Method and apparatus for wellbore fluid treatment

Abstract

A fluid treatment method includes positioning a tubing string in a non-vertical borehole section, and applying a sliding-sleeve-actuating fluid pressure within the tubing string's inner bore such that a first sliding sleeve moves from a position in which a first port is covered to another position in which the first port is exposed to the inner bore. The method further includes pumping fluid through the first port. The method also includes conveying first and second fluid conveyed sealing devices through the inner bore such that the first and second fluid conveyed sealing device seal against the seats of second and third sliding sleeves, respectively, thereby moving the second and third sliding sleeves to open port positions exposing second and third ports, respectively. The method also includes pumping fluid through the second and third ports to treat first and second portions of the formation, respectively.

Description

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

An oil or gas well relies on inflow of petroleum products. When drilling an oil or gas well, an operator may decide to leave productive intervals uncased (open hole) to expose porosity and permit unrestricted wellbore inflow of petroleum products. Alternately, the hole may be cased with a liner, which is then perforated to permit inflow through the openings created by perforating.

When natural inflow from the well is not economical, the well may require wellbore treatment termed stimulation. This is accomplished by pumping stimulation fluids such as fracturing fluids, acid, cleaning chemicals and/or proppant laden fluids to improve wellbore inflow.

In one previous method, the well is isolated in segments and each segment is individually treated so that concentrated and controlled fluid treatment can be provided along the wellbore. Often, in this method a tubing string is used with inflatable element packers thereabout which provide for segment isolation. The packers, which are inflated with pressure using a bladder, are used to isolate segments of the well and the tubing is used to convey treatment fluids to the isolated segment. Such inflatable packers may be limited with respect to pressure capabilities as well as durability under high pressure conditions. Generally, the packers are run for a wellbore treatment, but must be moved after each treatment if it is desired to isolate other segments of the well for treatment. This process can be expensive and time consuming. Furthermore, it may require stimulation pumping equipment to be at the well site for long periods of time or for multiple visits. This method can be very time consuming and costly.

Other procedures for stimulation treatments use foam diverters, gelled diverters and/or limited entry procedures through tubulars to distribute fluids. Each of these may or may not be effective in distributing fluids to the desired segments in the wellbore.

The tubing string, which conveys the treatment fluid, can include ports or openings for the fluid to pass therethrough into the borehole. Where more concentrated fluid treatment is desired in one position along the wellbore, a small number of larger ports are used. In another method, where it is desired to distribute treatment fluids over a greater area, a perforated tubing string is used having a plurality of spaced apart perforations through its wall. The perforations can be distributed along the length of the tube or only at selected segments. The open area of each perforation can be pre-selected to control the volume of fluid passing from the tube during use. When fluids are pumped into the liner, a pressure drop is created across the sized ports. The pressure drop causes approximate equal volumes of fluid to exit each port in order to distribute stimulation fluids to desired segments of the well. Where there are significant numbers of perforations, the fluid must be pumped at high rates to achieve a consistent distribution of treatment fluids along the wellbore.

In many previous systems, it is necessary to run the tubing string into the bore hole with the ports or perforations already opened. This is especially true where a distributed application of treatment fluid is desired such that a plurality of ports or perforations must be open at the same time for passage therethrough of fluid. This need to run in a tube already including open perforations can hinder the running operation and limit usefulness of the tubing string.

SUMMARY OF THE INVENTION

A method and apparatus has been invented which provides for selective communication to a wellbore for fluid treatment. In one aspect of the invention the method and apparatus provide for staged injection of treatment fluids wherein fluid is injected into selected intervals of the wellbore, while other intervals are closed. In another aspect, the method and apparatus provide for the running in of a fluid treatment string, the fluid treatment string having ports substantially closed against the passage of fluid therethrough, but which are openable when desired to permit fluid flow into the wellbore. The apparatus and methods of the present invention can be used in various borehole conditions including open holes, cased holes, vertical holes, horizontal holes, straight holes or deviated holes.

In one embodiment, there is provided an apparatus for fluid treatment of a borehole, the apparatus comprising a tubing string having a long axis, a first port opened through the wall of the tubing string, a second port opened through the wall of the tubing string, the second port offset from the first port along the long axis of the tubing string, a first packer operable to seal about the tubing string and mounted on the tubing string to act in a position offset from the first port along the long axis of the tubing string, a second packer operable to seal about the tubing string and mounted on the tubing string to act in a position between the first port and the second port along the long axis of the tubing string; a third packer operable to seal about the tubing string and mounted on the tubing string to act in a position offset from the second port along the long axis of the tubing string and on a side of the second port opposite the second packer; a first sleeve positioned relative to the first port, the first sleeve being moveable relative to the first port between a closed port position and a position permitting fluid flow through the first port from the tubing string inner bore and a second sleeve being moveable relative to the second port between a closed port position and a position permitting fluid flow through the second port from the tubing string inner bore; and a sleeve shifting means for moving the second sleeve from the closed port position to the position permitting fluid flow, the means for moving the second sleeve selected to create a seal in the tubing string against fluid flow past the second sleeve through the tubing string inner bore.

In one embodiment, the second sleeve has formed thereon a seat and the means for moving the second sleeve includes a sealing device selected to seal against the seat, such that fluid pressure can be applied to move the second sleeve and the sealing device can seal against fluid passage past the second sleeve. The sealing device can be, for example, a plug or a ball, which can be deployed without connection to surface. Thereby avoiding the need for tripping in a string or wire line for manipulation.

The means for moving the second sleeve can be selected to move the second sleeve without also moving the first sleeve. In one such embodiment, the first sleeve has formed thereon a first seat and the means for moving the first sleeve includes a first sealing device selected to seal against the first seat, such that once the first sealing device is seated against the first seat fluid pressure can be applied to move the first sleeve and the first sealing device can seal against fluid passage past the first sleeve and the second sleeve has formed thereon a second seat and the means for moving the second sleeve includes a second sealing device selected to seal against the second seat, such that when the second sealing device is seated against the second seat pressure can be applied to move the second sleeve and the second sealing device can seal against fluid passage past the second sleeve, the first seat having a larger diameter than the second seat, such that the second sealing device can move past the first seat without sealing thereagainst to reach and seal against the second seat.

In the closed port position, the first sleeve can be positioned over the first port to close the first port against fluid flow therethrough. In another embodiment, the first port has mounted thereon a cap extending into the tubing string inner bore and in the position permitting fluid flow, the first sleeve has engaged against and opened the cap. The cap can be opened, for example, by action of the first sleeve shearing the cap from its position over the port. In another embodiment, the apparatus further comprises a third port having mounted thereon a cap extending into the tubing string inner bore and in the position permitting fluid flow, the first sleeve also engages against the cap of the third port to open it.

