Patent application title: Multistage Production System Incorporating Valve Assembly With Collapsible or Expandable C-Ring
Raymond Hofman (Midland, TX, US)
Raymond Hofman (Midland, TX, US)
William Sloane Muscroft (Midland, TX, US)
IPC8 Class: AE21B3406FI
Class name: Wells processes operating valve, closure, or changeable restrictor in a well
Publication date: 2013-03-21
Patent application number: 20130068475
A valve assembly, and related system and method, with an annular sleeve
having an inner surface with a diameter, a first cylindrical outer
surface, and a plurality of openings extending between the inner surface
and the first cylindrical outer surface. The annular sleeve includes a
second cylindrical outer surface having a different diameter than the
first cylindrical outer surface. A first C-ring having a body with a
seating surface, opposing terminal ends, and an outer diameter extending
from the body is at least partially within the inner surface of the
sleeve. A coil spring is positioned around a portion of the sleeve and in
an annular space at least partially defined by an annular body and the
second cylindrical outer surface.
1. A valve assembly for use in a subterranean well for oil, gas, or other
hydrocarbons, said valve assembly comprising: an annular sleeve having an
inner surface with a diameter, a first cylindrical outer surface, and a
plurality of openings extending between said inner surface and said first
cylindrical outer surface, wherein said annular sleeve further comprises
a second cylindrical outer surface having a different diameter than the
first cylindrical outer surface. a first C-ring having a body with a
seating surface, opposing terminal ends, and an outer diameter extending
from the body, wherein the first C-ring is at least partially within the
inner surface of the sleeve; and a coil spring positioned around a
portion of the sleeve and in an annular space at least partially defined
by an annular body and the second cylindrical outer surface.
2. The valve assembly of claim 1 wherein said first C-ring is aligned with a circumferential groove formed in the inner surface of the sleeve.
3. The valve assembly of claim 1 further comprising a plurality of dogs positioned between radially outward of the outer diameter.
4. The valve assembly of claim 1 further comprising a second seating surface having a second seating diameter.
5. The valve assembly of claim 4 wherein the second seating surface is formed in a ball seat.
6. The valve assembly of claim 4 wherein the second seating surface is formed in a second C-ring having a body, opposing terminal ends, and an outer diameter extending from the body, wherein the second C-ring is at least partially within the inner surface of the sleeve.
7. The valve assembly of claim 6 wherein when one of said first C-ring and said second C-ring is compressed, the other of said first C-ring and said second is uncompressed.
8. The valve assembly of claim 6 wherein the diameter of the seating surface of the first C-ring in a compressed state is smaller than the diameter of the seating surface of the second seating surface; and wherein the diameter of the seating surface of the first C-ring in an uncompressed state is larger than the diameter of the seating surface of the second seating surface.
9. The valve assembly of claim 6 wherein one of the first C-ring and the second C-ring is compressed and the other of the first C-ring and the second C-rings is uncompressed.
10. The valve assembly of claim 1 further comprising at least one first mounting element having a first diameter and at least one mounting element having a second diameter, wherein the sleeve is movable between a first position wherein the openings are aligned with the at least one first mounting element to the first C-ring and a second position wherein the openings are aligned with the at least one second mounting element.
11. A system of valve assemblies for use in a subterranean well for oil, gas, or other hydrocarbons, said valve assembly comprising: a first set of at least two tools, wherein each tool of the first set of tools comprises a C-ring sized to be actuated by a first resistor element having a first size and movable within the tool interior between a first position in which the C-ring is compressed and a second position in which the C-ring is uncompressed; a second set of at least two tools, wherein each tool of the second set of tools comprises a C-ring sized to be actuated by a second resistor element having a second size that is smaller than the first size, and is further movable within the tool interior between a first position in which the C-ring is compressed and a second position in which the C-ring is uncompressed; a first static seat tool positioned between the first set of tools and the second set of tools, said first static seat having seating surface sized to engage with the first resistor element and not engage with the second resistor element; and wherein each tool of said first set of tools and said second set of tools comprises an annular sleeve at least partially encircling the corresponding C-ring and a spring positioned in an annular space partially defined by the corresponding sleeve and operative to exert an expansive force against the sleeve to resist a force applied to the seat by an resistor element of corresponding ball size.
