Abstract:
A downhole tool for use in a hydrocarbon production well. The downhole tool has a housing defining a flowpath around a longitudinal axis and a seat radially expandable between an unstressed state and an expanded state. The seat has a frame comprising at least one annular sealing element and a plurality of unconnected seat segments. The seat segments are engaged with the frame. The annular sealing element are engaged with an outer surface of each of the plurality of seat segments. The seat forms a tubular structure in the unstressed state.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This is continuation application claiming the benefit of the filing date of U.S. application Ser. No. 13/936,805, filed on Jul. 8, 2013, which is a continuation application claiming the benefit of the filing date of U.S. application Ser. No. 12/702,169, filed Feb. 8, 2010, both of which are incorporated by reference herein. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a downhole tool for oil and/or gas production. More specifically, the invention is a well stimulation tool having an expandable seat for use with a tubing string disposed in a hydrocarbon well. 
     2. Description of the Related Art 
     In hydrocarbon wells, fracturing (or “fracing”) is a technique used by well operators to create and/or extend a fracture from the wellbore deeper into the surrounding formation, thus increasing the surface area for formation fluids to flow into the well. Fracing is typically accomplished by either injecting fluids into the formation at high pressure (hydraulic fracturing) or injecting fluids laced with round granular material (proppant fracturing) into the formation. 
     Fracing multiple-stage production wells requires selective actuation of downhole tools, such as fracing valves, 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 ball-and-seat tools, each having a differently-sized ball seat and corresponding ball. Ball-and-seat systems are simpler actuating mechanisms than shifting tools and do not require running such tools thousands of feet into the tubing string. Most ball-and-seat systems allow a one-quarter inch difference between sleeves and the inner diameters of the seats of the valves within the string. For example, in a 4.5-inch liner, it would be common to drop balls from 1.25-inches in diameter to 3.5-inches in diameters in one-quarter inch or one-eighth inch increments, with the smallest ball seat positioned in the last valve in the tubing string. This, however, limits the number of valves that can be used in a given tubing string because each ball would only be able to actuate a single valve, the size of the liner only provides for a set number of valves with differently-sized ball seats. In other words, because a ball must be larger than the ball seat of the valve to be actuated and smaller than the ball seats of all upwell valve, each ball can only actuate one tool. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention allows a well operator to increase the number of flow ports to the formation in each stage of a formation and to supplement the number of flow ports in unlimited numbers and multiple orientations to increase the ability of fracing the formation. 
     The present invention is a downhole tool comprising a housing having at least one flow port providing a communication path between the interior and exterior of the tool. A sleeve assembly containing an inner sleeve and an expandable seat is moveable within the housing between a first position and a second position. In the first position, the sleeve assembly is radially positioned between the flow ports and the flowpath to substantially prevent fluid communication therebetween. Shearable port inserts are initially positioned within the flow ports, with each port insert having a shearable portion extending into the interior of the housing and engaging the sleeve assembly when the inner sleeve is in the first position. 
     According to one aspect of the present invention, the expandable seat is comprised of a plurality of seat segments connected to a plurality of elastomeric members. Upon application of sufficient pressure, the ball engages the expandable seat substantially preventing fluid from flowing through the expandable seat. When an adequate pressure differential is caused above and below the engaged ball, the differential forces the sleeve assembly to shear the port inserts and move to the second position. Continued pressure differential of at least that pressure thereafter causes radial expansion of the elastomeric members and separation of the seat segments relative to the expandable seats unstressed state, allowing the ball to proceed through the expandable seat. In this manner, a single ball may be used to actuate multiple downhole tools within the same tubing string. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a partial sectional elevation of the preferred embodiment of the present invention in a “closed” state wherein fluid communication through flow ports is substantially prevented. 
         FIG. 2  is an enlarged sectional elevation of the port insert shown in  FIG. 1 . 
         FIG. 3  is a partial sectional elevation of the preferred embodiment of the present invention in an “opened” state wherein fluid communication through the flow ports is permitted. 
         FIG. 4  is an enlarged sectional view of the port insert shown in  FIG. 3 . 
         FIG. 5  is a sectional elevation of the expandable seat of the preferred embodiment. 
         FIG. 6  is side elevation of the expandable seat of the preferred embodiment. 
         FIG. 7  is a sectional view of the expandable seat through section line  7 - 7  of  FIG. 6 . 
         FIG. 8  is a section view of an alternative embodiment of an expandable seat. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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 through the tool and wellbore. Thus, normal production of hydrocarbons 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 the fracing process, fracing fluids moves from the surface in the downwell direction to the portion of the tubing string within the formation. 
       FIG. 1  depicts a partial sectional elevation of a preferred embodiment of a downhole tool  20  having the features of the present invention. The tool  20  comprises a housing  22  attached to a top connection  24  at an upper end  26  and a bottom connection  28  at a lower end  30 , respectively. Grub screws  36  secure the connection between the housing  22  and the top and bottom connections  24 ,  28 . Annular upper and lower sealing elements  38 ,  40  are positioned circumferentially around the top connection  24  and bottom connection  28 , respectively, and inside the housing  22 . The inner surface of the housing  22  includes a locking section  57  having a plurality of downwardly-directed annular ridges. 
