A technique that is usable with a well includes providing a sequencing valve to in a first state to communicate a first flow through a first port of the valve and in a second state close fluid communication through the first port. The technique includes communicating a second flow through an orifice of the sequencing valve during the second state of the valve and using a pressure drop across the orifice the bias the sequencing valve to remain in the second state.

[0001]     This application claims the benefit, pursuant to 35 U.S.C. § 119(e), to U.S. Provisional Application Ser. No. 60/580,751, entitled, “Methods And Apparatus For Use In Downhole Operations,” filed on Jun. 18, 2004. 
     
    
     BACKGROUND  
       [0002]     The present invention relates to methods and apparatus useful in operations in a downhole environment, and in particular useful for operations in multi-lateral wellbores having a main wellbore from which multiple bores (laterals) extend or radiate.  
         [0003]     Operations in multi-lateral wells are commonly run on coiled tubing and use a Multi Lateral Tool (MLT) to find the desired lateral leg of the well. Common operations for example include washing, cleaning out the wellbore, scale removal and stimulation. When a wellbore operation is required in a multi-lateral well, two separate operations must be performed. First, the desired bore must be found and entered using a MLT. The MLT operates at a high flow rate and a low pressure. As fluid is pumped through the MLT, the tool is manipulated in the well bore. When the end of the tool encounters a lateral, the fluid flow changes, and the associated change in flow pressure is detected at the surface. In response to this detection, the tool is then conveyed into the lateral for the desired operation. Then to perform many desired operations, such as cleanout, stimulation, or scale removal in the targeted lateral, a higher pressure is often required. However, the higher pressure required for the desired operation in the tool is often too great of a pressure at which to operate the pumping system. Therefore a shift in system flow rate and pressure is required between the steps of operating the MLT and performing the desired operation using the tool.  
       SUMMARY  
       [0004]     In an embodiment of the invention, a technique that is usable with a well includes providing a sequencing valve to in a first state, allow communication of a first flow through a first port of the valve and in a second state, close fluid communication through the first port. The technique includes communicating a second flow through an orifice of the sequencing valve during the second state of the valve and using a pressure drop across the orifice to bias the sequencing valve to remain in the second state.  
         [0005]     In another embodiment of the invention, a sequencing valve includes a body, a movable member and an orifice. The body includes a first port to communicate a first fluid flow in a first state of the valve. The movable member is located in the body and has a fluid passageway. The moveable member closes fluid communication through the first port during a second state of the valve. The orifice is attached to the moveable member to restrict a second flow through the fluid passageway of the member in the second state of the valve to create a pressure drop across the orifice to bias the moveable member to close the first port.  
         [0006]     Advantages and other features of the invention will become apparent from the following description, drawing and claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0007]      FIG. 1  depicts a work string in a lateral wellbore detection operation according to an embodiment of the invention.  
         [0008]      FIG. 2  depicts the work string in a subsequent operation in a located lateral wellbore according to an embodiment of the invention.  
         [0009]      FIG. 3  is a cross-sectional view of a sequencing valve of the work string according to an embodiment of the invention.  
         [0010]      FIG. 4  is an expanded view of a selected section of the sequencing valve taken from  FIG. 3  according to an embodiment of the invention.  
         [0011]      FIG. 5  is a flow diagram depicting a technique to locate and perform operations in lateral wellbores of a multilateral well according to an embodiment of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0012]     Referring to  FIG. 1 , in accordance with an embodiment of the invention, a work string  18  is used for purposes of locating lateral wellbores (such as an exemplary lateral wellbore  14 ) of a multilateral well  10  and performing an operation, such as an operation that involves cleaning, stimulating or removing scale deposits (as examples), in each located lateral wellbore. More specifically, in accordance with some embodiments of the invention, the work string  18  includes a tool assembly  20  that, among its other features, includes a shuttle, or sequencing, valve  28  that generally has two states: an open state (depicted in  FIG. 1 ) in which the sequencing valve  28  allows fluid communication through radial circulation ports  31  (to configure the work string  18  to be used to locate a lateral wellbore, for example); and a closed state (depicted in  FIG. 2 ) in which the sequencing valve closes fluid communication through the radial circulation ports  31  (to configure the work string to be used to perform an operation in the lateral wellbore, for example). Although fluid communication through the radial circulation ports are blocked off during the closed state of the sequencing valve  28 , the valve  28  directs a fluid flow through a central passageway of the valve  28  to a lower work tool  20 .  
