Patent Publication Number: US-7712540-B2

Title: Flow control device

Description:
RELATED APPLICATIONS 
   This application is a continuation of U.S. application Ser. No. 11/307,079, filed Jan. 23, 2006, the contents of which are herein incorporated by reference. 

   BACKGROUND 
   1. Field of the Invention 
   The invention generally relates to a flow control device, and more particularly, the invention generally relates to a flow control device for use in a well. 
   2. Description of the Related Art 
   The following descriptions and examples are not admitted to be prior art by virtue of their inclusion in this section. 
   A choke is a device that is typically used in a well for purposes of controlling a flow. For example, the choke may be used for purposes of regulating a rate of production flow from a particular zone of the well, or alternatively, the choke may be used for purposes of regulating the rate at which a particular fluid is injected into the well. 
   Due to the restriction of flow by the choke, the choke typically has to operate under a high differential pressure, i.e., the difference in pressure between the choke&#39;s inlet and outlet flows. A potential challenge with a high differential pressure is that flow limiting surfaces of the choke may erode. 
   Thus, there exists a continuing need for better ways to control a fluid flow in a well. 
   SUMMARY 
   In an embodiment of the invention, a choke that is usable with a well includes an inlet port and an outlet port. The choke also includes pressure drop stages between the inlet and outlet ports. Each of the pressure drop stages is adapted to create part of an overall pressure differential between the inlet and outlet ports. 
   In another embodiment of the invention, a system that is usable with a well includes a string and a flow control device. The string communicates fluid between a position that is downhole in the well and the surface of the well. The flow control device regulates a flow of the fluid and includes an inlet port, an outlet port and pressure drop stages between the inlet and outlet ports. Each of the pressure drop stages is adapted to create part of an overall pressure differential between the inlet and outlet ports. 
   In yet another embodiment of the invention, a technique that is usable with a well includes forming flow control stages between inlet and outlet ports of a downhole flow control tool. The technique includes distributing an overall pressure differential between the inlet and outlet ports among the flow control stages. 
   Advantages and other features of the invention will become apparent from the following drawing, description and claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying drawings illustrate only the various implementations described herein and are not meant to limit the scope of various technologies described herein. The drawings are as follows: 
       FIG. 1  is a schematic diagram of a well according to an embodiment of the invention; 
       FIG. 2  is a schematic diagram depicting a flow control section of the flow control device of  FIG. 1  when open according to an embodiment of the invention; 
       FIG. 3  illustrates a flow control stage of the flow control section of  FIG. 2  according to an embodiment of the invention; 
       FIG. 4  is a schematic diagram of the flow control section when closed according to an embodiment of the invention; 
       FIG. 5  is a schematic diagram of a flow control section when closed according to another embodiment of the invention; 
       FIG. 6  is a schematic diagram of a flow control section when open according to another embodiment of the invention; and 
       FIG. 7  is a perspective view of an internal choke sleeve according to another embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   As used here, the terms “up” and “down”; “upper” and “lower”; “upwardly” and “downwardly”; “below” and “above”; and other similar terms indicating relative positions above or below a given point or element may be used in connection with some implementations of various technologies described herein. However, when applied to equipment and methods for use in wells that are deviated or horizontal, or when applied to equipment and methods that when arranged in a well are in a deviated or horizontal orientation, such terms may refer to a left to right, right to left, or other relationships as appropriate. 
   In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments are possible. 
   Referring to  FIG. 1 , an embodiment  10  of a well in accordance with an embodiment of the invention includes a string  20  that extends into a wellbore  12 . The wellbore  12  may be cased with a casing string  14 , in accordance with some embodiments of the invention. However, the wellbore  12  may be uncased in accordance with other embodiments of the invention. Additionally, the well  10  may be a subterranean or subsea well, depending on the particular embodiment of the invention. 
   The string  20  may be a production string in accordance with some embodiments of the invention, and the string  20  may include a choke, or flow control device  50 , which is positioned inside a particular production zone  30  of the well  10  for purposes of regulating the rate at which production fluid flows from the zone  30  into the central passageway of the string  20 . The production zone  30  may be formed via upper  32  and lower  34  packers (for example) that seal off the annulus between the interior of the well casing  14  and the exterior of the string  20  above and below the production zone  30 . 