12. A method for treating a well for oil, gas or other hydrocarbons, the method comprising: causing a first resistor element to pass through a first set of tools and a first static seat to at least one compressed C-ring of a second set of tools; seating the first resistor element to against the seating surface of the at least one compressed C-ring, wherein the at least one compressed C-ring is associated with at least one sleeve in a first position; causing a pressure differential of a first pressure value across the first resistor element, said pressure value greater than an opposing expansive force of at least one spring associated with the at least one compressed C-ring to move the at least one sleeve to a second position wherein the at least one C-ring becomes uncompressed; causing the first resistor element to flow through the at least one C-ring; and returning the at least one sleeve to the first position using an expansive force of the at least one spring.
CROSS-REFERENCES TO RELATED APPLICATIONS
 This original nonprovisional application claims the benefit of U.S. Provisional Application Ser. No. 61/453,288, filed Mar. 16, 2011 entitled "Multistage Production System Incorporating Valve assembly With Collapsible or Expandable Split Ring," and U.S. Provisional Application 61/475,333 filed Apr. 14, 2011 entitled "Valve Assembly and System for Producing Hydrocarbons", each of which is incorporated by reference herein.
STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT
 Not applicable.
BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The described embodiments and claimed invention relate to a tool for sequentially engaging and releasing a restrictor element onto and from its corresponding valve seat, as well as systems and methods incorporating such a tool for producing hydrocarbons from multiple stages in a hydrocarbon production well.
 2. Background of the Art
 In hydrocarbon wells, tools incorporating valve assemblies having a restrictor element such as a ball or dart and a seat element such as a ball seat or dart seat have been used for a number of different operations. Such valve assemblies prevent the flow of fluid past the assembly and, with the application of a desired pressure, can actuate one or more tools associated with the assembly.
 One use for such remotely operated valve assemblies is in fracturing (or "fracing"), a technique used by well operators to create and/or extend one or more cracks, called "fractures" from the wellbore deeper into the surrounding formation in order to improve the flow of formation fluids into the wellbore. Fracing is typically accomplished by injecting fluids from the surface, through the wellbore, and into the formation at high pressure to create the fractures and to force them to both open wider and to extend further. In many case, the injected fluids contain a granular material, such as sand, which functions to hold the fracture open after the fluid pressure is reduced.
 Fracing multiple-stage production wells requires selective actuation of valve assemblies, such as fracing sleeves, to control fluid flow from the tubing string to the formation. For example, U.S. Published Application No. 2008/0302538, entitled Cemented Open Hole Selective Fracing System and which is incorporated by reference herein, describes one system for selectively actuating a fracing sleeve that incorporates a shifting tool. The tool is run into the tubing string and engages with a profile within the interior of the valve. An inner sleeve may then be moved to an open position to allow fracing or to a closed position to prevent fluid flow to or from the formation.
 That same application describes a system using multiple valve assemblies which incorporate ball-and-seat seals, each having a differently-sized ball seat and corresponding ball. Frac valves connected to ball and seat seals do not require the running of a shifting tool thousands of feet into the tubing string and are simpler to actuate than frac valves requiring such shifting tools. Such ball and seat seals are operated by placing an appropriately sized ball into the well bore and bringing the ball into contact with a corresponding ball seat. The ball engages on a sealing section of the ball seat to block the flow of fluids past the valve assembly. Application of pressure to the valve assembly causes the valve assembly to "shift", opening the frac sleeve.
 Some valve assemblies are selected for tool actuation by the size of ball or other restrictor element introduced into the well. If the well or tubing string contains multiple ball seats, the ball must be small enough that it will not seal against any of the ball seats it encounters prior to reaching the desired ball seat. For this reason, the smallest ball to be used for the planned operation is the first ball placed into the well or tubing and the smallest ball seat is positioned in the well or tubing the furthest from the wellhead. Thus, these traditional valve assemblies limit the number of valves that can be used in a given tubing string because each ball size is only able to actuate a single valve. Further, systems using these valve assemblies require each ball to be at least 0.125 inches larger than the immediately preceding ball. Therefore, the size of the liner restricts the number of valve assemblies with differently-sized ball seats. In other words, because a ball must be larger than its corresponding ball seat and smaller than the ball seats of all upwell valves, each ball can only seal against a single ball seat and, if desired, actuate one tool.