     A plurality of flow ports  32  is circumferentially positioned around and through a first section of the housing  22  having a first inner diameter. The flow ports  32  provide a number of fluid communication paths between the interior and exterior of the tool  20 . A sleeve assembly  50  nested within the housing  22  comprises an expandable seat  52  and an inner sleeve  54 , and is moveable between a first position, as shown in  FIG. 1 , and a second position as shown in  FIG. 3 . The expandable seat  52  has an annular upper shoulder  53  adjacent the top connection  24 , and an annular lower shoulder  56  adjacent to inner sleeve  54 . Two annular sealing elements  51  are circumferentially disposed around the expandable seat  52  in corresponding circumferential grooves. 
     In the first position, the expandable ball seat  52  is positioned in the first section of the housing  22 , with the upper shoulder  53  contacting a lower annular shoulder  55  of the top connection  24 . The outer diameter of the expandable seat  52  in a normal state is only slightly smaller than the inner diameter of the first section of the housing  22 . 
       FIG. 2  shows a sectional view of a shearable port insert  42  in greater detail, with hatching removed for clarity. In the first position, the port insert  42  is positioned in the flow port  32  to close the communication path to the exterior of the housing  22 . The shearable port insert  42  comprises a cylindrical body portion  44  having approximately the same circumference as the corresponding flow port  32 , and a cylindrical shearable portion  46  extending into the interior of the housing  22  and having a smaller circumference than the body portion  44 . The junction of the shearable portion  46  and body portion  44  is a shear joint  47  created with a shear riser cut and shearable at a predetermined amount of shear force, which in the preferred embodiment can be adjusted between eight hundred psi and four thousand psi by altering the depth of the stress riser cut. A channel  48  extends through the body portion  44  and partially through the shearable portion  46  such that, once sheared, the channel  48  provides a fluid communication path through the port insert  42  between the interior and exterior of the housing  22 . 
     In the first position, the shearable portion  46  of each port insert  42  extends into a corresponding circumferential insert groove  49  in the outer surface of the expandable seat  52 . Two annular sealing elements  51  are disposed circumferentially around the expandable seat  52  in two circumferential grooves. Alternative embodiments contemplate a plurality of recesses formed in the outer surface of and spaced radially about the expandable seat  52  and aligned with the port inserts  42 . 
     The port insert  42  is retained in the flow port  32  with a snap ring  70  disposed in a groove  63  formed in the sidewall  65  of the flow port  32 . The snap ring  70  constricts around a cylindrical top portion  67  of the port insert  42 . An annular sealing element  72  is located between an annular shoulder portion  74  of the port insert  42  to prevent fluid communication into or out of the flow ports  32  around the exterior of the port insert  42 . An exemplary snap ring  70  is Smalley Snap Ring XFHE-0125-502. 
     In the preferred embodiment, the port inserts  42  are made of erodible (i.e., non-erosion resistant) material (e.g., 6061-T651 or 7075-T651 aluminum alloy) such that flow of fracing fluid through the channel  48  at typical fracing flow rates erodes the insert  42  to increase the diameter of the channel  48 . When sheared as a system, the port inserts  42  will erode to or past the internal sidewall of the housing  22  as a result of downwell flow, which thereafter allows the full open flow area of the tubing to be used for upwell or downwell flow. In alternative embodiments, however, the port inserts may be constructed of an erosion resistant material when the full flow area of the housing  22  is not desired. 
     An expandable ratchet ring  59  is positioned circumferentially around the outer surface of the expandable seat  52 , downwell from the cylindrical insert groove  49 , in a snap ring groove  61 , and has a plurality of upwardly-directed ridges engagable with the locking section  57  to prevent upwell movement. Operation of the ratchet ring  59  will be described more fully with reference to  FIG. 3  and  FIG. 5  infra. 
       FIG. 3  and  FIG. 4  more fully show the downhole tool  20  in an “opened” state, wherein the sleeve assembly  50  is in the second position. The port inserts  42  are sheared at the shear joints  47  to provide a communication path from the interior to the exterior of the tool  20  through the channel  48 . The lower end  56  of the inner sleeve  54  contacts the lower annular shoulder  58  of the bottom connection  28 . The ratchet ring  59  is engaged with the locking section  57  of the housing  22  to prevent upwell movement of the sleeve assembly  50  due to flow pressure or friction load during remedial completion operations. A ball  60  is seated against the expandable seat  52  to prevent further downwell fluid flow.  FIG. 3  does not show the expandable seat  52  in a radially expanded state and is the precursor stage prior to the ball  60  being forced through the expandable seat  52 , as will be discussed infra. 
       FIG. 5  more fully shows the expandable seat  52  in a radially expanded state nested within a second section of the housing  22  in the second position. The expandable seat  52  is comprised of a plurality of seat segments  62  interconnected with elastomeric members  64  in a generally tubular shape with outwardly flared upper and lowered ends, with each set segment  62  having an inner surface  71  partially defining the seat flowpath  43 . The elastomeric members  64  are bonded to the seat segments  62  with a suitable bonding agent. Although in the preferred embodiment the expandable seat  52  is attached to the inner sleeve  54 , in alternative embodiments the expandable seat  52  may be integrally formed with the inner sleeve  54  at an end thereof. The elastomeric members  64  are preferably formed of HNBR rubber. 