   In accordance with some embodiments of the invention, the flow control device  50  includes a flow control section  54 , which includes radial ports  57  for purposes of receiving well fluid into the central passageway of the production string  20  when the flow control device  50  is open. The rate at which the fluid flows into the central passageway is a function of the effective cross-sectional flow area that is presented by the flow control section  50 . 
   More specifically, in accordance with some embodiments of the invention, the flow control section  54  includes an internal choke sleeve (not shown in  FIG. 1 ), which is moved up and down along the longitudinal axis of the flow control device  50  by an actuator  52  of the flow control device  50 . The actuator  52 , in turn, may be remotely controlled from the surface of the well  10  or, alternatively, may be automatically controlled downhole in response to certain states of the production zone  30 . 
   As further described below, the internal choke sleeve regulates the flow rate through multiple flow control stages of the flow control section  54 . Each flow control stage drops part (the same pressure drop, for example) of the overall pressure difference between the central passageway of the string  20  and the annulus of the well, which surrounds the production string  20  near the flow control device  50 . Due to this design, local velocities and erosion rates are considerably reduced throughout the flow control section  54 , as compared to a conventional choke. 
     FIG. 2 , which depicts an exemplary embodiment of the flow control section  54  when open, depicts the left half of the flow control section  54  about a longitudinal axis  58  of the section  54 . Although the right half of the flow control section  54  is not shown, the flow control section  54  is symmetrical about the longitudinal axis  58 . 
   The flow control section  54  is formed from an internal choke sleeve  100  that is concentric with the longitudinal axis  58 . The internal choke sleeve  100  includes an outer surface  102  that has certain features (described further below) that cooperate with corresponding features of an inner surface  72  of a housing  70  of the flow control section  54 . As depicted in  FIG. 2 , the housing  70  generally circumscribes the choke sleeve  100 . 
   The well fluid enters the flow control section  54  through the radial ports  57  (one port  57  being depicted in  FIG. 2 ); flows between the annular space that exists between the housing  70  and the choke sleeve  100 ; and exits the flow control section  54  through radial ports  60  (one port  60  being depicted in  FIG. 2 ) that are formed in the choke sleeve  100  and are in communication with the central passageway of the string  20 . The actuator  52  ( FIG. 1 ) of the flow control device  50  controls the longitudinal position of the choke sleeve  100  relative to the housing  70 , as the relative positions between the surfaces  72  and  102  control the effective cross-sectional flow area between the radial ports  57  and  60 . 
   For the position of the choke sleeve  100 , that is depicted in  FIG. 2 , the flow control section  54  is open to flow in that a continuous annular space is formed between the inlet  57  and outlet  60  ports. By moving the choke sleeve  100  in a downward direction, the effective cross-sectional flow area between the surfaces  72  and  102  is increased and thus, the flow rate through the flow control section  54  is increased. Conversely, by moving the choke sleeve  100  in an upward direction from the position depicted in  FIG. 2 , the effective cross-sectional flow area is restricted, thereby decreasing the flow rate. 
   In accordance with embodiments of the invention described herein, the inner surface  72  of the housing  70  defines N flow control stages  150  (stages  150 .sub. 1  . . .  150 .sub.N−1 and  150 .sub.N being depicted as examples), which are present along the fluid flow path from the inlet port  57  to the outlet port  60 . Each of the stages  150  drops a portion of the overall pressure difference between the inlet  57  and outlet  70  ports. The overall flow rate between the inlet  57  and outlet  60  ports is a function of the position of the choke sleeve  100  relative to the housing  70 . 
   In some embodiments of the invention, the flow control stages  150  may be constructed to experience identical pressure drops. More specifically, for the case in which the flow control section  54  includes N stages  150  that drop the same pressure, each stage  150  experiences the following pressure drop (assuming that each stage  150  is identical):
 
 P .sub.STAGE=.DELTA. P/N   Equation 1
 
   wherein “P.sub.STAGE” represents the pressure drop across the stage  150 ; “.DELTA.P” represents the total pressure drop across the flow control section  54 ; and “N” represents the number of stages  50 . Thus, each flow control stage  150  experiences a fraction (1/N) of the total pressure differential across the flow control section  54 . 
