locked by pins 117. As such, pins 117 connect sleeve 114 to an axially slidable locking ring 1 19. Locking ring 1 19 rides within a groove 1 19a in housing 1 13 and permits sleeve 1 14 to move axially along an initial stroke length from a starting position to a second position, the initial stroke length may be determined by the length from the sleeve's starting position to the downhole end of the groove 119a.

However, sleeve 1 14 can only move further axially if the shear pins are sheared. The range of travel of the sleeve along the housing is restricted by the ring's movement in groove 1 19a, but sleeve 114 can move axially further along housing 113 if pins 117 are sheared, that is if sufficient force is applied when ring 119 is stopped against the downhole end of groove 119a, to shear sleeve 114 from its engagement with ring 119. A selected pressure is required to shear pins 117.

Sleeve 114 carries ball seat 1 12, Ball seat 1 12 is secured to the sleeve, such that axial movement of the ball seat causes axial movement of the sleeve. As with any ball seat, ball seat 1 12 provides a reduced seat diameter (SD) in inner bore (SD<ID) that will stop and create a seal with any actuating device, referred to herein after as a ball 126 or a dart, with a diameter larger than the seat diameter SD. The ball seat, therefore, can be employed to create a force downhole due to the formation of a pressure differential across the seat when a ball is landed therein. The ball seat is constructed in such a way that it is flexible, to thereby permit the seat diameter to be stretched (in other words yielded, expanded or collapsed) such that a ball can be pumped through the seat when the pressure differential creates a force greater than the ability of the ball seat to hold its form. This is known as a pass through pressure: each flexible seat has a pass through pressure above which a ball can be pushed through the seat. The seat's flexibility may be selected due to material properties (flexural modulus, compression modulus, etc.), seat geometry or by provision of a flexing mechanism such as a friction spring, a pivotal connection, etc.

Seals 121 may be employed to seal between the seat and the sleeve to prevent fluid bypass around the seat and preferably to prevent infiltration of debris behind the seat. The seat may be installed in a recess 114a in the sleeve, such that the seat is axially fixed against a shoulder of the recess and transition from the sleeve diameter to the seat is gradual and the ends of the seat do not protrude into the inner bore in way that would collect debris or present a catch surface for tools moving therepast.

In one embodiment, the seat is selected to flex in such a way that its seat diameter is enlarged but a gap substantially does not open up between sleeve 1 14 and seat 1 12. The seat may be a continuous, but expandable ring without ports, slits and gaps, again to prevent infiltration of debris. In the illustrated embodiment, for example, seat 1 12 is a ring with a hollow backside 1 12a such that the material of the seat protrudes inwardly to form a diameter constriction SD and is v-shaped in axial section, but the material thinning caused by hollowing out the back side causes the seat to be relatively more resiliently flexible than the seat material would otherwise be.

Seat 1 12, however, can be reconfigured to an inflexible condition wherein it cannot be expanded and a structure that lands and seals therein cannot pass. In the illustrated embodiment, for example, the seat includes a seat locking system 134 behind the seat 112. Seat locking system 134 is normally inactive, but can be configured to lock the seat against flexing. The illustrated seat locking system 134 includes an expandable support ring 136 positioned behind seat 112, particularly at the backside 1 12a of the seat at its constriction. Ring 136 is expandable, formed as a split ring or as an annular arrangement of ring segments or dogs. Ring 136 is installed behind, and is axially moveable with, seat 112 and thereby with sleeve 1 14. Ring 136 acts with housing 1 13 to determine whether or not seat 1 12 can flex: (a) seat 1 12 can flex when ring 136 can or is expanded and (b) seat 1 12 is inflexible when ring 136 is positioned against the backside of seat 1 12 and cannot expand. In particular, housing 1 13 has a recess 1 13a positioned behind the sleeve. Ring 136 can expand when it is positioned over recess 113a and ring 136 cannot expand when it is not positioned over recess 113a. Seat 1 12, and therefore support ring 136 which is held behind and moves with the seat, is normally positioned over recess 1 13a. However, when a ball lands in seat 1 12, the ball will move the seat axially as driven by fluid pressure and, therefore, ring 136 will move with seat 112 towards the end of the recess 1 13a. If ball 1 18 passes through the seat before ring 136 is axially moved beyond recess 1 13a, the seat can flex to allow the ball to pass (Figure 2A). However, if a ball, such as ball 126, remains in seat 112 long enough that ring 136 has moved axially out of (i.e. away from or beyond) recess 113a, ring 136 is supported against expansion and seat 1 12 becomes inflexible (Figure 2B). When seat becomes inflexible, ball 126 cannot pass through (Figure 2C). This is the same ball 126 that moved the seat and ring 136 beyond recess 1 13a. Since the seat is inflexible, he ball cannot pass seat 1 12 and pressure can be applied to shear pins 117 and move sleeve to open ports 128. Movement of the sleeve valve from the starting position to the second position is towards the bottom end of the housing and movement of the sleeve valve to open the ports is towards the bottom end.