         [0013]     As further described below, the sequencing valve  28  is constructed to rely on a fluid flow that is present in the closed state of the valve  28  to bias the valve  28  to remain in the closed state. Due to this bias, when the flow that flows through the central passageway of the sequencing valve  28  during its closed state decreases below a certain threshold flow (a fluid flow that is less than one half of the fluid flow used to close the valve  28 , as an example), the valve  28  transitions back to the open state. Thus, the re-opening of the sequencing valve  28  is not affected by underbalanced well conditions.  
         [0014]     In accordance with some embodiments of the invention, in its open state, the sequencing valve  28  is configured to communicate fluid to the annulus that surrounds the tool assembly  20  at a relatively low pressure and a relatively high flow rate. More particularly, as depicted in  FIG. 1 , in the open state of the sequencing valve  28 , a fluid flow  32  exits the radial circulation ports  31  into the annulus  19  of the well. When the sequencing valve  28  is in the open state, the work string  18  may be used to, for example, communicate fluid from the surface to the annulus in an operation (herein called a “wellbore detection operation”) to locate a lateral wellbore. This operation may, for example, use a flow rate of approximately 1.5 barrels per minute (BPM), although other flow rates may be used in other embodiments of the invention.  
         [0015]     During the wellbore location operation, when a target or expected flow rate is encountered, a lateral wellbore detection tool  26  of the work string  18  generates a pressure signal that is sensed at the surface (via a detector  14  that is coupled to a pressure sensor  13  at the surface, for example) to indicate a lateral wellbore has been located. At this point, the flow to the sequencing valve  28  is increased (to a flow rate of approximately 1.8 BPM, as an example) to transition the valve  28  to its closed state to reconfigure the tool assembly  20  to use the work tool  30 .  
         [0016]     More particularly, when the sequencing valve  28  is in the closed state, the fluid from the work string  18  flows in its entirety (due to the closing of the radial circulation ports  31 ) to nozzles  36  of the work tool  30  so that an operation may be performed in the lateral wellbore. As examples, the work tool  30  may be used in an operation to clean, stimulate or remove scale from the lateral wellbore when the sequencing valve  28  is in its closed state.  
         [0017]     As depicted in  FIG. 1 , in accordance with some embodiments of the invention, the nozzles  36  communicate a flow  38  into the well during both the open and closed states of the sequencing valve  28 . However, due to the relatively low pressure of the flow when the sequencing valve  28  is in its open state (i.e., when the radial circulation ports  31  are open), very little flow (as compared to the overall flow through the valve  28 ) exits the nozzles  36 . This is to be compared to closed state of the valve  28  in which all of the flow through the valve  28  exits the nozzles  36 .  
         [0018]     In addition to the work tool  30  and the lateral wellbore detection tool  26 , the tool assembly  20  may include, for example, a motor head assembly  24  that receives fluid (via the central passageway of the work string  18 ) that is pumped downhole via a surface pump  11  (as an example). The motor head assembly  24  may be controlled from the surface of the well for purposes of controlling the rate and pressure of the fluid that is communicated downstream from the assembly  24  to the sequencing valve  28 . The tool assembly  20  may also include a connector  22  for purposes of connecting the tool assembly  20  to the portion of the work string  18  above the assembly  20 . In accordance with some embodiments of the invention, the work string  18  may be formed from coiled tubing, although other types of conveyance mechanisms (such as jointed tubing, for example) for the tool assembly  20  may be used, in other embodiments of the invention.  
         [0019]      FIG. 2  depicts the tool assembly  20  when the sequencing valve  28  is in its open state and upon location of the exemplary lateral wellbore  14 . As shown in  FIG. 2 , when the tool assembly  20  lands inside the entrance portion of the lateral wellbore  14 , the tool assembly  20  bends. This bending, in turn, may be detected by a bending sub of the lateral wellbore detection tool  26 . In response to this bending, the lateral wellbore detection tool  26  communicates a pressure signal to the surface of the well that may be detected for purposes of indicating to an operator at the surface that the lateral wellbore  14  has been located. At this point, the operator at the surface of the well may then transition the sequencing valve  28  into its closed state by increasing the flow rate of the fluid flow to the sequencing valve  28  above a predetermined threshold. The sequencing valve  28  responds to the increased flow rate (as further described below) to close the radial circulation ports  31  and transition to the closed state. In this state, all flow through the sequencing valve  38  is routed through the nozzles  36  in accordance with the lateral wellbore operation to be performed inside the lateral wellbore  14 .  
         [0020]     Although embodiments of the invention are described herein in which the tool string  20  transitions between a relatively high flow rate, low pressure operation and a relatively low flow rate, lower pressure operation, the embodiments that are described herein are applicable in general to all types of operations that may be performed with a lateral wellbore detecting tool.  