   Referring to  FIG. 3 , as a more specific example, each flow control stage  150  may form three basic sections in accordance with some embodiments of the invention: a flow restriction section  190 ; a diffuser section  192 ; and a mixing section  194 . The flow restriction section  190  establishes the flow rate through the stage  150  and produces a jet that is diffused by the diffuser section  192 . The mixing section  194  breaks down the jet and aims at re-establishing a regular flow pattern across the cross-section of the flow area. 
   In accordance with some embodiments of the invention, for each flow control stage  150 , the interior surface  72  of the housing  70  includes a beveled, or sloped, diffuser surface  170 , which in combination with the radially opposing part of the outer surface  102  of the choke sleeve  100 , defines the flow restriction  190  and diffuser  192  sections. The diffuser surface  170 , in accordance with some embodiments of the invention, radially varies along the longitudinal axis  58  of the flow control stage  150  to create the sloped surface that is characterized by a diffuser angle (called “.theta.” in  FIG. 3 ). 
   More specifically, in accordance with some embodiments of the invention, the diffuser surface  170  is formed between annular surface transition edges  175  and  177 . From the surface transition edge  175  to the surface transition edge  177 , the radius of the surface  170  linearly increases to create the .theta. diffuser angle. 
   Across from the diffuser surface  170 , the outer surface  102  of the choke sleeve  100  includes a protrusion  180 , which has a relatively constant radius and resides between an annular upper shoulder  181  and an annular lower shoulder  183  of the surface  102 . The flow restriction section  190  is formed by the region of the protrusion  180  near the upper shoulder  181  and the radially opposing portion of the diffuser surface  170 . The diffuser section  192  is formed from the region of the protrusion  180  below the upper shoulder  181  and the radially opposing portion of the diffuser surface  170 . Below the diffuser surface  170  the inner surface  72  of the housing  70  transitions at the edge  177  to form an annular groove  178 , a surface feature that in conjunction with the radially opposing portion of the protrusion  180  forms the mixing section  194 . 
   The annular groove  178  longitudinally extends from the edge  177  to an annular shoulder  179 . At the annular shoulder  179 , the inner surface  72  of the housing  70  has a reduced radius to form a radial protrusion  174 . The radial protrusion  174  has a radius about the longitudinal axis  58 , which is approximately the same as the radius of the radial protrusion  180  of the outer surface  102  of the choke sleeve  100 . When the choke sleeve  100  is moved to the appropriate position so that the protrusions  174  and  180  are radially opposed, flow through the stage  150  is reduced to a minimum, which may mean no flow, in some embodiments of the invention. 
   In accordance with some embodiments of the invention, the radial protrusions  180  of the outer surface  102  of the choke sleeve  100  have the same spacing along the longitudinal axis  58  as the diffuser surfaces  170  of the inner surface  72  of the housing  70 . Therefore, the stages  150  are identical and drop the same pressure in accordance with some embodiments of the invention. However, in other embodiments of the invention, the surfaces  72  and  102  may be configured to cause the stages  150  to differ and produce different pressure drops. Thus, many variations are possible and are within the scope of the appended claims. 
   Stages may also be designed to feature cuts or protrusions along the circumference of the flow channel. This may be used to further optimize flow and choking characteristics for certain applications, as described further below in connection with  FIG. 7 . 
   By moving the choke sleeve  100  in an upward longitudinal direction relative to the housing  70 , flow through the flow restriction section  190  is further restricted, as the gap between the radial protrusion  180  and the diffuser surface  72  narrows. Eventually, when the protrusions  174  and  180  radially align, a minimum flow (no flow, for example) exists through the flow control stage  150 . Conversely, by moving the choke sleeve  100  in a downward longitudinal direction relative to the housing  70 , the flow is increased, as the gap between the radial protrusion  180  and the diffuser surface  72  increases. 
     FIG. 4  depicts the flow control section  54  for the case in which the protrusions  174  and  180  are aligned and the minimum flow (no flow, for example) exists through the flow control section  54 . To completely shut off flow through the flow control section  54 , fluid seals may be used either within the choking stages or external to them. 
