Abstract:
A variable downhole choke is disclosed wherein an outer housing includes a selected port pattern of ports and subports and a sleeve having similar ports and subports wherein subports depend from ports on each of the housing and sleeve. The ports/subports are oriented so that upon converging movement of housing and sleeve the sleeve subports align with housing subports before the sleeve ports align with housing ports.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/140,879 filed Jun. 24, 1999, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to oil field tools. More particularly, the invention relates to downhole tools providing variable choking capability. 
     2. Prior Art 
     Oil wells can be productive to the point of over productiveness when the flow is not controlled downhole. Oil and gas in underground/under sea reservoirs are at extremely high pressure and can be all too willing to be expressed from these reservoirs. As one of skill in the art is painfully aware, this condition is hazardous and must avoided. 
     In order to prevent the outflow of oil or gas at a rate greater than can be accommodated at the surface and to control production of unwanted fluids, many systems have traditionally been employed. One of the tools that is used both to control the rate of expulsion of hydrocarbons from the reservoir and in some cases to limit the penetration into the well of undesired fluids is a choke. Chokes conventionally employ inner and outer sleeves having alignable and misalignable ports that are of the same size and shape. In these systems the degree of alignment of ports regulates the speed of the flow, thus how choked the system is. A drawback of such system is that erosion characteristics tend to make the system cost prohibitive. 
     SUMMARY OF THE INVENTION 
     A variable choke as disclosed herein employs, in the broadest sense, a choke housing and choke insert which are variably positionable relative to one another to align and misalign, to varying degrees, sets of ports in the housing and insert. Specially shaped and oriented ports provide for pressure equalization and choking capabilities while minimizing erosion of the components of the choke. In particular, a preferred port shape comprises a port and a subport depending therefrom. The subport is of smaller area than the port and preferably is elongated. An elongated subport reduces erosion of the subport itself when subject to flowing fluid because of fluid dynamics which cause the stream to become thinner than the actual dimension of the subport. Thus while fluid passes through the subport at high velocity the shape of the subport and its construction from an erosion resistant material, help to minimize erosion. 
     A further feature of the choke is that a seal stack is not subject directly to flowing fluid thus providing a longer life. 
     Finally, with respect to pressure equalization, the choke is resistant to the deleterious effects of equalization of a large pressure differential by incorporating at least one and preferably two diffuser rings to restrict flow and introduce turbulence which reduces flow velocity. These cooperate to allow the choke to effectively equalize a pressure differential. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings wherein like elements are numbered alike in the several FIGURES: 
     FIG. 1 is a quarter section view of a variable choke embodiment as disclosed herein in a closed position; 
     FIG. 2 is a quarter section view of the choke embodiment of FIG. 1 in an initial equalizing position; 
     FIG. 3 is a quarter section view of the choke embodiment of FIG. 1 in a fully equalizing position; 
     FIG. 4 is a quarter section view of the choke embodiment of FIG. 1 in a fully choked position; 
     FIG. 5 is a quarter section view of the choke embodiment of FIG. 1 in a partially choked position; 
     FIG. 6 is a quarter section view of the choke embodiment of FIG. 1 in a fully open position; 
     FIG. 7 is a longitudinal cross-sectional view of a choke housing; 
     FIG. 8 is a longitudinal cross-sectional view of a housing sleeve; 
     FIG. 9 is a cross-sectional view of the housing sleeve of FIG. 8 taken along section line  9 — 9  in FIG. 8; 
     FIG. 10 is a longitudinal cross-section of a first diffuser ring; 
     FIG. 11 is a longitudinal cross-section of a second diffuser ring; 
     FIG. 12 is a longitudinal cross-section of a lower sub of the variable choke; 
     FIG. 13 is a long cross-sectional of a first portion of a choke insert; 
     FIG. 14 is a detail view taken along line  14 — 14 ; 
     FIG. 15 is a long cross-sectional of an insert sleeve embodiment of the choke; 
     FIG. 16 is a cross-sectional view of the sleeve of FIG. 15 taken along section line  16 — 16 ; 
     FIG. 17 is an end view of the sleeve of FIG. 15 taken along line  17 — 17 ; 
     FIG. 18 is a detail view of the sleeve from FIG. 17 defined by circumscription  18  in FIG. 17; 
     FIG. 19 is a long cross-sectional view of a second portion of an insert embodiment of the choke; and 
     FIG. 20 is a long cross-sectional of a single piece alternate embodiment of the insert of the choke. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the variable choke is illustrated in several different operating positions in FIGS. 1-6. Each of the components are identified while referring to FIG. 1, these components being illustrated in different positions in FIGS. 2-6 to convey the various operating positions of the choke. Individual components and alternative components are illustrated and further discussed to the extent necessary with reference to FIGS. 7-20. As will be appreciated by one of skill in the art, the left side of a figure is intended to be the uphole side of the device with the right side being more downhole. It should be understood however that components discussed as downhole or uphole could be reversed with similar results providing the concepts of the variable choke are maintained. 