         [0021]     Referring now to a more specific example of a possible embodiment of the sequencing valve  28 ,  FIG. 3  depicts an embodiment of the valve  28  in its open state, i.e., the state in which fluid communication may occur through the radial circulation ports  31 . In accordance with some embodiments of the invention, the sequencing valve  28  includes a housing that is formed from an upper tubular housing section  50   a , a middle tubular housing section  50   b  and a lower tubular housing section  50   c . The housing sections  50   a ,  50   b  and  50   c  are concentric with each other, share a common longitudinal axis  51  and include central passageways  52 ,  54  and  56 , respectively, in some embodiments of the invention. Regardless of the state of the sequencing valve  28 , the central passageways  52 ,  54  and  56  are always in communication in that the sequencing valve  28  always permits fluid communication between its top opening  60  (leading to the central passageway  52  and in communication with the central passageway of the string  18  above the sequencing valve  28 ) and its bottom opening  62  (exiting the central passageway  56  and in communication with the wash tool  32 ). As depicted in  FIG. 3 , in some embodiments of the invention, the radial ports  31  may be formed in the sidewall of the middle housing section  50   b.    
         [0022]      FIG. 4  depicts a detailed section  80  (see  FIG. 3 ) of the sequencing valve  28  to illustrate certain features of the valve  80 , which regulate the communication of fluid through the radial circulation ports  31 . Referring to  FIG. 4 , in accordance with some embodiments of the invention, the sequencing valve  28  includes a moveable member, a piston  109 , which is generally concentric with the longitudinal axis  51  of the valve  28 . The piston  109  includes an inner passageway  111  and has an upper surface  122  that presents an area (herein called the “A1 area”) on which certain forces may act on the piston  109 , as further described below. The inner passageway  111  of the piston  109  receives an upper end of a tubular valve seat  84  and a control orifice sleeve  100 . The piston  109  is attached to the upper end of the tubular valve seat  84  and is concentric with the valve seat  84 . The valve seat  84  forms part of the passageway  54 , and the lower end  86  of the valve seat  84  has a lower surface  130  that presents an area (herein called the “A3 area”) on which certain forces act on the valve seat  84 , as further described below. A lower end  86  of the valve seat  84  is constructed to form a seal with a sealing element  88  of the sequencing valve  28  when the valve seat  84  is in its lowest position (a position not depicted in  FIG. 4 ) and presses against the element  88 .  
         [0023]     In the lowest position of the valve seat  84 , the sequencing valve  28  is in its closed state so that the tubular sidewall of the valve seat  84  blocks fluid communication through the radial circulation ports  31 . Therefore, in the closed state of the sequencing valve  28 , fluid is communicated through the valve  28  only through the central passageways  52 ,  54  and  56  (and to the work tool  32  (see  FIG. 2 , for example), as no fluid exits the radial circulation ports  31 .  
         [0024]     The sequencing valve  28  is biased to remain in the closed state by the flow that passes through the valve  28  in this state due to the presence of the control orifice sleeve  100 . More specifically, in some embodiments of the invention, the control orifice sleeve  100  is concentric with the longitudinal axis  51  and has a radially-outwardly extending shoulder  113  that is located between the top end of the valve seat  84  and a radially-inwardly extending shoulder of the piston  109  to secure the control orifice sleeve  100  to the piston  109  and the valve seat  84 . The control orifice sleeve  100  creates a flow restriction that introduces a pressure differential, or drop, which biases the sequencing valve  28  to remain in its closed state. The control orifice sleeve  100  has a central passageway  105  that is generally aligned with the longitudinal axis  51  of the sequencing valve  28  and presents a cross-sectional flow area  117  (herein called the “A2 area”).  
         [0025]     In accordance with some embodiments of the invention, during the open state of the sequencing valve  28 , all of the flow passes through the central passageway  105  of the control orifice sleeve  109  and creates a pressure differential across the piston  109 . This pressure differential is proportional to the A1 area less the A2 area and produces a downward force on the piston  109  and the attached valve seat  84 . This downward force, however, is countered by an upward force that is exerted by a coil spring  120  (of the sequencing valve  28 ), which is compressed by downward displacement of the piston  109 .  
         [0026]     At a predetermined flow rate, such as 1.8 barrels per minute (BPM) (as an example), the pressure differential across the control orifice sleeve  100  becomes sufficient to compress the coil spring  120  enough to allow the valve seat  84  to seal against the sealing element  88  to close off the radial ports  31  and transition the sequencing valve  28  from the open to the closed state.  
         [0027]     In the closed state of the sequencing valve  28 , the pressure differential across the control orifice sleeve  100  acts on the effective piston area, which is the A3 area less the A2 area. An additional force acts on the piston  109  equal to the pressure difference between the inside of the sequencing valve  28  and the annular area that surrounds the sequencing valve. This pressure difference acts on the A1 area less the A3 area. In this configuration, the primary force that keeps the sequencing valve  28  in the closed state is the pressure drop across the control orifice sleeve  100 . The proportion of the force that acts downwardly on the piston  109  created by the flow through the orifice sleeve  100  and a force that is created by the inside-to-outside pressure differential may be changed by increasing or decreasing the A3 area relative to the A1 area and the A2 area. Adjusting the area ratio allows the sequencing valve  28  to be designed to open at any portion of closing pressure in the range of, for example, 0.1 to 1.2 times the closing pressure, in accordance with some embodiments of the invention.  
         [0028]     When the sequencing valve  28  transitions to the closed state, the flow through the radial circulation ports  31  is shut off, diverting all of the flow to the work tool  30  (see  FIG. 2 , for example). Since more flow is exiting the nozzles  36  of the tool  30  and not through the radial circulation ports  31 , the pressure inside the string  18  rises. This pressure increase is detectable at the surface, and in response to detection of the pressure increase, the flow rate may be decreased to approximately one BPM (as an example) to limit the surface pressure. This flow rate may then be maintained while the operation is performed in the lateral wellbore.  
         [0029]     In accordance with some embodiments of the invention, after the wellbore processing operation is completed, the flow rate may be decreased to approximately 0.75 BPM. The pressure drop across the control orifice sleeve  100  decreases accordingly; and as a result of this pressure drop, the valve seat  84  moves in a upward direction, and the sequencing valve  28  open transitions back to the open state. At this point, the string  18  may be moved to the next lateral wellbore and then the above-described process may be repeated.  
         [0030]     It is noted that the sequencing valve  28  may have a number of sealing elements, such as o-rings, to form fluid barriers between different the parts of the sequencing valve  28 . For example, in some embodiments of the invention, the sequencing valve  28  includes an o-ring  152  that is located in an annular slot that is formed in the outer surface of the lower end of the upper housing section  50   a  for purposes of forming a seal between the upper housing section  50   a  and the middle housing section  50   b . Similarly, a seal may be formed between the middle housing section  50   b  and the lower housing section  50   c , in some embodiments of the invention. Additionally, in accordance with some embodiments of the invention, the outer surface of the piston  109  includes in an annular slot that houses an o-ring  150  that forms a seal between the outer surface of the piston  109  and the inner surface of the middle housing section  50   b . Additionally, in accordance with some embodiments of the invention, an annular slot is formed in the inner of the piston  109  for purposes of receiving an o-ring  107  to form a seal between the inner surface of the piston  109  and the outer surface of the valve seat  84 .  
         [0031]     To summarize, referring to  FIG. 5 , a technique  200  may be used in accordance with embodiments of the invention for purposes of locating lateral wellbores and performing operations in the located wellbores. Pursuant to the technique  200 , a flow is communicated to the sequencing valve  28 , which has a relatively high flow rate and a low pressure, as depicted in block  202 . Based on the resultant pressure signal that is detected at the surface of the well in response to the bending of the sub of the lateral wellbore detection tool  26  (see  FIG. 1 ), the next lateral wellbore may be located. If a determination (diamond  208 ) is made that a lateral wellbore has been located, then control transitions to block  212  in which a flow is communicated to the sequencing valve  28 , which has a relatively low flow rate and a high pressure to close the sequencing valve. As pointed out above, in connection with block  212 , the pressure inside the string  18  may rise upon closing of the sequencing valve  28 , and in response to the pressure increase that is detected at the surface of the well, the flow rate may be decreased to limit surface pressure. When the operation is complete, the flow rate is reduced to the appropriate level to remove the pressure bias that is introduced by the control orifice sleeve  100  to cause the sequencing valve  28  to transition to its open state.  
         [0032]     If it is determined (diamond  216 ) that the wellbore operation is complete, then a decision is made (diamond  220 ) whether another wellbore is to be processed. If so, control transitions to block  202 .  
         [0033]     While the use of terms of orientation and direction, such as “up,” “vertical,” “lower,” etc. have been used herein for purposes of simplicity to describe certain embodiments of the invention, it is understood that other directions and orientations are within the scope of the appended claims. For example, in other embodiments of the invention, the piston of the sequencing valve may move in an upward direction for purposes of closing off radial circulation ports. Thus, many variations are possible and are within the scope of the appended claims.  
         [0034]     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.