In another embodiment, the first port has mounted thereover a sliding sleeve and in the position permitting fluid flow, the first sleeve has engaged and moved the sliding sleeve away from the first port. The sliding sleeve can include, for example, a groove and the first sleeve includes a locking dog biased outwardly therefrom and selected to lock into the groove on the sleeve. In another embodiment, there is a third port with a sliding sleeve mounted thereover and the first sleeve is selected to engage and move the third port sliding sleeve after it has moved the sliding sleeve of the first port.

The packers can be of any desired type to seal between the wellbore and the tubing string. In one embodiment, at least one of the first, second and third packer is a solid body packer including multiple packing elements. In such a packer, it is desirable that the multiple packing elements are spaced apart.

In view of the foregoing there is provided a method for fluid treatment of a borehole, the method comprising: providing an apparatus for wellbore treatment according to one of the various embodiments of the invention; running the tubing string into a wellbore in a desired position for treating the wellbore; setting the packers; conveying the means for moving the second sleeve to move the second sleeve and increasing fluid pressure to wellbore treatment fluid out through the second port.

In one method according to the present invention, the fluid treatment is borehole stimulation using stimulation fluids such as one or more of acid, gelled acid, gelled water, gelled oil, CO₂, nitrogen and any of these fluids containing proppants, such as for example, sand or bauxite. The method can be conducted in an open hole or in a cased hole. In a cased hole, the casing may have to be perforated prior to running the tubing string into the wellbore, in order to provide access to the formation.

In an open hole, preferably, the packers include solid body packers including a solid, extrudable packing element and, in some embodiments, solid body packers include a plurality of extrudable packing elements.

In one embodiment, there is provided an apparatus for fluid treatment of a borehole, the apparatus comprising a tubing string having a long axis, a port opened through the wall of the tubing string, a first packer operable to seal about the tubing string and mounted on the tubing string to act in a position offset from the port along the long axis of the tubing string, a second packer operable to seal about the tubing string and mounted on the tubing string to act in a position offset from the port along the long axis of the tubing string and on a side of the port opposite the first packer; a sleeve positioned relative to the port, the sleeve being moveable relative to the port between a closed port position and a position permitting fluid flow through the port from the tubing string inner bore and a sleeve shifting means for moving the sleeve from the closed port position to the position permitting fluid flow. In this embodiment of the invention, there can be a second port spaced along the long axis of the tubing string from the first port and the sleeve can be moveable to a position permitting flow through the port and the second port.

As noted hereinbefore, the sleeve can be positioned in various ways when in the closed port position. For example, in the closed port position, the sleeve can be positioned over the port to close the port against fluid flow therethrough. Alternately, when in the closed port position, the sleeve can be offset from the port, and the port can be closed by other means such as by a cap or another sliding sleeve which is acted upon, as by breaking open or shearing the cap, by engaging against the sleeve, etc., by the sleeve to open the port.

There can be more than one port spaced along the long axis of the tubing string and the sleeve can act upon all of the ports to open them.

The sleeve can be actuated in any way to move into the position permitted fluid flow through the port. Preferably, however, the sleeve is actuated remotely, without the need to trip a work string such as a tubing string or a wire line. In one embodiment, the sleeve has formed thereon a seat and the means for moving the sleeve includes a sealing device selected to seal against the seat, such that fluid pressure can be applied to move the sleeve and the sealing device can seal against fluid passage past the sleeve.

The first packer and the second packer can be formed as a solid body packer including multiple packing elements, for example, in spaced apart relation.

In view of the forgoing there is provided a method for fluid treatment of a borehole, the method comprising: providing an apparatus for wellbore treatment including a tubing string having a long axis, a port opened through the wall of the tubing string, a first packer operable to seal about the tubing string and mounted on the tubing string to act in a position offset from the port along the long axis of the tubing string, a second packer operable to seal about the tubing string and mounted on the tubing string to act in a position offset from the port along the long axis of the tubing string and on a side of the port opposite the first packer; a sleeve positioned relative to the port, the sleeve being moveable relative to the port between a closed port position and a position permitting fluid flow through the port from the tubing string inner bore and a sleeve shifting means for moving the sleeve from the closed port position to the position permitting fluid flow; running the tubing string into a wellbore in a desired position for treating the wellbore; setting the packers; conveying the means for moving the sleeve to move the sleeve and increasing fluid pressure to permit the flow of wellbore treatment fluid out through the port.

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:

FIG. 1a is a sectional view through a wellbore having positioned therein a fluid treatment assembly according to the present invention;

FIG. 1b is an enlarged view of a portion of the wellbore of FIG. 1a with the fluid treatment assembly also shown in section;

FIG. 2 is a sectional view along the long axis of a packer useful in the present invention;

FIG. 3a is a sectional view along the long axis of a tubing string sub useful in the present invention containing a sleeve in a closed port position;

FIG. 3b is a sectional view along the long axis of a tubing string sub useful in the present invention containing a sleeve in a position allowing fluid flow through fluid treatment ports;

FIG. 4a is a quarter sectional view along the long axis of a tubing string sub useful in the present invention containing a sleeve and fluid treatment ports;

FIG. 4b is a side elevation of a flow control sleeve positionable in the sub of FIG. 4a;

FIG. 5 is a section through another wellbore having positioned therein a fluid treatment assembly according to the present invention;

FIG. 6a is a section through another wellbore having positioned therein another fluid treatment assembly according to the present invention, the fluid treatment assembly being in a first stage of wellbore treatment;

FIG. 6b is a section through the wellbore of FIG. 6a with the fluid treatment assembly in a second stage of wellbore treatment;

FIG. 6c is a section through the wellbore of FIG. 6a with the fluid treatment assembly in a third stage of wellbore treatment;

FIG. 7 is a sectional view along the long axis of a tubing string according to the present invention containing a sleeve and axially spaced fluid treatment ports;

FIG. 8 is a sectional view along the long axis of a tubing string according to the present invention containing a sleeve and axially spaced fluid treatment ports;

FIG. 9a is a section through another wellbore having positioned therein another fluid treatment assembly according to the present invention, the fluid treatment assembly being in a first stage of wellbore treatment;

FIG. 9b is a section through the wellbore of FIG. 9a with the fluid treatment assembly in a second stage of wellbore treatment;

FIG. 9c is a section through the wellbore of FIG. 9a with the fluid treatment assembly in a third stage of wellbore treatment; and

FIG. 9d is a section through the wellbore of FIG. 9a with the fluid treatment assembly in a fourth stage of wellbore treatment.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Referring to FIGS. 1a and 1b, a wellbore fluid treatment assembly is shown, which can be used to effect fluid treatment of a formation 10 through a wellbore 12. The wellbore assembly includes a tubing string 14 having a lower end 14a and an upper end extending to surface (not shown). Tubing string 14 includes a plurality of spaced apart ported intervals 16a to 16e each including a plurality of ports 17 opened through the tubing string wall to permit access between the tubing string inner bore 18 and the wellbore.

