You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND 
       [0001]    The invention generally relates to a downhole valve that has incrementally adjustable open positions and a quick close feature. 
         [0002]    In well testing and production, it is often desirable to regulate the flow of well fluid into a tubing string. For this purpose, the tubing string may include a valve. As a more specific example, a particular type of valve is a multiple position valve, or choke. In general, the choke may have a closed setting that blocks well fluid communication through the valve, and the choke may also have multiple discrete open settings. Each open setting establishes a different cross-sectional flow area for the choke, and thus, the choke may have multiple incrementally adjustable open positions. 
         [0003]    A conventional choke may contain a J-slot mechanism to transition the choke through its settings. With a J-slot mechanism, the choke cannot be randomly changed between settings; but rather, the choke&#39;s open and closed settings follow a predefined order, or sequence, which is established by the corresponding J-slot groove. Each setting change may be effected, for example, by cycling the pressure in a control line. 
         [0004]    The sequence that is imposed by the J-slot mechanism may limit how quickly the choke can be closed. For example, the choke may currently be at open setting number two, out of eight open settings (as an example). To transition the choke to the closed setting from open setting number two, the choke may need to transition through all of the intervening settings (i.e., open setting number three through open setting number eight) before the closed setting is reached. 
       SUMMARY 
       [0005]    In an embodiment of the invention, a valve that is usable with a well includes an indexer and a closing mechanism. The indexer includes a profile to establish a sequence of open settings for the valve, and the indexer is adapted to respond to first control stimuli to transition the valve through the settings according to the sequence. The closing mechanism is adapted to operate independently of the sequence in response to a second control stimulus to close the valve. 
         [0006]    In another embodiment of the invention, a system that is usable with a well includes a string, a first control line and a second control line. The string includes a valve to control fluid communication between the well and a central passageway of the string. The valve includes an indexer and a closing mechanism. The indexer includes a profile to establish a sequence of open settings for the valve, and the indexer is adapted to respond to first signals to transition the valve through the settings according to the sequence. The closing mechanism is adapted to operate independently of the sequence in response to a second signal to close the valve. 
         [0007]    In yet another embodiment of the invention, a technique that is usable with a well includes providing a profile to establish a sequence of open settings for a valve. The technique includes transitioning the valve through the open settings in response to first stimuli; and in response to a second stimulus, closing the valve. The closing of the valve is independent of the sequence. 
         [0008]    Advantages and other features of the invention will become apparent from the following drawing, description and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0009]      FIG. 1  is a schematic diagram of a well according to an embodiment of the invention. 
           [0010]      FIGS. 2 and 3  are partial cross-sectional views of the choke of  FIG. 1  for different operational states of the choke taken along line  2 - 2  of  FIG. 1  according to an embodiment of the invention. 
           [0011]      FIG. 4  is an exploded perspective view of incrementing and indexing sleeves of the choke according to an embodiment of the invention. 
           [0012]      FIGS. 5 ,  6 ,  7 ,  8  and  9  are illustrations depicting interaction between the incrementing and indexing sleeves according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Referring to  FIG. 1 , an embodiment 10 of a well in accordance with the invention includes a wellbore  20  that is lined with a casing string  22 , although the wellbore  20  may be cased or uncased, depending on the particular embodiment of the invention. A tubular string  30  extends into the wellbore  20 , and as depicted in  FIG. 1 , the string  30  extends through a particular production zone  50 , which may be isolated by upper  54  and lower  58  packers, for example. 
         [0014]    It is noted that although  FIG. 1  depicts the wellbore  20  as being a vertical wellbore, the string  30  may likewise extend through a lateral, or deviated wellbore, in accordance with other embodiments of the invention. Additionally, the well  10  may be a subterranean or a subsea well, depending on the particular embodiment of the invention. Thus, many variations are contemplated and are within the scope of the appended claims. 
         [0015]    The string  30  includes a flow control device, or valve, such as a downhole multi-position choke  60 . As described herein, the choke  60  has a closed setting to block all well fluid through the choke and multiple discrete open settings. Each open setting establishes a different cross-sectional area through the choke&#39;s well fluid flow path. For example, one of the open settings may establish a twenty-five percent cross-sectional area; another open setting may establish a seventy-five percent cross-sectional area; and another open setting may fully open well fluid communication through the choke  60 . 
