Subsea Heat Exchangers For Offshore Hydrocarbon Production Operations

Abstract

A subsea heat exchanger is disclosed that includes a production fluid inlet, a production fluid outlet, and first and second heat exchanger units coupled to the inlet and outlet. Each heat exchanger unit includes an outer tubular member, an inner tubular member disposed within the outer tubular member, and an annulus radially disposed between the inner tubular member and the outer tubular member. In addition, each heat exchanger unit includes a bridging assembly coupled between the first heat exchanger unit and the second heat exchanger unit. The bridging assembly includes a connector including a throughbore in communication with the inner tubular member of the first heat exchanger unit and the inner tubular member of the second heat exchanger unit. In addition, the bridging assembly includes a tubular stab that fluidly couples the annulus of the first heat exchanger unit to the annulus of the second heat exchanger unit.

What is claimed is: 
     
         1 . A subsea heat exchanger, comprising:
 a production fluid inlet;   a production fluid outlet;   a first heat exchanger unit and a second heat exchanger unit each coupled to the inlet and the outlet, wherein each heat exchanger unit has a central axis, a first end, and a second end opposite the first end, and wherein each heat exchanger unit comprises:
 an outer tubular member extending axially from the first end to the second end of the heat exchanger unit; 
 an inner tubular member disposed within the outer tubular member, wherein the inner tubular member extends axially from the first end to the second of the heat exchanger unit; 
 an annulus radially disposed between the inner tubular member and the outer tubular member; and 
   a bridging assembly coupled to the second end of the first heat exchanger unit and the second end of the second heat exchanger unit, wherein the bridging assembly includes:
 a connector having a central connector axis, a first end coupled to the second end of the first heat exchanger unit, a second end coupled to the second end of the second heat exchanger unit, and a throughbore in communication with the inner tubular member of the first heat exchanger unit and the inner tubular member of the second heat exchanger unit; and 
 a tubular stab having a central stab axis oriented parallel to and radially spaced from the connector axis, wherein the tubular stab fluidly couples the annulus of the first heat exchanger unit to the annulus of the second heat exchanger unit. 
   
     
     
         2 . The subsea heat exchanger of  claim 1 , wherein the inner tubular member of each heat exchanger unit includes a flange disposed at the second end of the heat exchanger unit;
 wherein each flange includes a port extending parallel to and radially spaced from the central axis of the corresponding heat exchanger unit; and   wherein a first end of the tubular stab is received within the port in the flange of the inner tubular member of the first heat exchanger unit, and a second end of the tubular stab is received within a port in the flange of the inner tubular member of the second heat exchanger unit.   
     
     
         3 . The subsea heat exchanger of  claim 2 , wherein at least one of the first end and the second end of the tubular stab is freely slidable within the corresponding port. 
     
     
         4 . The subsea heat exchanger of  claim 2 , wherein each flange further includes a radially outer annular surface that slidingly and sealingly engages a radially inner surface of the corresponding outer tubular member. 
     
     
         5 . The subsea heat exchanger of  claim 1 , wherein the bridging assembly includes a plurality of tubular stabs uniformly circumferentially spaced about the central connector, wherein each tubular stab has a central stab axis oriented parallel to and radially spaced from the connector axis, wherein the plurality of tubular stabs fluidly couple the annulus of the first heat exchanger unit to the annulus of the second heat exchanger unit. 
     
     
         6 . The subsea heat exchanger of  claim 1 , further comprising a closed thermal processing loop in fluid communication with the annulus of each of the first heat exchanger unit and the second heat exchanger unit, wherein the thermal processing loop is configured to circulate a thermal transfer fluid through the annulus of the first heat exchanger unit, the tubular stab, and the annulus of the second heat exchanger unit. 
     
     
         7 . The subsea heat exchanger of  claim 6 , wherein the thermal processing loop further includes a radiator configured to cool the thermal transfer fluid. 
     
     
         8 . The subsea heat exchanger of  claim 1 , further comprising:
 a third heat exchanger unit coupled to the inlet and the outlet, wherein the third heat exchanger unit includes a central axis, a first end, and a second end opposite the first end, and wherein the third heat exchanger unit further comprises:
 an outer tubular member extending axially from the first end to the second end of the third heat exchanger unit; 
 an inner tubular member disposed within the outer tubular member, wherein the inner tubular member extends axially from the first end to the second of the third heat exchanger unit; and 
 an annulus radially disposed between the inner tubular member and the outer tubular member; 
   a first stiffening plate secured to the first end of the first heat exchanger unit and the first end of the third heat exchanger unit; and   a second stiffening plate secured to the second end of the first heat exchanger unit and the second end of the third heat exchanger unit;   wherein the first stiffening plate and the second stiffening plate are configured to support all of the weight of the first heat exchanger unit and the third heat exchanger unit.   
     
     
         9 . The subsea heat exchanger of  claim 8 , wherein the central axis of the first heat exchanger unit is parallel to and radially spaced from the central axis of the third heat exchanger unit. 
     
     
         10 . The subsea heat exchanger of  claim 1 , where each heat exchanger unit further comprises a plurality of baffles disposed within the annulus, wherein the baffles are configured to induce a sinusoidal flow path for thermal transfer fluid. 
     
     
         11 . The subsea heat exchanger of  claim 10 , where each baffle includes a radially outer curved surface that sealingly engages with a radially inner surface of the corresponding outer tubular member. 
     