Seat 112 cannot flex when it is held by ring 136 at its backside in a position where ring 136 also is unable to expand. Movement of seat 112 moves ring 136 axially away from the end of recess 1 13a, where the ring is no longer able to expand and, as such, ball 126 cannot be released.

The backside 136a of the expandable ring may be rounded and/or end wall 1 13a' of recess 1 13a may be ramped to permit ease of movement of the ring up out of the recess.

The regulator in Figures 2A - 2C that determines the residence time includes the axial length from the starting position of the sleeve to the downhole end of recess 113a, which determines the stroke length through which sleeve 114 can move before seat 1 12 is supported at its backside against flexing expansion.

The stroke length through which ball seat can move before ring 136 supports the seat against flexing determines the time delay before the seat reconfigures to an inflexible condition. Stated another way, the residence time required for a ball to remain in ball seat before seat is reconfigured to an inflexible state is the time it takes from a ball landing against seat, for the sleeve to move along the stroke length from its starting position to the second position where ring 136 is supported against expansion on the smaller diameter landing beyond, for example downhole, of the recess. When the sleeve reaches the second position, ring 1 19 may be stopped against or close to downhole shoulder of recess 1 19a.

Without a delay mechanism, the time required to move ring 136 along recess 113a may be quite short. In fact, in some cases, even a ball being driven by a pressure over pass through pressure may reside in the seat long enough to move the sleeve sufficiently to cause the seat to reconfigure. As such a delay mechanism 116 may be useful in combination with the sleeve 1 14 stroke length components to lengthen the set time, which is the length of time that a ball must remain in the seat before the seat is reconfigured to the inflexible condition. Delay mechanism 116 resists movement of the sleeve and seat, and thereby expandable ring 136, such that the amount of time necessary to move ring 136 along recess is slow enough to be controllable by pump operations.

The delay mechanism allows the seat and the sleeve components to move and the flexible ball seat to flex until such time that components have moved into a position that the seat locking system prevents the flexible ball seat from flexing, thus preventing the ball from being pumped through the ball seat.

In the illustrated embodiment, delay mechanism 1 16 acts to slow movement of the sleeve such that ring 136 can only reach the end of recess 1 13a if the ball stays in the seat for a selected time, that selected time being longer than the normal time it would take the ball to move through the seat once the pump through pressure is reached and longer than the time it would take for ring 136 to normally move (without supplemental resistance) from its upper most position to a position downhole of recess 1 13a.

The delay mechanism 116 is configured to resist, and therefore slow, axial movement of sleeve 114 such that the residence time is longer than it would talce the sleeve to move if unrestricted. In this embodiment, the delay mechanism includes a hydraulic chamber between housing 1 13 and sleeve 1 14 that has a resisted, metered movement of hydraulic fluid therein to slow any movement between the parts. In particular, in the embodiment of Figures 2A to 2C, the delay mechanism 1 16 includes a hydraulic chamber with a metering valve 142, which separates the chamber into a first hydraulic chamber 144 and a second hydraulic chamber 146. The metering valve is driven by relative movement between the housing and sleeve 114 to move through the chamber, reducing the size of one chamber, while at the same time increasing the size of the other chamber such that fluid must move through a restriction in metering valve 142 from one chamber to the other. Thus, while the sleeve can move ring 136 toward the end of recess 113a, that movement slowed by the resistance exerted by metering valve in the hydraulic chamber.