         [0016]    In accordance with embodiments of the invention described herein, the open settings of the choke  60  cannot be randomly selected, but rather, the setting selection is subject to a predefined selection order, or sequence. As a more specific example, in accordance with some embodiments of the invention, the choke  60  transitions from one open setting to the next in response to control stimuli, such as pressure signals, which are communicated through an open choke control line  64 . The control line  64  may, for example, extend between the choke  60  and a surface pressure source  70  (as an example). 
         [0017]    As a specific example, an exemplary pressure signal to transition the choke  60  from one open setting to the next may involve pressurizing the control line  64  (via the pressure source  70 ) above a pressure threshold and thereafter bleeding the control line pressure below the pressure threshold. For example, if the choke  60  is currently at the fifty percent open setting (as a non-limiting example), then the application of the next pressure signal may cause the choke  60  to transition to the sixty-seven percent open setting (as a non-limiting example). It is noted that other types of pressure signals other than a simple pressure up and down cycle may be used to cycle the choke  60  through its open settings, in accordance with other embodiments of the invention. 
         [0018]    For purposes of closing the choke  60 , a control stimulus, such as a pressure signal (a pressure that exceeds a predefined threshold, for example), may be applied via a close control line  62 , a control line that may extend between the choke  60  and a surface pressure source  68  (as an example). The ability of the choke  60  to transition to the closed setting is independent of the above-described selection sequence for the open settings and thus, does not depend on the current setting of the choke  60 . Therefore, in response to a single pressure cycle in the control line  62 , the choke  60  is capable of bypassing any part of the selection sequence to immediately transition from any one of the open settings to the closed setting. In accordance with some embodiments of the invention, a single pressurization of the control line  62  causes the choke  60  to rapidly close, regardless of the current setting of the choke  60 . 
         [0019]    As a more specific example, the control lines  62  and  64  may be pressurized in the following manner for purposes of controlling the choke  60  in accordance with some embodiments of the invention. In general, to select a particular open setting, the pressure in the control line  62  may be maintained below a minimum threshold; and the pressure in the control line  64  may then be manipulated to cycle the choke  60  until the desired setting is reached. More specifically, in accordance with some embodiments of the invention, each time the pressure in the control line  64  is pressurized above a certain threshold, the choke  60  advances pursuant to the selection sequence from one open setting to the next. After each setting change, the control line  64  may be bled off, or de-pressurized, below the minimum pressure threshold and subsequently re-pressurized to advance the choke  60  to the next setting. As set forth above, at any time, the control line  64  may be de-pressurized and the control line  62  may be pressurized for purposes of closing the choke  60 . 
         [0020]      FIG. 2  depicts a partial cross-sectional view of the choke  60 , taken along line  2 - 2  of  FIG. 1 . In particular,  FIG. 2  depicts the left-hand view of the cross-sectional diagram on the left-hand side of a longitudinal axis  100 . The longitudinal axis  100 , in general, is coaxial with the longitudinal axis of the string  30  near the choke  60 . As can be appreciated by one of skill in the art, the choke  60  is generally symmetrical about the longitudinal axis  100 , with the right-hand cross-section being omitted from  FIG. 2 . 
         [0021]    In general, the choke  60  includes a housing  110  that includes radial ports  120  (one radial port  120  being depicted in  FIG. 2 ) that are formed in the housing  110 . Although the housing  110  is depicted in the figures as being an outer housing, it is noted that in other embodiments of the invention, the housing  110  may be an inner housing. Fluid communication between the radial ports  120  and a central passageway  111  (which is in fluid communication with a central passageway of the string  30 ) of the choke  60  is controlled by the axial position of a sleeve  140 , which may be an inner (as depicted in the figures) or outer sleeve, depending on the particular embodiment of the invention. 
         [0022]    For the state of the choke depicted in  FIG. 2 , the choke  60  is fully open, i.e., the choke  60  is in the open setting at which full fluid communication occurs through the ports  120 . For the other open settings of the choke  60 , the sleeve  140  moves upwardly to partially close fluid communication through the ports  120 , and the extent of the upward travel of the sleeve  40  is a function of the particular open setting. 
         [0023]    The sequencing of the choke  60  is controlled by the action of an indexer, which, as an example, may include an incrementer, such as an exemplary incrementing sleeve  160 , and an indexing sleeve  180 . The incrementing  160  and indexing  180  sleeves generally circumscribe the longitudinal axis  100 . In general, the indexing sleeve  180  includes an outer cam groove  182  that spirally, or helically, extends around the longitudinal axis  100  and is engaged by a pin  190  that is attached to and radially extends from the interior of the housing  110 . 
