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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional patent application Ser. No. 62/109,729 filed Jan. 30, 2015, and entitled: “Subsea Heat Exchangers for Offshore Hydrocarbon Production Operations,” which is hereby incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

This disclosure relates generally to subsea hydrocarbon production. More particularly, this disclosure relates to subsea heat exchangers for use with offshore hydrocarbon production systems.

The temperatures of hydrocarbon bearing subterranean reservoirs can range from very high (e.g., higher than 400° F.) to very low (e.g., lower than −75° F.). The temperature of any given reservoir is typically dictated by factors such as, for example, the composition of the materials and fluids within the reservoir, the depth of the reservoir, and proximity to other geological features (e.g., hot spots, faults, etc.). During production from a reservoir, produced fluids having extreme temperatures can push the operational limits of the production equipment (e.g., manifolds, risers, piping, etc.), potentially resulting in damage to such equipment. These problems are exacerbated when the production operations are conducted offshore, where the wellhead and much of the production equipment is located on the sea floor, which may be several thousand feet down from the sea surface.

BRIEF SUMMARY OF THE DISCLOSURE

Some embodiments disclosed herein are directed to a subsea heat exchanger. In an embodiment, the subsea heat exchanger includes a production fluid inlet and a production fluid outlet. In addition, the subsea heat exchanger includes 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. Each heat exchanger unit includes 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 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 to the second end of the first heat exchanger unit and the second end of the second heat exchanger unit. 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. In addition, the bridging assembly includes 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.

Other embodiments disclosed herein are directed to an offshore production system for producing hydrocarbon fluids from a subterranean well. In an embodiment, the system includes 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. In addition, the system includes a riser assembly fluidly coupled to the production tree and configured to flow the hydrocarbon fluids to a vessel disposed at the sea surface. Further, the system includes a heat exchanger disposed on the sea floor. The heat exchanger includes an inlet configured to receive the hydrocarbon fluids from the production tree and an outlet configured to supply the hydrocarbon fluids to the riser assembly. In addition, the heat exchanger includes a plurality of heat exchanger units coupled to the inlet and the outlet. Each heat exchanger unit has a central axis, a first end, and a second end opposite the first end. In addition, each heat exchanger unit includes an outer tubular member extending axially from the first end to the second end of the heat exchanger unit. Further, each heat exchanger unit includes 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. Still further, each heat exchanger unit includes an annulus radially disposed between the inner tubular member and the outer tubular member. Further, the heat exchanger includes 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.

Still other embodiments disclosed herein are directed to a method for cooling hydrocarbon fluids produced from an offshore subterranean well. In an embodiment, the method includes producing hydrocarbon fluids from a production tree disposed at the sea floor to an inlet, and flowing the hydrocarbon fluids from the inlet through an inner tubular member of a first heat exchanger unit. In addition, the method includes flowing the hydrocarbon fluids through a connector of a bridging assembly into an inner tubular member of a second heat exchanger unit, and flowing a thermal transfer fluid through an annulus of the first heat exchanger unit. Further, the method includes flowing the thermal transfer fluid through a tubular stab of the bridging assembly into an annulus of the second heat exchanger unit.

Embodiments described herein comprise a combination of features and advantages intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical advantages of the disclosed exemplary embodiments in order that the detailed description that follows may be better understood. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the embodiments described herein. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the disclosed embodiments, reference will now be made to the accompanying drawings in which:

FIG. 1 is a schematic view of an embodiment of an offshore production system including a subsea heat exchanger in accordance with the principles disclosed herein;

FIG. 2 is a perspective view of the subsea heat exchanger of FIG. 1;

FIG. 3 is a cross-sectional side view of the subsea heat exchanger of FIG. 1;

FIG. 4 is an enlarged cross-sectional view of an outer end of a heat exchanger unit within the subsea heat exchanger of FIG. 1;

FIG. 5 is a cross-sectional view of a bridging assembly extending between two adjacent heat exchanger units within the subsea heat exchanger of FIG. 1;

FIG. 6 is an exploded, perspective view of a heat exchanger unit of the subsea heat exchanger of FIG. 1;

FIG. 7 is an enlarged, perspective view of a baffle of the heat exchanger unit of FIG. 6;

FIG. 8 is a top schematic view of the subsea heat exchanger of FIG. 1 illustrating the respective flow paths of the production fluid and thermal transfer fluid;

FIG. 9 is an enlarged perspective view of one end of the subsea heat exchanger of FIG. 1 illustrating the transfer pipes and tubes interconnecting adjacent rows of heat exchanger units;

FIG. 10 is a perspective view of an embodiment of a subsea heat exchanger for use within the offshore production system of FIG. 1;

FIG. 11 is a perspective view of an embodiment of a subsea heat exchanger for use within the offshore production system of FIG. 1; and

FIG. 12 is a top schematic view of an embodiment of a subsea heat exchanger for use within the offshore production system of FIG. 1.

DETAILED DESCRIPTION

The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis.

As previously described, production fluids having an extremely hot or cold temperature can stress production equipment (e.g., manifolds, risers, piping, etc.), potentially causing damage to such production equipment. This can be particularly problematic in offshore production operations where much of the production hardware is disposed at the sea floor. Embodiments disclosed herein include heat exchangers and related equipment for use within a subsea hydrocarbon production system to either raise the temperature of produced fluids having a very low temperature and lower the temperature of produced fluids having a very high temperature to reduce the thermal stresses experienced by production equipment, thereby offering the potential to reduce the likelihood of damage to such equipment and enhance the operating lifetime of such equipment. In addition, the heat exchangers of at least some of the embodiments disclosed herein reduce the rate of corrosion for subsea production equipment due, at least in part, to the reduction in the temperature of produced fluids. Further, the heat exchangers of at least some of the embodiments disclosed herein reduce (or eliminate) the need for specialized equipment within the subsea production system that are designed and rated to receive and flow fluid of an extreme temperature (e.g., equipment including increased wall thickness, specialized materials, etc.).

Referring now to FIG. 1, an embodiment of an offshore hydrocarbon production system 10 in accordance with the principles described herein is shown. Production system 10 facilitates the production of fluids from a wellbore 14 extending into a subterranean reservoir. In this embodiment, production fluids comprise hydrocarbons, such as, for example, liquid petroleum, natural gas, hydrocarbon condensate, and combinations thereof. Production system 10 generally includes a subsea production tree 12 mounted to a wellhead 13, a subsea heat exchanger 100, a manifold 16, a pipeline end termination (PLET) 18, and a riser assembly 20. Production tree 12, wellhead 14, heat exchanger 100, manifold 16, and PLET 18 are positioned along the sea floor 7. In addition, tree 12, heat exchanger 100, manifold 16, PLET 18, and riser assembly 20 are fluidly connected to one another with a plurality of fluid conduits or jumper lines 17.