The chamber is, in this embodiment an annular space between housing 1 13 and the sleeve. Seal 148, such as an o-ring in an annular gland, is positioned between sleeve 114 and the inner wall of the tubular housing 113 at end of the chamber opposite metering valve 142, to pressure isolate chamber 146 from inner diameter ID and from fluid pressures about outer surface of the tool. As such any fluid in the chamber 146 is trapped in that chamber unless it passes through the metering valve. If desired, receiving chamber 144 can also be sealed as by seals 1 15, 121. In the illustrated embodiment, chamber 146 is filled with a hydraulic fluid, such as oil, at atmospheric pressure. While the chamber could be filled with any fluid, a hydraulic fluid offers predictable viscosity and cannot immediately flow through valve 142 such that the flow, while capable of occurring through valve, occurs at a slow rate. The receiving chamber 144 can be filled the same fluid or a different fluid from that in chamber 146. In one embodiment, chamber 144 is filled with air, while the other chamber is filled with hydraulic fluid, since having a compressible fluid in the receiving chamber allows for pressure relief should the hydraulic-fluid filled chamber undergo pressure fluctuations while handling, such as when being moved from surface into borehole conditions.

Metering valve 142, in this embodiment, is secured to the outer surface of sleeve 114. The metering valve therefore moves with the sleeve. Metering valve 142 includes an annular ring that separates the annular chamber into the two chambers 144, 146. The movement of sleeve 1 14 to achieve port-opening, forces metering valve 142 to move to increase the volume of first chamber 144 while reducing the volume of second chamber 146. In response to this relative volume change between the two chambers, one chamber's volume is increasing and the other's volume is decreasing, hydraulic fluid in the chamber of decreasing volume must pass the restriction presented by metering valve 142 to permit the sleeve movement. In the illustrated embodiment, the restriction includes an annular piston with apertures extending through the piston between chambers 144, 146. Orifices in the apertures provide limited fluid movement between the two chambers 144, 146 through the apertures. Seals prevent fluid from bypassing around the piston. While sleeve could otherwise move readily within the housing, the movement is resisted by the restriction of metering valve 142 moving through the hydraulic-fluid-filled chamber. Thus, the valve 142 slows movement of the sleeve, corresponding to the rate at which the hydraulic fluid in the chamber may pass through the valve's fluid orifice 152.

Chamber 146 in one embodiment, may include a wider open space such that eventually metering valve 142 may pass into an area of the chamber where it no longer fills the annular space of chamber (Figure 2C) and therefore no longer has a metering effect.

It will be appreciated that various modifications can be made to the delay mechanism. For example, the piston could be carried on the housing. In one embodiment, the delay mechanism is adjustable to control the degree of resistance imparted thereby. For example in an embodiment employing a hydraulic chamber, the viscosity of the hydraulic fluid and/or the size of the valve orifice can be selected, to control the metering effect and therefore the delay imparted by the mechanism.

If desired, the metering piston can be re-configured to be hydrostatically unbalanced, causing additional resistive force. This resistive force can be employed to drive a build in mill (to remove ball seat) and/or closing mechanism for the sleeve.

The sub may include a power spring 160 to bias the sleeve in various ways.

In one embodiment, power spring 160 may act as a driver to urge continued movement of the sleeve to the port open position even after the ports have opened and driving pressure has been lost. In another embodiment, for example, the power spring may be an expansion-type spring to further resist movement of sleeve 1 14. While the metering device keeps the sleeve from axially shifting quickly, seat 112 and sleeve 1 14 will move axially together at least some amount when each ball lands on the seat. The power spring 160 may act to return the sleeve/seat to the initial, unsupported position, after each ball passes. Power spring 160 may urge the sleeve towards the flexible seat condition to resist movement or as a form of reset for seat 1 12 after a ball passes. In particular, spring 160 may bias sleeve such that ring 136 remains in recess 1 13a unless suitable force is applied to overcome the biasing force of the spring.

Locks may also be employed to hold the parts in their final positions. For example, a C- ring lock 162 may be employed to ensure sleeve 114 remains in its open port position. C-ring lock 162 may be positioned to engage between sleeve 114 and housing 113 after the sleeve has moved to the port-open position, to ensure that sleeve 114 does not inadvertently move out of the port-open position. In one embodiment, lock ring 162 can be releasable to allow the sleeve to be moved intentionally, by application of sufficient force to the port closed position (Figure 2A or 2B). In such an operation, power spring 160 may be configured to assist with the return movement once the lock ring holding force is overcome.