         [0024]    The incrementing sleeve  160 , as described below, responds to pressure signals in the control line  64  (via a floating piston  150  described below) to move axially, rotate and engage the indexing sleeve  180 . The engagement of the indexing sleeve  180  by the incrementing sleeve  160  causes the indexing sleeve  180  to axially change positions and rotate. The axial translation of the indexing sleeve  180 , in turn, causes a corresponding axial position translation of the sleeve  140  to change the position of the sleeve  140  with respect to the radial ports  120 . Therefore, from the fully open setting of the choke  60  that is depicted in  FIG. 2 , each cycle of the incrementing sleeve  160  (as described below) causes a corresponding translation and rotation of the indexing sleeve  180  to incrementally advance the sleeve  140  upwardly to a different position and thus, establish a different open setting for the choke  60 . 
         [0025]    As depicted in  FIG. 2 , the choke  60  includes a spring  170  (a coiled spring, for example) that resides between an inner annular shoulder  112  of the housing  110  and an outer annular shoulder  165  of the incrementing sleeve  160  for purposes of returning the incrementing sleeve  160  to an initial position after the incrementing sleeve  160  incrementally adjusts the position of the indexing sleeve  180 , as described below. The floating piston  150  resides in an annular cavity that is formed between the incrementing sleeve  160  and a lower shoulder  142  of the sleeve  140 . The piston  150  isolates the control lines  62  and  64 . As depicted in  FIG. 2 , the control line  62  extends through a radial port of the housing  110  to establish fluid communication between the control line  62  and the region below the piston  150 ; and the control line  64 , via a radial port in the housing  110 , establishes fluid communication above the piston  150 . 
         [0026]    Referring to  FIG. 4  in conjunction with  FIG. 2 , the choke  60  may be operated in the following manner. It is assumed for this discussion that the close control line  62  is de-pressurized (i.e., the control line  64  has a pressure below a minimum pressure threshold). When pressure is applied to the control line  64 , the floating piston  150  moves in a downward position and moves the incrementing sleeve  160  toward the indexing sleeve  180  while compressing the spring  170 . Due to this downward translation of the incrementing sleeve  160  a lower finger  168  of the incrementing sleeve  160  contacts one of a plurality of stepped faces  186  of the indexing sleeve  180 . The stepped faces  186  collectively form a profile that establishes the selection sequence for the open settings of the choke  60 . As depicted in  FIG. 4 , in accordance with some embodiments of the invention, the stepped faces  186  may be formed in the upper end of the indexing sleeve  180 . 
         [0027]    In other embodiments of the invention, the incrementing sleeve  160  may include a plurality of fingers  168 . For these embodiments of the invention, the pattern of stepped faces  186  depicted in  FIG. 4  is repeated on the circumference of the indexing sleeve  180 , so that each finger  168  has an associated pattern of stepped faces  186 . 
         [0028]    Upon the engagement of the lower finger  168  with one of the stepped faces  186 , the incrementing sleeve  160  pushes the indexing sleeve  180  downwardly, which causes the indexing sleeve  180  to engage an annular shoulder  194  of the sleeve  140 , thereby resulting in incrementing the choke&#39;s position. Because the incrementing sleeve  160  and indexing sleeve  180  have cam grooves  162  and  182 , respectively, both of these sleeves rotate while axially translating as soon as they engage with each other. This rotational movement is not transmitted to the sleeve  140 . The translation movement stops when the incrementing sleeve  160  contacts the housing  110 . 
         [0029]    When the pressure in the open control line  64  is bled off, the spring  170  axially translates the incrementing sleeve  160  in an upward direction and the sleeve  160  engages the floating piston  150 . Because displacement of the incrementing sleeve  160  is controlled by the cam groove  162  (as further described below in connection with  FIGS. 5-9 ), the incrementing sleeve  160  rotates and translates back to its initial position and is therefore ready to engage the next stepped face  186  of the indexing sleeve  180  (which has rotated one incremental position since the last engagement). 