     
         12 . An offshore production system for producing hydrocarbon fluids from a subterranean well, the system comprising:
 a production tree disposed at the sea floor, wherein the production tree includes a plurality of valves configured to control a flow of hydrocarbon fluids from the subterranean well;   a riser assembly fluidly coupled to the production tree and configured to flow the hydrocarbon fluids to a vessel disposed at the sea surface;   a heat exchanger disposed on the sea floor and including:
 an inlet configured to receive the hydrocarbon fluids from the production tree; 
 an outlet configured to supply the hydrocarbon fluids to the riser assembly; 
 a plurality of heat exchanger units coupled to the inlet and the outlet, wherein each heat exchanger unit has a central axis, a first end, and a second end opposite the first end, and wherein each heat exchanger unit comprises:
 an outer tubular member extending axially from the first end to the second end of the heat exchanger unit; 
 an inner tubular member disposed within the outer tubular member, wherein the inner tubular member extends axially from the first end to the second of the heat exchanger unit, and wherein the inner tubular member of each heat exchanger unit is in fluid communication with the inlet and the outlet; and 
 an annulus radially disposed between the inner tubular member and the outer tubular member; and 
 
 a closed thermal processing loop in fluid communication with the annulus of each of the heat exchanger units, wherein the thermal processing loop is configured to circulate a thermal processing fluid through the annuli of the plurality of heat exchanger units. 
   
     
     
         13 . The offshore production system of  claim 12 , wherein the inner tubular member of each heat exchanger unit includes a pair of flanges, with one flange is disposed at each of the first end and the second end of the corresponding heat exchanger unit;
 wherein each flange includes a port extending parallel to and radially spaced from the central axis of the corresponding heat exchanger unit.   
     
     
         14 . The offshore production system of  claim 13 , wherein each flange further includes a radially outer annular surface that slidingly and sealingly engages a radially inner surface of the corresponding outer tubular member. 
     
     
         15 . The offshore production system of  claim 13 , wherein the heat exchanger further includes a bridging assembly coupled to the second end of a first of the plurality of heat exchanger units and the second end of a second of the plurality of heat exchanger units, wherein the bridging assembly includes:
 a connector having a central connector axis, a first end coupled to the flange at the second end of the first heat exchanger unit, a second end coupled to the flange at the second end of the second heat exchanger unit, and a throughbore in communication with the inner tubular member of the first heat exchanger unit and the inner tubular member of the second heat exchanger unit; and   a tubular stab having a first end disposed within the port in the flange at the second end of the first heat exchanger unit and a second end disposed within the port in the flange at the second end of the second heat exchanger unit.   
     
     
         16 . The offshore production system of  claim 15 , wherein at least one of the first end and the second end of the tubular stab member is freely slidable within the corresponding port. 
     
     
         17 . The offshore production system of  claim 15 , wherein the heat exchanger further includes:
 a transfer pipe in fluid communication with the inner tubular member of the first heat exchanger unit and the inner tubular member of a third of the plurality of heat exchanger units; and   a transfer tube in fluid communication with the annulus of the first heat exchanger member and the annulus of the third heat exchanger member;   wherein the transfer tube has a first end disposed within the port in the flange at the first end of the first heat exchanger unit and a second end disposed within the port in the flange at the first end of the third heat exchanger unit; and   wherein central axis of the third heat exchanger unit is parallel to and radially spaced from the central axis of the first heat exchanger unit.   
     
     
         18 . The offshore production system of  claim 17 , wherein the heat exchanger further includes:
 a first stiffening plate secured to the first end of the first heat exchanger unit and the first end of the third heat exchanger unit; and   a second stiffening plate secured to the second end of the first heat exchanger unit and the second end of the third heat exchanger unit;   wherein the first stiffening plate and the second stiffening plate are configured to support all of the weight of the first heat exchanger unit and the third heat exchanger unit   
     
     
         19 . The offshore production system of  claim 12 , wherein each of the plurality of heat exchanger units further includes a plurality of baffles disposed within the annulus, wherein the baffles are configured to induce a sinusoidal flow path for thermal transfer fluid. 
     
     
         20 . The offshore production system of  claim 19 , wherein each baffle includes a radially outer surfaced surface that sealingly engages with a radially inner surface of the corresponding outer tubular member. 
     
     
         21 . A method for cooling hydrocarbon fluids produced from an offshore subterranean well, the method comprising:
 (a) producing hydrocarbon fluids from a production tree disposed at the sea floor to an inlet;   (b) flowing the hydrocarbon fluids from the inlet through an inner tubular member of a first heat exchanger unit;   (c) flowing the hydrocarbon fluids through a connector of a bridging assembly into an inner tubular member of a second heat exchanger unit;   (d) flowing a thermal transfer fluid through an annulus of the first heat exchanger unit; and   (e) flowing the thermal transfer fluid through a tubular stab of the bridging assembly into an annulus of the second heat exchanger unit.   
     
     
         22 . The method of  claim 21 , further comprising cooling the thermal transfer fluid after (d) and (e). 
     
     
         23 . The method of  claim 22 , wherein cooling the thermal transfer fluid comprises flowing the thermal transfer fluid through a radiator. 
     
     
         24 . The method of  claim 21 , further comprising heating the thermal transfer fluid before (d) and (e). 
     
     
         25 . The method of  claim 21 , further comprising:
 (f) flowing the hydrocarbon fluids through a transfer pipe into an inner tubular member of a third heat exchanger unit after (c); and   (g) flowing the thermal transfer fluid through a transfer tube into an annulus of the third heat exchanger unit after (e).   
     
     
         26 . The method of  claim 21 , further comprising recirculating the thermal transfer fluid to the annulus of the first heat exchanger unit after (d) and (e).