 The valve assembly provides a method for sequentially sealing multiple valve seats with a single restrictor element and, where desired, actuating tools associated with the valve assembly. One embodiment allows multiple balls of the same size to actuate tools in sequential stages.
 The valve assembly described herein comprises a C-ring (also called a split ring) having a body with a seating surface, opposing terminal ends, and an external diameter extending radially from the body. The C-ring may be compressed such that terminal ends of the C-ring are in contact. In addition, the C-ring may be in an uncompressed state wherein the terminal ends are not in contact. The valve assembly further comprises one or more mounting elements to engage the outer diameter of the split ring. Engagement of mounting elements with the outer diameter causes the split ring to expand or contract.
 Valve assemblies as described herein may further comprise a sleeve contained within a tubular housing, the sleeve having an inner surface, an outer surface, and a plurality of openings extending between said inner and outer surfaces. The openings are aligned to engage with the external diameter of the split ring. The tubular housing may have one or more mounting elements aligned within the openings in the sleeve, such that the mounting elements may engage the external diameter of the split ring when the sleeve is located at a desired position in the housing.
BRIEF DESCRIPTION OF THE DRAWINGS
 FIG. 1 is a side partial sectional view of a preferred embodiment valve assembly with an inner sleeve in an upwell first position.
 FIG. 2 is a front elevation of the C-ring of the preferred embodiment shown in FIG. 1.
 FIG. 3 is a sectional view through line 3-3 in FIG. 1.
 FIG. 4 is a side partial sectional view of a preferred embodiment valve assembly shown in FIG. 1 with the inner sleeve in a downwell second position.
 FIG. 5 is a sectional view through line 5-5 of FIG. 4.
 FIG. 6 is a side partial sectional view of the preferred embodiment with the inner sleeve in an intermediate position between the first and second positions described with reference to FIG. 1 and FIG. 4, respectively.
 FIG. 7 is a side sectional elevation of a system incorporating multiple tools having the features of the preferred embodiment.
 FIGS. 8A & 8B illustrate an alternative embodiment showing a valve assembly with two seating elements
 When used with reference to the figures, unless otherwise specified, the terms "upwell," "above," "top," "upper," "downwell," "below," "bottom," "lower," and like terms are used relative to the direction of normal production and/or flow of fluids and or gas through the tool and wellbore. Thus, normal production results in migration through the wellbore and production string from the downwell to upwell direction without regard to whether the tubing string is disposed in a vertical wellbore, a horizontal wellbore, or some combination of both. Similarly, during treatment of a well, which may include a fracturing, or "fracing," process, fluids move from the surface in the downwell direction to the portion of the tubing string within the formation to be treated.
 FIG. 1 shows a preferred embodiment tool 20, which comprises a housing 22 connected to a bottom connection 24 at a threaded section 26. The housing 22 has a plurality of radially-oriented, circumferentially-aligned ports 28 providing communication paths to and from the exterior of the tool.
 The housing 22 has a first cylindrical inner surface 30 having a first inner diameter, a second cylindrical inner surface 32 located downwell of the first inner surface 30 and having a second inner diameter that is greater than the first inner diameter, and a third cylindrical inner surface 34 having a third inner diameter that is greater than the second cylindrical inner surface 32. The first inner surface 30 is longitudinally adjacent to the second inner surface 32, forming a downwell-facing shoulder having an annular shoulder surface 38. The second and third inner surfaces 32, 34 are separated by a partially-conical surface 40.
 The bottom connection 24 includes a first cylindrical inner surface 42 having a first inner diameter and a second cylindrical inner surface 44 having a second inner diameter. The first and second inner cylindrical surfaces 42, 44 are separated by an inner partially-conical inner surface 46. An annular upper end surface 47 is adjacent to the first inner surface 42.
 The tool 20 comprises an annular sleeve 48 nested radially within the housing 22 and positioned downwell of the shoulder 38. The sleeve 48 has an upper outer surface 50 with a first outer diameter and a second outer surface 52 with a second outer diameter less than the first inner diameter. The first outer surface 50 and second outer surface 52 are separated by an annular shoulder surface 54. The sleeve 48 further comprises a cylindrical inner surface 56 that extends between annular upper and lower end surfaces 58, 60 of the sleeve 48.