If desired, the ball seat, the expandable ring, and any other desired components may be formed of degradable material that is removed by degradation such as dissolution due to exposure in wellbore conditions such as by exposure to natural wellbore fluids, stimulation fluids or intentionally introduced dissolution fluids. In one embodiment, movement of the sleeve to the port open position releases a pre-installed dissolution fluid from the sub to remove the components made of degradable material. For example, in one embodiment the metering fluid in chamber 144 may be also used as the dissolution fluid.

The balls may also be formed of degradable material, if desired.

In another embodiment, the metering fluid can serve to carry an indicator such as a tracer that is released during opening of the sleeve and can be detected, as by conveying to surface in circulating fluids, to indicate that a sleeve has been moved to the port open position. This may provide fracture quality assurance and/or by use of unique tracers for various seats, may provide feedback on zone selection. This sliding sleeve sub allows a string to be configured with an unlimited number of valves that each are selectively openable to expose their ports. Since the sub is devoid of any indexing mechanism and the valves may all be the similar or even identical, the string design and construction is simple and requires less inventory. Whether the ball is caught, or is allowed to pass, at each valve in the string is completely controlled by the operator, for example, by increasing/decreasing pump rate.

One size ball can be employed to actuate any of the valves of a similar size (which could be all of the valves in the string), with actuation being dependent on pump control rather than unique features of the ball or the target valves. The sub may be free of indexing mechanisms. Since no indexing mechanisms are required, there is less concern with regards to malfunction, planning, setup or debris contamination.

In use, pump conditions are selected to either (i) move the ball through the ball seat rapidly such that there is insufficient time to reconfigure the seat from the flexible to the inflexible condition or (ii) land the ball with at least some force against the seat, but to retain the ball in the seat long enough that the seat is reconfigured from being flexible to being inflexible. A ball moving along the string can be stopped in a ball seat or be moved through the ball seat simply by controlling fluid pressure moving the ball through the seat. In particular, by reducing fluid pressure, as by reducing the pump rate, to a pressure less that the seat's pass through pressure, the ball is forced against the ball seat, but the pressure is insufficient to move the ball through the seat, even though the seat is in fact flexible. To reconfigure the seat to an inflexible condition, the ball is retained in the ball seat for a length of time longer than a set time established by a regulator. When the set time established by the regulator lapses, then the ball seat reconfigures to the inflexible condition while the ball remains therein. Once in the inflexible condition, the pressure can be raised even beyond the pass through pressure and the ball cannot pass.

Therefore, a method may employ a sub with (a) a ball seat, the ball seat being initially flexible and having a pass through pressure at which the ball seat flexes to allow a ball to pass through and (b) a regulator configured to monitor the time a ball remains in the ball seat and configured to allow reconfiguration of the ball seat to an inflexible condition after the ball resides in the ball seat for a set time. The method may include landing a ball in the ball seat, maintaining the pressure lower than the pass through pressure to provide a residence time of the ball in the ball seat long enough for the regulator to reconfigure the ball seat to the inflexible condition and raising the pressure to actuate the sub.

The sub may be in a string and the method may include moving the ball through one or more additional tools uphole of the sub, each of the additional tools may include (a) a ball seat, the ball seat being initially flexible with a snap through pressure (which is the pressure at which the ball seat flexes to allow a ball to pass through) and (b) a regulator configured to monitor the time a ball remains in the ball seat and configured to allow reconfiguration of the ball seat to an inflexible condition after the ball resides in the ball seat for a set time. The method of moving the ball through one or more additional tools uphole of the sub may include landing a ball in the ball seat of the one or more additional tools and applying a pressure greater than the snap through pressure to move the ball through the ball seat faster than the time needed by the regulator to reconfigure the ball seat to the inflexible condition.

The method may include monitoring movement of the ball through the additional tools. Such a method may include monitoring string pressure as the ball passes through the one or more additional tools and possibly noting that some of the one or more additional tools have higher pass through pressures than others. Alternately or in addition, the method may include lowering the pump pressure after the ball passes all of the one or more additional tools and before the ball arrives at the sub.

