FLUID HEATING

Description

FIELD

The present invention relates to a method and apparatus for providing a working fluid having a desired temperature at a predetermined location. In particular, but not exclusively, the present invention relates to using flexible pipes in a Down Bore Heat Exchanger (DBHX) to transport thermal energy extracted from the ground via the working fluid upwards to a surface level heat exchanger.

BACKGROUND

Flexible pipes are widely used in the oil and gas industry in both onshore and offshore applications for the transportation of oil, gas, water, or other fluids from one location to another. Offshore flexible pipe is particularly useful in connecting sea-level supporting structures and subsea locations (which may be deep underwater, say 1000 metres or more), where the pipe may act as a riser. Onshore flexible pipe is typically arranged underground or on the surface of the ground to connect two onshore structures, and to transport a fluid from one of these structures to another. Due to their location in use, flexible pipes are exposed to a range of challenging conditions that may have high pressures, seawater, high tensile strain, and corrosive environments, for example. Flexible pipe body is therefore often composed of several concentric polymeric, metallic, and/or composite layers. For example, pipe body may include polymer and metal layers, or polymer and composite layers, or polymer, metal and composite layers. Layers may be formed from a single piece such as an extruded tube or by helically winding one or more wires or tapes at a desired pitch or by connecting together multiple discrete hoops that are arranged concentrically side-by-side. Depending upon the layers of flexible pipe used and the type of flexible pipe some of the pipe layers may be bonded together or remain unbonded. The polymeric layers generally provide sealing from fluids and/or dirt ingress and the composite and/or metallic layers provide structural rigidity.

Examples of types of non-metallic flexible pipe include Reinforced Thermoplastic Pipe (RTP), Thermoplastic Composite Pipe (TCP), and the like. Reinforced thermoplastic pipe (RTP) may either be of an unbonded construction, where the layers of the pipe are unbonded to each other, i.e. the inner fluid containing polymer liner layer is not bonded to the reinforcement layer, which is in turn not bonded to the outer protective sheath polymer layer, or of a bonded construction, i.e. all layers are bonded to each other as part of the pipe manufacturing resulting in a pipe which is in effect a single, consolidated layer comprising sub-layers. Non-metallic flexible pipe may be suitable for use in transporting and/or distributing oilfield fluids, such as water, gas (methane, ethane, CO₂ etc.) and/or the transport and distribution of hydrocarbon liquids, or other fluids such as hydrogen may be used onshore (over land) or in very shallow water applications (for instance less than 50 m water depth).

Structurally, non-metallic flexible pipe body may have a non-complex construction, comprising two or more polymer layers each of which may be similar or different polymer types and/or composite material(s). See also American Petroleum Institute Specification 15S as a reference for an example of these types of pipes. The inner and outer polymer layers (often termed a liner and protective sheath respectively) are non-porous tubes usually consisting of at least one type of polymer. Aptly for some applications the inner polymer layer may comprise sub-layers similar or different polymer compositions which are co-extruded to form a liner.

It is known that down bore heat exchangers (DBHXs) can harness geothermal heat from the ground for a number of applications. For example, geothermal heat is sometimes utilised to heat a working fluid for heating buildings, district heating, and the like. Additionally, geothermal heat is sometimes utilised to heat a working fluid and this heat can be utilised to generate electricity. In some cases, the geothermal heat is used directly or indirectly to drive a turbine that converts mechanical energy into electrical energy. DBHXs can be installed in newly-drilled wells, used to repurpose existing end of life wells, or the like. Typically DBHXs consist of an outer metallic casing located in a borehole that extends downwardly into the ground and a concentric inner insulated tubing separated from the casing by an annulus region. Cool working fluid is pumped downwards in the annulus region where it is heated by contact with the outer metallic casing, reaching a closed bottom end of the casing and then is driven upwards through the inner insulated tubing.

Conventionally the inner insulated tubing is provided by Vacuum Insulated Tubing (VIT). VIT often includes an inner tubing concentric with an outer tubing with a vacuum provided therebetween to help reduce heat loss of geothermically heated fluid in the inner tubing of the VIT. Manufacturing and/or assembly VIT can thus be a costly process. Installing VIT in a bore (for use in a DBHX) often requires many rigid sections of VIT to be welded together. Also, VIT is heavy, requiring significant support when suspended from a support at surface level. As such, the installation of VIT in a DBHX is a time consuming and costly process. Furthermore, it is known that problems associated with VIT use in DBHX systems occur should the VIT annulus region (the region between the inner and outer VIT tubing) become damaged, flooded, or the like. For example, flooding of the annular region can result in a significant loss of insulation of the VIT. This can limit the overall performance of the DBHX, for example by limiting the heat that can be utilised from working fluid provided in the VIT.

SUMMARY

It is an aim of certain embodiments disclosed herein to at least partly mitigate one or more of the above-mentioned problems.

It is an aim of certain embodiments disclosed herein to transfer heat from an existing location to a desired location (e.g., a heat exchange surface or the like) through circulation of working fluid in a geothermal bore (well).

It is an aim of certain embodiments disclosed herein to use a closed loop geothermal well to transfer heat from an underground source to an above-ground interface for providing district heating, power generation, or the like.

It is an aim of certain embodiments disclosed herein to increase the commercial viability of existing end of life wells as closed loop geothermal wells through the use of a Down Bore Heat Exchanger (DBHX).

It is an aim of certain embodiments disclosed herein to provide a method for reducing the time required to install a DBHX compared to conventional techniques.

It is an aim of certain embodiments disclosed herein to provide apparatus that facilitates more rapid and economic installation of a DBHX compared to conventional techniques.

It is an aim of certain embodiments disclosed herein to provide apparatus for repurposing end of life wells as a DBHX even when the bore of the well is angled.

It is an aim of certain embodiments disclosed herein to provide apparatus for increasing the reliability and/or decreasing maintenance requirements for a DBHX.

According to a first aspect there is provided apparatus for providing a working fluid having a desired temperature at a predetermined location, comprising:

• • a downhole casing disposed in a pre-drilled borehole; and
  • at least a portion of at least one flexible pipe comprising flexible pipe body, disposed in the casing, wherein
  • a working fluid is moveable in a first direction in an annular region, between the casing and the flexible pipe body and a bore region of the flexible pipe body, and in a further direction opposite to the first direction via the bore region.

In certain embodiments, the apparatus further comprises:

• • the downhole casing is fluidically sealed at a lower casing end region and movement of the working fluid is via a closed loop fluid communication pathway.

In certain embodiments, the apparatus further comprises:

• • the flexible pipe body comprises a fluid retaining layer having a radially inner surface that defines the bore region, an outer layer, having an outer surface that defines a radially inner surface of the annular region, coaxial with the fluid retaining layer and at least one intermediate layer between the fluid retaining layer and the outer layer.

In certain embodiments, the apparatus further comprises:

• • the casing comprises a hollow elongate wall body that surrounds a region of the borehole in which said a portion of the flexible pipe is located and optionally an end cap that is integrally formed with or is secured to a lower end of the wall body to provide a sealed end to the casing.

In certain embodiments, the apparatus further comprises:

• • said a portion comprises a portion of a single flexible pipe or a portion of a full length of a plurality of flexible pipes disposed in an end-to-end configuration and optionally said a portion extends for more than 60% of a casing length of the downhole casing.

In certain embodiments, the apparatus further comprises:

• • the downhole casing is fluid tight.

In certain embodiments, the apparatus further comprises:

• • the wall body is integrally formed or comprises a plurality of elongate wall body elements secured together in an end-to-end configuration.

In certain embodiments, the apparatus further comprises:

• • the wall body is cylindrical or has a rectangular or elliptical cross section that optionally is substantially common at all positions along a casing length of the downhole casing.

In certain embodiments, the apparatus further comprises:

• • the flexible pipe body is disposed in a substantially coaxial spaced apart relationship with the downhole casing.