A packer 20a is mounted between the upper-most ported interval 16a and the surface and further packers 20b to 20e are mounted between each pair of adjacent ported intervals. In the illustrated embodiment, a packer 20f is also mounted below the lower most ported interval 16e and lower end 14a of the tubing string. The packers are disposed about the tubing string and selected to seal the annulus between the tubing string and the wellbore wall, when the assembly is disposed in the wellbore. The packers divide the wellbore into isolated segments wherein fluid can be applied to one segment of the well, but is prevented from passing through the annulus into adjacent segments. As will be appreciated the packers can be spaced in any way relative to the ported intervals to achieve a desired interval length or number of ported intervals per segment. In addition, packer 20f need not be present in some applications.

The packers are of the solid body-type with at least one extrudable packing element, for example, formed of rubber. Solid body packers including multiple, spaced apart packing elements 21a, 21b on a single packer are particularly useful especially for example in open hole (unlined wellbore) operations. In another embodiment, a plurality of packers are positioned in side by side relation on the tubing string, rather than using one packer between each ported interval.

Sliding sleeves 22c to 22e are disposed in the tubing string to control the opening of the ports. In this embodiment, a sliding sleeve is mounted over each ported interval to close them against fluid flow therethrough, but can be moved away from their positions covering the ports to open the ports and allow fluid flow therethrough. In particular, the sliding sleeves are disposed to control the opening of the ported intervals through the tubing string and are each moveable from a closed port position covering its associated ported interval (as shown by sleeves 22c and 22d) to a position away from the ports wherein fluid flow of, for example, stimulation fluid is permitted through the ports of the ported interval (as shown by sleeve 22e).

The assembly is run in and positioned downhole with the sliding sleeves each in their closed port position. The sleeves are moved to their open position when the tubing string is ready for use in fluid treatment of the wellbore. Preferably, the sleeves for each isolated interval between adjacent packers are opened individually to permit fluid flow to one wellbore segment at a time, in a staged, concentrated treatment process.

Preferably, the sliding sleeves are each moveable remotely from their closed port position to their position permitting through-port fluid flow, for example, without having to run in a line or string for manipulation thereof. In one embodiment, the sliding sleeves are each actuated by a device, such as a ball 24e (as shown) or plug, which can be conveyed by gravity or fluid flow through the tubing string. The device engages against the sleeve, in this case ball 24e engages against sleeve 22e, and, when pressure is applied through the tubing string inner bore 18 from surface, ball 24e seats against and creates a pressure differential above and below the sleeve which drives the sleeve toward the lower pressure side.

In the illustrated embodiment, the inner surface of each sleeve which is open to the inner bore of the tubing string defines a seat 26e onto which an associated ball 24e, when launched from surface, can land and seal thereagainst. When the ball seals against the sleeve seat and pressure is applied or increased from surface, a pressure differential is set up which causes the sliding sleeve on which the ball has landed to slide to a port-open position. When the ports of the ported interval 16e are opened, fluid can flow therethrough to the annulus between the tubing string and the wellbore and thereafter into contact with formation 10.

Each of the plurality of sliding sleeves has a different diameter seat and therefore each accept different sized balls. In particular, the lower-most sliding sleeve 22e has the smallest diameter D1 seat and accepts the smallest sized ball 24e and each sleeve that is progressively closer to surface has a larger seat. For example, as shown in FIG. 1b, the sleeve 22c includes a seat 26c having a diameter D3, sleeve 22d includes a seat 26d having a diameter D2, which is less than D3 and sleeve 22e includes a seat 26e having a diameter D1, which is less than D2. This provides that the lowest sleeve can be actuated to open first by first launching the smallest ball 24e, which can pass through all of the seats of the sleeves closer to surface but which will land in and seal against seat 26e of sleeve 22e. Likewise, penultimate sleeve 22d can be actuated to move away from ported interval 16d by launching a ball 24d which is sized to pass through all of the seats closer to surface, including seat 26c, but which will land in and seal against seat 26d.

Lower end 14a of the tubing string can be open, closed or fitted in various ways, depending on the operational characteristics of the tubing string which are desired. In the illustrated embodiment, includes a pump out plug assembly 28. Pump out plug assembly acts to close off end 14a during run in of the tubing string, to maintain the inner bore of the tubing string relatively clear. However, by application of fluid pressure, for example at a pressure of about 3000 psi, the plug can be blown out to permit actuation of the lower most sleeve 22e by generation of a pressure differential. As will be appreciated, an opening adjacent end 14a is only needed where pressure, as opposed to gravity, is needed to convey the first ball to land in the lower-most sleeve. Alternately, the lower most sleeve can be hydraulically actuated, including a fluid actuated piston secured by shear pins, so that the sleeve can be opened remotely without the need to land a ball or plug therein.

In other embodiments, not shown, end 14a can be left open or can be closed for example by installation of a welded or threaded plug.

While the illustrated tubing string includes five ported intervals, it is to be understood that any number of ported intervals could be used. In a fluid treatment assembly desired to be used for staged fluid treatment, at least two openable ports from the tubing string inner bore to the wellbore must be provided such as at least two ported intervals or an openable end and one ported interval. It is also to be understood that any number of ports can be used in each interval.

Centralizer 29 and other standard tubing string attachments can be used.