In one embodiment, the set time monitored by the regulator is determined by an initial stroke length of a sleeve on which the ball seat is mounted. In such an embodiment, maintaining the pressure lower than the pass through pressure may include providing a residence time of the ball in the ball seat long enough for the sleeve to move through its initial stroke length from a starting position to a second position wherein a seat locking system locks the ball seat in an inflexible condition. In one embodiment, raising the pressure to actuate the sub includes moving the sleeve through an additional stroke length to open ports covered by the sleeve. Moving the sleeve may include shearing out the sleeve from a shear pin system to continue to move beyond the second position.

The valve may be one such as is shown in Figures 2A to 2C, including a flexible ball seat 1 12 (Figure 2A) that can be reconfigured to an inflexible condition (Figure 2B and 2C) and only when the seat is in the inflexible condition can a ball create a force sufficient to move sleeve 114 sufficiently to open the ports of the valve. Whether the ball seat remains in the flexible condition or moves to the inflexible condition depends on the length of time that a ball landing at the seat remains in the seat. The sliding sleeve sub includes: a tubular housing including an inner bore defined by an inner wall; and a sleeve installed in the inner bore and axially slidable therein at least from a first position to a second position, the sleeve including an inner diameter, an outer diameter facing the tubular inner wall, wherein the ball seat is installed on the sleeve and the ball seat in the flexible condition being flexible to allow passage of the actuating device axially through the ball seat in a normal period of time and the ball seat in the inflexible condition stopping the actuating device to generate an actuating force against the sleeve to move it to the second position; and a regulator to resist reconfiguration of the ball seat to the inflexible condition until the actuation device is retained in the ball seat for a selected minimum period of time greater than the normal period of time. The reconfiguration of the ball seat from the flexible to the inflexible condition will occur if the ball remains in the seat long enough to allow a seat locking mechanism 134 to be activated. In the illustrated embodiment, of Figures 2A to 2C, the seat on which the seat is located has an initial stroke length and, if the ball remains in the ball seat long enough to move the sleeve to the end of its initial stroke length, the seat reconfigures to the inflexible condition. Since the movement through a stroke length can, in some cases, happen quite quickly, a delay mechanism 1 16 is employed to resist movement the sleeve stroking speed such that the seat can only reconfigure to the inflexible condition after a set time determined by the delay mechanism's resistance to movement of the sleeve. As such, if a ball is pumped through at a pumping rate that generates a pressure on the ball higher than the seat's pass through pressure, the ball can pass right through without actuating the seat to assume the inflexible condition and the sleeve will remain in a port-closed position. A ball that is pumped through a ball seat at a pumping rate that generates a pressure on the ball higher than the seat's pass through pressure, causes the ball to pass through, for example, in less than five seconds and perhaps about one second or less.

To open the sleeve, the ball can be pumped onto the seat at a controlled, lower rate. For example, as the ball approaches the ball seat of interest, pumping may be stopped or slowed considerably such that pressure pushing the ball against the seat is less than the pass through pressure. At such a lower pressure, the ball lands on the seat and remains on the seat for a set time, which is long enough to permit the seat to reconfigure to the inflexible condition while the ball remains on the seat. In one embodiment, the set time (or required residence time) is greater than a minute, but can be reduced considerably to greater than 15 seconds or sometimes only about 5 seconds.

The delay mechanism, which is this embodiment, is a fluid metering device between the sleeve and the housing, can resist movement of the sleeve when the ball lands and a pressure differential develops such that the residence time of the ball is the seat is long enough to be predictable and repeatable, but short enough to be time efficient. Axial movement of the seat and the sleeve, for example, can be slowed by the metering device to ensure that only after a set time, will the seat be able to move axially a sufficient degree for example to the end of the initial stroke length to allow the seat to move to the inflexible condition.