 In FIG. 1, the sleeve 48 is in a first position radially between the plurality of housing ports 28 and the center of the flowpath. In this position, the annular sleeve 48 inhibits fluid flow between the flowpath and the exterior of the tool. The sleeve 48 extends between the shoulder 38 of the housing and the first inner surface 42 of the bottom connection 24.
 The valve assembly may further comprise a guide element to position the split ring in the desired location. The guide element in the embodiment of FIG. 1 is a spring 64 residing in an annular spring return space 62. The annular spring return space 62 is partially defined by the second outer surface 52 of the sleeve 48 and the third inner surface 34 of the housing 22. The spring return space is further defined by the upper end surface 47 of the bottom connection 24, the partially-conical surface 40 of the housing 22, and the shoulder surface 54 and first outer surface 50 of the sleeve 48.
 In the embodiment illustrated by the figures, the C-ring 70 is positioned within the annular sleeve 48 between the upper end surface 58 and the shoulder surface 54. The C-ring 70 fits into a groove formed in the inner surface 56 of the shifting sleeve 48. The groove is sufficiently deep to allow the C-ring seating surface to expand to the desired maximum diameter. In some embodiments, the desired maximum diameter may be as large as or larger than the inner diameter of the shifting sleeve. Those of skill in the art will appreciate that, in embodiments in which the C-ring activates a sleeve or other valve assembly, the C-ring 70 may be positioned at any point along the sleeve or tool, or above or below the sleeve, provided that the C-ring and the sleeve or other tool are connected such that sufficient pressure applied to the C-ring will slide the sleeve in relation to the inner housing or otherwise activate the tool.
 The C-ring 70 has an inner surface 74 an outer surface 76 defining the outer perimeter of the C-ring, and a seating surface 72 engagable with a restrictor element having a corresponding size. In the illustrated embodiment, the C-ring 70 is held in a radially compressed state by the first inner surface 50 of the housing 22.
 FIG. 2 shows a front elevation of one embodiment of the C-ring 70 in a normal uncompressed state. In this embodiment, the outer surface 76 of the C-ring 70 is castellated with a plurality of radial protrusions 78, said radial protrusions defining the outer diameter of the C-ring. The circumference of the outer surface of the C-ring 70 may be larger than the circumference of inner surface 56 of the sleeve 48. The C-ring 70 has a machined slot 80 forming terminal ends 82. The slot 80 shown in the illustrative figures is within a protrusion 78, but the slot 80 may be formed at any point along the C-ring and does not have to be formed in a protrusion 78.
 Referring to the embodiment in FIG. 3, each of the radial protrusions 78 of the illustrated C-ring 70 is aligned with and extends through an opening 84 in the sleeve 48 between the first outer surface 50 and the inner surface 56. When the C-ring 70 is upwell of the partially-conical shoulder 40 of the housing 22, the C-ring 70 has the operating diameter shown in FIG. 3 and terminal ends 82 of C-ring 70 are in contact to form the seat defined by the seating surface 72. An associated ball may thereafter seat against the seating surface 72 and a pressure differential created across the ball to move the sleeve 48 in the downwell direction.
 FIGS. 4-5 show the tool 20 with the sleeve 48 in a second position, which is downwell of the first position in one preferred embodiment. The upper end surface 58 of the sleeve 48 has moved past the ports 28, allowing fluid flow therethrough between the flowpath and the exterior of the tool 20. The coil spring 64 is under compression between the sleeve 48 and the bottom connection 24, with the upper end coil 66 of the spring 64 in contact with the sleeve shoulder 54 and the spring lower end 68 is in contact with the upper end surface 47 of the bottom connection 24. In this position, the spring 64 exerts an expansive force to urge the sleeve 48 in the upwell direction relative to the bottom connection 24.
 Referring to FIG. 5, the C-ring 70 is positioned adjacent to the third inner surface 34. Because the third inner surface 34 has a larger diameter than the second inner surface 32, the C-ring 70 radially expands towards its uncompressed shape shown in FIG. 2. The protrusions 78 extend past the outer surface 50 of the sleeve 48, opening the seating surface 72 and allowing the associated restrictor element to pass through the C-ring 70, after which the spring 64 pushes against the sleeve shoulder 54 to move the sleeve 48 upwell toward the first position shown in FIG. 1. Movement of the sleeve 48 past the position shown in FIG. 1 is limited by contact of the upper end surface 58 with the housing shoulder 38.