     Referring to FIG. 1, a choke housing  10  is preferably formed from a durable material such as steel. Housing  10  is provided with at least one and preferably a plurality of port/subport combinations identified as ports  12  and subports  14 . Housing  10  and a lower sub  16  are threadable together (or otherwise attached) at thread  18  and together house all other components of the variable choke. Housing  10  as noted is provided with port/subport combinations whose shape is better ascertainable in FIG.  7 . The inventors hereof prefer the complex port/subport configuration because of benefits realized with respect to pressure differential control and erosion resistance. The housing ports/subports  12 ,  14  have counterpart port/subport combinations on a choke insert described more fully hereunder. 
     Still referring to FIGS. 1 and 7, housing  10  preferably is milled to include a larger I.D.  20  on part of the housing to receive an erosion resistant sleeve  22 . Sleeve  22  is illustrated independently in FIGS. 8 and 9. Sleeve  22  is constructible of any erosion resistant material, ceramic or tungsten carbide material being preferred. The sleeve  22  may also be constructible of another material and coated with an erosion resistant material. Sleeve  22  may be mounted in a number of ways (known to the art) in housing  10  such as but not limited to epoxy, shrink fitting, press fitting, etc. It should also be appreciated that the housing could be constructed of a single piece of material which either is or is coated with an erosion resistant material such as ceramic or tungsten carbide. 
     Sleeve  22  is not intended to move relative to housing  10  once installed therein and thus has specific port/subport shape and locations to complement the housing  10 . Ports  24  and subports  26 , well shown in FIG. 8, are clearly similar in configuration to housing ports/subports  12 ,  14 , however it is noted that the overall length of the combination, and indeed the length of each port and subport individually is shorter than that of housing ports  12  and subports  14 . This arrangement protects the metal housing from erosion by directing the most erosional flow to impact the sleeve  22  which as stated preferably comprises an erosion resistant material. 
     It is further noted from FIG. 8 that sleeve  22  is enlarged in I.D. in the area  28  corresponding to ports  24 . This enhances operation of the variable choke by facilitating circumferential flow of fluid. 
     Adjacent sleeve  22  in the downhole direction, referring again to FIG. 1 is an annular first diffuser ring  30  preferably constructed of an erosion resistant material. In a preferred embodiment, diffuser ring  30  is of a ceramic tungsten carbide material. Referring to FIG. 10, the I.D. of diffuser ring  30  is illustrated to have preferably a pair of circumferential grooves  32  therein. Grooves  32  need only be shallow grooves in surface  34  of ring  30  to cause turbulence to occur in fluid flowing between surface  34  and an insert discussed hereunder. In a preferred embodiment, the clearance between surface  34  and the insert is on the order of about a few thousandths of an inch. Further, there is a clearance at the O.D. of ring  30  of about a few thousandths of an inch. 
     Moving downhole from first diffuser ring  30  a second diffuser ring  36  is disposed in the same annulus as first diffuser ring  30 . It will be noted that the second diffuser ring  36 , referring to FIG. 11, is provided with a groove  38  on its O.D. but that its I.D.  40  is smooth. It is preferable that I.D.  40  of second diffuser ring  36  is of a tolerance with respect to the insert (discussed hereunder) that is tighter than that of diffuser ring  30  so that flow of fluid is caused to migrate radially between first ring  30  and second ring  36  and then to travel axially again on the O.D. of second ring  36 . The second diffuser ring  36  slides within the annulus in the direction of fluid flow to help further restrict flow as it contacts an adjacent part (production-spacer; injection-first diffuser ring). This is a tortuous path for the fluid and creates additional turbulence while reducing velocity further. 
     Referring again to FIG. 1, first diffuser ring  30  and second diffuser ring  36  are located in housing  10  by spacer  42  which includes an annular flange  44  received in a recess  46  formed by the convergence of downhole end  48  of housing  10  and shoulder  50  of lower sub  16 . Upon assembly of housing  10  and lower sub  16  with the above discussed components therein, movement of spacer  42  is restricted by annular flange  44  which assists in retaining first ring  30  and second ring  36 . 
     A secondary function of spacer  42  is to provide a stop for seal stack  52 . Seal stack  52  is preferably a non-elastomeric chevron seal stack although other seal types are possible, as known to the art. Seal stack  52  is located in lower sub  16  in recess  54  therein which is illustrated in FIGS. 1 and 12. 
     Radially inwardly of all components thus far discussed is a choke insert which can be in multiple components or a single component as desired. 
     Referring to FIGS. 1,  13  and  14 , a first portion of one embodiment of an insert is illustrated. The first portion  60  of the insert is preferably formed of metal and includes ports  62  and subports  64  which are similar in configuration to sleeve  22  ports  24 /subports  26  but are oriented oppositely such that upon movement of the insert axially to converge the ports/subports of housing and insert, the subports  64  will communicate with subports  26  first. Other features of first portion  60  are appreciated from FIG.  14 . More specifically, FIG. 14 is a detail view of a downhole end  66  of portion  60 . FIG. 14 illustrates areas  68  that have a larger O.D. and area  70  having a smaller O.D. Area  70  is provided to allow more epoxy to act on the surface of portion  60  and an erosion resistant insert sleeve  74  to better retain that sleeve. At the downhole end  66  of portion  60 , preferably a thread  69  is located. Finally portion  60  includes pin receptacle  72  to receive a pin, (not shown) which locates the insert sleeve  74  (FIGS. 1,  15 - 18 ) on portion  60  and prevents rotation thereon. 
     Insert sleeve  74  includes port  76 /subport  78  combinations to substantially match first portion  60  ports  62 /subports  64  and is configured to fit over portion  60  to be secured thereto as above noted. It is important to note that in a preferred embodiment, the insert sleeve ports  76 /subports  78  are the same shape as the ports  62 /subports  64  in the first portion  60 , similar to the housing sleeve  22 , to protect the portion  60  from erosion. Insert sleeve  74  is an erosion resistant material, preferably a ceramic tungsten carbide material, and further includes recess  80  (FIGS. 15 and 18) to receive a pin (not shown) preventing rotation relative to the first portion  60 . Recess  80  receives the same pin that communicates with pin receptacle  72 . 
     Referring to FIGS. 1 and 19, a second portion  90  of the insert is illustrated. The second portion  90  includes preferably a thread  92  to communicate with thread  69  to bind first portion  60  with second portion  90  thereby axially retaining choke insert sleeve  74 . 
     Referring to FIG. 20 it is important to note that the choke insert can also be constructed in a single piece and be coated with an erosion resistant material. A perusal of the figure in connection with the foregoing will provide one of ordinary skill an understanding of the embodiment. 
     Moving back to focus on operation of the tool and referring to FIGS. 1-6, FIG. 1 illustrates the tool in the closed position with ports  62 /subports  64  and ports  76 /subports  78  fully sealed off to fluid flow by seal stack  52 . Moving to FIG. 2, the pressure equalization process is initiated by shifting of the insert, referred to at this point as 100 for simplicity, one of ordinary skill in the art being expected to realize that 100 is made of up first portion  60 , second portion  90  and insert sleeve  74  or a single piece as in FIG. 20, until subports  64 ,  78  are just uphole of seal stack  52 . Fluid from the annulus will move through the tortuous path around the first and second diffuser rings  30 ,  36  and along spacer  42  to access subports  64 ,  78 . The reverse is true for an injection situation. This is an initial equalizing position. 
     Referring to FIG. 3, the ports  62 ,  76  and subports  64 ,  78  have been shifted to be entirely out from under seal stack  52  which is the full equalizing position. More fluid can pass in this position because the fluid need pass through less of the tortuous path of the diffuser rings  30 ,  36  and spacer  42 . 
     In FIG. 4 the device is illustrated in the fully choked position where subports  64 ,  78  have not yet overlapped subports  14 ,  26  but are positioned closely thereto. 
     In FIG. 5 the device is illustrated in the partially choked position where there is some overlap of subports  64 ,  78  and subports  14 ,  26 . Fluid can move rapidly through the subports and the erosion resistant character of the material thereof is important. 
     In FIG. 6 the tool is in its fully open position where the ports  62 ,  76  are aligned with ports  12 ,  24 . It will be noted in this view that the ceramic tungsten carbide portions extend into the ports/subports more than the metal areas to reduce erosion. 
     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.