       FIG. 6  is an elevation of the expandable ball seat  52  and annular sealing elements  51  shown in  FIG. 5 .  FIG. 7  is a sectional perspective through section line  7 - 7  of  FIG. 6 . The expandable seat  52  is formed with eight seat segments  62  interconnected with the elastomeric members  64 . The annular sealing elements  51  are circumferentially disposed in grooves formed in and around the seat segments  62 . A portion of each of the grooves is formed in the outer surface of each seat segment. Seven of the seat segments  62  are identically shaped, with the eight seat segment having a clutch profile  69  that engages with a profile of bottom connection to prevent rotation during milling out of the tool. The elastomeric members  64  are in the unstressed configuration shown in  FIG. 1  and  FIG. 3 . When in the first position and prior to shearing, the port inserts are engaged with the circumferential insert groove  49 . The ratchet ring groove  61  receives the expandable ratchet ring for engagement with a locking section of the housing. 
       FIG. 8  is a sectional elevation through a plane intersection the longitudinal axis  100  of an alternative embodiment of an expandable seat  152  comprising only six seat segments  162  interconnected with elastomeric members  164 . Grooves  151  are formed around the seat segments  162  to receive annular sealing elements. An insert groove  149  is circumferentially formed in the outer surface between the sealing element grooves  151  for engagement with the port inserts when in the first position. A ratchet ring groove  161  receives an expandable ratchet ring for engagement with a locking section  57  of the housing  22 . A series of tabs  166  are spaced around the lower end of, and extend longitudinally from, the expandable seat  152  to engage with the bottom shoulder of an alternative embodiment of a bottom connection (not shown), thus preventing rotation of the seat  152  during milling out. 
     Operation of the invention is initially described with reference to  FIG. 1  and  FIG. 2 . While in the first position, the associated ball  60  (not shown) flows down the tubing string and seats against the seat segments  62  and elastomeric members  64  that compose the expandable seat  52 . In this manner, the ball  60  engages with and seals against the expandable seat  52  to substantially prevent fluid flow through the expandable seat  52  and connected inner sleeve  54 , causing an increase in pressure applied to the ball  60  and sleeve assembly  50  relative to the pressure below the sleeve assembly  50 . When this pressure differential is sufficient to cause the sleeve assembly  50  to exert a shearing force on the port inserts  32  greater than the shear strength of the shear joints  47 , the force exerted by the expandable seat  52  separates the shearable portions  46  of the port inserts  42  and releases the sleeve assembly  50 . The pressure differential causes downward movement of the sleeve assembly  50 , with the ball  60  engaged to the expandable seat  52 , to the second position shown in  FIG. 3 . 
     As shown in  FIGS. 3 and 4 , the insert sleeve  54  is impeded from further downwell movement once in contact with the lower annular shoulder  58 . After moving to the second position, the ball  60  is impeded from further downwell movement and initially remains engaged with the expandable seat  52 , which is in an unstressed state. The ratchet ring  59  engages with the locking section  57  to prevent upwell movement of the sleeve assembly  50 . 
     As a result of the shearing, the channels  48  of the port inserts  42  provide fluid communication paths to the exterior of the housing  22 . In this “opened” state, fracing may commence through the channels  48 . Flow of fracing material at normal fracing velocities causes erosion of the port inserts  42  and increases the diameter of the channels  48 . 
     As shown in  FIG. 5 , while the sleeve assembly  50  is in the second position, the ball  60  may be forced through the expandable seat  52  by increasing the pressure differential within the tubing string to overcome the radially-inwardly contracting forces exerted by the elastomeric members  64  on the seat segments  62 . As the ball  60  is forced into the expandable seat  52 , the elastomeric members  64  expand resulting in increased separation between the seat segments  62  and allowing the ball  60  to pass. Whereas in the first position the outer diameter of the expandable seat is only slightly larger than the first inner diameter of the housing, in the open state the second inner diameter of the housing  22  is sufficiently large to permit outward expansion of the elastomeric members  64  such that the seat segments  62  can separate to allow the ball  60  to pass. 
     After exiting the lower end of the expandable seat  52 , pressure within the housing  22  decreases and the expandable seat  52  returns to its unstressed state. The ball  60  continues to travel downwell to the next downhole tool in the tubing string, if any. The furthest downwell tool each stage of a multi-stage well is typically a standard (i.e., non-expandable) seat valve on which the ball  60  would seat to allow the tubing string pressure to be elevated to fracture the isolated stage. 
     The present invention is described above in terms of a preferred illustrative embodiment of a specifically described downhole tool. Those skilled in the art will recognize that alternative constructions of such an apparatus can be used in carrying out the present invention. Other aspects, features, and advantages of the present invention may be obtained from a study of this disclosure and the drawings, along with the appended claims.