Thus, whether or not the sub is actuated by a ball is determined by the speed with which the ball is pumped through the seat. If the ball stays on seat long enough for the metering device to move the seat locking system 134 to support the seat in the inflexible (i.e. non- expandable, non-passable) position, then the seat is inflexible. If the balls pumps through the seat more quickly, then the seat does not have time to shift to become fully supported by seat locking system 134. Thus, the seat remains flexible and the ball goes through. The operator seeking to actuate a target tool can slow the pumps as the ball approaches the target tool to ensure the fluid pressure pushing against the ball is low enough to keep the ball in the seat long enough to reconfigure the seat to the inflexible condition. The target tool may be installed in a string with a number of similarly actuated tools that are actuated by the same ball size. For example, a number of tools such as those of Figures 2A to 2C can be installed in series in a tubing string and then installed in a well. In such a string, the target tool may be downhole of a number of the other tools, such as is shown in Figure 1 A. In such an embodiment, the operator who is seeking to actuate the target tool can pump the ball at a fast rate through all of the seats of the tools uphole of the target tool. Then, when the ball is approaching the target tool and landed on the seat of the target tool, the pump rate can be slowed to reduce the pressure at which the ball pushes against the seat to a pressure below the pass through pressure. If the lower pressure is maintained for a sufficient period of time to allow the sleeve to stroke while being delayed by the metering device, the seat reconfigures to the inflexible condition. As shown in Figure 2B, at the end of the initial stroke, the seat is supported by the seat locking system. Thereafter, using the same ball, the pressure can be maintained or increased to overcome the shear system 1 17 to move the sleeve to open the ports. A wellbore treatment can be injected through the ports to treat the wellbore.

If for some reason the ball passes through the seat of the target tool before the seat configures to the inflexible condition, another ball can be launched to try again to reconfigure the ball seat to the inflexible condition, so that the sleeve can be moved to open the ports.

As the ball moves through the string, a pressure signature can be observed at surface. Each time the ball has landed in a flexible seat, the string pressure is observed to increase to the pass through pressure and then fall off when the ball has passed through the seat. To assist with monitoring the ball movement through the string, the tools in the string can be selected and installed in the string with consideration as to their pass through pressure. A particular pattern of tools can be used such that an observable pressure signature is developed. For example, string can include a regular number of tools with a similar pass through pressure, followed one tool with a higher pass through pressure. Thus, as the ball is pumped through the string a number of similar pressure pulses may be observed followed by a higher pressure pulse. The passage of a ball through the string will therefore create a distinctive signature of pressure pulses with a regular number of pressure pulses at one level, such as for example about 2000psi, followed by one pressure pulse at a different level, such as 4000 psi. Such a system facilitates location monitoring.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article "a" or "an" is not intended to mean "one and only one" unless specifically so stated, but rather "one or more". All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are know or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 USC 1 12, sixth paragraph, unless the element is expressly recited using the phrase "means for" or "step for".

Claims

Claims:

1. A sliding sleeve sub comprising: a housing; a sleeve valve axially slidable along the housing; and a ball seat on the sleeve valve, the ball seat being flexible and configured to respond to a length of time an actuating device resides in the ball seat to either (a) maintain the seat as flexible to allow the actuating device to be pushed through the ball seat without actuating the tool or (b) to reconfigure the seat to an inflexible condition to stop the actuating device from passing through the ball seat, to thereby allow actuation of the sliding sleeve sub by the actuating device.

2. The sliding sleeve sub of claim 1 wherein the ball seat has a pass through pressure and the actuating device can be pushed through the ball seat by a pressure exceeding the pass through pressure.

3. The sliding sleeve sub of claim 1 wherein the length of time is determined by a regulator for the ball seat.

4. The sliding sleeve sub of claim 1 wherein the sleeve valve has an initial stroke length from a starting position to a second position; and further comprising a seat locking mechanism actuatable to lock the seat in the inflexible condition, the seat locking mechanism acting to lock the ball seat in the inflexible condition when the sleeve is in the second position; a delay mechanism to slow movement of the sleeve valve through the initial stroke length.

5. The sliding sleeve sub of claim 4 further comprising ports through the housing normally covered by the sleeve valve and opened by movement of the sleeve valve from the second position to a further position.

6. The sliding sleeve sub of claim 5 wherein movement of the sleeve valve from the starting position to the second position is towards the bottom end and movement of the sleeve valve to open the ports is towards the bottom end.