Wellhead 13 is disposed at the upper end of a cased wellbore 14, thereby fluidly coupling production tree 12 to wellbore 14. Production tree 12 includes a plurality of valves 15 that control the flow of produced fluids from wellbore 14. Subsea heat exchanger 100 receives production fluids from tree 12 and either raises or lowers the temperature of the produced fluids, as appropriate, such that when the produced fluids exit exchanger 100 they are at an acceptable and/or predetermined temperature within the safe operating temperature range of each piece of downstream equipment (e.g., manifold 16, PLET 18, riser assembly 20, etc.). Manifold 16 receives production fluids from heat exchanger 100, and, in certain embodiments, also receives production fluids from other wellbores (not shown). Thereafter, the production fluids are passed from manifold 16, through PLET 18, and are routed to riser assembly 20. In this embodiment, riser assembly 20 includes a lower riser assembly 19 disposed at or proximate the sea floor 7 and a marine riser 21 extending vertically from lower riser assembly 19 to a surface vessel 22 disposed at the sea surface 9. Thus, during production operations, production fluids are received by riser assembly 20 from PLET 18 at the lower riser assembly 19, and are subsequently routed to vessel 22 at the sea surface 9 through riser 21. In general, riser 21 can be any suitable riser or conduit for routing production fluids from the sea floor to the sea surface, such as, for example, a free standing riser, a catenary riser, a top tensioned riser, or some combination thereof all while still complying with the principles disclosed herein.

Referring now to FIG. 2, subsea heat exchanger 100 generally includes a production fluid inlet 101, a production fluid outlet 102, a plurality of modular heat exchanger units 120 disposed between and fluidly coupled to the inlet 101 and outlet 102, and a thermal processing loop 200 fluidly coupled to each of the units 120. In this embodiment, exchanger 100 is configured to cool (i.e., remove thermal energy from) relatively hot production fluids as they pass from inlet 101 to outlet 102; however, in other embodiments, the heat exchanger (e.g., exchanger 100) is configured to heat (i.e., transfer thermal energy to) relatively cold production fluids with. As will be described in more detail below, exchanger 100 may be referred to herein as a “modular” heat exchanger, since it is constructed from a plurality of modular heat exchanger units 120 that can be added or removed as needed based on the specific heat transfer requirements and specifications of the associated production system (e.g., system 10).

Referring now to FIGS. 2 and 3, in this embodiment, each heat exchanger unit 120 includes a central or longitudinal axis 125, a first or outer end 120a, a second or inner end 120b opposite outer end 120a, an outer tubular member 130 extending axially between ends 120a, 120b, and an inner tubular member 140 concentrically disposed within outer tubular member 130 and extending axially between ends 120a, 120b. Each end 120a, 120b further includes a stiffening plate 122 that is connected to and supports each outer tubular member 130 and inner tubular member 140 within unit 120.

In this embodiment, heat exchanger units 120 are arranged into three adjacent, parallel rows 110A, 110B, 110C. In particular, two units 120 are disposed within each row 110A, 110B, 110C such that the units 120 within each row 110A, 110B, 110C share a pair of common stiffening plate 122 at each end 120a, 120b with the corresponding adjacent units within the other rows 110A, 110B, 110C. One or more of the plates 122 may include(s) a pad eye or other similar attachment device (not shown) configured to receive cables and rigging for lowering and/or raising that particular exchanger to and/or from the sea floor 7, respectively. Moreover, as best shown in FIG. 3, the units 120 within each row 110A, 110B, 110C are arranged such that the inner end 120b of each unit 120 in a given row 110A, 110B, 110C is positioned axially adjacent the inner end 120b of a corresponding unit 120 within that same row 110A, 110B, 110C, and the central axes 125 of the units 120 within each respective row 110A, 110B, 110C are coaxially aligned (note: while only row 110A is shown in FIG. 3, it should be appreciated that each of the other rows 110B, 110C are arranged the same).

Each outer tubular member 130 is concentrically disposed about axis 125 and includes a first or outer end 130a, a second or inner end 130b opposite outer end 130a, a radially outer cylindrical surface 130c extending axially between ends 130a, 130b, and a radially inner cylindrical surface 130d extending axially between ends 130a, 130b. Each outer tubular member 130 extends axially between ends 120a, 120b of the corresponding heat exchanger unit 120, and thus, ends 120a, 130a axially aligned and ends 120b, 130b are axially aligned. In this embodiment, outer tubular member 130 is comprised of a metallic material (e.g., steel); however, it should be appreciated that a wide range of materials may be used to construct member 130, such as, for example, carbon-fiber composite.

Outer ends 130a are secured to the corresponding plate 122 and inner ends 130b are secured to the corresponding plate 122. In this embodiment, ends 130a, 130b are rigidly secured to the corresponding plate 122 at ends 120a, 120b, respectively, by welding; however, in general, any suitable method for securing two rigid components to one another may be used, such as, for example, bolts, rivets, adhesive, etc. In addition, each end 130a, 130b is coaxially aligned with an aperture or port 123 extending through plates 122 at ends 120a, 120b, respectively, such that when outer tubular member 130 is secured to plates 122 at ends 130a, 130b, an open passage is defined along axis 125 between plates 122 by outer tubular member 130.

Each inner tubular member 140 is concentrically disposed within a corresponding outer tubular member 130 and includes a first or outer end 140a, a second or inner end 140b opposite outer end 140a, a radially outer surface 140c extending axially between ends 140a, 140b, and a radially inner surface 140d also extending axially between ends 140a, 140b. Each inner tubular member 140 extends axially between ends 120a, 120b of the corresponding heat exchanger unit 120, and thus, ends 120a, 140a are axially aligned and ends 120b, 140b are axially aligned. Radially inner surface 140d defines a throughbore 142 extending axially between ends 140a, 140b. As will be described in more detail below, production fluids flow through throughbore 142 during production operations.

During assembly, inner tubular member 140 is inserted within the corresponding outer tubular member 130 through port 123 of one of the plates 122 such that (a) inner tubular member 140 is concentrically disposed within outer tubular member 130 as shown in FIG. 3; (b) outer end 140a is proximate outer end 130a; and (c) inner end 140b is proximate inner end 130b. In addition, once tubular member 140 is fully inserted within tubular member 130 an annulus 132 is formed radially between outer surface 140c and inner surface 130d that extends axially between ends 120a, 120b. As will be described in more detail below, during production operations, a thermal transfer fluid flows through annulus 132 to facilitate the transfer thermal energy (e.g., heat) away from production fluids flowing within throughbore 142. Thermal transfer fluid may comprise any suitable fluid for facilitating heat transfer (e.g., convective heat transfer) with another fluid or body. For example, thermal transfer fluid may comprise, for example, seawater, fresh water, corrosion inhibitors, ethylene glycol, propylene glycol, organic acid technology fluid (e.g., DEX-COOL® or ZEREX™), water-soluble oil, mineral oil or combinations thereof.