         [0030]      FIG. 3  depicts a partial cross-sectional view of the choke  60 , illustrating the choke  60  when in its closed position. For this state of the choke  60 , pressure in the control line  64  is bled off, and the closed control line  62  is pressurized. The floating piston  150  and the sleeve  140  form at least part of a closing mechanism of the choke  60 , in accordance with some embodiments of the invention. More specifically, when pressure is applied to the control line  62  (regardless of the current setting of the choke  60 ), the floating piston  150  moves upwardly and engages the sleeve  140 , thereby pushing the sleeve  140  in an upward direction until the floating piston  150  lodges against an interior annular shoulder  191  of the housing  110 . During this movement, the sleeve  140  engages the incrementing sleeve  180 , which rotates in return due to the cam profile  182  (see  FIG. 4 ). Once the sleeve  140  reaches this fully closed position, the indexing sleeve  180  has fully rotated so that it is ready to increment to open setting number one when pressure is once again applied to the open control line  64 . The structure of the closing mechanism may be varied in other embodiments of the invention. 
         [0031]    Referring back to  FIG. 4 , the cam groove  162  of the increment sleeve  160  has a profile that permits the increment sleeve  160  to rotate after each engagement with the indexing sleeve  180  and then return to its initial position (ready to increment to open setting number one) after engagement with the sleeve  140 .  FIGS. 5 ,  6 ,  7 ,  8  and  9  illustrate the interaction between the increment  160  and indexing  180  sleeves and the role of the cam groove  162 , in accordance with some embodiments of the invention. 
         [0032]      FIG. 5  depicts the state of the incrementing sleeve  160  and indexing sleeve  180  sleeves when pressure is applied to the open control line  64  (the close control line  62  is assumed to be de-pressurized). This pressure produces an axial force  200  via the floating piston  150  that pushes the incrementing sleeve  160  towards the indexing sleeve  180 , until the indexing sleeve  180  is engaged by the lower finger  168  of the incrementing sleeve  160 . Referring to  FIG. 6 , the finger  168  comes into contact with one of the stepped faces of the indexing sleeve  180 . During this translation of the incrementing sleeve  160  towards the indexing sleeve  180 , the pin  164  (see  FIG. 3 , for example) traverses the portion  162   a  of the cam groove  162 . 
         [0033]    Referring to  FIG. 6 , after the indexing sleeve  160  and the incrementing sleeve  180  are in contact, they both rotate and axially translate at the same time due to the cam profile  162  of the indexing sleeve  160  and the cam profile  182  of the incrementing sleeve  180 . This interaction transitions the choke  60  to the next open setting. During this translation and rotation of the indexing sleeve  160  with the incrementing sleeve  180 , the pin  164  (see  FIG. 3 , for example) traverses the portion  162   b  of the cam groove  162 . 
         [0034]    Referring to  FIG. 7 , upon bleeding of the pressure from the open control line  64 , an axial force  210  is produced by the spring  170  (see  FIG. 3 , for example) to push the incrementing sleeve  160  and floating piston  150  (see  FIG. 2 , for example) back to their initial positions. Before the axial force  210  is produced the pin  164  is at the intersection of the portion  162   b  and  162   c . It has already traversed  162   b  and is ready to move into  162   c  as soon as the axial force  210  starts being produced. 
         [0035]    Referring to  FIG. 8 , the pin  164  has finished traversing the portion  162   c  of the cam groove  162 , and is ready to cause the incrementing sleeve  160  to rotate and translate on the last portion of the return stroke. Referring to  FIG. 9 , the pin  164  then traverses the portion  162   d  of the cam groove  162  to place the incrementing sleeve  160  ready to engage to the next position on the next pressurization of the control line  64 . 
         [0036]    Other embodiments are within the scope of the appended claims. For example, in accordance with other embodiments of the invention, control stimuli other than pressure signals (such as electrical signals, for example) may be used to select the choke&#39;s settings, regardless of whether the setting is one of the multiple open settings or the closed setting. For these embodiments of the invention, the choke may include an electro-mechanical actuator, for example. As another example, in other embodiments of the invention, at least part of the choke&#39;s operation may be controlled using stimuli that are applied using a downhole tool (a shifting tool, for example). As other examples, the stimuli used to control the choke may be wireless, hard-wired, etc. Thus, the choke may contain a variety of different control mechanism to responds to the many different types of stimuli, and all of these variations are within the scope of the appended claims. 
         [0037]    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.

Summary:
A valve that is usable with a well includes an indexer and a closing mechanism. The indexer includes a profile to establish a sequence of open settings for the valve, and the indexer is adapted to respond to first control stimuli to transition the valve through the settings according to the sequence. The closing mechanism is adapted to operate independently of the sequence in response to a second control stimulus to close the valve.