In use, the wellbore fluid treatment apparatus, as described with respect to FIGS. 1a and 1b, can be used in the fluid treatment of a wellbore. For selectively treating formation 10 through wellbore 12, the above-described assembly is run into the borehole and the packers are set to seal the annulus at each location creating a plurality of isolated annulus zones. Fluids can then be pumped down the tubing string and into a selected zone of the annulus, such as by increasing the pressure to pump out plug assembly 28. Alternately, a plurality of open ports or an open end can be provided or the lower most sleeve can be hydraulically openable. Once that selected zone is treated, as desired, ball 24e or another sealing plug is launched from surface and conveyed by gravity or fluid pressure to seal against seat 26e of the lower most sliding sleeve 22e, this seals off the tubing string below sleeve 22e and opens ported interval 16e to allow the next annulus zone, the zone between packer 20e and 20f to be treated with fluid. The treating fluids will be diverted through the ports of interval 16e exposed by moving the sliding sleeve and be directed to a specific area of the formation. Ball 24e is sized to pass through all of the seats, including 26c, 26d closer to surface without sealing thereagainst. When the fluid treatment through ports of interval 16e is complete, a ball 24d is launched, which is sized to pass through all of the seats, including seat 26c closer to surface, and to seat in and move sleeve 22d. This opens ported interval 16d and permits fluid treatment of the annulus between packers 20d and 20e. This process of launching progressively larger balls or plugs is repeated until all of the zones are treated. The balls can be launched without stopping the flow of treating fluids. After treatment, fluids can be shut in or flowed back immediately. Once fluid pressure is reduced from surface, any balls seated in sleeve seats can be unseated by pressure from below to permit fluid flow upwardly therethrough.

The apparatus is particularly useful for stimulation of a formation, using stimulation fluids, such as for example, acid, gelled acid, gelled water, gelled oil, CO₂, nitrogen and/or proppant laden fluids.

Referring to FIG. 2, a packer 20 is shown which is useful in the present invention. The packer can be set using pressure or mechanical forces. Packer 20 includes extrudable packing elements 21a, 21b, a hydraulically actuated setting mechanism and a mechanical body lock system 31 including a locking ratchet arrangement. These parts are mounted on an inner mandrel 32. Multiple packing elements 21a, 21b are formed of elastomer, such as for example, rubber and include an enlarged cross section to provide excellent expansion ratios to set in oversized holes. The multiple packing elements 21a, 21b can be separated by at least 0.3M and preferably 0.8M or more. This arrangement of packing elements aid in providing high pressure sealing in an open borehole, as the elements load into each other to provide additional pack-off.

Packing element 21a is mounted between fixed stop ring 34a and compressing ring 34b and packing element 21b is mounted between fixed stop ring 34c and compressing ring 34d. The hydraulically actuated setting mechanism includes a port 35 through inner mandrel 32 which provides fluid access to a hydraulic chamber defined by first piston 36a and second piston 36b. First piston 36a acts against compressing ring 34b to drive compression and, therefore, expansion of packing element 21a, while second piston 36b acts against compressing ring 34d to drive compression and, therefore, expansion of packing element 21b. First piston 36a includes a skirt 37, which encloses the hydraulic chamber between the pistons and is telescopically disposed to ride over piston 36b. Seals 39 seal against the leakage of fluid between the parts. Mechanical body lock system 31, including for example a ratchet system, acts between skirt 37 and piston 36b permitting movement therebetween driving pistons 36a, 36b away from each other but locking against reverse movement of the pistons toward each other, thereby locking the packing elements into a compressed, expanded configuration.

Thus, the packer is set by pressuring up the tubing string such that fluid enters the hydraulic chamber and acts against pistons 36a, 36b to drive them apart, thereby compressing the packing elements and extruding them outwardly. This movement is permitted by body lock system 31 but is locked against retraction to lock the packing elements in extruded position.

Ring 34a includes shears 38 which mount the ring to mandrel 32. Thus, for release of the packing elements from sealing position the tubing string into which mandrel 32 is connected, can be pulled up to release shears 38 and thereby release the compressing force on the packing elements.

Referring to FIGS. 3a and 3b, a tubing string sub 40 is shown having a sleeve 22, positionable over a plurality of ports 17 to close them against fluid flow therethrough and moveable to a position, as shown in FIG. 3b, wherein the ports are open and fluid can flow therethrough.

The sub 40 includes threaded ends 42a, 42b for connection into a tubing string. Sub includes a wall 44 having formed on its inner surface a cylindrical groove 46 for retaining sleeve 22. Shoulders 46a, 46b define the ends of the groove 46 and limit the range of movement of the sleeve. Shoulders 46a, 46b can be formed in any way as by casting, milling, etc. the wall material of the sub or by threading parts together, as at connection 48. The tubing string if preferably formed to hold pressure. Therefore, any connection should, in the preferred embodiment, be selected to be substantially pressure tight.

In the closed port position, sleeve 22 is positioned adjacent shoulder 46a and over ports 17. Shear pins 50 are secured between wall 44 and sleeve 22 to hold the sleeve in this position. A ball 24 is used to shear pins 50 and to move the sleeve to the port-open position. In particular, the inner facing surface of sleeve 22 defines a seat 26 having a diameter Dseat, and ball 24, is sized, having a diameter Dball, to engage and seal against seat 26. When pressure is applied, as shown by arrows P, against ball 24, shears 50 will release allowing sleeve 22 to be driven against shoulder 46b. The length of the sleeve is selected with consideration as to the distance between shoulder 46b and ports 17 to permit the ports to be open, to some degree, when the sleeve is driven against shoulder 46b.

Preferably, the tubing string is resistant to fluid flow outwardly therefrom except through open ports and downwardly past a sleeve in which a ball is seated. Thus, ball 24 is selected to seal in seat 26 and seals 52, such as o-rings, are disposed in glands 54 on the outer surface of the sleeve, so that fluid bypass between the sleeve and wall 42 is substantially prevented.

Ball 24 can be formed of ceramics, steel, plastics or other durable materials and is preferably formed to seal against its seat.

When sub 40 is used in series with other subs, any subs in the tubing string below sub 40 have seats selected to accept balls having diameters less than Dseat and any subs in the tubing string above sub 40 have seats with diameters greater than the ball diameter Dball useful with seat 26 of sub 40.

In one embodiment, as shown in FIG. 4a, a sub 60 is used with a retrievable sliding sleeve 62 such that when stimulation and flow back are completed, the ball activated sliding sleeve can be removed from the sub. This facilitates use of the tubing string containing sub 60 for production. This leaves the ports 17 of the sub open or, alternately, a flow control device 66, such as that shown in FIG. 4b, can be installed in sub 60.

In sub 60, sliding sleeve 62 is secured by means of shear pins 50 to cover ports 17. When sheared out, sleeve 62 can move within sub until it engages against no-go shoulder 68. Sleeve 62 includes a seat 26, glands 54 for seals 52 and a recess 70 for engagement by a retrieval tool (not shown). Since there is no upper shoulder on the sub, the sleeve can be removed by pulling it upwardly, as by use of a retrieval tool on wireline. This opens the tubing string inner bore to facilitate access through the tubing string such as by tools or production fluids. Where a series of these subs are used in a tubing string, the diameter across shoulders 68 should be graduated to permit passage of sleeves therebelow.

