Choke Assembly

Abstract

A choke assembly comprises an inlet ( 48 ) for a multiphase fluid stream, the stream comprising a first relatively heavy fluid phase and a second relatively light fluid phase; a first fluid outlet ( 116 ); a choke element ( 22 ) disposed between the inlet and the first fluid outlet operable to control the flow of fluid between the inlet and the first fluid outlet; a separation chamber ( 40, 114 ) disposed to provide separation of phases in the fluid stream upstream of the choke element; and a second outlet ( 118 ) for removing fluid from the separation cavity. The choke assembly is of particular use in the control of fluid streams produced from a subterranean well, in particular oil and gas produced from a subsea well.

What is claimed is: 
     
         1 . A method of controlling and separating the flow of multiphase fluid streams, the method comprising:
 introducing a first fluid stream rich in lighter fluid phases into a separation zone;   introducing a second fluid stream rich in heavier fluid phases into a separation zone to form a combined fluid stream in which the first fluid stream and the second fluid stream are in contact;   allowing separation of the fluid phases in the combined fluid stream to occur in the separation zone;   causing lighter fluid phases separated in the separation zone to flow through a choke element to a first outlet;   controlling the flow of fluid phases through the choke element by adjusting the choke element; and   causing the remaining fluid phases to flow to a second outlet.   
     
     
         2 . The method according to  claim 1 , wherein the first fluid stream is introduced into the separation zone upstream of the second fluid stream. 
     
     
         3 . The method according to  claim 2 , wherein either one or both of the first and second streams is preconditioned prior to being introduced into the separation zone. 
     
     
         4 . The method according to  claim 3 , wherein the preconditioning comprises initiating separation of the phases in the fluid stream. 
     
     
         5 . The method according to  claim 1 , further comprising subjecting the fluid passing through the choke element to further separation. 
     
     
         6 . A choke assembly comprising:
 a choke element for controlling the flow of fluid therethrough;   a first inlet for a lighter fluid stream;   a second inlet for a heavier fluid stream; and   at least one outlet for fluid.   
     
     
         7 . A choke assembly comprising:
 a choke element comprising a moveable choke component;   a stem connected to the moveable choke component;   wherein the stem has a bore therethrough to provide an outlet for fluid from within the choke element; and   wherein the choke element comprises a cage having a plurality of openings therein and a plug, the plug being moveable longitudinally with respect to the cage.   
     
     
         8 . The choke assembly according to  claim 7 , wherein the plug is disposed inside the cage. 
     
     
         9 . The choke assembly according to  claim 7 , wherein the choke element is arranged to induce a rotational flow pattern in fluid passing through the choke element. 
     
     
         10 . The choke assembly according to  claim 7 , further comprising means for subjecting fluid leaving through the outlet to further separation. 
     
     
         11 . The choke assembly according to  claim 10 , wherein the said means comprises a separation chamber. 
     
     
         12 . A method for controlling and separating a multiphase fluid stream, the method comprising:
 passing the fluid stream through a choke element and controlling the flow of fluid using the choke element;   introducing the fluid stream into a separation zone and causing phases of the fluid stream to separate; and   removing a lighter fluid phase from the separation zone through an actuation stem extending from the choke element.   
     
     
         13 . A choke assembly comprising a choke element comprising:
 a cage having a plurality of openings therethrough for the passage of fluid;   a plug moveable with respect to the cage to open and close the openings in the cage; and   wherein the openings in the cage extend tangentially to the cage, each opening comprising an outer portion extending from the outer surface of the cage having a first cross-sectional area and an inner portion extending from the inner surface of the cage having a second cross-sectional area, the first cross-sectional area being greater than the second cross-sectional area.   
     
     
         14 . The choke assembly according to  claim 13 , wherein the change in the cross-sectional area of each opening is gradual or continuous through the cage. 
     
     
         15 . The choke assembly according to  claim 14 , wherein at least a portion of each opening is curved and/or tapered. 
     
     
         16 . The choke assembly according to  claim 15 , wherein the taper is asymmetrical, being offset in the reverse direction of flow of fluid around the exterior of the cage. 
     
     
         17 . The choke assembly according to  claim 13 , wherein the cage comprises an inner cage element and an outer cage element arranged concentrically around the inner cage element. 
     
     
         18 . The choke assembly according to  claim 17 , wherein the portion of each opening extending through the outer cage element reduces in cross-sectional area in the inward direction and the portion of each opening extending through the inner cage element has a constant cross-sectional area. 
     
     
         19 . The choke assembly according to  claim 13 , wherein the ratio of the cross-sectional area of each opening at its inner end to the cross-sectional area at its outer end is from 1:1.5 to 1:5. 
     
     
         20 . A choke assembly comprising a choke element comprising:
 a cage having a plurality of openings therethrough for the passage of fluid;   a plug moveable with respect to the cage to open and close the openings in the cage;   wherein the openings in the cage extend tangentially to the cage, the cage comprising openings arranged in a plurality of bands extending circumferentially around the cage, the cross-sectional area of the openings of the bands increasing in the upstream direction of the cage.   
     
     
         21 . The choke assembly according to  claim 20 , wherein all the openings have the same cross-sectional area, the increase in cross-sectional area from band to band provided by an increasing number of openings. 
     
     
         22 . The choke assembly according to  claim 20 , wherein the bands of openings are in groups, each group comprising a plurality of bands with the bands in each group all having the same number of openings. 
     
     
         23 . The choke assembly according to  claim 22 , wherein each group comprises two bands of openings. 
     
     
         24 . The choke assembly according to  claim 20 , wherein the openings in a given band are offset circumferentially from the openings in an adjacent band. 
     
     
         25 . The choke assembly according to  claim 20 , wherein the plug is disposed within the cage. 
     
     
         26 . A method of controlling the flow of a fluid, the method comprising:
 introducing the fluid into a flow control zone having a general downstream direction in which the fluid is required to flow, the fluid being introduced into the flow control zone through a plurality of openings;   wherein fluid introduced through a first group of openings, downstream of a second group of openings, establishes a generally toroidal flow pattern within the flow control zone, whereby the effective cross-sectional area available for the flow of fluid introduced through the second group of openings in the downstream direction is reduced.   
     
     
         27 . The method according to  claim 26 , wherein the first group comprises a plurality of openings. 
     
     
         28 . The method according to  claim 26 , wherein fluid introduced through the second group of openings is caused to form a second generally toroidal flow pattern disposed upstream of the first group of openings. 
     
     
         29 . The method according to  claim 28 , further comprising introducing fluid through a third group of openings to form a third generally toroidal flow pattern upstream of the second. 
     
     
         30 . A choke installation comprising two or more of a choke assembly as claimed in  claim 6 ,  7 ,  13 , or  20 . 
     
     
         31 . A wellhead installation comprising a choke assembly as claimed in any of  claim 6 ,  7 ,  13 , or  20 . 
     
     
         32 . The wellhead installation according to  claim 31 , wherein the wellhead is a subsea wellhead.