In certain embodiments, the apparatus further comprises:

• • a lower end of the flexible pipe body is located around 1000 m below an upper terrain surface and working fluid proximate to the lower end is at a temperature that comprises a downhole heated temperature of around 40° C. or a lower end of the flexible pipe body is located around 3000 m below the surface and working fluid proximate to the lower end is at a temperature that comprises a downhole heated temperature of 90° C. or the lower end of the flexible pipe body is located around 5000 m below the surface and working fluid proximate to the lower end is at a temperature that comprises a downhole heated temperature of around 140° C.

In certain embodiments, the apparatus further comprises:

• • at least one pump element in fluid communication with at least one of the annular region and the bore region of the flexible pipe body.

In certain embodiments, the apparatus further comprises:

• • each borehole is a repurposed well or a purpose drilled well and optionally each well is a geothermal well for transferring heat from earth's ground temperature to a predetermined location that comprises a surface location, a heat pump system or a heating system for homes/business or district heating.

In certain embodiments, the apparatus further comprises:

• • providing a working fluid at a predetermined location comprises providing working fluid having a thermal temperature elevated via geothermal heating from a geothermal reservoir to a surface location where heat is extractable for return of the working fluid downhole.

In certain embodiments, the apparatus further comprises:

• • the desired temperature at the predetermined location is within 20% of a downhole heated temperature accumulated by the working fluid at a lower end of the flexible pipe body disposed in the casing and optionally the desired temperature at the predetermined location is within 10% of the downhole heated temperature.

In certain embodiments, the apparatus further comprises:

• • the flexible pipe body comprises multi-layer unbonded Reinforced Thermoplastic Pipe (RTP) body or multi-layer bonded RTP body or single layer RTP body or unbonded flexible pipe body or bonded Thermoplastic Composite Pipe (TCP) body.

In certain embodiments, the apparatus further comprises:

• • the working fluid comprises water or Isobutane or N-butane or Isopentane or N-pentane or Cyclopentane or Propane.

In certain embodiments, the apparatus further comprises:

• • at least one spacer element comprising a spacer body, each supported at a respective axial location along the flexible pipe body for maintaining a spaced apart relationship between the flexible pipe body and a radially inner surface of the downhole casing.

In certain embodiments, the apparatus further comprises:

• • the spacer body comprises a through bore with a circular cross section having a diameter that mates with a diameter of the outer surface of the outer sheath of the flexible pipe body.

In certain embodiments, the apparatus further comprises:

• • the spacer body comprises a radially outer surface that provides at least one abutment zone that each abut with a radially inner surface of the downhole casing.

In certain embodiments, the apparatus further comprises:

• • said at least one abutment zone comprises a cylindrical outer surface of the spacer body wherein a cross section of the cylindrical outer surface falls on an imaginary circle that falls on and is coaxial with an inner surface of the downhole casing.

In certain embodiments, the apparatus further comprises:

• • said at least one abutment zone comprises a plurality of spaced apart regions that extend circumferentially around an outer surface of the spacer body.

In certain embodiments, the apparatus further comprises:

• • a radially outer surface of the spacer body and/or a radially inner surface of the downhole casing comprises at least one strake element disposed to engender circulating fluid flow in a region between the flexible pipe body and the downhole casing.

According to a second aspect, there is provided a method for providing a working fluid having a desired temperature at a predetermined location, comprising:

• • urging a working fluid along an annular region between a downhole casing disposed in a pre-drilled borehole and a portion of at least one flexible pipe that comprises flexible pipe body, disposed in the casing;
  • heating the working fluid at a lower end region of flexible pipe body; and
  • urging the heated working fluid along a bore region of the flexible pipe to a predetermined location.

In certain embodiments, the method further comprises:

• • urging the working fluid along the annular region in a first axial flow direction and urging the working fluid along the bore region in a further axial flow direction that is opposite to the first axial flow direction.

In certain embodiments, the method further comprises:

• • urging the working fluid along a closed loop fluid communication pathway that comprises an annular region pathway portion and a bore region pathway portion.

In certain embodiments, the flexible pipe body and casing are disposed in a pipe-in-pipe substantially coaxial relationship and the method further comprises:

• • urging working fluid down a borehole via an annular region that surrounds the flexible pipe body and is inside the casing; and
  • urging working fluid up the borehole towards the predetermined location via the bore region of the flexible pipe body.

In certain embodiments, the method further comprises:

• • providing thermal insulation, between working fluid that moves vertically down away from an upper terrain surface and is relatively cool relative to rising heated working fluid that moves vertically upwards via the bore region, via a layer of the flexible pipe body.

In certain embodiments, the method further comprises:

• • providing the thermal insulation via a fluid retaining layer of the flexible pipe body and/or an outer polymer layer of the flexible pipe body and/or a polymer intermediate layer of the flexible pipe body.

In certain embodiments, the method further comprises:

• • providing geothermal fluid from a geothermal reservoir via at least one feed zone to the downhole casing;
  • via heat conduction, heating the casing via the geothermal fluid; and
  • heating the working fluid in a lower region of the annular region via the heated casing.

In certain embodiments, the method further comprises:

• • providing heated working fluid to a heat pump system or a heating system for homes/business or district heating of the predetermined location.

According to a third aspect there is provided apparatus for providing a working fluid having a desired temperature at a predetermined location, comprising:

• • a downhole casing disposed in a pre-drilled borehole; and
  • at least a portion of at least one flexible pipe comprising pipe body, disposed in the casing, wherein
  • a working fluid is moveable in a first direction in an annular region, between the casing and the pipe body and a bore region of the pipe body, and in a further direction opposite to the first direction via the bore region.

According to a fourth aspect, there is provided a method for providing a working fluid having a desired temperature at a predetermined location, comprising:

• • urging a working fluid along an annular region between a downhole casing disposed in a pre-drilled borehole and a portion of at least one flexible pipe that comprises pipe body, disposed in the casing;
  • heating the working fluid at a lower end region of pipe body; and
  • urging the heated working fluid along a bore region of the flexible pipe to a predetermined location.

Certain embodiments provide a transfer of heat to a predetermined location using the circulation of a working fluid through flexible pipe body from an underground heat source.

Certain embodiments provide apparatus for repurposing an end of life bore as a Down Bore Heat Exchanger (DBHX) using flexible pipe to transfer working fluid heated in the bore by geothermal energy to a heat exchanger. The heat exchanger may transfer heat to a district heating system, a second working fluid of an Organic Rankine Cycle (ORC) power plant, or the like.

Certain embodiments provide a DBHX that utilises low-grade heat emitted by a newly drilled or end of life well for district heating.

Certain embodiments a method for installing flexible pipe in an angled downhole bore from ground level.

Certain embodiments provide apparatus that simplifies the process of installing insulated tubing in a DBHX by replacing rigid, fragile, unwieldly Vacuum Insulated Tubing (VIT) with flexible, lighter, more durable flexible pipes. When considering the performance of the flexible pipes and the installation costs, the overall capital expenditure and operation expenditure is reduced.

Certain embodiments provide flexible pipes that can be deployed in continuous lengths when installed as part of a DBHX without the flexible pipes needing to be welded together in sections, unlike the rigid sections of VIT.

Certain embodiments provide flexible pipes that are not susceptible to failure of an annulus region because the insulating properties of the annulus do not rely on vacuum insulation, unlike the annulus of VIT. Failure to maintain a vacuum drastically reduces the insulative performance of VIT.