In this embodiment, the axial lengths of outer tubular members 130 (e.g., the length measured axially between ends 130a, 130b) and inner tubular members 140 (e.g., length measured axially between ends 140a, 140b) are no larger than the standard length of commercially available pipe, which in some cases is approximately 45 feet. Consequently, the tubulars for constructing tubular members 130, 140 may be purchased or otherwise acquired directly from the existing stock of a given supplier without the need to order custom length pipes. In addition, such a length also eliminates the need to weld or otherwise join multiple lengths of pipe to construct tubular members 130, 140, an activity which adds time and costs to the manufacturing of exchanger 100. However, it should be appreciated that such a length for shells 130 and tubes 140 is not required and each may be disposed at any suitable length while still complying with the principle disclosed herein.

Outer end 120a of each heat exchanger unit 120 is fluidly connected to either inlet 101, outlet 102, or outer end 120a of another exchanger unit 120 in the immediately adjacent row (e.g., row 110A, 110B, 110C). Specifically, referring now to FIG. 4, in this embodiment, outer end 140a of each member 140 includes a flange 150 disposed within a corresponding port 123 on one of the plates 122 that mates with a corresponding flange connector (e.g., flange connector 60) on adjacent piping in the manner described below in order to fluidly connect unit 120 within exchanger 100. While only one end 120a of a single exchanger unit 120 is shown in FIG. 4, it should be appreciated that each end 120a is generally configured to same. Flange 150 generally includes a radially outer annular surface 152 and an end face 154. Annular surface 152 includes a pair of axially adjacent seal assemblies 151. Each seal assembly 151 includes an annular recess 153 extending radially inward from annular surface 152 and an annular sealing member 155 (e.g., an S-Seal, lip seal, T-seal, O-ring, etc.) disposed within recess 153. When inner tubular member 140 is installed within outer tubular member 130, annular surface 152 slidingly engages both port 123 and radially inner surface 130d and each sealing member 155 is radially compressed between surface 130d and the corresponding recess 153. As a result, during production operations, fluid flow between surfaces 130d, 153 is restricted and/or prevented by the annular sealing assemblies 151. Face 154 includes a generally planar engagement surface 154a that extends annularly about throughbore 142 and includes an annular recess 156 that extends axially inward from engagement surface 154a.

As is shown in FIG. 4, flange 150 at outer end 140a mates and engages a corresponding flange 160 disposed on an end of an exterior pipe (e.g., inlet 101, outlet 102, etc.). In particular, engagement surface 154a on face 154 mates and engages a corresponding engagement surface 164a on a face of mating flange 160. Engagement surface 164a on mating flange 160 also includes an annular recess 166 that extends radially inward from surface 164a such that when flanges 150, 160, are mated (e.g., bolted) with one another as shown, recesses 156, 166 are generally aligned. An annular sealing member 158 (e.g., metallic or elastomeric gasket) is disposed within the aligned recesses 156, 166 and is compressed therebetween such that fluid flow between the surfaces 154a, 164a is restricted and/or prevented by the compressed sealing member 158. Additional sealing member(s) (e.g., elastomeric sealing ring(s)) may be disposed about the outer periphery of sealing member 158 to prevent seawater from contacting and thus compromising the integrity of member 158 and/or serve as a secondary barrier to prevent fluid flow between surfaces 154a, 164a.

Referring still to FIG. 4, the radially outer portion of each flange 150 includes a plurality of uniformly circumferentially-spaced apertures or ports 159 extending axially therethrough. Each port 159 receives the end of a transfer tubing member 222 which, as will be described in more detail below, delivers thermal transfer fluid into and out of annulus 132 to facilitate thermal energy transfer with production fluid flowing within throughbore 142 during production operations. Fluid flow between each tubing member 222 and the corresponding flange 150 is restricted and/or prevented by an annular sealing assembly (not shown) disposed radially therebetween. In addition, as is best shown in FIG. 9, the diameter of each flange 160 is smaller than the diameter of the corresponding flange 150 such that each tubing member 222 is positioned radially outside connector 160 as it extends axially into the corresponding port 159.

Referring now to FIGS. 3 and 5, inner ends 120b of the coaxially aligned heat exchanger units 120 within each row 110A, 110B, 110C are connected to one another with a connection or bridging assembly 170. One bridging assembly 170 will now be described it being understood the other bridging assemblies 170 are the same. As best shown in FIG. 5, in this embodiment, bridging assembly 170 includes a central connector 172 extending between opposed inner ends 140b and a plurality of uniformly circumferentially-spaced tubular members or stabs 176 disposed about connector 172. Central connector 172 is an elongate tubular member including a central axis 173 that is aligned with the axes 125 of each of the heat exchanger units 120 within row 110A, a first end 172a, a second end 172b opposite first end 172a, a radially outer surface 172c extending axially between ends 172a, 172b, and a radially inner surface 172d extending axially between ends 172a, 172b. Inner surface 172d defines a throughbore 174 extending axially between ends 172a, 172b. Each end 172a, 172b includes an annular flange 160 as previously described. In addition, inner ends 140b of tubes 140 each include a flange 150 that is configured the same as flange 150 on outer ends 140a. Thus, as is shown in FIG. 5, annular surface 152 of flange 150 at inner end 140b slidingly and sealing engages with the radially inner surface 130d and aperture 123 of the corresponding shell 130 and plate 122, respectively, in the same manner as described above for outer end 120a.

Each end 172a, 172b is connected to the inner end 140b of one of the tubular members 140 via engagement of mating flanges 150, 160. Specifically, as shown in FIG. 5, flange 160 at first end 172a of central connector 172 mates with and engages flange 150 of inner end 140b of inner tubular member 140 disposed within one of the units 120 within row 110A (i.e., the unit 120 on the left side of FIG. 5), while flange 160 at second end 172b mates with and engages flange 150 on inner end 140b of inner tubular member 140 disposed within the other unit 120 within row 110A (i.e., the unit 120 on the right side of FIG. 5). As a result, throughbore 174 in central connector 172 is coaxially aligned with both throughbores 142 in tubes 140 within row 110A, thereby forming a continuous production fluid flow path 112A extending axially between units 120 of row 110A. As is shown schematically in FIG. 8, production fluid flow paths 112B, 112C extend axially through rows 110B, 110C, respectively, and are configured the same as fluid flow path 112A described above.