 FIG. 6 shows the sleeve 48 in an intermediate third position between the first position shown in FIG. 1 and the second position shown in FIG. 4. A restrictor element 100 is seated against the seating surface 72 and obstructs fluid flow from through the C-ring 70 to create a differential pressure to move the sleeve 48 against the expansive force of the spring 64. The upper end surface 58 of the sleeve 48 is positioned such that the flow ports 28 are in fluid communication with the interior of the tool 20, allowing fluid communication between the interior of the tool 20 with the exterior of the tool 20. The C-ring 70 is held in a closed state by the second inner surface 32 of the housing 22. In some embodiments, a retaining element, not shown, may be placed in the sleeve to define this intermediate position, such retaining element being set such that it stops movement of the C-ring and sleeve up to a first pressure, but allows movement of the c-ring at a second pressure. Those of skill in the art will appreciate that many retaining elements such as a shear ring, shear pins, or other device may be used in conjunction with the valve assemblies described herein. Further, mechanisms, assemblies, methods or devices other than a retaining element may be used for defining the intermediate third position in a valve assembly and any such method or element is within the scope of the valve assemblies contemplated herein.
 When the sleeve 48 is in the second position shown in FIG. 6, the well operator may thereafter cause the flow of fluids, including acid, fracing fluids, or other fluid desired by the operator, through the housing ports and into the formation adjacent to the tool. In the illustrated embodiment, flow of such materials will be blocked from downwell flow by the ball 100 positioned against the seating surface 72, causing flow to be directed to the surrounding formation through the housing ports 28. After fracing, the differential pressure across the ball 100 may be increased to cause the ball 100 to move the sleeve 48 further downwell to the position shown in FIG. 3, where upon the ball will be released by the expanding C-ring.
 FIG. 7 shows a hydrocarbon producing formation 200 and a system comprising an upper set of tools 202 positioned in an upper stage 204 of the formation 200, an intermediate set of tools 206 positioned in an intermediate stage 208, and a lower set of tools 210 positioned within a lower stage 212. An upper static-seat tool 214 is positioned between the upper set of tools 202 and the intermediate set of tools 206 and has an internal ball seat corresponding to an upper-stage ball. An intermediate static-seat tool 216 is positioned between the intermediate set of tools 206 and the lower set of tools 210 and has an internal ball seat corresponding to an intermediate-stage ball. A lower static-seat tool 218 is positioned downwell of the lower set of tools and has an internal ball seat corresponding to a lower-stage ball. The static-seat tools 214, 216, 218 have ball seats designed to allow fluid flow therethough in either the upwell direction or the downwell direction, but the ball seats are not connected to sleeves or other movable components.
 Each tool of the sets of the tools 202, 206, 210 has the features described with reference to FIGS. 1-6. Each tool within the upper set of tools 202 has a C-ring and associated sleeve sized to be actuated by the associated upper-stage ball. Each tool within the intermediate set of tools 206 has a C-ring and associated sleeve sized to be actuated by an associated intermediate ball smaller than the upper-stage ball. Each tool within the lower set of tools 210 has a C-ring and associated sleeve sized to be actuated by an associated lower-stage ball, which is smaller than the upper ball, and the intermediate-stage ball.
 To actuate the lower set of tools 210, the lower-stage ball is caused to move through the tubing string and upper and intermediate sets of tools 202, 206. The lower-stage ball is sized to pass through the upper and intermediate sets of tools 202, 206 without being inhibited from further downwell flow by the corresponding ball seat inserts.