   For example,  FIG. 5  depicts a flow control section  300  of a flow control device according to another embodiment of the invention. The flow control section  300  has a similar design to the flow control section  54 , with the same reference numerals being used to depict similar elements. However, the flow control section  300 , unlike the flow control section  54 , includes radial seals  302  to form fluid seals between the radial protrusions  174  and  180  when aligned. As a more specific example, in accordance with some embodiments of the invention, the seals  302  (o-rings, for example) may be located in annular grooves, which are formed in the interior surface  72  of the housing  70 . Other seals and scaling arrangements may be used in accordance with other embodiments of the invention. 
   For the embodiments of the flow control sections  54  and  300  that are discussed above, a unidirectional flow is assumed. In this regard, the discussion above assumes a flow from the inlet  57  to the outlet  60  ports, such as a flow that occurs in connection with fluid that is produced from the well. It is noted that flow may be communicated in an opposite direction in accordance with other embodiments of the invention. More particularly, in accordance with other embodiments of the invention, instead of the surface normals of the diffuser angles having downward components, the surface normals may have upward components, as fluid may flow from the ports  60  to the ports  57  for the case in which the flow control section is part of an injection choke in which fluids are injected into the well. Thus, many variations are possible and are within the scope of the appended claims. 
   In accordance with other embodiments of the invention, a flow restriction section of a choke may be bidirectional in nature in that the flow may be in either longitudinal direction. As a more specific example,  FIG. 6  depicts an exemplary flow control section  350  in accordance with some embodiments of the invention. As depicted in  FIG. 6 , the flow control section  350  includes a housing  359  that generally circumscribes an internal choke sleeve  400 . The housing  359  includes radial ports  409  (one port  409  being depicted in  FIG. 6 ) that is generally open to the well; and the choke sleeve  400  includes radial ports (one port  410  being depicted in  FIG. 6 ) that is generally open to the central passageway of a string. As depicted in  FIG. 6 , the flow control section  350  generally circumscribes and may be symmetrical about a longitudinal axis  352  of the section  350 ; and thus, the symmetrical other half of the section  350  is not depicted in  FIG. 6 . 
   Unlike the flow control sections that are described above, the housing  359  includes an interior surface  360  that accommodates flow in either an upward direction or a downward direction. The surface  360  defines flow control stages  410  (flow control stages  410 .sub. 1 ,  410 .sub. 2  . . .  410 .sub.N, being depicted as examples in  FIG. 6 ) along the longitudinal axis  352 . Each flow control stage  410  includes a beveled diffuser surface  370  (part of the surface  360 ) that has a surface normal with an upward component and a diffuser surface  372  (part of the surface  360 ) with a surface normal that has a downward component. A radial protrusion  366  of the surface  360  extends inwardly and separates the diffuser surfaces  370  and  372 . 
   The choke sleeve  400  has an outer surface  402  that is generally complementary to the inner surface  360  of the housing  359 . As can be seen in  FIG. 6 , movement of the choke sleeve  400  in an upward longitudinal direction relative to the housing  359 , further restricts flow. Eventually, when the radial protrusions  366  of the surface  360  of the housing  359  align with corresponding radial protrusions  420  of the surface  402  of the choke sleeve  400 , the flow is reduced to a minimum (no flow, for example). Conversely, by moving the choke sleeve  400  in a downward longitudinal direction relative to the housing  359 , the flow is increased. Fluid seals may be located in annular grooves that are formed in the radial protrusions  366  for purposes of completely blocking off flow when the protrusions  306  and  420  align, in accordance with some embodiments of the invention. 
   In some embodiments of the invention, adjustment of flow rates may be achieved by translation and/or rotation of either the inner or outer sleeve. 
   In some embodiments of the invention, the flow control choke may be designed to accommodate injection and production flows while in operation. In such designs, the geometry of each stage may be symmetrical about a center plane that is perpendicular to the longitudinal axis of the choke. However, non-symmetric variations are equally envisioned under this invention and offer more flexibility to optimize performance for specific applications. 
   Referring to  FIG. 7 , as an example of another embodiment of the invention, an internal choke sleeve  500  (to replace any of the choke sleeves described herein) includes additional cuts  510  for purposes of further optimizing flow and choke characteristics. As depicted in  FIG. 7 , for a particular stage, the cuts  510  may be uniformly spaced in about a longitudinal axis  514  of the sleeves  500 . Between stages, the cuts  510  of one stage may be rotated with respect to the cuts of another adjacent stage. Thus, many variations are possible and are within the scope of the appended claims. 
   While the present invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.