Certain embodiments provide insulated tubing in the form of flexible pipes that is lighter than VIT and therefore exerts a smaller tensile load during suspension of the tubing in a well on a topside landing located at the top of the well. This reduces complexity and material costs of the topside landing.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the present disclosure will now be described hereinafter, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 illustrates a segment of flexible pipe body;

FIG. 2 illustrates flexible pipes joined end-to-end;

FIG. 3 illustrates an end fitting for certain kinds of flexible pipe;

FIG. 4 illustrates a down bore heat exchanger (DBHX) system;

FIG. 5 illustrates the down bore heat exchanger (DBHX) system of FIG. 4 in more detail;

FIG. 6 illustrates a perspective cross sectional view of downhole casing and flexible pipe of a down bore heat exchanger (DBHX) system;

FIG. 7 illustrates a spool of flexible pipe;

FIG. 8 illustrates a method of installing a down bore heat exchanger (DBHX) system;

FIG. 9 illustrates an alternative down bore heat exchanger (DBHX) system;

FIG. 10 illustrates an Organic Rankine Cycle (ORC) system for generating electricity;

FIG. 11 illustrates installation of another alternative down bore heat exchanger (DBHX) system;

FIG. 12 illustrates a centralizer; and

FIG. 13 illustrates alternative flexible pipe body.

In the drawings like reference numerals refer to like parts.

DETAILED DESCRIPTION

FIG. 1 illustrates a segment of geothermal downhole pipe body 100. It will be appreciated that the segment of geothermal downhole pipe body 100 is an example of flexible pipe body. The segment of flexible pipe body illustrated in FIG. 1 is generally utilised in onshore applications however it will be appreciated that flexible pipe body of a type used in offshore applications may also alternatively be utilised. It will be appreciated that the flexible pipe body 100 may alternatively be any bonded or unbonded non-metallic pipe body including thermoplastic composite pipe (TCP), thermoflex composite pipe, reinforced thermoplastic pipe (RTP), or the like.

The flexible pipe body 100 shown has a central axis marked by A-A in FIG. 1. Although a number of particular layers are illustrated in FIG. 1, it is to be understood that certain embodiments are broadly applicable to coaxial pipe body structures including two or more layers manufactured from a variety of possible materials. Pipe body 100 may include one or more layers comprising composite materials, forming a tubular composite layer. It is to be further noted that the layer thicknesses are shown for illustrative purposes only. As used herein, the term “composite” is used to broadly refer to a material that is formed from two or more different materials, for example a material formed from a matrix material and reinforcement fibres. Pipe body may include one or more layers of a single material, forming a tubular uniform layer.

A tubular composite layer may thus be a layer having a generally tubular shape formed of composite material. Alternatively, a tubular composite layer is a layer having a generally tubular shape formed from multiple components one or more of which is formed of a composite material. The layer or any element of the composite layer may be manufactured via an extrusion, pultrusion or deposition process or, by a winding process in which adjacent windings of tape which themselves have a composite structure are bonded together with adjacent windings.

The composite material, regardless of manufacturing technique used, may optionally include a matrix or body of material having a first characteristic in which further elements having different physical characteristics are embedded. That is to say elongate fibres which are aligned to some extent and/or smaller fibres randomly orientated can be set into a main body, or spheres or other regular or irregular shaped particles can be embedded in a matrix material, or a combination of more than one of the above. In certain embodiments, the matrix material is a thermoplastic material. In certain embodiments, the thermoplastic material is polyethylene or polypropylene or nylon or PPS or PVC or PVDF or PFA or PEEK or PTFE, alloys of such materials, or alloys of such materials with reinforcing fibres manufactured from one or more of ceramic, carbon, carbon nanotubes, aramid, steel, nickel alloy, titanium alloy, aluminium alloy or the like or fillers manufactured from ceramic, carbon, metals, buckminsterfullerenes, metal silicates, carbides, carbonates, oxides or the like.

As illustrated in FIG. 1, the segment of flexible pipe body 100 includes a number of concentric layers 110, 120, 130, 135. A liner 110, that is an example of an inner fluid retaining layer 110, constitutes the radially inner layer 110 of the segment of flexible pipe body 100 illustrated in FIG. 1. The liner 110 of FIG. 1 is non-porous and made from polyvinylidene fluoride (PVDF). Optionally the liner 110 may be made from polymeric material or any other suitable material. The polymeric material optionally is a thermoplastic material. The thermoplastic material is optionally high-density polyethylene (HDPE), nylon, or the like. The liner 110 radially surrounds a central bore 140 of the segment of flexible pipe body 100. It will be appreciated that the fluid can be transported through the bore 140 from one end of the segment of flexible pipe body 100 to another. It will also be appreciated that the liner 110 is a fluid retaining layer which helps prevent fluid in the bore 140 from leaking out of the bore 140. Aptly, the internal diameter of the fluid retaining layer—which defines the bore 140—is about 2 inches (50.8 mm). It will be appreciated that in other embodiments the pipe bore 115 may be larger (e.g., 100, 200, 300 mm or the like) or smaller (e.g., 75, 50, 25, 10 mm or the like) in diameter.

FIG. 1 illustrates how a reinforcement layer 120 is provided radially around the liner 110. Although only one reinforcement layer is illustrated in FIG. 1, it will be appreciated that the segment of flexible pipe body may instead include two, three, four or more reinforcement layers and further layer (for example polymer layers) may be disposed between respective reinforcement layers. The reinforcement layer 120 provides structural support to the flexible body. The reinforcement layer illustrated in FIG. 1 is made from aramid fibre formed into filament, tape, or the like. Alternatively, continuous fibre high-strength reinforced thermoplastic composite (CF-RTP) tape or any other suitable material may be utilised to provide the reinforcement layer 120.

The reinforcement layer 120 is formed of pairs of aramid fibre tapes cross-wound around the liner 110 with a lay angle of around +/−55° (not shown). In other words, each pair of tapes is wound helically in clockwise and counterclockwise directions respectively. It will be appreciated that, in other embodiments, the lay angle may be between 10° and 90°. It will be appreciated that the lay angle may be chosen depending on the reinforcement requirements of the reinforcement layer 120. For example, a shallower lay angle may provide greater resistance to axial forces along flexible body.

It will also be appreciated that in some embodiments, the reinforcement layer 120 may comprise conductive fibres or strands or bunches of fibres which may be applied to the pipe without being incorporated into a tape (i.e. without a polymer matrix around the fibres).

An optional thermal insulation 130 layer radially surrounds the reinforcement layer 120. Optionally the insulation layer may be disposed between the liner 110 and the reinforcement layer 120. Optionally the insulation layer 130 shown includes a plurality of insulation layers. It will be appreciated that the insulation layer 130 helps thermally insulate fluid in the bore 140 from a surrounding environment in which the segment of flexible pipe body 100 is arranged.

The insulation layer may for instance include glass microspheres, hollow fibres, or the like, in a polymer matrix such as polypropylene, polyethylene, Polyvinyl chloride or any other suitable polymer. Such an insulation is sometimes known as a syntactic material. Alternatively the insulation may be formed of a foamed material. Aptly a plurality of insulation layers may be provided in the form of rectilinear or zeta cross-section tapes of insulating material helically wound around an underlying layer of pipe body to form an insulation layer. The tapes may be applied so that they overlap an adjacent wrap or butt up to the edge of an adjacent tape wrap and applied layer-on-layer to form a “brick structure”. Alternatively the insulation layer may be applied via extrusion or spraying, or the like.

FIG. 1 additionally shows how a radially outer layer 135, that is an outer sheath, radially surrounds the insulation layer 130. The outer sheath 135 defines an outer surface 150 of flexible pipe body 100. If no insulation layer is included radially outside of the reinforcement layer 120, it will be appreciated that the outer sheath 135 may be disposed radially over the reinforcement layer 120. The outer sheath 135 of FIG. 1 is non-porous and is made from PVDF. Optionally the outer sheath 135 may be made from high-density polyethylene (HDPE), nylon, any polymeric material or any other suitable material. The polymeric material optionally is a thermoplastic material. It will also be appreciated that the outer sheath 135 is a fluid retaining layer which helps prevent ingress of fluid in the environment in which the segment of flexible pipe body 100 is arranged into the segment of flexible pipe body 100. The outer sheath 135 may also provide protection to the segment of flexible pipe body 100 against mechanical damage and the like, for example abrasion.