 Upon reaching the upwell tool 210a of the lower set of tools 210, the lower-stage ball seats against the closed C-ring of the tool. The well operator can then increase the pressure within the tubing string to overcome the expansive force of the associated coil spring and shift the sleeve to the intermediate third position described with reference to FIG. 6. When desired, the pressure within the flowpath may be increased further to move the sleeve to the second position described with reference to FIG. 4. After moving the lower-stage ball through the C-ring, the pressure may be decreased to cause the lower-stage ball to seat against the closed C-ring of the lower tool 210b of the lower set of tools 210. While the lower set of tools 210 only shows two tools 210a, 210b, any number of similar tools may compose this stage. After moving through all of such tools, the lower-stage ball seals against the lower static-seat ball 218, which is sized to prevent passage therethrough up to a pressure which damages the structure of the ball This process may then be repeated, first with the intermediate stage 208 using the intermediate-stage ball with the intermediate sets of tools 206 and the intermediate static-seat tool 216, and second with the upper stage 204 using the upper-stage ball with the upper sets of tools 202 and upper static seat tool 214.
 While the lower set of tools is shown comprising only three stages of tools, the process could be repeated for any number of tools within this stage. In addition, the same process described above with respect to the lower set of tools is repeatable in similar fashion for the intermediate and upper sets of tools 202, 206.
 In an additional embodiment, the inwardly directed force exerted on the outer surface of the C-ring is caused by a plurality of dogs. In a preferred embodiment, the dogs are positioned in the openings 84 of the sleeve, and each dog has a surface corresponding to the curvature of the second inner surface 50 of the housing 22. The surface profile of the dogs may have other shapes provided the dogs can engage the protrusions 78 defining the outer surface of the C-ring 70 as desired. The dogs are aligned with and adapted to contact and exert a radially inward force on the protrusions 78 of the C-ring 70 to force the C-ring 70 into the compressed state. In this embodiment, the openings 84 have a length along the longitudinal axis of the sleeve to allow the C-ring and sleeve to move in relation to the dogs.
 The dogs extend past first outer surface 50 of the sleeve 48, effectively reducing the diameter available to the protrusions. When the C-ring 70 is positioned such that that protrusions 78 engage the dogs, the terminal ends 82 are in contact and the diameter of the seating surface 72 and inner surface 74 of the C-ring 70 are such that a properly-sized ball flowing through the shifting sleeve will engage with the seat of the C-ring 70 as described with reference to FIGS. 1-7. In one embodiment, the C-ring and sleeve are engaged near the bottom of each of the openings 84 such that movement of the C-ring in the downwell direction moves the sleeve in the same direction and movement of the sleeve in the upwell direction, typically by the force of a spring or other guide device, will move the C-ring in the upwell direction.
 FIGS. 8A-8B show yet another embodiment in which a C-ring 70 starts in an uncompressed state and a sleeve 48 is oriented such that the protrusions 78 comprising the outer surface of the C-ring are in a larger-diameter section 300 of the housing 22 (shown in FIG. 8A) The sleeve 48 is then shifted to the position shown in FIG. 8B so that the protrusions 78 or forced from the larger-diameter section 300 to a smaller-diameter section 302 of the housing 22, which forces the C-ring 70 to a compressed state. Thereafter, a properly-sized ball flowing 308 through the sleeve would seat against compressed C-ring 70.
 Still referring to FIG. 8A-8B, a system incorporating the above-described embodiments may comprise multiple ball seats, including multiple C-rings initially in either compressed and uncompressed states. One such system would have an upper C-ring 70 fixed to the sleeve 48 and a lower seat 304 spaced sufficiently apart to allow a first ball 306 of a particular size to seat on the lower seat 304 without engaging or interfering with the upper seat 72. Systems in which the first ball engages the upper seat 72 without interfering with the lower seat 304 are also possible. A first ball 306 engages the lower seat 304 and, using fluid pressure, shifts the sleeve 48 to allow compression of the upper seat 72 by positioning the upper seat 72 such that the outer surface 76 of the C-ring 70 engages a smaller diameter surface 302 or appropriately positioned dogs. The C-ring 70 of the upper seat 72 becomes compressed and can thereafter engage a second ball 308 of a diameter selected for use with the upper seat 72. Those of skill in the art will appreciate that, in the uncompressed state, the upper C-ring 70 is configured such that balls large enough to engage the lower seat 300 will pass without engaging the upper C-ring 70. Further, the upper C-ring 70, when compressed, will engage balls with a diameter that is too small to engage and hold pressure on the lower seat 304.