Referring again to FIGS. 3 and 5, each stab 176 of bridging assembly 170 is an elongate tubular member including a first end 176a, a second end 176b opposite first end 176a, a radially outer cylindrical surface 176c extending axially between ends 176a, 176b, and a radially inner cylindrical surface 176d extending axially between ends 176a, 176b. Inner surface 176d defines a throughbore 178 extending axially through stab 176. As best shown in FIG. 5, each port 159 of flange 150 on one inner end 140b is circumferentially aligned with one port 159 of the opposed flange 150 of the other inner end 140b. One stab 176 extends axially through each pair of aligned ports 159—first end 176a being received within one port 159 on one of the units 120 within row 110A and second end 176b being received within the aligned port 159 on the other unit 120 within row 110A. Radially outer surface 176c of each stab 176 is allowed to slidingly engage at least one of the corresponding ports 159 such that units 120 within row 110A may move axially relative to stabs 176, thereby allowing bridging assembly 170 to accommodate the thermal expansion of units 120 during production operations. In this embodiment, one end (e.g., end 176a) is fixed within the corresponding port 159 such that this “fixed” end does not move axially relative to that port 159, whereas the other end (e.g., end 176b) is movably disposed within its corresponding port 159 such that this “free” end can move axially relative to its port 159. In general, any suitable method for fixing an end 176a, 176b within the corresponding port 159 may be used while still complying with the principles disclosed herein, such as, for example, welding, a retention sleeve or locking ring disposed within one of the ports 159, etc. In addition, one or more sealing assemblies (not shown) are included between radially outer surface 176c of stabs and ports 159 to restrict fluid flow therebetween during operations. For example, in some embodiments, an annular seal gland extends radially inward from radially outer surface 176c and houses an annular sealing member (e.g., an O-ring, sealing ring, etc.) that further engages with port 159; however, it should be appreciated that any other suitable sealing assembly may be used while still complying with the principles disclosed herein. Together the annuli 132 and throughbores 178 of stabs 176 define a continuous thermal fluid flow path 113A through adjacent units 120 within row 110A. As is shown schematically in FIG. 8, thermal fluid flow paths 113B, 113C extend axially through rows 110B, 110C, respectively, and are configured the same as thermal fluid flow path 113A described above.

Referring again to FIG. 3, each heat exchanger unit 120 is supported on sea floor 7 with a plurality of support members 126. More specifically, each outer end 120a is supported by a pair of outer support members 126a, and each inner end 120b is supported by an inner support member 126b. Each support member 126a, 126b includes a base or foot 127 disposed along the sea floor 7 and a plurality of columns 128 extending vertically upward from foot 127. In this embodiment, inner support member 126b includes two rows 129′, 129″ of columns 128 and outer support members 126a each include only a single row of columns 128. Each support column 128 on both inner and outer support members 126a, 126b, respectively, includes a saddle 124 that receives one of the stiffening plates 122 on ends 120a, 120b. Specifically, saddles 124 in columns 128 on outer support members 126a receive the stiffening plates 122 disposed at outer ends 120a of units 120 within rows 110A, 110B, 110C, while the saddles 124 on columns 128 on inner support member 126b receive stiffening plates 122 disposed at inner ends 120b of units 120 in rows 110A, 110B, 110C. In addition, as is best shown in FIGS. 4 and 5, each saddle 124 has an width W₁₂₄ measured axially relative to axis 125 that is greater than the axial thickness T₁₂₂ of each plate 122. Each plate 122 slidingly engages the corresponding saddle 124, and thus, during production operations, plates 122 are free to slide axially within saddles 124, such as, for example, to accommodate thermal expansion or contraction of units 120. In some embodiments, engaged surfaces of plates 122 and saddles 124 are finished or coated with a suitable surface treatment in order to reduce friction therebetween during operations. In still other embodiments, additional friction reducing mechanisms may be employed between plates 122 and saddles 124, such as, for example, rollers, bearings, etc.

Referring now to FIGS. 3, 6, and 7, each unit 120 includes a plurality of axially-spaced generally D-shaped baffles 180 disposed within annulus 132 and fixably attached to the corresponding inner tubular member 140 between ends 140a, 140b. As will be described in more detail below, baffles 180 function primarily to direct the flow of heat transfer fluid within annulus 132 during production operations. In addition, in at least some embodiments, baffles 180 also form fin-like appendages along each inner tubular member 140 that effectively increases the surface area of outer surface 140c, thereby enhancing thermal energy transfer between thermal transfer fluids in annulus 132 and production fluids within throughbore 142 during operations. In this embodiment, each unit 120 includes a total of five uniformly axially spaced baffles 180 mounted to each inner tubular member 140; however, it should be appreciated that the number, arrangement, and axial spacing of baffles 180 may be greatly varied while still complying with the principles disclosed herein.

Referring now to FIG. 7, one baffle 180 will now be described it being understood each baffle 180 is the same. In this embodiment, each baffle 180 is constructed from a pair of rigid plate members that are joined to one another. In particular, each baffle 180 includes a first or main plate member 182 and a second or locking plate member 190 secured to main plate member 182 with a pair of attachment assemblies 188. Main plate member 182 is generally C-shaped and includes a first planar side 180a, a second planar side 180b facing in the opposite direction as first side 180a, a planar end surface 181 extending axially between sides 180a, 180b, and a generally cylindrical surface 183 extending axially between sides 180a, 180b and circumferentially between the ends of planar end surface 181. A U-shaped recess or notch 184 extends radially inward from end surface 181. Recess 184 is defined by a pair of radially oriented planar surfaces 185 and a curved surface 186 extending circumferentially about axis 125 between planar surfaces 185. As will be described in more detail below, inner tubular member 140 is received within notch 184, and thus, the radius of curvature of surface 186 is the same as the radius of curvature of radially outer surface 140c of inner tubular member 140. Similarly, as will also be described in more detail below, curved outer surface 183 engages the inner surface 130d of outer tubular member 130 when baffle 180 is installed within unit 120, and thus, the radius of curvature of outer surface 130 is the same as the radius of curvature of inner surface 130d of outer tubular member 130. A pair of apertures or through holes 187 extend axially between sides 180a, 180b on opposite sides of notch 184. As will be described in more detail below, each aperture 187 receives a bolt 189 to secure main plate member 182 to locking plate member 190.

Referring still to FIG. 7, locking plate member 190 includes a first planar side 190a, a second planar side 190b facing away from first side 190a, a first planar end surface 191 extending axially between sides 190a, 190b, a second planar end surface 192 extending axially between sides 190a, 190b, and a pair of radially outer generally cylindrical surfaces 193 extending circumferentially between planar end surfaces 191, 192. A cylindrical recess or notch 194 extends radially inward from second planar end surface 192 and is defined by a curved surface 195. As will be described in more detail below, inner tubular member 140 is received within notch 194, and thus, the radius of curvature of surface 195 is the same as the radius of curvature of radially outer surface 140c of inner tubular member 140. A pair of apertures or throughbore holes 196 extend axially between sides 190a, 190b on opposite sides of notch 194. When baffle 180 is installed within the corresponding heat exchanger unit 120, curved surfaces 193 generally align with the curved surface 183, and thus, like surface 183, each of the surfaces 193 also engage with the radially inner surface 130d of outer tubular member 130. Accordingly, like surface 183, the radius of curvature of surface 193 is the same as the radius of curvature of radially inner surface 130d.