The segment of flexible pipe body 100 may optionally include one or more further protective layers, for example abrasion resistant layers, radially outside of the outer sheath 135. The segment of flexible pipe body may additionally include further insulation layers or the like disposed radially outside of the outer sheath 135. It will also be appreciated that the segment of flexible pipe body may include additional armouring layers disposed between the liner 110 and the outer sheath 135, for example one or more pressure armour layers and/or one or more tensile armour layers may be included. Such armour layers may be made from metallic or composite material or the like. In addition, while the segment of flexible pipe body 100 illustrated in FIG. 1 is for a so-called smooth bore pipe (and thus does not include any armouring or crush resistant layers radially within the liner 110), it will be appreciated that the segment of flexible pipe body 100 may instead be for a rough bore pipe and thus may include, for example, a crush resistant carcass layer radially within the inner fluid retaining layer 110. In this case the inner fluid retaining layer 110 is commonly referred to as a barrier layer instead of a liner. The carcass layer may be made from at least one interlocked helically wound tape and may be made from a metallic or composite material or the like.

FIG. 2 illustrates how a plurality of segments 205_1-3 of flexible pipe body 100 can be connected in an end-to-end configuration to form flexible pipes 200. Aptly the flexible pipes 200 may be collectively referred to as a pipeline or a flexible pipeline. As is illustrated in FIG. 2, the plurality of segments of flexible pipe body 100 are joined via respective end fittings 210. That is to say, a free end of a first segment 205₁ of flexible pipe body 100 is connected to a free end of an adjacent segment 205₂ of flexible pipe body 100 via an end fitting. Each flexible pipe 200 includes one segment 205 of flexible pipe body 100 and at least one end fitting 210 joined at a free end of the segment 205. It will be appreciated that the segments 205 of flexible pipe body 100 are able to flex and thus the flexible pipe 200 is able to flex as a whole.

The end fitting 210 has a central bore (shown in detail in FIG. 3) which allows bore fluid from the bore 140 of a first segment of flexible pipe body 100 to flow freely into the bore 140 of an adjacent segment of flexible pipe body 100. Adjacent segments of flexible pipe body 100 are thus in fluid communication. It will be appreciated that each segment 205 of flexible pipe body 100 is around 1 km in length, or alternatively 100, 250, 500, 2000 m or the like. To join the first segment 205₁ of flexible pipe body 100 to the adjacent segment 205₂, the first segment 205₁ and the adjacent segment 205₂ are secured to an end fitting 210. Alternatively, a first end fitting may be secured to the first segment and a second end fitting may be secured to the adjacent segment; via the first and second end fittings, the respective flexible pipes 200 are bolted together optionally with a seal ring between them. This arrangement is shown in FIG. 11. Alternatively the end fittings may be joined by welding, clamps, or the like.

It will be appreciated that alternatively flexible pipe 200 may include a single segment of flexible pipe body 100 with one end fitting 210 attached at a first free end. Alternatively, more than two end fittings 210 may be used to form a longer pipeline.

FIG. 3 illustrates a cross sectional view of an flanged end fitting 210 that can be utilised to terminate a segment 205 of flexible pipe body 100 and adjoin two segments 205_1,2 of flexible pipe body 100. The end fitting 210 shown in FIG. 3 is an example of a pipe-to-pipe connection type. It will be appreciated that alternative end fittings or other components may instead be used to terminate flexible pipe body 100 including but not limited to a flanged end fitting as illustrated in FIGS. 4 and 11. The end fitting 210 includes a stem 310 and a ferrule 320. The stem 310 is a generally cylindrical hollow tube that is partially inserted into the bore 140 of the segment of flexible pipe body 100. The ferrule 320 is also hollow and generally cylindrical for securing over the outer surface 150 of flexible pipe body 100 providing a friction fit therebetween. The ferrule 320 thus grips the outer diameter of the segment of flexible pipe body 100.

The end fitting 210 may be swaged on a free end 330 of a segment 205 of flexible pipe body 100 as follows. The free end of flexible pipe body 100 is cut perpendicular to its layers 110, 120, 130, 135 and prepared for swaging. The ferrule 320 is screwed onto the stem 310. The segment of flexible pipe body 100 is driven between the stem 310 (radially inside) and the ferrule 320 (radially outside). A swaging die can be used to radially reduce the ferrule 320, thereby squeezing the flexible pipe body 100 between the reduced ferrule 320 and the stem 310, resulting in the end fitting 210 being securely attached to the segment 205 of flexible pipe body 100. It will be appreciated that one or more machines may be used to drive the end fitting 210 and flexible pipe body 100 together and/or for swaging.

Once the end fitting 210 has been fixed to the first segment 205₁, forming the flexible pipe 200, the end fitting 210 can be secured at its other end to the adjacent segment 205₂ using the same swaging process that was described above. Alternatively, as illustrated in FIG. 11, individual flexible pipes 200 can be secured together by bolting respective flanged end fittings together. It will be appreciated that flanged end fittings may also be used to secure a flexible pipe to another component (e.g., a different end fitting, hanger, or the like) as shown in FIG. 4. The flexible pipe 200 can be suspended, as shown in FIG. 4, whereby the end fitting of an uppermost flexible pipe 200 is secured to a hanger allowing the pipeline to hang freely. It will be appreciated that the end fitting 210 may have further uses.

FIG. 4 illustrates how a flexible pipe can be arranged in a down bore heat exchanger (DBHX) system 400 for providing a working fluid having a desired temperature at a predetermined location. As illustrated in FIG. 4, the DBHX includes a pre-drilled borehole 404 that extends generally downwardly into the ground 408. That is to say that the borehole 404 extends into the earth. The borehole may extend between 10 and 1000 m into the ground 408, for example around 100, 200 or 500 m into the ground 408. Optionally, the borehole 404 may extend deeper into the ground 408. For example, particularly if the borehole 404 was originally drilled for extraction of production fluids, the borehole 404 may extend up to 3000 m into the ground 408, for example between 1000 m and 2000 m into the ground 408. Optionally the borehole 404 may be referred to as a well or wellbore, particular if the borehole 404 was initially drilled for extraction of production fluids. As indicated the borehole 404 may have been previously provided for other applications (for example for oil and/or gas applications) or may be a newly drilled borehole for specific use in a DBHX system 400. Furthermore it will be appreciated that the borehole 404 may alternatively have one or more inclines relative to a vertical axis (perpendicular to the ground 408), for example, as illustrated in FIG. 11. In some cases the borehole 404 may include or form a curved path instead of a straight vertical one.

A downhole casing 412 extends down into the borehole 412. Aptly, the downhole casing 412 may extend along or through an entire length of the borehole. The downhole casing 412 may instead only extend along or through a portion of the length of the borehole 404. Aptly the casing extends between 10 and 500 m into the ground 408, for example around 50 m into the ground or around 100 m into the ground or around 150 m into the ground or around 200 m into the ground. It will be appreciated that the casing extends, through the bore, into an underground region 416 where the environment temperature is between 50° C. and 300° C. or more. It will be appreciated that the underground region 416 may contain rock formations and the like which are heated due to the temperature of the earth at such depths. Alternatively, warm subterranean fluids may ingress into the borehole 404 and may be located between the inner surface of the borehole and the outer surface of the casing 412. The fluids may have a two-phase composition of water and steam. Although not shown in FIG. 4, it will be appreciated that further tubular members or structural members or framework members may aptly be located between a radially outer surface of the casing 412 and a radially inner surface of the borehole 404. Aptly, no further members or elements are arranged between the casing 412 and the borehole 404.