Flow control device 66 can be installed in any way in the sub. The flow control device acts to control inflow from the segments in the well through ports 17. In the illustrated embodiment, flow control device 66 includes a running neck 72, a lock section 74 including outwardly biased collet fingers 76 or dogs and a flow control section including a solid cylinder 78 and seals 80a, 80b disposed at either end thereof. Solid cylinder 78 is sized to cover the ports 17 of the sub 60 with seals 80a, 80b disposed above and below, respectively, the ports. Flow control device 66 can be conveyed by wire line or a tubing string such as coil tubing and is installed by engagement of collet fingers 76 in a groove 82 formed in the sub.

As shown in FIG. 5, multiple intervals in a wellbore 112 lined with casing 84 can be treated with fluid using an assembly and method similar to that of FIG. 1a. In a cased wellbore, perforations 86 are formed through the casing to provide access to the formation 10 therebehind. The fluid treatment assembly includes a tubing string 114 with packers 120, suitable for use in cased holes, positioned therealong. Between each set of packers is a ported interval 16 through which flow is controlled by a ball or plug activated sliding sleeve (cannot be seen in this view). Each sleeve has a seat sized to permit staged opening of the sleeves. A blast joint 88 can be provided on the tubing string in alignable position with each perforated section. End 114a includes a sump valve permitting release of sand during production.

In use, the tubing string is run into the well and the packers are placed between the perforated intervals. If blast joints are included in the tubing string, they are preferably positioned at the same depth as the perforated sections. The packers are then set by mechanical or pressure actuation. Once the packers are set, stimulation fluids are then pumped down the tubing string. The packers will divert the fluids to a specific segment of the wellbore. A ball or plug is then pumped to shut off the lower segment of the well and to open a siding sleeve to allow fluid to be forced into the next interval, where packers will again divert fluids into specific segment of the well. The process is continued until all desired segments of the wellbore are stimulated or treated. When completed, the treating fluids can be either shut in or flowed back immediately. The assembly can be pulled to surface or left downhole and produced therethrough.

Referring to FIGS. 6a to 6c, there is shown another embodiment of a fluid treatment apparatus and method according to the present invention. In previously illustrated embodiments, such as FIGS. 1 and 5, each ported interval has included ports about a plane orthogonal to the long axis of the tubing string thus permitting a flow of fluid therethrough which is focused along the wellbore. In the embodiment of FIGS. 6a to 6b, however, an assembly for fluid treatment by sprinkling is shown, wherein fluid supplied to an isolated interval is introduced in a distributed fashion along a length of that interval. The assembly includes a tubing string 214 and ported intervals 216a, 216b, 216c each including a plurality of ports 217 spaced along the long axis of the tubing string. Packers 220a, 220b are provided between each interval to form an isolated segment in the wellbore 212.

While the ports of interval 216c are open during run in of the tubing string, the ports of intervals 216b and 216a, are closed during run in and sleeves 222a and 222b are mounted within the tubing string and actuatable to selectively open the ports of intervals 216a and 216b, respectively. In particular, in FIG. 6a, the position of sleeve 222b is shown when the ports of interval 216b are closed. The ports in any of the intervals can be size restricted to create a selected pressure drop therethrough, permitting distribution of fluid along the entire ported interval.

Once the tubing string is run into the well, stage 1 is initiated wherein stimulation fluids are pumped into the end section of the well to ported interval 216c to begin the stimulation treatment (FIG. 6a). Fluids will be forced to the lower section of the well below packer 220b. In this illustrated embodiment, the ports of interval 216c are normally open size restricted ports, which do not require opening for stimulation fluids to be jetted therethrough. However it is to be understood that the ports can be installed in closed configuration, but opened once the tubing is in place.

When desired to stimulate another section of the well (FIG. 6b), a ball or plug (not shown) is pumped by fluid pressure, arrow P, down the well and will seat in a selected sleeve 222b sized to accept the ball or plug. The pressure of the fluid behind the ball will push the cutter sleeve against any force, such as a shear pin, holding the sleeve in position and down the tubing string, arrow S. As it moves down, it will open the ports of interval 216b as it passes by them in its segment of the tubing string. Sleeve 222b reaches eventually stops against a stop means. Since fluid pressure will hold the ball in the sleeve, this effectively shuts off the lower segment of the well including previously treated interval 216c. Treating fluids will then be forced through the newly opened ports. Using limited entry or a flow regulator, a tubing to annulus pressure drop insures distribution. The fluid will be isolated to treat the formation between packers 220a and 220b.

After the desired volume of stimulation fluids are pumped, a slightly larger second ball or plug is injected into the tubing and pumped down the well, and will seat in sleeve 222a which is selected to retain the larger ball or plug. The force of the moving fluid will push sleeve 222a down the tubing string and as it moves down, it will open the ports in interval 216a. Once the sleeve reaches a desired depth as shown in FIG. 6c, it will be stopped, effectively shutting off the lower segment of the well including previously treated intervals 216b and 216c. This process can be repeated a number of times until most or all of the wellbore is treated in stages, using a sprinkler approach over each individual section.

The above noted method can also be used for wellbore circulation to circulate existing wellbore fluids (drilling mud for example) out of a wellbore and to replace that fluid with another fluid. In such a method, a staged approach need not be used, but the sleeve can be used to open ports along the length of the tubing string. In addition, packers need not be used as it is often desirable to circulate the fluids to surface through the wellbore.

The sleeves 222a and 222b can be formed in various ways to cooperate with ports 217 to open those ports as they pass through the tubing string.

With reference to FIG. 7, a tubing string 214 according to the present invention is shown including a movable sleeve 222 and a plurality of normally closed ports 217 spaced along the long axis x of the string. Ports 217 each include a pressure holding, internal cap 223. Cap 223 extends into the bore 218 of the tubing string and is formed of shearable material at least at its base, so that it can be sheared off to open the port. Cap 223 can be, for example, a cobe sub or other modified subs. The caps are selected to be resistant to shearing by movement of a ball therepast.

Sleeve 222 is mounted in the tubing string and includes an outer surface having a diameter to substantially conform to the inner diameter of, but capable of sliding through, the section of the tubing string in which the sleeve is selected to act. Sleeve 222 is mounted in tubing string by use of a shear pin 250 and has a seat 226 formed on its inner facing surface to accept a selected sized ball 224, which when fluid pressure is applied therebehind, arrow P, will shear pin 250 and drive the sleeve, with the ball seated therein along the length of the tubing string until stopped by shoulder 246.

Sleeve 222 includes a profiled leading end 247 which is selected to shear or cut off the protective caps 223 from the ports as it passes, thereby opening the ports. Shoulder 246 is preferably spaced from the ports 217 with consideration as to the length of sleeve 222 such that when the sleeve is stopped against the shoulder, the sleeve does not cover any ports.

Sleeve 222 can include seals 252 to seal between the interface of the sleeve and the tubing string, where it is desired to seal off fluid flow therebetween.

Caps can also be used to close off ports disposed in a plane orthogonal to the long axis of the tubing string, if desired.

Referring to FIG. 8, there is shown another tubing string 314 according to the present invention. The tubing string includes a movable sleeve 322 and a plurality of normally closed ports 317a, 317b spaced along the long axis x of the string. Sleeve 322, while normally mounted by shear 350, can be moved (arrows S), by fluid pressure created by seating of ball 324 therein, along the tubing string until it butts against a shoulder 346.

Ports 317a, 317b each include a sliding sleeve 325a, 325b, respectively, in association therewith. In particular, with reference to port 317a, each port includes an associated sliding sleeve disposed in a cylindrical groove, defined by shoulders 327a, 327b about the port. The groove is formed in the inner wall of the tubing string and sleeve 325a is selected to have an inner diameter that is generally equal to the tubing string inner diameter and an outer diameter that substantially conforms to but is slidable along the groove between shoulders 327a, 327b. Seals 329 are provided between sleeve 325a and the groove, such that fluid leakage therebetween is substantially avoided.

Sliding sleeves 325a are normally positioned over their associated port 317a adjacent shoulder 327a, but can be slid along the groove until stopped by shoulder 327b. In each case, the shoulder 327b is spaced from its port 317a with consideration as to the length of the associated sleeve so that when the sleeve is butted against shoulder 327b, the port is open to allow at least some fluid flow therethrough.

The port-associated sliding sleeves 325a, 325b are each formed to be engaged and moved by sleeve 322 as it passes through the tubing string from its pinned position to its position against shoulder 346. In the illustrated embodiments, sleeves 325a, 325b are moved by engagement of outwardly biased dogs 351 on the sleeve 322. In particular, each sleeve 325a, 325b includes a profile 353a, 353b into which dogs 351 can releasably engage. The spring force of dogs and the configuration of profile 353 are together selected to be greater than the resistance of sleeve 325 moving within the groove, but less than the fluid pressure selected to be applied against ball 324, such that when sleeve 322 is driven through the tubing string, it will engage against each sleeve 325a to move it away from its port 317a and against its associated shoulder 327b. However, continued application of fluid pressure will drive the dogs 351 of the sleeve 322 against their spring force to remove the sleeve from engagement with a first port-associated sleeve 325a, along the tubing string 314 and into engagement with the profile 353b of the next-port associated sleeve 325b and so on, until sleeve 322 is stopped against shoulder 346.

Referring to FIGS. 9a to 9c, the wellbore fluid treatment assemblies described above with respect to FIGS. 1a and 6a to can also be combined with a series of ball activated sliding sleeves and packers to allow some segments of the well to be stimulated using a sprinkler approach and other segments of the well to be stimulated using a focused fracturing approach.

In this embodiment, a tubing or casing string 414 is made up with two ported intervals 316b, 316d formed of subs having a series of size restricted ports 317 therethrough and in which the ports are each covered, for example, with protective pressure holding internal caps and in which each interval includes a movable sleeve 322b, 322d with profiles that can act as a cutter to cut off the protective caps to open the ports. Other ported intervals 16a, 16c include a plurality of ports 17 disposed about a circumference of the tubing string and are closed by a ball or plug activated sliding sleeves 22a, 22c. Packers 420a, 420b, 420c, 420d are disposed between each interval to create isolated segments along the wellbore 412.

Once the system is run into the well (FIG. 9a), the tubing string can be pressured to set some or all of the open hole packers. When the packers are set, stimulation fluids are pumped into the end section of the tubing to begin the stimulation treatment, identified as stage 1 sprinkler treatment in the illustrated embodiment. Initially, fluids will be forced to the lower section of the well below packer 420d. In stage 2, shown in FIG. 9b, a focused frac is conducted between packers 420c and 420d; in stage 3, shown in FIG. 9c, a sprinkler approach is used between packers 420b and 420c; and in stage 4, shown in FIG. 9d, a focused frac is conducted between packers 420a and 420b

Sections of the well that use a “sprinkler approach”, intervals 316b, 316d, will be treated as follows: When desired, a ball or plug is pumped down the well, and will seat in one of the cutter sleeves 322b, 322d. The force of the moving fluid will push the cutter sleeve down the tubing string and as it moves down, it will remove the pressure holding caps from the segment of the well through which it passes. Once the cutter reaches a desired depth, it will be stopped by a no-go shoulder and the ball will remain in the sleeve effectively shutting off the lower segment of the well. Stimulation fluids are then pumped as required.

Segments of the well that use a “focused stimulation approach”, intervals 16a, 16c, will be treated as follows: Another ball or plug is launched and will seat in and shift open a pressure shifted sliding sleeve 22a, 22c, and block off the lower segment(s) of the well. Stimulation fluids are directed out the ports 17 exposed for fluid flow by moving the sliding sleeve.

Fluid passing through each interval is contained by the packers 420a to 420d on either side of that interval to allow for treating only that section of the well.

The stimulation process can be continued using “sprinkler” and/or “focused” placement of fluids, depending on the segment which is opened along the tubing string.

Claims

1. A method for fluid treating a formation, the method comprising: positioning a tubing string in a non-vertical section of a borehole in the formation, the tubing string comprising: a first port configured to pass fluid from an inner bore of the tubing string to outside the tubing string,a second port configured to pass fluid from the inner bore of the tubing string to outside the tubing string, the second port being down hole from the first port,a third port configured to pass fluid from the inner bore of the tubing string to outside the tubing string, the third port being down hole from the second port,a first sliding sleeve having a seat with a first diameter, the first sliding sleeve being moveable between (i) a closed port position wherein the first sliding sleeve covers the first port and allows fluid to pass down hole of the seat of the first sliding sleeve and (ii) an open port position wherein the first sliding sleeve exposes the first port to the inner bore of the tubing string, the first sliding sleeve being actuatable, by a first fluid conveyed sealing device, to move from the closed port position to the open port position,a second sliding sleeve having a seat with a second diameter smaller than the first diameter, the second sliding sleeve being moveable between (i) a closed port position wherein the second sliding sleeve covers the second port and allows fluid to pass down hole of the seat of the second sliding sleeve and (ii) an open port position wherein the second sliding sleeve exposes the second port to the inner bore of the tubing string, the second sliding sleeve being actuatable, by a second fluid conveyed sealing device, to move from the closed port position to the open port position, anda third sliding sleeve configured to move by fluid pressure within the inner bore of the tubing string, without requiring engagement with any sealing device, between (i) a closed port position wherein the third sliding sleeve covers the third port and (ii) an open port position wherein the third sliding sleeve exposes the third port to the inner bore of the tubing string;applying a sliding-sleeve-actuating fluid pressure within the inner bore of the tubing string such that the third sliding sleeve moves, without requiring engagement with any sealing device, from the closed port position to the open port position, thereby permitting fluid flow through the tubing string;pumping fluid from the inner bore of the tubing string through the third port;conveying the second fluid conveyed sealing device through the inner bore of the tubing string such that the second fluid conveyed sealing device passes the first sliding sleeve and lands in and seals against the seat of the second sliding sleeve thereby sealing against fluid flow down hole of the seat of the second sliding sleeve and moving the second sliding sleeve to the open port position exposing the second port to the inner bore of the tubing string;pumping fluid through the second port to treat a first portion of the formation;conveying the first fluid conveyed sealing device through the inner bore of the tubing string such that the first fluid conveyed sealing device lands in and seals against the seat of the first sliding sleeve thereby sealing against fluid flow down hole of the seat of the first sliding sleeve and moving the first sliding sleeve to the open port position exposing the first port to the inner bore of the tubing string; andpumping fluid through the first port to treat a second portion of the formation.

2. The method of claim 1, wherein the pumping fluid through the second port to treat the first portion of the formation comprises pumping fracturing fluid through the second port to fracture the first portion of the formation; wherein the pumping fluid through the first port to treat the second portion of the formation comprises pumping fracturing fluid through the first port to fracture the second portion of the formation; and wherein the pumping the fluid through the third port comprises pumping fracturing fluid through the third port to fracture a third portion of the formation.

3. The method of claim 2, wherein the third port is the down-hole-most port of the tubing string through which fracturing fluid is pumped.

4. The method of claim 3, wherein the third port is adjacent a down hole end of the tubing string.

5. The method of claim 2, wherein the fracturing fluid comprises proppants.

6. The method of claim 5, wherein the proppants comprise sand.

7. The method of claim 5, wherein the proppants comprise bauxite.

8. The method of claim 2, wherein the first fluid conveyed sealing device comprises a first ball, and wherein the second fluid conveyed sealing device comprises a second ball.

9. The method of claim 2, further comprising: setting a first packer of the tubing string, the first packer being up hole from the first port;setting a second packer of the tubing string, the second packer being between the first port and the second port; andsetting a third packer of the tubing string, the third packer being down hole from the second port,wherein the first, second, and third packers, when set, create a first annular segment between the first and second packers, a second annular segment between the second and third packers, and a third annular segment down hole of the third packer,wherein the first annular segment is substantially isolated from fluid communication with the second annular segment by the second packer,wherein the second annular segment is substantially isolated from fluid communication with the third segment by the third packer, andwherein the first, second, and third annular segments provide access to the formation.

10. The method of claim 9, wherein the first, second, and third packers each seal against a corresponding open hole and uncased portion of the borehole.

11. The method of claim 10, wherein at least one of the first, second, and third packers comprises a solid element that extrudes when the packer is set.

12. The method of claim 11, wherein the at least one of the first, second, and third packers is hydraulically actuated.

13. The method of claim 12, further comprising applying a packer-setting fluid pressure within the inner bore of the tubing string before the applying the sliding-sleeve-actuating fluid pressure within the inner bore, thereby setting at least one of the first, second, and third packers.

14. The method of claim 13, wherein the packer-setting fluid pressure is less than the sliding-sleeve-actuating fluid pressure.

15. The method of claim 1, further comprising: setting a first packer of the tubing string, the first packer being up hole from the first port;setting a second packer of the tubing string, the second packer being between the first port and the second port; andsetting a third packer of the tubing string, the third packer being down hole from the second port,wherein the first, second, and third packers, when set, create a first annular segment between the first and second packers, a second annular segment between the second and third packers, and a third annular segment down hole of the third packer,wherein the first annular segment is substantially isolated from fluid communication with the second annular segment by the second packer,wherein the second annular segment is substantially isolated from fluid communication with the third segment by the third packer, andwherein the first, second, and third annular segments provide access to the formation.

16. The method of claim 15, wherein the first, second, and third packers each seal against a corresponding open hole and uncased portion of the borehole.

17. The method of claim 16, wherein at least one of the first, second, and third packers comprises a solid element that extrudes when the packer is set; and wherein the at least one of the first, second, and third packers is hydraulically actuated.

18. The method of claim 17, further comprising applying a packer-setting fluid pressure within the inner bore of the tubing string before applying the sliding-sleeve-actuating fluid pressure within the inner bore, and wherein the packer-setting fluid pressure is less than the sliding-sleeve-actuating fluid pressure.

19. A tubing string for fluid treating a formation, comprising: a first port configured to pass fluid from an inner bore of the tubing string to outside the tubing string;a second port configured to pass fluid from the inner bore of the tubing string to outside the tubing string;a third port configured to pass fluid from the inner bore of the tubing string to outside the tubing string;a first sliding sleeve having a seat with a first diameter, the first sliding sleeve being moveable between (i) a closed port position wherein the first sliding sleeve covers the first port and allows fluid to pass down hole of the seat of the first sliding sleeve and (ii) an open port position wherein the first sliding sleeve exposes the first port to the inner bore of the tubing string, the first sliding sleeve being actuatable, by a first fluid conveyed sealing device, to move from the closed port position to the open port position;a second sliding sleeve having a seat with a second diameter smaller than the first diameter, the second sliding sleeve being moveable between (i) a closed port position wherein the second sliding sleeve covers the second port and allows fluid to pass down hole of the seat of the second sliding sleeve and (ii) an open port position wherein the second sliding sleeve exposes the second port to the inner bore of the tubing string, the second sliding sleeve being actuatable, by a second fluid conveyed sealing device, to move from the closed port position to the open port position; anda third sliding sleeve configured to move by fluid pressure within the inner bore of the tubing string, without requiring engagement with any sealing device, between (i) a closed port position wherein the third sliding sleeve covers the third port and (ii) an open port position wherein the third sliding sleeve exposes the third port to the inner bore of the tubing string, thereby permitting fluid flow through the tubing string.

20. The tubing string of claim 19, wherein the third sliding sleeve comprises a fluid actuated piston.

21. The tubing string of claim 19, wherein the first, second, and third ports are configured to pass fracturing fluid comprising proppants.

22. The tubing string of claim 21, wherein the proppants comprise sand.

23. The tubing string of claim 21, wherein the proppants comprise bauxite.

24. The tubing string of claim 21, wherein the third port is the down-hole-most port of the tubing string, is configured to pass fracturing fluid, and is adjacent a down hole end of the tubing string.

25. The tubing string of claim 21, further comprising: a first packer up hole from the first port;a second packer between the first port and the second port; anda third packer down hole from the second port,wherein the first, second, and third packers are configured, when set, to create a first annular segment between the first and second packers, a second annular segment between the second and third packers, and a third annular segment down hole of the third packer,wherein the first annular segment is substantially isolated from fluid communication with the second annular segment by the second packer,wherein the second annular segment is substantially isolated from fluid communication with the third segment by the third packer,wherein the first, second, and third annular segments provide access to the formation, andwherein at least one of the first, second, and third packers comprises a solid element that extrudes when the respective packer is set.

26. The tubing string of claim 25, wherein each of the first, second, and third packers is configured to seal against an open hole and uncased section of the borehole.

27. The tubing string of claim 26, wherein at least one of the first, second, and third packers is configured to be set by application of a packer-setting fluid pressure within the inner bore of the tubing string; wherein the third sliding sleeve is configured to move from the closed port position to the open port position by application of a sliding-sleeve-actuating pressure within the inner bore of the tubing string; and wherein the packer-setting fluid pressure is less than the sliding-sleeve-actuating fluid pressure.

28. The tubing string of claim 19, further comprising: a first packer up hole from the first port;a second packer between the first port and the second port; anda third packer down hole from the second port,wherein at least one of the first, second, and third packers comprises a solid element that extrudes when the respective packer is set,wherein each of the first, second, and third packers is configured to seal against an open hole and uncased section of the borehole,wherein the at least one of the first, second, and third packers is configured to set by application of a packer-setting fluid pressure within the inner bore of the tubing string; and wherein the third sliding sleeve is configured to move from the closed port position to the open port position by application of a sliding-sleeve-actuating pressure within the inner bore of the tubing string, andwherein the packer-setting fluid pressure is less than the sliding-sleeve-actuating fluid pressure.

29. A method for fracturing a formation, the method comprising: positioning a tubing string in a non-vertical section of a borehole in the formation, the tubing string comprising: a first port configured to pass fracturing fluid from an inner bore of the tubing string to outside the tubing string,a second port configured to pass fracturing fluid from the inner bore of the tubing string to outside the tubing string,a third port configured to pass fracturing fluid from the inner bore of the tubing string to outside the tubing string,a first sliding sleeve having a seat with a first diameter, the first sliding sleeve being moveable between (i) a closed port position wherein the first sliding sleeve covers the first port and allows fluid to pass down hole of the seat of the first sliding sleeve and (ii) an open port position wherein the first sliding sleeve exposes the first port to the inner bore of the tubing string, the first sliding sleeve being actuatable, by a first fluid conveyed ball, to move from the closed port position to the open port position,a second sliding sleeve having a seat with a second diameter smaller than the first diameter, the second sliding sleeve being moveable between (i) a closed port position wherein the second sliding sleeve covers the second port and allows fluid to pass down hole of the seat of the second sliding sleeve and (ii) an open port position wherein the second sliding sleeve exposes the second port to the inner bore of the tubing string, the second sliding sleeve being actuatable, by a second fluid conveyed ball, to move from the closed port position to the open port position,a third sliding sleeve configured to move by fluid pressure within the inner bore of the tubing string, without requiring engagement with any sealing device, between (i) a closed port position wherein the third sliding sleeve covers the third port and (ii) an open port position wherein the third sliding sleeve exposes the third port to the inner bore of the tubing string,a first hydraulically actuatable packer up hole from the first port,a second hydraulically actuatable packer between the first port and the second port, anda third hydraulically actuatable packer down hole from the second port;setting the first packer;setting the second packer;setting the third packer, wherein the first, second, and third packers, when set, create a first annular segment between the first and second packers, a second annular segment between the second and third packers, and a third annular segment down hole of the third packer,the first annular segment is substantially isolated from fluid communication with the second annular segment by the second packer,the second annular segment is substantially isolated from fluid communication with the third segment by the third packer,the first, second, and third annular segments provide access to the formation,at least one of the first, second, and third packers comprises a solid element that extrudes when the respective packer is set;applying a sliding-sleeve-actuating fluid pressure within the inner bore of the tubing string such that the third sliding sleeve moves from the closed port position to the open port position without the third sliding sleeve engaging any sealing device;pumping fracturing fluid comprising proppants from the inner bore of the tubing string through the third port to fracture a first portion of the formation;conveying the second fluid conveyed ball through the inner bore of the tubing string such that the second fluid conveyed ball passes the first sliding sleeve and lands in and seals against the seat of the second sliding sleeve thereby sealing against fluid flow down hole of the seat of the second sliding sleeve and moving the second sliding sleeve to the open port position exposing the second port to the inner bore of the tubing string;pumping fracturing fluid comprising proppants through the second port to fracture a second portion of the formation;conveying the first fluid conveyed ball through the inner bore of the tubing string such that the first fluid ball lands in and seals against the seat of the first sliding sleeve thereby sealing against fluid flow down hole of the seat of the first sliding sleeve and moving the first sliding sleeve to the open port position exposing the first port to the inner bore of the tubing string; andpumping fracturing fluid comprising proppants through the first port to fracture a third portion of the formation.

30. The method of claim 29, further comprising, before the applying the sliding-sleeve-actuating fluid pressure within the inner bore, applying a packer-setting fluid pressure within the inner bore of the tubing string to set the first, second, and third packers; wherein the packer-setting fluid pressure is less than the sliding-sleeve-actuating fluid pressure; andwherein the first, second, and third packers each seal against a corresponding open hole and uncased portion of the borehole.