7. The sliding sleeve sub of claim 4 further comprising a shear pin assembly

shearable to permit movement of the sleeve valve from the second position to the further position.

8. The sliding sleeve sub of claim 7 wherein the shear pin assembly is configured to releasably lock the sleeve valve in a position only to be movable through the initial stroke length.

9. The sliding sleeve sub of claim 4 wherein the delay mechanism is a metering device to resist movement of hydraulic fluid between the sleeve valve and the housing.

10. A method for actuating a downhole tool, the method comprising: modifying a pumping condition driving the actuating device against the tool such that a tool component is signaled that the actuating device is to be retained by the tool, thereby actuating the downhole tool.

1 1. The method of claim 10 wherein modifying a pumping condition is selected to either (i) move the actuating device through a ball seat in the downhole tool rapidly such that there is insufficient time to reconfigure the ball seat from a flexible condition to an inflexible condition or (ii) land the actuating device with at least some force against the ball seat and retain the actuating device in the ball seat long enough that the seat is reconfigured from being flexible to being inflexible.

12. The method of claim 10 wherein modifying a pumping condition controls fluid pressure moving the actuating device relative to the ball seat.

13. The method of claim 10 wherein modifying a pumping condition reduces fluid pressure to less than a pass through pressure for the ball seat.

14. The method of claim 13 further comprising maintaining the actuating device in the ball seat for a length of time longer than a set time established by a regulator and when the set time established by the regulator lapses, then the ball seat reconfigures to the inflexible condition while the ball remains therein such that the actuating device is to be retained by the tool to thereby actuate the downhole tool.

15. The method of claim 10 wherein actuating the downhole tool includes

reconfiguring a ball seat from a flexible condition to an inflexible condition, while the actuating device is retained by the ball seat and increasing pressure in the string uphole of the actuating device to apply a force through the actuating device into the ball seat in the inflexible condition.

16. The method of claim 10 wherein the downhole tool is in a tubing string and the method includes: moving the actuating device through the tubing string, the tubing string including additional tools uphole of the downhole tool, each of the additional tools include (a) a ball seat, the ball seat being initially flexible with a snap through pressure and (b) a regulator configured to monitor the time a ball remains in the ball seat and configured to allow reconfiguration of the ball seat to an inflexible condition after the actuating device resides in the ball seat for a set time; and landing the actuating device in each of the additional tools in series, each landing including landing the actuating device in the ball seat and applying a pressure greater than the snap through pressure to move the actuating device through the ball seat faster than the time needed by the regulator to reconfigure the ball seat to the inflexible condition.

17. The method of claim 16 further comprising monitoring movement of the actuating device through the additional tools by monitoring string pressure and observing the string pressure for pressure pulses indicative of a selected tool having a higher pass through pressure than at least some of the additional tools.

18. A wellbore tubular string comprising: a first sliding sleeve sub including: a tubular housing including an inner bore defined by an inner wall; a sleeve installed in the inner bore and axially slidable therein at least from a first position to a final position, the sleeve including an inner diameter, an outer diameter facing the tubular inner wall, a ball seat installed on the sleeve in the inner diameter, the ball seat normally having a flexible condition wherein the ball seat is flexible to allow passage of an actuating device axially through the ball seat in a normal period of time and the ball seat being reconfigurable into an inflexible condition configured to stop the actuating device and to transfer an actuating force to the sleeve to move it to the final position; and a regulator to resist reconfiguration of the ball seat to the inflexible condition until the actuating device is retained in the ball seat for a selected minimum period of time greater than the normal period of time; and a second sliding sleeve sub axially spaced from the first sliding sleeve sub, the second sliding sleeve sub including: a normally flexible ball seat also being reconfigurable to an inflexible conditioned by a second actuating device of substantially the same size as the actuating device and being reconfigurable based on the residence time of the second actuating device in the normally flexible ball seat.

19. The wellbore tubular string of claim 18 wherein the first position is a port closed position, where the sleeve overlies a port through the tubular housing, and the final position is a port open position, where the sleeve is retracted at least in part from the port to permit fluid flow through the port from the inner bore to an outer surface of the tubular housing.

20. The wellbore tubular string of claim 18 wherein the regulator monitors the

selected period of time as the time required for the sleeve to move from the first position along an initial stroke length to a second position.