Aptly the casing 412 may extend to around 1000 m below an upper terrain surface such that the working fluid proximate to a lower end of flexible pipe body 100 in the casing 412 is at a temperature of around 40° C. Alternatively the lower end of flexible pipe body 100 is located around 3000 m below the surface and working fluid proximate to the lower end is at a temperature that comprises a downhole heated temperature of 90° C. Alternatively the lower end of flexible pipe body 100 is located around 5000 m below the surface and working fluid proximate to the lower end is at a temperature that comprises a downhole heated temperature of around 140° C. Alternatively at certain below ground locations a well depth of around 110 m or more may facilitate the working fluid to be heated to between 110° C. and 200° C. or more.

Aptly, the casing 412 is made from a material through which a working fluid to be utilised in the DBHX system 400 cannot pass. The casing 412 may be made from a metallic material, for example steel or stainless steel. Aptly the casing 412 may be made from a polymeric material. Aptly the casing may be made from any other suitable material. Aptly the casing 412 may be made from a material that is a good conductor of heat. That is to say the casing may be made from a material that does not substantially inhibit heat transfer from the underground region 416 through the casing 412 (into a bore 420 of the casing 412).

FIG. 4 additionally shows how the flexible pipes 200 are arranged in a bore 420 of the casing 412. The flexible pipes 200 are substantially centralised in the casing bore 420 so that an annular region 424 is located between a radially inner surface of the casing 412 and the radially outer surface 150 of the flexible pipe. It will be appreciated that spacer elements such as the centralizing elements shown in FIGS. 11-13 may be provided between the flexible pipe 200 and the casing 412 to help fix the position of the flexible pipe 200 inside the casing bore 420. It will be understood that any spacers utilised would not completely obstruct fluid flow in the annular region 424. Such spacers may be include spoke elements or disk elements with fluid flow openings around the circumference of the disk element or the like. Alternatively the spacer elements may hold the flexible pipe 200 at a predetermined non-central offset relative to a longitudinal axis of the casing bore 420. Spacer bodies are illustrated in FIGS. 12 and 13 along with description of further alternative spacers. It will be appreciated that in some alternatives the centralising elements may be a feature of a layer of the flexible pipe body 100.

As shown in FIG. 4, the flexible pipes 200 are supported proximate to or in a DBHX facility 428 by one or more hangers 430 that are secured to a flanged end fitting 425 at a free end of the top segment 205₁ of the pipeline. The facility 428 shown in FIG. 4 includes a building at ground level however it will be appreciated that any other suitable type of facility could be utilised. The facility 428 includes an optional pump 432 for pumping working fluid through the DBHX system 400. It will appreciated that alternatively the working fluid may be transported through the DBHX system 400 by convection, for example using a thermosiphon. The facility further includes a heat exchanger (HX) 436 for exchanging heat in the working fluid. That is to say the HX 436 extracts heat from so-called hot working fluid (that has been geothermically heated via passage through the DBHX system 400, for example through the underground region 416. Although not shown in FIG. 4, it will be appreciated that the facility 428 includes one or more suitable power sources to provide necessary power to the pump 432 and HX 436. The power source or sources may include one or more generators, one or more connections to mains electricity or the like.

It will be appreciated that the DBHX system 400 illustrated in FIG. 4 is a closed loop system. That is to say that the DBHX system 400 includes one or more closed loop geothermal wells 440 in which working fluid is repeatedly circulated. This will be described in more detail in FIG. 5. It will further be appreciated that the DBHX system could alternatively be an open loop system in which fluid is not circulated.

Whilst FIG. 4 illustrates a broadly vertical down bore heat exchanger (DBHX) system 400, it will be appreciated that the flexible pipe(s) 200 may alternatively be used in a shallow horizontal heat exchanger system, a lake or pond heat collector, or the like. Furthermore, when the heat exchanger (HX) 436 transfers heat to a district heating system, it will be appreciated that the district heating system may consist of a surface-level distribution of a working fluid transported through flexible pipes 200.

FIG. 5 illustrates the DBHX system 400 of FIG. 4 in more detail. FIG. 5 illustrates how working fluid 504 (geothermal fluid) flows through the DBHX system 400 in use. The working fluid 504 utilised in the DBHX system 400 may include water. Alternatively, the working fluid 504 utilised in the DBHX system 400 may include a hydrocarbon fluid, for example Isobutane, N-butane, Isopentane, N-pentane, Cyclopentane, Propane or any other suitable hydrocarbon fluid. Alternatively, any other suitable working fluid 504 could be utilised. The working fluid 504 is pumped, via the pump 432, into the annular region 424 of the closed loop geothermal well 440 (that is to say in the region between the casing 412 and the flexible pipe 200). It will be appreciated that the pump 432 utilised can be any pump that is suitable for moving fluid through the DBHX system 400, for example a centrifugal or impeller pump. While only one pump 432 is illustrated in FIG. 5, it will be appreciated that numerous pumps could be utilised in the DBHX system 400. The pumps could be positioned proximate to one other or could be distributed around the DBHX system 400 to help move fluid at different positions. For example, one or more pumps could be located at one or more downhole locations (that is to say in the borehole 404).

It will be appreciated that the working fluid 504 pumped into and down the annular region 424 is so-called cold working fluid 508, that is to say incoming working fluid that has not yet been geothermically heated in the current cycle. It will be appreciated that as the cold working fluid 508 is urged down the annular region 424 and into the ground under pressure (via the pump 432), the working fluid 504 is heated by the environmental temperature of the earth and the depths through which the annular region 424 extends. If the casing 412 is provided from a relatively heat conductive material, for example a metallic material, it will be appreciated that the working fluid 504 flowing through the annular region 424 may be heated by a greater extent. That is to say, as the working fluid 504 passes through the underground region 416, the working fluid is heated due to the temperature of the underground region 416.

As is shown in FIG. 5, when the working fluid 504 reaches a downhole extremity end region 516 of the casing 412, the fluid 504 (due to the pressure exerted on the fluid 504 by the pump 432 and/or the weight of denser cold working fluid relative to hotter working fluid) is then urged into the downhole-most end region 516 of the flexible pipe 200. It will be appreciated that the working fluid 504 is urged into one or more opening associated with the flexible pipe 200. The opening may be an open mouth of the flexible pipe 200 at the downhole-most end region 516 of the flexible pipe. It will be understood that such an open mouth is a portion of the bore 140 of the flexible pipe 200.

Alternatively, the working fluid 504 may be urged through other openings that might be provided in the downhole most end region 526 of the flexible pipe 200. For example, the flexible pipe 200 might include one or more perforations in a side of a segment of flexible pipe body 100 that is located at the downhole-most end region 516 of the flexible pipe 200. Similarly, a plurality of circumferentially arranged openings may be provided around the flexible pipe 200 at the downhole-most end region 516 of the flexible pipe. Aptly, an end cap (for instance a blind flange or the like) may be attached to a terminal end fitting of the flexible pipe 200. It will be appreciated that the end cap may be an example of an end fitting. The end cap may be provided with perforations or suitable orifices to allow a predetermined volumetric flow rate of the working fluid 504 into the bore 140 of the flexible pipe 200. It will be understood that, via the opening (perforation(s), orifice(s), or the like), the annular region 424 and the bore 140 of the flexible pipe are in fluid communication at or around the downhole-most end region 516 of the flexible pipe 200.

Aptly, the point at which the working fluid 504 (which started the cycle as cold working fluid 508) has achieved the greatest temperature increase may be when it has reached the downhole-most end region 516. At this time the working fluid 504 is effected to be a hot working fluid 520 (see FIG. 6).

