Patent Publication Number: US-6338385-B1

Title: Retrievable downhole adjustable choke

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of provisional application serial No. 60/129,572, filed on Apr. 16, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates generally to devices for regulating flow in oil and gas wells. More specifically, the invention relates to a downhole adjustable choke which is suited for metering of well fluid. 
     2. Background Art 
     In a multi-zone production well, it is often desirable to produce well fluid over a range of flow rates from different production zones. This flow control may be achieved through a downhole adjustable choke in each production zone. Typically, the downhole adjustable choke includes an orifice with a flow area that can be suitably adjusted to achieve different flow rates. This orifice is typically provided by a tapered plug which extends into a tapered valve seat. The flow area of the orifice is increased or decreased by moving the tapered plug relative to the tapered valve seat. When the tapered plug tightly engages the tapered valve seat, flow through the orifice is prevented. The downhole adjustable choke, however, operates in the presence of highly corrosive fluids and solid particles which can erode the tapered plug and/or valve seat such that the tapered plug can no longer tightly engage the tapered valve seat or the condition of the flow through the orifice is undesirably altered. In such a situation, the tapered plug and/or valve seat will need to be replaced to allow the adjustable choke to function properly. This valve-seat replacement operation is generally time consuming and expensive and may need to be repeated frequently to ensure that flow is properly controlled. 
     SUMMARY OF THE INVENTION 
     The invention is a downhole adjustable choke which comprises a choke body that is adapted to be lowered into a borehole. The choke body has a bore and an orifice connected to the bore. A sleeve is disposed inside the bore of the choke body. The sleeve has an orifice which is aligned with the orifice in the choke body. A flow plug is movably disposed inside the sleeve. An actuator coupled to the flow plug moves the flow plug relative to the sleeve so that the flow area of the orifice in the sleeve is adjustable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross section view of a downhole adjustable choke. 
     FIG. 2 shows the downhole adjustable choke of FIG. 1 in a retrievable side pocket mandrel of a production tubing. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 depicts a downhole choke  1  which comprises a choke body  2 . The choke body  2  is provided with a bore  4  and one or more orifices  6  which are in communication with the bore  4 . An outlet nipple or sub  8  is received in the lower end of the choke body  2 . The outlet nipple  8  is secured to the lower end of the choke body  2  by a threaded connection  11 . A sleeve  10  is disposed in the bore  4 . The wall of the sleeve  10  includes one ore more orifices  12 . The upper end of the sleeve  10  is secured to an indexing ring  14 , which is disposed in the bore  4 , by a tongue and groove connection (not shown). The indexing ring  14  is attached to a shoulder  16  in the choke body  2 . When the sleeve  10  engages the indexing ring  14  as shown, the orifices  12  in the wall of the sleeve  10  are aligned with the orifices  6  in the choke body  2 , thus allowing fluid to flow inside the sleeve  10 . A valve seat  15  is arranged between the sleeve  10  and the outlet nipple  8 . The lower end of the valve seat  15  abuts the outlet nipple  8  so that the valve seat  15  is retained within the bore  4  by the outlet nipple  8 . Seals  17  are provided to seal between the choke body  2  and the sleeve  10 , between the choke body  2  and the outlet nipple  8 , and between the choke body  2  and the valve seat  15 . The seals  17  prevents fluid leakage from between the choke body  2  and the outlet nipple  8 . 
     A flow plug  18  is disposed inside the sleeve  10  to control the rate at which fluid flows through the orifices  12 . The flow plug  18  is movable within the sleeve  10  to increase or decrease the flow area of the orifices  12  or to close the orifices  12 . A seal  20  is provided between the flow plug  18  and the sleeve  10 . The seal  20  prevents fluid leakage from between the flow plug  18  and the sleeve  10 . The flow plug  18  has a profile  22  which is adapted to mate with a similar profile  24  in the valve seat  15  so as to allow the valve seat  15  to provide a positive stop for the flow plug  18 . When the profiles  22  and  24  contact, the flow plug  18  is in the closed position, i.e., there in no flow through the orifices  12 . An actuator  26  is mounted at the upper end of the choke body  2 . The actuator  26  is coupled to the flow plug  18  by a plunger  28 . As shown, the plunger  28  extends from the actuator  26  into the flow plug  18 . The free end  30  of the plunger  28  abuts a shoulder  32  in the flow plug  18  such that when the actuator  26  moves the plunger  28  relative to the sleeve  10 , the flow plug  18  also moves. 
     The plunger  28  is provided with an anti-rotation feature which prevents it from rotating when the output shaft  25  of the actuator  26  rotates. This anti-rotation feature includes a key  9 , which is attached to the indexing ring  14  with pins  11 , and a key way  13  in the plunger  28 . The key  9  engages the key way  13  in the plunger  28 , thereby preventing the plunger  28  from rotating. A cup  34  is secured to the plunger  28  by a split ring  36  and pins  38 . The cup  34  prevents the plunger  28  from falling through the flow plug  18 . A chamber  40  is defined between the sleeve  10 , the plunger  28 , the flow plug  18 , and the seat indexing ring  14 . Pressure in the interior of the flow plug  18  is communicated to the chamber  40  through a flow channel  42  and a flow port  44  in the plunger  28 , so that the pressure in the chamber  40  is equalized with the pressure below the plunger  28 . By equalizing the pressure in the chamber  40  with the pressure below the plunger  28 , the actuator  26  acts against minimal differential force. A packing seal set  45  seals between the choke body  2  and the plunger  28 . 
     FIG. 2 shows the downhole choke  1  in a retrievable side pocket mandrel  46  of a production tubing  48  that is suspended in a borehole  50 . The downhole choke  1  may be run into the side pocket mandrel  46  on the end of a wireline or coiled tubing. A control module  52  at the upper section of the mandrel  46  communicates with the actuator  26 . The control module  52  includes the electronic circuitry required to control the operation of the actuator  26 . Power and commands may be transmitted to the control module  52  and the actuator  26  through a power/communications cable  54  that runs from the surface. Alternatively, the downhole choke  1  may be run into the side pocket mandrel  46  on a composite coiled tubing that includes integrated power/data conductors. The pocket mandrel  46  includes flow ports  56  through which fluid in the borehole  50  can flow into the orifices  6  in the choke body  2 . The outlet nipple  8  is hydraulically connected to the interior of the tubing  48 . 
     In operation, commands are sent to the control module  52 , and the control module  52  in turn controls the actuator  26  to move the flow plug  18 . The commands may be sent to the control module  52  through the cable  54  as previously described or by modulating a column of fluid in the borehole  50 . Alternatively, commands may also be sent to the actuator  26  directly from the surface through integrated power/data conductors in a composite coiled tubing. Fluid flows into the sleeve  10  through the orifices  12  when the actuator  26  lifts the flow plug  18  from the valve seat  15 . The amount of fluid flowing through the orifices  12  is controlled by how much of the flow area of the orifices  12  is exposed. In an alternate embodiment, rows of orifices can be provided in the choke body  2  and the sleeve  10 , and the flow plug  18  can selectively open the orifices on a row so that fluid can flow into the sleeve  10  at a selected rate. The fluid which flows into the sleeve  10  exits the choke body  2  through the outlet nipple  8  and flows into the tubing  48 . 
     While the invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.