 One advantage to the system illustrated in FIGS. 8A-8B is that restrictor elements which would activate the sleeve if the C-ring were compressed can pass through the valve assembly of this embodiment to activate tools further downwell. In other words, this embodiment will allow the placement of valve seats configured to utilize smaller restrictor elements upwell of valve seats configured to use larger restrictor elements. This will increase the flexibility of systems incorporating such valve assemblies and can increase the number of valves that can be operating in a single well.
 This arrangement can be continued with any number of valve assemblies in series per stage, with no limit on the number of sleeves. Moreover, this system allows for an increase in the number of stages. For example, a trio of tools using single valve seats configured for a 2.0 inch, 1.875 inch, and 1.75 inch ball respectively, can be placed in a well. A second trio of tools using double valve seats with upper valves configured for use with 2.0 inch, 1.875 inches, and 1.75 inches are then placed upwell of the first trio. The upper valve seats of this second trio of stages are C-rings in the uncompressed state (as described with referenced with respect to FIG. 8A) such that a 2.0 inch ball can pass through each upper seat without engaging the seat sufficiently to move the valve assembly in a downwell direction. The lower valve seats of the second trio comprise C-ring valve seats configured to engage a 2.0 inch ball and to shift the assembly in response thereto.
 In operation, a first 1.75 inch ball is placed in the well and allowed to engage and activate the 1.75 inch stage of the first trio of stages. A first 1.875 ball is placed in the well and allowed to engage and activate the 1.875 inch stage of the first trio of stages. Following the 1.875 inch ball, a first 2.0 inch ball is placed in the well. This ball first engages the lower seat of the 2.0 inch stage of the second trio of stages causing the seat to shift and moving the upper ring from an uncompressed state to a compressed state. The first 2.0 ball then engages the lower seat of the 1.875 inch stage of the second trio of stages, causing the seat to shift and moving the upper ring from an uncompressed to a compressed state. The first 2.0 inch ball then engages the lower seat of the 1.75 inch stage of second trio of stages, causing the seat to shift and moving the upper ring from an uncompressed state to a compressed state. Finally, the first 2.0 inch ball engages the 2.0 inch stage of the first trio of stages and activates the tools associated with the valve assemblies of this stage.
 At this point, three stages, associated with a 1.75 inch, a 1.875 inch, and a 2.0 inch valve assembly have been activated. Further, the well now contains three additional stages that can be activated by sequentially placing a 1.75 inch ball, a 1.875 inch ball, and 2.0 inch ball into the well and allowing the balls to engage their respective seats. This means that 6 stages, each stage having the potential for multiple sleeves, can be activated through use of 3 ball sizes. Further, the embodiments are not limited to the nesting of three sizes. Further nesting is possible with the valve assemblies and method of use contemplated herein, such nesting limited only by the ability of the uncompressed ring to allow larger sized balls to pass without shifting the seat.
 It is possible that the lower seat is not a C-ring but rather a solid seat for the ball or other restrictor means. Such a solid seat can be paired with the applicants' resilient deformable ball, described in applicant's U.S. patent application Ser. No. 13/423,154, entitled "Downhole System and Apparatus Incorporating Valve Assembly With Resilient Deformable Engaging Element," filed Mar. 16, 2012 and incorporated by reference herein, to allow for engagement and subsequent release of the lower seat. In fact, any method or device for engaging the lower seat to initially shift the sleeve is permissible provided that it does not prevent the treatment of any previously untreated stage.
 The ball or other restrictor devices of the present valve assemblies can either seat on the C-ring itself or the inside diameter of the sleeve above the C-ring, where the sleeve is sized sufficiently small such that the ball creates an interference seal between the ball and sleeve, in which case the C-ring provides only the mechanical restriction required to impart a load on the sleeve for shifting.
 This specification contains description of preferred embodiments in which a specific system and apparatus are described. Those skilled in the art will recognize that alternative embodiments of such system and apparatus can be used. Other aspects and advantages of the embodiments the invention as claimed may be obtained from a study of this disclosure and the drawings, along with the appended claims. Moreover, the recited order of the steps of any method described herein is not meant to limit the order in which those steps may be performed.
Patent applications by Raymond Hofman, Midland, TX US
Patent applications by William Sloane Muscroft, Midland, TX US
Patent applications in class Operating valve, closure, or changeable restrictor in a well
Patent applications in all subclasses Operating valve, closure, or changeable restrictor in a well