It will thus be appreciated that hot (heated) working fluid 520, that is to say output working fluid that has been geothermically heated in the current fluid cycle, is pumped from the downhole-most end region 516 into the bore 140 of the flexible pipe 200. The hot working fluid 520 is driven up the bore of the flexible pipe back towards the surface 524 of the ground in which the bore 404 is provided. It will be appreciated that any optional thermal insulation layers included in the flexible pipe 200 may help reduce heat loss of the hot working fluid 520 flowing up the pipe bore 140 due to cold working fluid 508 or partially heated working fluid flowing in the annulus region 424. When the hot working fluid 520 reaches the top of the flexible pipe 200 at or proximate to the facility 428, the hot working fluid 520 is provided to (or transported to) the HX 436. It will be appreciated that the hot working fluid 520 may be provided to the HX 436 via one or more further tubes or pipes or the like. Alternatively, the flexible pipe 200 may be connected directly to one or more parts of the HX.

As the hot working fluid 520 passes through the HX 436, heat is transferred out of the working fluid 504 to a heating target. The heating target may be a secondary working fluid for further heat transport. The heating target may form a component of a district heating system, a power plant (such as an organic rankine cycle system), or the like. Cold working fluid 508 is thus output from the HX 436. Thus through the DBHX system 400 illustrated in FIG. 5, the working fluid 504 is provided at a desired temperature at a predetermined location (the HX 436) for further use.

The working fluid 504, once output from the HX 436 as the cold working fluid 508, is then provided to the pump 432 where it is once again pumped into the annular region 424 to be heated in the borehole 404. The DBHX system 400 is thus a closed loop system where working fluid is circulated into and out of the borehole 404 (via the annular region 424 and the pipe bore 140 respectively).

FIG. 5 further illustrates how the borehole includes optional feedzones 540 that are openings disposed in the borehole 404. It will be appreciated that the feedzones 540 may be included in a circumferential wall of a borehole support structure, for example metal or concrete tubing or the like. Alternatively or additionally the feedzones 540 may be holes or openings provided laterally into the ground surrounding the borehole 404 that help permit fluid communication between the borehole 404 and the environment 544 at the underground region 416. It will be appreciated that the feedzones 540 may be remaining features from a prior use of the borehole 404 (for example for enabling oil and/or gas and/or other production fluids to ingress into the borehole for extraction). The feedzones 540 allow for subterranean fluid 548 to ingress into the borehole and may permit the partial or entire flooding of the borehole 404 with subterranean fluid 548. Aptly the subterranean fluid 548 may consist of a single phase or multiple phases of one or more fluids. Aptly the subterranean fluid 548 may consist of a two-phase mixture of water and steam. This subterranean fluid 548 thus may be located between an outer surface of the casing 412 and an inner surface of the borehole 404 along some or all of a length of the casing 412. It will be appreciated that the subterranean fluid 548 will be at around the same temperature as the environment (of the ground/earth) at a particular given depth beneath the surface. Thus, it will be appreciated that surrounding the casing with hot subterranean fluid 548 may help more effectively transmit heat to the working fluid 504 in the annular region 424. It will be appreciated that in alternative environments in which the downhole casing 412 is surrounded by dry rock, there may be no subterranean fluid 548 to percolate through the feedzones 540.

Although not shown in FIG. 5, as discussed briefly above it will be appreciated that heat is output from the HX 436 for use in further applications. One such application is heating regions and/or buildings for example district heating or heating of homes or the like. It will be appreciated that the HX 436 may include a fluid communication passageway in which a heating fluid, for example water or the like, may pass. The fluid communication passageway may be made from a substantially conductive material. The working fluid 504 may pass through a substantially thermally conductive region of the HX 436 that extends proximate to the fluid communication passageway. It will be appreciated that when hot working fluid 520 passes proximate to the fluid communication passageway, heat exchange between the hot working fluid 520 and a heating fluid passing through the fluid communication passageway occurs. Thus, the heating fluid is heated. It will be appreciated that this heating fluid can be passed or transported to a location at which heating is desired, for example one or more buildings and the like. It will be appreciated that the heating fluid may flow in a loop around a desired location and back to and through the HX 436 so that the heating fluid can be continuously heated and utilised for heating of a desired location.

FIG. 6 illustrates a perspective view cross-section of the casing 412 radially surrounding the flexible pipe 200 in the DBHX system 400 of FIG. 4 providing the annular region 424 therebetween. FIG. 6 helps illustrate how hot working fluid 520 is transported along the bore 140 of the flexible pipe 200 in an upwards direction (in the bore orientation illustrated in FIG. 6) while cold working fluid 508 is transported in a downwards direction (in the bore orientation illustrated in FIG. 6). Alternatively cold working fluid 508 may be transported in a downwards direction along the bore 140 of the flexible pipe 200 and hot working fluid 520 may be transported in an upwards direction in the annular region 424. It will be appreciated that, at any given particular location of the bore, the working fluid 504 in the annular region 424 and the working fluid in the pipe bore 140 are being transported in substantially opposite directions. The insulative properties of the flexible pipe 200 help to reduce loss of heat from the hot working fluid 520 to the cold working fluid 508.

FIG. 7 illustrates how one or more flexible pipes 200 (or alternatively a segment of flexible pipe body 100) can be stored on a reel element 710 or spool element prior to installation in the DBHX system 400. It will be appreciated that the flexible pipes 200 can be preassembled (via connecting multiple segments of flexible pipe body 100 via end fittings 210) and then wound around the spool element 710 for storage and to facilitate convenient transport from a storage location to a use location in which the DBHX 400 is to be arranged. For example, the use location may be a location in which a pre-existing borehole is located (that may be a borehole previously used for oil and gas extraction or the like) or may be a location where a new borehole has been, or is to be provided, specifically for DBHX installation. It will be appreciated that, alternatively, only a single segment of flexible pipe body 100 may be provided around a spool. It will be appreciated that the entire length of flexible pipe 200 for use in a DBHX 400 may be assembled, and wound around the spool element 710, prior to transporting the flexible pipe 200 to the DBHX 400 use location or alternatively two or more portions of flexible pipe may be transported to the DBHX use location for assembly at that location. It will be appreciated that the ability of the flexible pipe to flex allows for improved ease of assembly, storage and transport particularly when compared with conventional Vacuum Insulated Tubing VIT. The reel 710 illustrated in FIG. 7 contains about 1700 m of flexible pipe body 100. Alternatively the reel 710 may hold between 100 m and 10 km of flexible pipe body 100 depending on its specification.

FIG. 8 illustrates steps of a method 800 for installing a flexible pipe 200 downhole in a DBHX 400. At a first step S810 of the method 800, the downhole casing 412 is arranged in a borehole 404 that extends into the ground (see FIGS. 4 and 5 for example). It will be appreciated that the borehole 404 has been drilled prior to the first step S810: either recently, as a new bore (well), or a pre-existing end of life well. The downhole casing 412 may be arranged as an assembly of multiple casing portions. The casing portions may be annular or tubular and may be connected together in an end-to-end manner via welding or the like. It will be appreciated that the casing 412 may be made from a metallic material. It will be appreciated that the casing may be made from any other suitable material. The casing may be made from a thermally conductive material. It will be appreciated that the casing 412 may be substantially centralised in the bore 404. It will be appreciated that the casing 412 may be secured to ground level at the top of the bore 404 and may be suspended in the bore 404. Optionally, the casing may be secured to portions of the sidewall of the bore.

It will be appreciated that a terminal end region of the casing 412 that is disposed at a most downhole position in the borehole is sealed. Sealing of the downhole casing end 412 may be undertaken prior to installing the casing 412 in the borehole 404. Optionally the casing may be evacuated before the seal is effected.

At an urging step S820 of the method 800 a flexible pipe 200 is lowered down into the bore 404 so that the flexible pipe 200 is located radially within the downhole casing 412. It will be appreciated that the flexible pipe 200 may be provided at the bore site coiled on the reel 710. Thus the flexible pipe 200 may be unloaded or unspooled from a reel as it is lowered into the borehole 404. It will be appreciated the flexible pipe may be fully assembled before it is lowered into the borehole. Alternatively, the flexible pipe 200 may be installed into the borehole in portions. For example, a portion of pipe may be lowered into the borehole before an end region of that portion of pipe is secured to a further portion of pipe, and the pipe is further lowered into the borehole.