Each attachment assembly 188 includes a threaded rod or bolt 189 and a pair of threaded nuts 197. To assemble baffle 180, main plate member 182 is disposed along inner tubular member 140 at a desired location such that inner tubular member 140 is seated within notch 184 and radially outer surface 140c is engaged with curved surface 186. Thereafter, first side 190a of locking plate body 190 is engaged with second side 180b of main plate member 182 such that the apertures 187 in member 182 are substantially aligned with the apertures 196 in member 190 and radially outer surface 140c of inner tubular member 140 is engaged with curved surface 195 within notch 194. Each of the bolts 189 of assemblies 188 is then inserted within one pair of the aligned apertures 187, 196 and nuts 197 are threadably engaged to bolts 189 along each of the first side 180a of member 182 and second side 190b of member 190, thereby urging second side 180b of member 182 into engagement with first side 190a of member 190, and securing baffle 180 to inner tubular member 140 through a friction fit. It should be appreciated that baffles 180, once assembled, can be further secured to radially outer surface 140c of tubular member 140 by welding, adhesive, or some other suitable method, while still complying with the principles disclosed herein.

Referring back now to FIGS. 3 and 6, baffles 180 are disposed along inner tubular member 140 in an alternating fashion with each baffle 180 being rotated approximately 180° relative to the each immediately axially adjacent baffle 180 with respect to axis 125. As a result, when thermal transfer fluid is routed through annulus 132 between ends 120a, 120b of each unit 120, it is forced to flow generally sinusoidally around baffles 180. Without being limited to this or any other theory, such a sinusoidal like flow pattern promotes turbulence within the thermal transfer fluid, which further enhances the transfer of thermal energy between production fluids flowing within throughbore 142 of inner tubular member 140 and the thermal transfer fluid flowing within annulus 132. To prevent fluid flow between outer curved surfaces 183, 193 of members 182, 190, respectively, radially outer curved surfaces 183, 193 of baffles 180 (e.g. see FIG. 7) sealingly engage with radially inner surface 130d. As a result, thermal transfer fluid flowing though annulus 132 is forced to flow around baffles 180 proximate planar end surfaces 181, 191, thereby promoting the sinusoidal like flow pattern described above. In general, surfaces 183 and/or 193 may sealingly engage radially inner surface 130d of shell through any suitable method while still complying with the principles disclosed herein. For example, surfaces 183 and/or 193 may engage surface 130d with an integral seal, a pre-formed seal, a molded seal, etc. Without being limited to this or any other theory, in embodiments where an elastomeric type seal is utilized between surfaces 183 and/or 193 and 130d, vibrational energy is at least partially absorbed by the elastomer forming the seal during operation, which thus reduces fatigue wear on inner tubular member 140. Further, in some embodiments, surfaces 183 and/or 193 are welded or otherwise adhered to radially inner surface 130d.

Referring now to FIGS. 2, 8, and 9, during production operations, production fluid flows between inlet 101 and outlet 102 of exchanger 100. During this process, thermal transfer fluid is also routed along thermal processing loop 200 in order to facilitate the transfer of thermal energy with production fluids. Specifically, in this embodiment, the flowing of thermal transfer fluid along thermal processing loop 200 causes cooling of production fluids such that the temperature of production fluid at outlet 102 is less than the temperature of production fluid at the inlet 101. Thermal processing loop 200 generally includes a pumping unit 210, an outlet line 220 extending from pumping unit 210 to heat exchanger units 120, a recirculation line 230 extending from units 120, a thermal expansion section 240, and a cooling unit or radiator 250.

As best shown in FIG. 2, pumping unit 210 includes one or more pumps that are disposed within a support frame 212 resting on a mud mat 213. In this embodiment, two pumps 211a, 211b are disposed within pumping unit 210. Pumps 211a, 211b are variable speed pumps configured such that their speeds may be adjusted by, for example, a controller unit. As the speed of the pumps 211a, 211b within unit 210 is increased, the flow rate and/or discharge pressure also increases. Similarly, as the speed of the pumps 211a, 211b within unit 210 is decreased, the flow rate and/or discharge pressure also decreases. During installation, after the other components of exchanger 100 are installed on the sea floor 7, the pumping unit 210 is lowered, such as, for example, by suspension from a pad eye 214 (e.g., See FIG. 2) attached to unit 210, until it is seated within support frame 212. Thereafter, all associated piping (e.g., outlet line 220) is fluidly connected to pumping unit 210 by any suitable method, such as, for example, with a remotely operated vehicle (ROV). If at some point, it becomes desirable to replace or repair the pumping unit 210, the steps for installing the pumping unit 210 are simply performed in reverse order. Specifically, all piping (e.g., outlet line 220) is disconnected and removed and unit 210 is lifted out of frame 212 to the surface by, for example, a cable connected to pad eye 214. Thus, pumping unit 210 may be referred to herein as a “retrievable” pumping unit 210 or a “separately retrievable” pumping unit 210, as its installation and removal is independent from the installation and removal of the other components of exchanger 100—meaning, for example, that pumping unit 210 may be removed without requiring the removal of any other components within exchanger 100.

Thermal expansion section 240 is included within loop 200 to accommodate any thermal expansion that might occur within any of the associated lines (e.g., recirculation line 230) during operations. As shown in FIGS. 2 and 8, expansion section 240 is disposed along recirculation line 230 upstream of radiator 250. Referring specifically to FIG. 2, in this embodiment expansion section 240 includes a U-shaped bend 242 that defines a space 244 sized to accommodate any axial increase in the length of recirculation line 230 due to thermal expansion.

Referring again to FIGS. 2 and 8, radiator 250 is disposed along loop 200 upstream of pumping unit 210 and downstream of expansion section 240. In this embodiment, radiator 250 is configured to remove thermal energy (e.g., heat) collected by thermal transfer fluid being circulated through heat exchanger units 120. Radiator 250 includes a series of pipe curves or bends 252 connected by a plurality of straight sections of pipe 254. Each of the bends 252 and straight sections 254 are exposed to the surrounding ocean environment. Specifically, without being limited to this or any other theory, each of the bends 252 and pipes 254 adds considerable length to the fluid path that spent thermal transfer fluid must traverse to return to pumping unit 210. This increased length greatly increases the surface area of pipe that is exposed to the relatively cool ocean environment, and thus promotes a greater transfer of thermal energy between the thermal transfer fluids flowing through radiator 250 and the surrounding sea water during operations.

Referring still to FIGS. 2, 8, and 9, during production operations, both production and fluid and thermal transfer fluid are routed through exchanger 100 to facilitate the transfer of thermal energy therebetween. For convenience, in FIG. 8 the flow path of production fluid within exchanger 100 is shown by solid line arrows 105, while the flow of thermal processing fluid through loop 200 is shown by broken line arrows 205. Specifically, during operations, production fluid enters exchanger 100 at inlet 101 and is then routed successively through each of the rows 110A, 110B, 110C toward outlet 102. As production fluid travels through rows 110A, 110B, 110C, it flows successively through the production fluids flow paths 112A, 112B, 112C within each row 110A, 110B, 110C, respectively. Upon exiting one of the production fluid flow paths 112A, 112B, 112C, production fluids are then routed through a transfer pipe to the next successive fluid flow path (e.g., path 112B, 112C in rows 110B, 110C, respectively). For example, upon exiting fluid flow path 112A within first row 110A, production fluids are routed through a first transfer pipe 104 to fluid flow path 112B within second row 110B, and upon exiting fluid flow path 112B, a second transfer pipe 106 routes the production fluids to fluid flow path 112C within third row 110C. Each transfer pipe 104, 106 includes a pair of flange connectors 160 that mate with the corresponding flange connectors 150 on the respective units 120 within rows 110A, 110B, 110C, in the same manner as previously described above (e.g., see FIG. 4 and the associated description) (see also FIG. 9). Similarly, both inlet 101 and outlet 102 include flange connectors 160 that mate with the corresponding flange connectors 150 on tubes 140 within rows 110A, 110C in the same manner as previously described above (e.g., see FIG. 4 and the associated description).

Referring still to FIGS. 2, 8, and 9, as production fluid is routed between inlet 101 and outlet 102 as described above, thermal transfer fluid is routed along thermal processing loop 200 to facilitate cooling of production fluids. Specifically, pressurized thermal transfer fluid is discharged by pumping unit 210 into outlet line 220 where it is routed into a manifold 221 and split into a plurality of transfer tubes 222, the ends of which are installed within the ports 159 on flange 150 at outer end 140a of inner tubular member 140 within one of the heat exchanger units 120 of first row 110A as previously described (e.g., See FIG. 4 and the associated description). Thus, tubes 222 provide fluid communication with the annulus 132 in one of the units 120 within first row 110A. Thereafter, thermal transfer fluid is routed successively through each of the thermal transfer fluid flow paths 113A, 113B, 113C within rows 110A, 110B, 110C, respectively, toward recirculation line 230. Specifically, upon exiting the fluid flow path 113A, 113B, 113C within a given row 110A, 110B, 110C, respectively, thermal transfer fluid is then routed through a plurality of transfer tubes 222 to the next successive row (e.g., row 110B, 110C). In this embodiment, upon exiting fluid flow path 113A within first row 110A, a first set of transfer tubes 222′ routes the thermal transfer fluid to the flow path 113B within second row 110B, and upon exiting flow path 113B, a second set of transfer tubes 222″ routes the thermal transfer fluid to fluid flow path 113C within third row 110C. After exiting fluid flow path 113C, the now spent thermal transfer fluid is routed through a third set of transfer tubes 222′″ into a manifold 223 (which is substantially the same as the manifold 221), which further directs the fluid into recirculation line 230. Thus, in this embodiment thermal transfer fluids are routed through heat exchanger units 120 in a parallel flow arrangement with production fluids (i.e., where thermal transfer fluids flow in the same general axial direction along paths 113A, 113B, 113C as production fluid along flow paths, 112A, 112B, 112C, respectively, during operations). However, it should be appreciated that in other embodiments, thermal transfer fluids are routed in a counter flow arrangement with production fluids (i.e., where thermal transfer fluids flow in a generally opposite axial direction along paths 113A, 113B, 113C as production fluid along flow paths 112A, 112B, 112C, respectively, during operations).

In this embodiment, thermal transfer fluid within flow paths 113A, 113B, 113C has a temperature less than the temperature of the production fluids within flow paths 112A, 112B, 112C, respectively (i.e., production fluids are relatively hot in this case). Thus, as thermal transfer fluid flows through the annuli 132 of heat exchanger units 120 and the relatively warm production fluids flow through tubes 140, thermal energy is transferred from the production fluids through tubes 140 to the thermal transfer fluid. Thus, as production fluid flows within throughbores 142 of tubes 140 in rows 110A, 110B, 110C it gradually decreases in temperature such that it is at a minimum temperature when it reaches outlet 102. Conversely, as thermal transfer fluid flows through the units 120 in rows 110A, 110B, 110C, it gradually increases in temperature such that it is at a maximum temperature when it reaches recirculation line 230. As a result, upon entering recirculation line 230, the spent, warm thermal transfer fluid flows through expansion section 240 into radiator 250 where the thermal transfer fluid is cooled in the manner described above. Thereafter, the now cooled thermal transfer fluid is once again routed through pumping unit 210, thereby repeating the process described above. Thus, the thermal transfer fluid is continuously re-circulated through exchanger 100 and loop 200 throughout heat transfer operations.

Referring now to FIG. 8, during the above described thermal processing operations, a plurality of parameter measurements (e.g., temperature, pressure, flow rate, viscosity, etc.) can be taken at various points within exchanger 100 and fed (e.g., wirelessly, through cables, etc.) to a controller unit (not shown) that may be disposed subsea, on vessel 20, or at some other location, such that performance of exchanger 100 can be monitored and adjusted as necessary based on the performance and specifications of the corresponding production system (e.g., system 10). In this embodiment, a plurality of measurement assemblies 260 are disposed throughout exchanger 100, namely at inlet 101, outlet 102, recirculation line 230, and outlet line 220. Each measurement assembly 260 measures one or more of the temperature, pressure, and flow rate of the fluid flowing through the corresponding tubular (e.g., production fluid, thermal transfer fluid), and then communicates the measurement(s) to the controller unit. In this embodiment, the controller unit is disposed on vessel 20. Thereafter, either personnel, software applications, or some combination thereof, analyze the measurements from assemblies 260 and determine what, if any, adjustments need to be made by the controller unit to the operating parameters of exchanger 100 (e.g., the pump speed) in order to achieve a predetermined, desired performance. Specifically, in some embodiments, the controller unit adjusts the flow rate of thermal transfer fluid based on the measurements made by assemblies 260 (e.g., temperature) to thereby adjust and control the rate of heat transfer (e.g., convective) between production fluids and thermal transfer fluids. In this embodiment, the flow rate of thermal transfer fluid through exchanger 100 is adjusted by adjusting the speed of pumps 211a, 211b within pumping unit 210. In addition, in at least some embodiments, the controller unit may either additionally or alternatively adjust the flow rate of production fluids flowing to inlet 101 by, for example, actuating a choke valve that is disposed upstream of exchanger 100 (e.g., on tree 12). Further, in at least some embodiments, one or more heating elements may be installed at certain locations within exchanger 100 (e.g., along line 220 between unit 210 and heat exchanger units 120) that can be utilized to alter (e.g., increase) the temperature of the thermal transfer fluid flowing therethrough and thus further adjust the performance of exchanger 100. Although sensors assemblies 260 are only shown at inlet 101, outlet 102, line 230, and line 220 in this embodiment, in general, sensor assemblies 260 can be disposed at various other locations within exchanger 100 (e.g., within one or more of the heat exchanger units 120) either in addition to or in lieu of the locations shown in FIG. 8.

Referring now to FIGS. 2, 8, 10, and 11, as previously described, exchanger 100 may be referred to herein as a “modular” heat exchanger since the construction of exchanger 100 is ultimately based on a plurality of interconnected heat exchanger units 120. Thus, depending on the needs and specifications of the given production system (e.g., system 10), the number and arrangement of heat exchanger units 120 may be modified such that the heat transfer performance delivered by exchanger 100 is optimized in light of those needs and specifications.

In particular, to increase the amount of thermal transfer within exchanger 100 (i.e., to increase the amount of temperature change for production fluids between inlet 101 and outlet 102), the number of heat exchanger units 120 may simply be increased. This increase in units 120 within exchanger 100 can be accomplished in a number of different ways, all while still complying with the principle disclosed herein, and essentially works to increase the ultimate length of the flow path for production fluids between inlet 101 and outlet 102. For example, in some embodiments, plates 122 may be enlarged (i.e., extended) in the radial direction relative to the direction of axes 125 and one or more additional rows (e.g., 110A, 110B, 110C) of units 120 may be added. As another example, in some embodiments, each row 110A, 110B, 110C may include one or more additional units 120 (other than simply two in the embodiment of FIGS. 2 and 8). In these embodiments, it should be appreciated that each of the units 120 of a given row 110A, 110B, 110C will be interconnected with bridging assemblies 170 as previously described above.

Conversely, to decrease the amount of thermal transfer within exchanger 100 (i.e., to decrease the amount of temperature change for production fluids between inlet 101 and outlet 102), the number of heat exchanger units 120 may simply be decreased. This decrease in units 120 within exchanger 100 can be accomplished in a number of different ways, all while still complying with the principle disclosed herein, and essentially works to decrease the ultimate length of the flow path for production fluids between inlet 101 and outlet 102. For example, as is shown in FIG. 10, in some embodiments, plates 122 may be shortened in the radial direction relative to the direction of axes 125 and one or more rows (e.g., rows 110A, 110B, 110C) of units 120 may be removed. As another example, in some embodiments, one or more heat exchanger units 120 may be removed from each row 110A, 110B, 110C. Specifically, as shown in FIG. 11, in some embodiments, each row 110A, 110B, 110C only includes a single unit 120, and thus, no bridging members 170 are included as no two units 120 are axially aligned along axes 125 in the manner described above.

Although subsea heat exchanger 100 is described above for use in transferring thermal energy from production fluids to the thermal transfer fluid to cool the production fluids, embodiments described herein can also be used to transfer thermal energy from the thermal transfer fluid to the production fluids to warm the production fluids. For example, referring now to FIG. 12, a subsea heat exchanger 300 for use within production system 10 is shown. In this embodiment, exchanger 300 transfers thermal energy to production fluids as they are routed between inlet 101 and outlet 102.

Exchanger 300 includes many of the same components and features as exchanger 100 previously described, and thus, like numerals are used to describe shared components between exchangers 100, 300 and the description below will focus only on the differences of exchanger 300 relative to exchanger 100. As shown in FIG. 12, in addition to features of exchanger 100, exchanger 300 generally includes a pumping unit 310 in place of pumping unit 210 previously described, and a warming recirculation line 330.

Pumping unit 310 is the same as pumping unit 210 except that pumping unit 310 additionally includes one or more warming devices 311 disposed therein that are configured to warm or heat the thermal transfer fluid that is discharged thereby. In particular, in some embodiments, warming devices 311 within pumping unit 310 include one or more energy elements (e.g., resistive coils) that are electrically powered to generate heat that is transfer to thermal transfer fluid during operations. However, it should be appreciated that any suitable heating elements for increasing the temperature of the thermal transfer fluid flowing through pumping unit 310 may be used while still complying with the principles disclosed herein. It should also be appreciated that in some embodiments, similar heating elements are disposed throughout the exchanger 300 at various locations (either in lieu of or in addition to the pumping unit 310). In some of these embodiments, heating elements are disposed within a separate retrievable unit, and in still others of these embodiments, heating elements are permanently installed at various locations within exchanger 300.

Warming recirculation line 330 extends from a valve assembly 320 disposed along recirculation line 230 to pumping assembly 310. As opposed to line 230, recirculation line 330 does not include a radiator 250 or similar component configured to cool the fluids flowing therethrough (e.g., along arrows 205). Rather, the intent in flowing thermal transfer fluid through line 330 is to maintain a given temperature of the spent fluid after it exits heat exchanger units 120 such that heating operations carried out in pumping unit 310 as previously described (e.g., with one or more energy elements) are enhanced. As a result, in this embodiment, all portions of recirculation line 330 are covered with thermal insulation such that heat loss from the thermal transfer fluid to the ocean environment is minimized. In this embodiment, valve assembly 320 is actuatable between at least three different positions: (1) a first position in which thermal transfer fluids are allowed to flow freely between fluid flow path 113C in row 110C and recirculation line 230 but are restricted from flowing into and through line 330; (2) a second position in which thermal fluids are allowed to flow freely between fluid flow path 113C in row 110C and recirculation line 330 but are restricted from flowing into and through line 230; and (3) a third position in which thermal fluids are restricted from flowing into and through both lines 230, 330. In general, valve assembly 320 can be actuated by any suitable method, such as, for example, manual actuation by ROV or other interaction device, automatic actuation by a remote controller unit, etc. In addition, in at least some embodiments, recirculation line 330 may include one or more thermal expansion sections 240 being the same as that included on line 230 and previously described above.

During operations, production fluid flows along fluid flow paths 112A, 112B, 112C within rows 110A, 110B, 110C, respectively, of heat exchanger units 120 as previously described. Similarly, thermal transfer fluid flows along fluid flow paths 113A, 113B, 113C within rows 110A, 110B, 110C, respectively, of heat exchanger units 120 as previously described. However, in this embodiment, prior to injection into heat exchanger units 120 and flowing along paths 113A, 113B, 113C, thermal transfer fluids are warmed/heated by the heating devices 311 disposed within pumping unit 310, preferably to a temperature that is greater than the temperature of the production fluids entering exchanger 100 at inlet 101. Due to the differences in temperature, as the production fluids and thermal transfer fluids flow along fluid flow paths 112A, 112B, 112C and 113A, 113B, 113C, respectively, thermal energy (e.g., heat) is transferred from thermal transfer fluid across inner tubular members 140 into production fluids. As a result, during operations with exchanger 300, the temperature of production fluid increases to a maximum at outlet 102 while the temperature of thermal transfer fluid decreases to a minimum when it enters recirculation line 330. Thus, through use of exchanger 300, relatively cool production fluids are warmed in order to avoid potential problems associated with such cool production fluids such as, for example hydrate formation.

Since exchanger 300 is designed to warm production fluids as previously described, in some embodiments, recirculation line 230 is not included while still complying with the principles disclosed herein. In addition, in at least some embodiments, an additional valve assembly (not shown) is disposed along outlet line 220 which is actuatable to selectively restrict the flow of thermal transfer fluids along line 220 into fluid flow path 113A in row 110A. Thus, in these embodiments, both the valve assembly along line 220 and valve assembly 320 may be actuated to prevent fluid flow of thermal transfer fluids both into and out of rows 110A, 110B, 110C of heat exchanger units 120. Without being limited to this or any other theory, such a flow arrangement may be used to provide a substantially stagnate volume of thermal transfer fluid around tubes 140 within exchanger units 120, which thus provides an additional insulative barrier to heat transfer between production fluids and the ocean environment. In at least some of these embodiments, additional heating devices, similar to those described above to be included within pumping unit 310 may be disposed throughout units 120 within exchanger 300 to thereby maintain a desired temperature of the stagnant thermal transfer fluids trapped between the closed valve assembly on line 220 (not shown) and valve assembly 320.

In addition, in at least some embodiments, an additional flushing line is included for flushing or removing spent thermal transfer fluid. For example, referring still to FIG. 12, exchanger 300 includes a flush line 400 extending from valve assembly 320 to a valve assembly disposed along jumper line 17 downstream of exchanger 300 (see FIG. 1). In this embodiment, valve assembly 320 is additionally actuatable (i.e., additional to the positions described above) to a position where thermal transfer fluid is allowed to flow from flow path 113C in row 110C to flush line 400 and is restricted from flowing into either of the lines 230, 330. During normal operations, when thermal transfer fluid is routed through either line 230 or line 330, valve assembly 320 is actuated to prevent thermal transfer fluid from entering flush line 400. Additional isolation valves 420 are disposed on each of the recirculation lines 230, 330 and flush line 420 to allow for further and finer control of the routing of fluids during operations. Also, in this embodiment flush line 400 includes a one way check valve 430 that is configured to only allow flow along line 400 from valve assembly 320 toward valve assembly 410. Further, in this embodiment, injection points (or ports) 415 (e.g., ROV injection points) are included along both recirculation lines 230, 330, and each provides an access point for the injection or withdrawal of fluids from the respective line 230, 330 by an ROV or other suitable device (e.g., umbilical) during operations.

During operations, when it becomes desirable to remove and/or replace the thermal transfer fluid flowing through exchanger 300, valve assembly 320 is actuated to prevent thermal transfer fluid from entering either of the recirculation lines 230, 330, but allow fluid flow into flush line 400 as previously described. Once thermal transfer fluid flows into line 400 it is routed toward valve assembly 410 and into line 17, where it can either be sent to the surface (e.g., through riser assembly 20) or routed subsea to some other suitable location or collection point (e.g., subsea tank). During these operations, pumping unit 310 continues to run in order to provide the necessary pressure differential to cause positive flow of thermal transfer fluid jumper 17 through line 400. After all or substantially all of the spent thermal transfer fluid is flushed from exchanger 300 through line 400, fresh thermal transfer fluid is injected (e.g., by an ROV, pipeline, umbilical, etc.) within line 230 and/or line 330 at injection points 415, thereby refilling exchanger 300. In addition, once all spent thermal transfer fluids are flushed from exchanger 300 through line 400, valve assembly 320 is actuated to once again restrict flow through line 400 while allowing flow through recirculation line 230 and/or line 330 as previously described above.

In addition to the flushing operations described above, it should also be appreciated that flush line 400 may also be utilized to flow displaced thermal transfer fluid from exchanger 300 to line 17 when other fluids and/or additives are being injected at injection points 415 in order to prevent an over pressurization of exchanger 300. Injected additives and/or fluid may include, for example, corrosion inhibitors, biocides, plasticizers, hydrate inhibitors, or some combination thereof. Further, it should also be appreciated that in some embodiments injection points 415 may also be used to induce an initial pressurization of the thermal transfer fluid within exchanger 300 to facilitate future sampling of the thermal transfer fluid for condition monitoring of the fluid properties.

In the manner described, embodiments of subsea heat exchangers described herein (e.g., exchangers 100, 300) can be used to cool production fluids that are produced with temperatures above the operating temperature range of downstream equipment in the production system (e.g., system 10) or heat production fluids that are produced with temperatures below the operating temperature range of downstream equipment in the production system (e.g., system 10). In addition, the modular design of embodiments of subsea heat exchangers described herein (e.g., exchangers 100, 300) enables the heat exchangers to be tailored for to the desired thermal transfer performance by adding or removing modular heat exchanger units (e.g., units 120) to closely match the specifications and/or needs of the associated production system (e.g., system 10).

While certain exemplary embodiments have been shown and described, modifications thereof can be made by one of ordinary skill in the art without departing from the scope of teachings herein. For example in some embodiments, thermal insulation may be disposed about each of the heat exchanger units 120 and all associated piping within exchangers 100, 300 in order to reduce the thermal influence of the ocean environment during operations. However, it should be appreciated that in at least some of these embodiments the sections and 254 and curves 252 within radiator 250 may be left uncovered to enhance heat transfer between the thermal fluid flowing therethrough and the ocean environment. As another example, while embodiments disclosed herein have shown a heat exchanger (e.g., exchanger 100, 300) receiving production from a single wellbore (e.g., wellbore 14), it should be appreciated that in other embodiments, exchanger 100 and/or 300 may receive production fluids from more than one such wellbores while still complying with the principles disclosed herein. In addition, in at least some embodiments, one or more of the tubes 140 may be replaced with a plurality of tubes extending parallel to one another (e.g., parallel to axis 125) rather than a single length of pipe. Further, some embodiments of exchangers 100, 300 may also include a hot stab panel or other suitable access point for an ROV or similar device, to enable injection of fluids (e.g., warm fluids, hydrate inhibitors, cleaning solutions, etc.) into any portion of exchanger 100, 300. Still further, in some embodiments, pumping units 210, 310 may be utilized to provide pressurized thermal transfer fluid to more than one exchanger 100, 300, respectively, while still complying with the principles disclosed herein. Also, in at least some embodiments, pumping units 210, 310 may include one or more filter modules to capture particulate matter that is disposed within thermal transfer fluid, thereby reducing the likelihood of clogging or other failures caused by such suspended particulate matter. Moreover, while the subsea heat exchangers shown and described herein (e.g., exchangers 100, 300) include a plurality of heat exchanger units 120 that are arranged such that fluids (e.g., production fluid, thermal transfer fluid) flows generally in an S-shaped pattern (e.g., see FIGS. 8 and 10), it should be appreciated that other arrangements may be used. For example, in some embodiments, heat exchanger units 120 are stacked vertically upon one another rather than being spread along sea floor 7 as shown. Thus, the embodiments described herein are exemplary only and are not limiting. While embodiments disclosed herein have included flanges (e.g., flanges 150, 160) for connecting heat exchangers 120 to one another (e.g., through tubing members 222 and transfer pipes 104, 106, bridging assemblies 170, etc.) other embodiments may replace one or more of the flanges 150, 160 with welded connections in order to eliminate the need for a hydrocarbon containing seal (e.g., seal assemblies 151). In addition, other suitable, non-flanged connections may be utilized such as a clamp connector (hydraulic or otherwise) and the like. Also, it should be appreciated that other valve assemblies may be utilized within the exchangers 100, 300 in addition to those specifically shown and described above, while still complying with the principles disclosed herein. For example, in some embodiments, additional valves/valve assemblies are attached in and/or around the pumping module 210, as well as along lines 220, 230, 330, etc.

In addition, many other variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of this disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.

Claims

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).