The flexible pipe 200 may be deployed using either a coiled tubing rig or tower with correct sizing based on an Outside Diameter (OD) of the flexible pipe 200. The reel 710 may be placed in a Coiled Tubing reel unit and unwound over a guide arch (gooseneck). A caterpuller unit will clamp on the segment 205 with its rotating belt(s) driving the flexible pipe body either into or out of the well (see FIG. 11 for example). If the bore 404 in which the flexible pipe 200 is being installed contains pressure, the flexible pipe 200 may pass through a Blowout Preventor (BOP), which contains sufficient kill valves and boundaries to kill/isolate the pipe 200 in an emergency. The flexible pipe 200 may be run through the BOP unit with midline connectors installed after the pipe has passed through the guide arch to connect continuous lengths of non-metallic tubing.

Next, at a locating step S830, a bottom free end of the flexible pipe(s) 200 is positioned at or near the downhole end region 516 of the casing 412. In certain circumstances the flexible pipe 200 may be secured using packers that do not block passage of fluids. The packers may alternatively be centralisers. An open end of the flexible pipe 200 is at the downhole end region 516 such that the working fluid 504 can enter the bore 140 after heating.

The flexible pipe(s) 200 can be centralised in the casing 412 by applying a downwards tensional load in a vertical or straight well. Alternatively centralizers such as a non-rotating stabilizer, a cylindrical centralizer, a bow spring centralizer, or the like can be installed along the length of the pipe to maintain centrality/concentricity of the inner non-metallic tube within the outer casing. According to still further alternatives sections of centralizer half-shells may be strapped onto the outer surface 150 of the flexible pipe 200 as will be discussed in more detail in respect of FIG. 13.

Then in a securing step S840, an upper free end of the flexible pipe 200 is attached to the DBHX system 400 using hangers 430 (see FIG. 4 for example). The end fitting 210 at the upper free end is bolted to the hanger 430 which is itself supported by the ground. It will be appreciated that alternatively a different type of end fitting may be used that allows connection to a suitable hanger designed to hang off topside bore (well) equipment. It will be appreciated that the type of end fitting required may differ based on a chosen surface well head configuration. The flexible pipe(s) 200/pipeline is therefore suspended from the hangers 430. The flexible pipe 200 and the casing 412 are connected to the remainder of the DBHX 400. Aptly the annular region 424 may be in fluid connection with the pump 432 and/or the bore region 140 may be in fluid connection with the heat exchanger (HX) 436.

Finally after the DBHX system 400 has been fully configured, in an operational step S850, the DBHX 400 may be used to provide working fluid 504 having a desired temperature at a predetermined location, for example as described with respect to FIG. 5.

It will be appreciated that recovery of the flexible pipe(s) 200 can be completed by following the installation process described above in reverse.

For example, the flexible pipe(s) 200 can be removed using a coiled tubing rig or tower, with the coiled tubing injector unit running in reverse to pull the flexible pipe(s) 200 out of the borehole 404 it has been installed in. The flexible pipe(s) 200 may then be respooled for disposal or reinstallation at a later point.

FIG. 9 illustrates an alternative DBHX system 900 for electricity generation. The DBHX system 900 of FIG. 9 is generally the same as the DBHX system 400 described with regard to FIGS. 4, 5 and 6, however the HX is connected to an Organic Rankine Cycle (ORC) system 910 for electricity generation. The Organic Rankine Cycle (ORC) system 910 may use an organic compound as the working fluid, such as Isobutane, N-butane, Isopentane, N-pentane, Cyclopentane, Propane, or the like. Optionally if the working fluid is water the ORC system 910 may instead be a Rankine Cycle system. The ORC system 910 of FIG. 9 is illustrated in more detail in FIG. 10.

It will be appreciated that the alternative DBHX system 900 illustrated in FIG. 9 is a binary cycle system in which one working (geothermal) fluid circulates through the bore 404 and heat from the geothermal fluid is transferred via a heat exchanger 910 to a secondary working fluid. The secondary working fluid may have a lower boiling point such that heat from the geothermal fluid causes the secondary fluid to flash to vapour, thus driving a turbine. Alternatively, depending on the phase and/or temperature of the heated (hot) working fluid 520, a turbine may be directly driven by the hot working fluid 520.

FIG. 10 illustrates the ORC system 910 of FIG. 9 in more detail. As illustrated in FIG. 10, the ORC system 910 includes an inlet 1010 in which hot working fluid 520 enters the ORC system 910 and an outlet 1020 out of which cold working fluid 508 exits the ORC system 910. The inlet and outlet are disposed in an evaporator 1030 of the ORC system 910. The evaporator 1030 includes generating fluid 1040, for example water, which is heated by the hot working fluid 520 such that the generating fluid 1040 transitions from a liquid to a gaseous state. The gaseous generating fluid 1040, for example steam, is fed into an expander 1050. The expander 1050 of FIG. 10 includes a turbine 1060. The steam passes over and/or through blades of the turbine 1060 and urges the turbine 1060 to rotate. The turbine 1060 is connected to a rotor 1070 of a generator 1080 which is rotated via the turbine 1060 which in turn induces a current in at least one stator 1090 of the generator 1080. Electricity generated in the generator 1080 is then passed to another location or device for utilisation, for example via one or more cables 1095 or the like. For example, generated electricity may be passed to an appropriate electricity consumer or stored for future use (e.g., using a battery or the like).

FIG. 11 illustrates how a DBHX system 1100 may be installed. It will be appreciated that the method described herein may be applied to any other DBHX system 400, 900. It will further be appreciated that the DBHX system 1100 contains many of the same elements as previously-described systems such as a pre-drilled borehole 1102, downhole casing 1104, flexible pipes 200, end fittings 210, ground 408, the underground region 416, the surface 524, the annular region 504 between the casing 1104 and the flexible pipe 200, and the like. One difference relative to previously-described systems is that the borehole 1102 (and thus the downhole casing 1104) is curved. The borehole 1102 broadly has two different inclines (alternatively more could be provided).

Flexible pipe body 100 is provided at the DBHX system 1100 for installation coiled on the reel element 710 (shown in more detail in FIG. 7). The reel of flexible pipe body 100 illustrated in FIG. 11 is deployed using a coiled tubing tower with correct sizing based on an outside diameter of the flexible pipe body 100.

The reel element 710 may be placed in a Coiled Tubing reel unit 1110 located on the surface 524 of the ground that can be rotated using hydraulics to unravel the reel. During installation the Coiled Tubing reel unit 1110 unwinds the flexible pipe 200 over a guide arch (gooseneck) 1120. The gooseneck 1120 controls the path of the flexible pipe 200 and helps to stop the pipe experiencing a sharper bend than its specified limit. The gooseneck 1120 guides the flexible pipe 200 towards a caterpuller unit 1130 which clamps the outer surface 150 of the flexible pipe 200. It will be appreciated that a caterpuller unit 1130 is an example of a tensioner which may be used to impart a force onto the outer surface 150 of a gripped segment of flexible pipe body 100 through contact with one, two, three or more rotating belts (tracks). At least one rotating caterpuller belt of the caterpuller unit 1130 drives the flexible pipe 200 into (or alternatively during retrieval out) of the borehole 1102. More than one caterpuller unit 1130 may be used to control the flexible pipe during installation. Optionally gravity may be sufficient to allow the flexible pipe 200 to be installed in the borehole 1102, and the caterpuller (if used) may just control the installation. If the borehole 1102 contains pressure, a Blowout Preventor (BOP) 1140 may optionally be used. The flexible pipe 200 passes through the optional BOP 1140, which contains sufficient kill valves and boundaries to kill/isolate the pipe 200 in an emergency. The non-metallic tubing will be run through the unit with midline connectors installed after the pipe has passed through the guide arch to connect continuous lengths of non-metallic tubing.

Flexible pipe body 100 can be centralised in the casing 1104 at any point along its length by using one or more cylindrical centralizers 1150 (four shown). See FIG. 12 for more detail regarding the centralizers. The centralizers help to maintain concentricity of the inner flexible pipe(s) 200 within the outer casing 1104 thereby maintaining the annular region 424 for working fluid 504 to pass through.

FIG. 12 illustrates the centralizer element 1150 in more detail. It will be appreciated that the centralizer element is an example of a spacer element. The centralizer element 1150 has a central through bore 1210 with a circular cross-section that flexible pipe 200 may be inserted into. Thereby, the outer surface 150 of the flexible pipe 200 contacts an inner abutment surface 1220 of the central through bore 1210. A diameter of the central bore 1210 is such that the bore is mateable with the outer surface 150 of flexible pipe body 100. Aptly a tight pressure fit may ensure that the centralizer element 1150 does not move relative to the flexible pipe 200. Alternatively the centralizer element 1150 may be fixed to the outer surface 150 of the flexible pipe 200 using other methods. A cylindrical radially outer surface 1230 of the centralizer element 1150 provides an abutment zone that, in use, abuts an inner surface of the outer casing 1104. The centralizer element 1150 thus helps to fix a gripped region of the flexible pipe 200 concentrically within the outer casing 1104. To allow working fluid 504 to pass freely through the centralizer element 1150 when installed, the element 1150 has one or more through-holes 1240 (eight shown) parallel to the central bore 1210. Alternatively a non-rotating stabilizer or a bow spring centralizer can be installed instead of the centralizer element 1150. It will be appreciated that an alternative spacer element could be used instead of the centralizer element 1150. Such a spacer element may fix the position of the gripped region of the flexible pipe 200 at a non-centralised position.

Turning to FIG. 13, alternative flexible pipe body 1300 is illustrated in axial cross-section. The flexible pipe body 1300 includes centralising elements, the outer sheath 135, the reinforcement layer 120 and the inner fluid retaining layer 110. It will be appreciated that the centralising elements are an example of spacer elements that form a spacer body. The spacer body is a feature of a further outside layer 1310 of the flexible pipe body 1300. The further outside layer 1310 provides protrusions 1320 (five shown but any number could be provided) in the outer surface 150 of flexible pipe body 1300.

The further outside layer 1310 (or alternatively the outer sheath, an additional outermost layer, an underlying layer, or the like) may be manufactured using a helical extrusion process that produces the outer surface 150 of flexible pipe body 1300 with a cross-section which does not have a concentric, largely circular outside diameter. Such a helical extrusion provides the pentagonal cross-section of the outer surface 150 shown in FIG. 13 (similar to a strake). Aptly the protrusions 1320 are examples of strakes. Aptly the cross-section of the outer surface 150 may alternatively be broadly triangular, square, star-like, or the like. The outer surface 150 includes one or more protrusions 1310 circumferentially spaced-apart, allowing working fluid to pass therebetween (into or out of the page) along the annulus 424.

The further outside layer 1310 or any layer containing the helical extrusion may be made from any suitable melt-processable high temperature polymer, for instance a polyolefin or polyamide, PPS or fluoropolymer or fluoroelastomer, and the like.

Aptly casing or half-shell elements may be strapped to the outer surface 150 of the flexible pipe body 1300. The elements may be manufactured from polyurethane, a polyolefin, a polyamide, PPS, a fluoropolymer, a fluoroelastomer, or the like. Aptly the elements may be secured to the outer surface 150 using straps of titanium or nickel alloy or composite.

Aptly sections of centralizer half-shells may be strapped onto the outer surface 150 of the flexible pipe body 1300. Aptly the half-shells may provide strake-like features on the outside which perform a dual function of centralizing the flexible pipe 200 and allowing free passage of working fluid 504 along the annulus 424. Aptly the any helical shape of a centralizer may provide a strake effect. Aptly the strake effect may be useful since it provides spiral passageways for the working fluid 504 to flow through the annulus 424, increasing the dwell-time for working fluid to accumulate thermal energy while on its journey to the downhole-most end region 516.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to” and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of the features and/or steps are mutually exclusive. The invention is not restricted to any details of any foregoing embodiments. The invention extends to any novel one, or novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

While certain arrangements of the inventions have been described, these arrangements have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the systems and methods described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure. Accordingly, the scope of the present inventions is defined only by reference to the appended claims.

Features, materials, characteristics, or groups described in conjunction with a particular aspect, arrangement, or example are to be understood to be applicable to any other aspect, arrangement or example described in this section or elsewhere in this specification unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The protection is not restricted to the details of any foregoing arrangements. The protection extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Furthermore, certain features that are described in this disclosure in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations, one or more features from a claimed combination can, in some cases, be excised from the combination, and the combination may be claimed as a subcombination or variation of a subcombination.

Moreover, while operations may be depicted in the drawings or described in the specification in a particular order, such operations need not be performed in the particular order shown or in sequential order, or that all operations be performed, to achieve desirable results. Other operations that are not depicted or described can be incorporated in the example methods and processes. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the described operations. Further, the operations may be rearranged or reordered in other implementations. Those skilled in the art will appreciate that in some arrangements, the actual steps taken in the processes illustrated and/or disclosed may differ from those shown in the figures. Depending on the arrangement, certain of the steps described above may be removed, others may be added. Furthermore, the features and attributes of the specific arrangements disclosed above may be combined in different ways to form additional arrangements, all of which fall within the scope of the present disclosure. Also, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described components and systems can generally be integrated together in a single product or packaged into multiple products.

For purposes of this disclosure, certain aspects, advantages, and novel features are described herein. Not necessarily all such advantages may be achieved in accordance with any particular arrangement. Thus, for example, those skilled in the art will recognize that the disclosure may be embodied or carried out in a manner that achieves one advantage or a group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

Conditional language, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain arrangements include, while other arrangements do not include, certain features, elements, and/or steps. Thus, such conditional language is not generally intended to imply that features, elements, and/or steps are in any way required for one or more arrangements or that one or more arrangements necessarily include logic for deciding, with or without user input or prompting, whether these features, elements, and/or steps are included or are to be performed in any particular arrangement.

Conjunctive language such as the phrase “at least one of X, Y, and Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to convey that an item, term, etc. may be either X, Y, or Z. Thus, such conjunctive language is not generally intended to imply that certain arrangements require the presence of at least one of X, at least one of Y, and at least one of Z.

Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially” as used herein represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, “generally,” and “substantially” may be used to refer to an amount that is within less than 10% of the stated amount. As another example, in certain arrangements, the terms “generally parallel” and “substantially parallel” refer to a value, amount, or characteristic that departs from exactly parallel by less than or equal to 15°, 10°, 5°, 3°, 1 degree, or 0.1 degree. The ranges disclosed herein also encompass any and all overlap, sub-ranges, and combinations thereof, and any specific values within those ranges. Language such as “up to,” “at least,” “greater than,” “less than,” “between,” and the like includes the number recited. Numbers and values used herein preceded by a term such as “about” or “approximately” include the recited numbers. For example, “approximately 7 mm” includes “7 mm” and numbers and ranges preceded by a term such as “about” or “approximately” should be interpreted as disclosing numbers and ranges with or without such a term in front of the number or value such that this application supports claiming the numbers, values and ranges disclosed in the specification and/or claims with or without the term such as “about” or “approximately” before such numbers, values or ranges such, for example, that “approximately two times to approximately five times” also includes the disclosure of the range of “two times to five times.” The scope of the present disclosure is not intended to be limited by the specific disclosures of preferred arrangements in this section or elsewhere in this specification, and may be defined by claims as presented in this section or elsewhere in this specification or as presented in the future. The language of the claims is to be interpreted broadly based on the language employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive.