Geothermal energy through expanded tubular section

Abstract

Method of extracting geothermal energy from the Earth's crust, comprising: - transporting a relatively cold fluid flow downstream into the Earth's crust through a borehole (102) with a tubular element (200) positioned therein, the tubular element (200) comprising an expanded tubular section (202) formed by radially expanding an unexpanded tubular section (204) inside the borehole (102); - allowing geothermal energy to be transferred into the relatively cold fluid flow transported through the tubular element (200) to increase the temperature of fluid in the fluid flow, such that the relatively cold fluid flow becomes a heated fluid flow; and - transporting the heated fluid flow up towards the Earth's surface (104) through the same tubular element (200).

Description

[0001] Title: Geothermal energy through expanded tubular section

[0002] TECHNICAL FIELD

[0003] The aspects and embodiments thereof relate to the field of extracting geothermal energy from the Earth’s crust.

[0004] BACKGROUND

[0005] Geothermal energy is the thermal energy in the Earth's crust which originates from the formation of the planet and from radioactive decay of materials. Geothermal energy is regarded as a renewable energy source, as any geothermal energy extracted is relatively small compared to the total heat energy of the Earth. Geothermal energy is also regarded to be a sustainable energy source.

[0006] Different methods of extracting geothermal energy from the Earth’s crust have been proposed. For example, naturally present water in underground layers, which has a relatively high temperature by virtue of geothermal energy, can be pumped up towards the Earth’s surface. This water is provided in a first well. After extracting thermal energy from this water, the water is pump back down again to be reheated into a second well. The first well is positioned at a distance from the second well.

[0007] Typically, a borehole is drilled to form a well. Subsequently, a casing is positioned into the borehole. The casing is then secured using cement, which cement may also protect the outside of the casing. The casing allows a fluid flow to be pumped up towards the Earth’s surface, or for a fluid flow to be transported back down into the Earth’s crust.

[0008] SUMMARY

[0009] An object of the present disclosure is to extract geothermal energy from the Earth’s crust. In particular, it may be an object to provide for a more economical, more efficient, and / or faster method of extract geothermal energy compared to conventional methods.

[0010] A first aspect provides a method of extracting geothermal energy from the Earth’s crust. The method comprises steps of transporting a relatively cold fluid flow downstream into the Earth’s crust through a borehole with a tubular element positioned therein, the tubular element comprising an expanded tubular section formed by radially expanding an unexpanded tubular section inside the borehole, allowing geothermal energy to be transferred into the relatively cold fluid flow transported through the tubular element to increase the temperature of fluid in the fluid flow, such that the relatively cold fluid flow becomes a heated fluid flow, and transporting the heated fluid flow up towards the Earth’s surface through the same tubular element.

[0011] By allowing a cold fluid flow to flow through the same tubular element as the heated fluid flow, it may become more economical and / or more efficient to extract geothermal energy from the Earth’s crust. It may be avoided that necessarily two boreholes have to be drilled or two tubular elements have to be used: one for transporting fluid from the Earth’s surface down into the Earth’s crust, and one for transporting heated fluid back up again from the Earth’s crust to the Earth’s surface.

[0012] By using a method of positioning the tubular element in the borehole by radially expanding an unexpanded tubular section into an expanded tubular section, conveniently the borehole can be lined and a liquid- tight tubular element for transporting a fluid flow through can be obtained.

[0013] By using an expanded tubular section for lining the borehole, use of cement between the tubular element and the borehole wall may be avoided.

[0014] An expanded tubular section is generally defined as a tubular section formed from a tubular section which before being expanded, had a smaller outer diameter. In particular, before being expanded, the tubular section is referred to as an unexpanded tubular section. Radially expanding the tubular element in the borehole typically comprises steps of bending the tubular element radially outward and in axially reverse direction so as to form an expanded tubular section extending around an unexpanded tubular section, wherein the bending occurs in a bending zone, and increasing the length of the expanded tubular section by pushing the unexpanded tubular section in axial direction relative to the expanded tubular section further into the borehole.

[0015] When the end of the borehole is reached - in particular at an exit at the Earth’s surface - the unexpanded tubular section may be removed from the tubular element, for example by cutting, sawing, or otherwise disconnecting the unexpanded tubular section from the expanded tubular section, for example at or near the bending zone. The disconnected unexpanded tubular section may be pulled out of the expanded tubular section, either at the beginning of the borehole or at the exit.

[0016] When the unexpanded tubular section is not removed, the tubular element may thus comprise an unexpanded tubular section inside the expanded tubular section. An annular space is provided between an inner wall of the expanded tubular section and an outer wall of the unexpanded tubular section, which annular space may be advantageously used to transport a fluid flow through.

[0017] In general, at least part of the unexpanded tubular section is thermally insulated, in particular part of the unexpanded tubular section in an upper section of the tubular element. Additionally, or alternatively, also for any embodiment disclosed herein, at least part of the unexpanded tubular section is thermally insulated, in particular part of the unexpanded tubular section in an upper section of the tubular element. Thermal insulation may be used to reduce transfer of thermal energy from a fluid flowing through the tubular element through the tubular element, or to reduce transfer of thermal energy from the surroundings into the fluid flowing through the tubular element through the tubular element. In any tubular element disclosed herein comprising an annular space between the unexpanded tubular section and the expanded tubular section, at least part of the annular space may be filled with one or more compounds, such as any liquid or gas, or thermally insulating compounds like a foam, during and / or after the tubular element is fully formed.

[0018] According to a first set of embodiments, the method further comprising placing a seal in the unexpanded tubular section and providing one or more openings in the unexpanded tubular section upstream of the seal, such that a passage through the unexpanded tubular section is in fluid communication with an annular space between the unexpanded tubular section and the expanded tubular section.

[0019] As such, a borehole can be used with a single entry which is also used as the exit for heated fluid. Conveniently, as such, less boreholes may have to be drilled.

[0020] By virtue of the seal, leakage of fluid through the unexpanded tubular section is prevented. Instead of leaking out of the distal end of the tubular element, the fluid can now pass through the one or more openings in the unexpanded tubular section which are positioned upstream of the seal.

[0021] The seal as an option may be placed in the unexpanded tubular section at or near an entry into the borehole, where for example the unexpanded tubular section may be easier to access that further into the borehole. The seal may then be transported into the borehole together with the unexpanded tubular section.

[0022] When one or more openings are provided through the unexpanded tubular section, transporting the fluid flow through the tubular element may comprise transporting the fluid flow through the unexpanded tubular section in a downstream direction, transporting the fluid flow subsequently through the one or more openings in the unexpanded tubular section, and transporting the fluid flow as the heated fluid flow through the annular space between the unexpanded tubular section and the expanded tubular section towards the Earth’s surface.

[0023] Alternatively, transporting the fluid flow through the tubular element may comprise transporting the fluid flow through the annular space between the unexpanded tubular section and the expanded tubular section in a downstream direction, transporting the fluid flow subsequently through the one or more openings in the unexpanded tubular section, and transporting the fluid flow through the unexpanded tubular section as the heated fluid flow towards the Earth’s surface.

[0024] In any embodiment disclosed herein, the borehole may be oriented vertically, for example in order to reach a maximum depth with a particular length of tubular element. Alternatively, at least part of the borehole may be oriented at an angle relative to vertical, or at least at an angle of 20 degrees relative to the vertical, or even at least part of the bore may be oriented generally horizontally, for example to allow the tubular element to extent over a horizontal distance.

[0025] According to a second set of embodiments of the present disclosure, the borehole in which the tubular element is positioned enters the Earth’s surface at a first entry, and exits the Earth’s surface at a first exit at a distance from the first entry. As such, fluid can be transported through the borehole from the first entry to the first exit. During transport, geothermal energy can be allowed to transfer into the fluid. The fluid flow may thus be transported from the first entry to the first exit, for example using a suitable pumping device.

[0026] It is envisioned to provide a second tubular element, which second tubular element is positioned in a second borehole and comprises an expanded tubular section formed by radially expanding an unexpanded tubular section inside the second borehole. The second borehole may enter the Earth’s surface at a second entry, and may exit the Earth’s surface at a second exit at a distance from the second entry. The second tubular element may be formed using any of the options disclosed in conjunction with any tubular element disclosed herein, for example but not limited to the option of using thermal insulation.

[0027] When a second tubular element is provided, the fluid flow can be transported through the first tubular element from first entry to the first exit, and subsequently through the second tubular element from the second entry to the second exit. As such, a closed loop system for circulating fluid through the first and second tubular elements may be achieved.

[0028] Preferably, the first exit and the second entry are positioned adjacent to each other, and the method further comprises extracting thermal energy from the fluid flow between the first exit and the second entry. Additionally, or alternatively, the second exit and the first entry may be positioned adjacent to each other, and the method further comprises extracting thermal energy from the fluid flow between the second exit and the first entry.

[0029] Whenever a tubular element comprises an unexpanded tubular section is of a different material composition than the expanded tubular section, in particular through which a fluid has to be transported, the unexpanded tubular section may be of a different material composition than the expanded tubular section. When the tubular element is fully formed, the remaining unexpanded tubular section does not have to be radially expanded anymore, and can thus be made of material which is unsuited to be radially expanded, can be coated and / or isolated, and / or can otherwise differ from the material used to form the expanded tubular section with.

[0030] A second aspect of the present disclosure provides a system for extracting geothermal energy. The system may be used to perform one or more or all steps in any method according to the first aspect.

[0031] The system comprises a first tubular element positioned in a first borehole, the first tubular element comprising an expanded tubular section formed by radially expanding an unexpanded tubular section, a first pumping device for pumping a fluid through the first tubular element between a first entry and a first exit, and a first heat exchanger for extracting thermal energy from fluid at the first exit.

[0032] When a fluid, such as but not limited to water, is fed through the tubular element using the first pumping device, geothermal energy can be transferred into the fluid. At the first exit, the heat exchanger can be used for extracting at least part of the geothermal energy from the fluid.

[0033] As an option, the system may comprise a second tubular element positioned in a second borehole, the second tubular element comprising an expanded tubular section formed by radially expanding an unexpanded tubular section, wherein the second tubular element is arranged for transporting a flow of fluid from a second entry to a second exit. In such embodiments, the second tubular element is preferably in fluid communication with the first tubular element.

[0034] When the system comprises the second tubular element, the first tubular element and second tubular element may form a closed loop through which fluid can be circulated. It will be appreciated that one or more inlets and / or outlets may be provided to supply additional fluid to the closed loop and / or to withdraw fluid from the closed loop.

[0035] As an option, a second heat exchanger may be comprised by the system for extracting thermal energy from fluid at the second exit. The first and second heat exchangers may be located at different locations, such that geothermal energy can be extracted at multiple different locations - for example two different towns, or different locations within a city.

[0036] Systems are envisioned wherein the first tubular element further comprises an unexpanded tubular section positioned inside the expanded tubular section. An annular space is thus formed between the unexpanded tubular section and the expanded tubular section, and separated fluid flows can flow through the annular space as well as through the unexpanded tubular section - for example one flow downstream and one flow upstream, in any combination.

[0037] When the tubular element comprises the unexpanded tubular section, the system may further comprise a seal sealing the unexpanded tubular section and one or more openings through the unexpanded tubular section positioned upstream of the seal. When the unexpanded tubular section is optionally cut and removed from the expanded tubular section, it is also envisioned to positioned a seal or a filter in the expanded tubular section.

[0038] BRIEF DESCRIPTION OF THE FIGURES

[0039] In the figures,

[0040] Fig. 1 schematically shows in a section view a well;

[0041] Figs. 2A and 2B depict a schematic section view of a well in two different method steps;

[0042] Fig. 3 A and 3B schematically show further examples of wells;

[0043] Fig. 4A and 4B schematically show even further examples of wells;

[0044] Fig. 4C shows a detailed view of part of a generally horizontal borehole; and

[0045] Figs. 5A and 5B respectively show in a schematic top view and a schematic section view an example of a system for extracting geothermal energy;

[0046] Fig. 6 schematically shows another example of a system for extracting geothermal energy; and

[0047] Figs. 7A-7B show a well for production of water from an underground source.

[0048] DETAILED DESCRIPTION OF THE FIGURES

[0049] The figures presented with the present disclosure are schematic drawings, which are not necessarily drawn to scale - for example to increase clarity and intelligibility of the figures. Fig. 1 schematically shows in a section view a well 100 comprising a vertical borehole 102. Any vertical borehole 102 may for example have a depth of at least 20 metres, at least 100 metres, or at most 500 metres. However, a depth of more than 500 metres, more than 2500, or even more than 6000 metres is also envisioned. Generally, it is an aim to have the depth of the borehole 102 correspond to a depth at which the temperature of the Earth’s crust is sufficient to heat a fluid flow passing through the borehole 102. The borehole 102 is generally drilled into the Earth’s surface 104. A downhole portion of the borehole 102 is generally indicated with reference numeral 101.

[0050] In the borehole 102, a tubular element 200 is being positioned. The tubular element 200 comprises an expanded tubular section 202 formed by radially expanding an unexpanded tubular section 204 inside the borehole 102. Shown as dotted lines in the shape of tubular element 200’ after further inserting the unexpanded tubular section 204’ into the borehole. As the unexpanded tubular section 204’ is moved further into the borehole 102, part of the unexpanded tubular section is expanded to form part of the expanded tubular section 202’. The radial expansion takes place in a bending zone 206. As the unexpanded tubular section 204’ is moved further into the borehole 102, the bending zone 206’ is also moved further into the borehole 102.

[0051] By radially expanding the tubular element 200, the borehole 102 can be lined with the expanded tubular section 202. The tubular element 200 may generally provide a liquid-tight passage into the borehole 102, through which one or more fluid flows may be transported, as will be elaborated on further in the present disclosure. A distal end of the tubular element 200, in particular a distal end of the unexpanded tubular section 204, may be sealed using a sealing and / or swelling material supplied through the tubular element 200, for example a self-hardening bentonite, cement, or grout.

[0052] Although not depicted in Fig. 1, it will be appreciated that a drill string may pass through the unexpanded tubular section. At a distal end of the drill string, a drill can be connected which can be supplied with torque and / or fluid via the drill string. The drill is typically positioned downstream of the bending zone.

[0053] Figs. 2A and 2B depict a particular method, wherein a seal 220 such as a liquid-tight and / or gas-tight seal is placed in the unexpanded tubular section 204. Furthermore, one or more openings 222 are provided through the unexpanded tubular section 204, in particular at a location upstream of the seal 220. Figs. 2A shows the seal 220 and the one or more openings 222 still at a location above or near ground level 104. Furthermore, the one or more openings 222 are positioned above or near ground level 104. It will thus be appreciated that method steps are envisioned including connecting the seal 220 to the unexpanded tubular section 204 above or near ground level and / or making the one or more openings 222 in the unexpanded tubular section 204 above or near ground level.

[0054] As the unexpanded tubular section 204 is moved further into the borehole 102, the seal 220 and the one or more openings 222 are also moved further into the borehole 102. Fig. 2B shows the downhole portion 101 of the borehole 102, which may be the final depth were the bending zone 206 of the tubular element 200 ends up. Compared to the situation depicted in Fig. 2A, in the situation depicted in Fig. 2B the unexpanded tubular section 204 has been pushed further into the borehole 102. Alternatively, an interface, such as the interface disclosed in conjunction with Figs. 7A-7B, may be used to positioned the seal 220.

[0055] As can be seen in Fig. 2B, the seal 220 and the one or more openings 222 may have been moved to a location near or even just above the bending zone 206 by virtue of the unexpanded tubular section 204 having been moved further into the borehole 102. It will be understood that the speed with which the bending zone 206 moves into the borehole 102 is half of the speed with which the unexpanded tubular section 204 moves into the borehole 102 by virtue of the expanded tubular section 202 being formed. As schematically indicated in Fig. 2B with a dash-dot-dotted line, a flow of fluid 302 can now be transported down into the borehole through an annulus 203 between the expanded tubular section 202 and the unexpanded tubular section 204. Subsequently, the flow of fluid 302 can pass through one or more openings 222 through the unexpanded tubular section 204, and flow back up towards the Earth’s surface through the unexpanded tubular section 204.

[0056] Alternatively, in an opposite direction as depicted with arrows 302 in Fig. 2B, the fluid flow 302 can be transported down into the borehole through the unexpanded tubular section 204, subsequently pass through one or more openings 222 through the unexpanded tubular section 204, and flow back up towards the Earth’s surface through the annulus 203 between the expanded tubular section 202 and the unexpanded tubular section 204.

[0057] Fluid flow 302 flowing downstream into the Earth’s crust through the borehole 102 is typically a relatively cold fluid flow. As the fluid flow flows through the Earth’s crust, thermal energy can be transferred through the Earth’s crust into the fluid flow, and when the fluid flow reaches the Earth’s surface again, the fluid flow has become a heated fluid flow. The heated fluid flow can for example be used for heating buildings.

[0058] Although in Fig. 2B, the one or more openings 222 are depicted at a single depth in the borehole 102, it is envisioned that one or more openings 222 may be positioned at different depths. For example, one or more openings may be positioned in a lower section of the tubular element 200, for example in a bottom quarter of the tubular element 200, or even in the bottom 10% or less of the tubular element 200. Although the borehole 102 is in Figs. 2A and 2B depicted as being vertical, the borehole 102 can also be at least partially oriented at an angle relative to vertical or even at least partially horizontal. In such cases, one or more openings may be positioned in a downhole section of the tubular element 200, for example in a quarter of the tubular element 200 furthest downhole, or even in the 10% or less of the tubular element 200 furthest downhole.

[0059] Fig. 3A shows another example of a well 100, with a borehole 102 in which a tubular element 200 has been placed, with an expanded tubular section 202 lining at least part of the borehole 102. As an option depicted in Fig. 3A but applicable to any tubular element 200 disclosed herein, part 234 of the unexpanded tubular section 204 is thermally insulated.

[0060] In general, thermally insulated here implies that it is an aim to reduce transfer of thermal energy through the thermally insulated section. For example, the resistance to transfer of thermal energy is higher in a thermally insulated section than in an adjacent not thermally insulated section. Thermal insulation may be provided against for example against conductive, convective, and / or radiative heat transfer. Thermal insulation may be applied to any part of parts of any expanded tubular section and / or unexpanded tubular section disclosed herein, in any vertical, horizontal, and / or curved borehole section, in any combination thereof.

[0061] Fig. 3B shows yet another example of a well 100, with a borehole 102 in which a tubular element 200 has been placed, with an expanded tubular section 202 lining at least part of the borehole 102. As an option depicted in Fig. 3B but applicable to any tubular element 200 disclosed herein, part 232 of the expanded tubular section 202 is thermally insulated.

[0062] By thermally insulating at least part of the expanded tubular section 202 and / or the unexpanded tubular section 204, the amount of thermal energy which can be retrieved from the heated fluid flow at the Earth’s surface can be increased. For example, leakage of thermal energy from the fluid flow to the surroundings of the borehole can be decreased. Additionally or alternatively, leakage of thermal energy from the heated fluid flow to the cold fluid flow flowing through the same tubular element can be decreased. By virtue of the radial expansion process by which the borehole 102 is lined with the expanded tubular section 202 by moving the unexpanded tubular section 204 into the borehole 102, the thermal insulation can be added already aboveground to the unexpanded tubular section 204. Thermal insulation may be connected or applied to the material of the unexpanded tubular section 204, and / or the material forming the unexpanded tubular section 204 itself may be thermally insulating.

[0063] As schematically depicted in Figs. 3 A and 3B, it may be generally desired to apply thermal insulation above a depth 130 at which the temperature of the Earth’s crust is above a certain threshold.

[0064] Although the borehole 102 is in Figs. 3A and 3B depicted as being vertical, the borehole 102 can also be at least partially oriented at an angle relative to vertical or even at least partially horizontal.

[0065] It will be appreciated that for any tubular element disclosed herein, also parts of both the unexpanded tubular section and the expanded tubular section can be thermally insulated.

[0066] Fig. 4A schematically shows another example of a well 100, in particular a partially horizontal well 100 with a borehole 102 which is oriented at least partially horizontally. It will be understood that whenever in the present disclosure the wording horizontally or generally horizontally is used, it will be understood that the well, borehole, and / or tubular element are not necessarily perfectly horizontal, and may thus be oriented at a slight angle relative to horizontal, for example with a 20 degree deviation, within a 10 degree deviation, or even within a 5 degree deviation.

[0067] Typical for a horizontal well 100, as generally depicted in Fig. 4A, is that it may be advantageous to have an entry 108 in which the borehole 102 can be entered, and an exit 110 at which the borehole 102 can be exited. In general, for any horizontal borehole 102 disclosed herein, a maximum depth of the borehole 102 may be between 10 and 6000 metres, in particular between 50 and 500 metres. From Fig. 4A, it will be appreciated that a horizontal borehole may have vertical of curved section near the entry and near the exit, for example to reach the desired depth for the horizontal section. Alternatively, essentially the entire borehole 102 may be curved, for example at a particular radius.

[0068] The borehole 102 of Fig. 4A is lined with an expanded tubular section 202 formed by radially expanding an unexpanded tubular section 204 of a tubular element 200. When the tubular element 200 extends between the entry 108 and the exit 110, a flow of fluid may be transported through the tubular element 200 from the entry 108 to the exit 110. While being transported through the tubular element 200, geothermal energy from the Earth’s crust may be transferred into the flow of fluid, and as such a temperature of the flow of fluid may be higher at the exit 110 than at the entry 108. In any embodiment disclosed herein, the flow of fluid may essentially consist of water.

[0069] Because the borehole 102 shown in Fig. 4A extends between the entry 108 and the exit 110, it is possible to remove the unexpanded tubular section 204 when the bending zone 206 reaches the exit 110. For example, the tubular element 200 may be severed for example at or near the bending zone 206 such that unexpanded tubular section 204 is disconnected from the expanded tubular section 202. The unexpanded tubular section 204, or at least part thereof, may then be removed from the borehole 102 for example through the entry 108 or the exit 110 while the expanded tubular section 202 is left in place. The material comprised by the unexpanded tubular section 204 may then for example recycled. When the unexpanded tubular section is removed, there is no longer an annulus 203 which might otherwise hinder transfer of thermal energy to a fluid flow transported through the tubular element 200.

[0070] Fig. 4B shows another example of a well 100, with a partially horizontal borehole 102 in which a tubular element 200 is placed. The tubular element 200 comprises an expanded tubular section lining the borehole 102, and an unexpanded tubular section positioned in the expanded tubular section. For example, at or near a downhole section 101, a seal and one or more openings may be present, similar to the situation depicted in Fig. 2B.

[0071] As such, a flow of fluid can be transported from the entry 108 of the borehole 102 towards a distal end 205 of the tubular element 200, through one of the unexpanded tubular section and the annulus between the unexpanded tubular section and the expanded tubular section, and the flow of fluid can be transported back to the exit 110 - corresponding to the entry 108 - through the other of the unexpanded tubular section and the annulus between the unexpanded tubular section and the expanded tubular section, via the one or more openings through the unexpanded tubular section.

[0072] An advantage of the example of Fig. 4B is that the flow of fluid has to be handled only at a single location, which simultaneously forms the entry 108 for fluid into the tubular element 200 and the exit 110 for fluid from the tubular element 200. For example by increasing a length of the horizontal part of the tubular element 200, more thermal energy can be transferred into the flow of fluid.

[0073] Fig. 4C shows a detailed view of part of a generally horizontal borehole 102, while a tubular element 200 is placed in the borehole 102. The tubular element 200 comprises the unexpanded tubular section 204 and the expanded tubular section 202 formed by radially expanding the unexpanded tubular section 204 in the bending zone 206. Shown as dotted lines are the unexpanded tubular section 204’ and the expanded tubular section 202’ as the unexpanded tubular section 204 is moved further into the borehole 102.

[0074] Figs. 5A and 5B respectively show in a schematic top view and a schematic section view an example of a system for extracting thermal energy 400. The system 400 comprises two boreholes 102, 102” in each of which respectively a tubular element 200, 200” is placed. The tubular elements 200, 200” each at least comprise an expanded tubular section formed by radially expanding an unexpanded tubular section, for example in accordance with any method of radially expanding disclosed herein.

[0075] At a first location 401, a first heat exchanger 402 is positioned which is comprised by the system 400. Also at the first location 401, a first entry 108 of a first tubular element 200 is positioned, as well as a second exit 110” of a second tubular element 200”. At a second location 403, which is at a distance from the first location 401, a second heat exchanger 404 is positioned, which is comprised by the system 400. Also at the second location 403, a first exit 110 of the first tubular element 200 is positioned, as well as a second entry 108” of the second tubular element 200”.

[0076] In use of the system 400, a first flow of fluid can be transported through the first tubular element 200 from the first entry 108 to the first exit 110, for example using a fluid pumping device comprised by the system 400. The fluid pumping device may be positioned at the first location 401 and / or at the second location 403. A second flow of fluid can be transported through the second tubular element 200” from the second entry 108” to the second exit 110”, for example using a fluid pumping device comprised by the system 400. It will be appreciated that the system 400 may comprise multiple fluid pumping devices.

[0077] When the first tubular element 200 and the second tubular element 200” are in fluid communication at the first location 401 and at the second location 403, a closed circuit may be obtained. Instead of the second heat exchanger, the first tubular element 200 and the second tubular element 200” may be coupled at the second location 403. As such, only a heat exchanger is required at a single location 401.

[0078] In conjunction with any of the wells 100 disclosed herein wherein a distal end of the tubular element 200 is positioned below the Earth’s surface 104, for example when a bending zone 206 of the tubular element 200 is positioned below the Earth’s surface 104, for example in conjunction with Figs. 1-3B, 4B, a system for extracting geothermal energy may be provided. The system comprises a pumping device for pumping a fluid through the tubular element 200 between an entry and an exit, which exit and entry are respectively formed by the unexpanded tubular section 204 and the annulus 203 or by the annulus 203 and the unexpanded tubular section 204. The system further comprises a heat exchanger for extracting thermal energy from fluid supplied through the exit. Optionally, the fluid may be recirculated into the entry, to form an at least partially closed loop system.

[0079] Fig. 6 schematically shows another example of a system 400 for extracting geothermal energy. According to this example, it is envisioned that the system 400 comprises at least two tubular elements 200, 200”, positioned each in their own borehole 102, 102”. At their distal ends 205, 205”, the tubular elements 200, 200” are in fluid communication with an underground reservoir 600. Using the first tubular element 200, fluid, such as water, may be transported into the underground reservoir 600. Through the second tubular element 200”, fluid, such as water, may be pumped up from the underground reservoir 600, for example using a pumping device 412. When the system 400 comprises a heat exchanger 408 in fluid communication with the second tubular element 200”, thermal energy may be extracted from fluid pumped up from the underground reservoir 600.

[0080] Optionally, a fluid connection 410 is comprised by the system 400 fluidly connecting the first tubular element 200 and the second tubular element 200 for example at a location above the Earth’s system 400. As such, a looped system may be obtained through which fluid can be circulated down through the first tubular element 200, via the underground reservoir 600, up through the second tubular element 200”, and optionally back to the first tubular element 200 via the fluid connection 410.

[0081] Any of the features disclosed herein relating to the tubular element, un expanded tubular section, expanded tubular section, borehole, are readily applicable to any one or both of the tubular sections of the system 400 depicted in Fig. 6. Independent from the system 400, in Fig. 6, a minimum depth 604 and a maximum depth 602 are indicated. For any system 400 and method of the present disclosure, it may be an aim to position any distal end of a tubular element, for example defined at or near the bending zone, between the minimum depth and the maximum depth. Alternatively, for example in case at least part of the tubular element is oriented horizontally, it may be an aim to have a maximum depth of the tubular element between the minimum depth and the maximum depth.

[0082] The minimum depth may for example be defined by a desired ground temperature to which fluid flowing through the tubular element is to be exposed, and / or the presence of any tunnels, waterways, or other manmade underground objects.

[0083] Although typically the underground temperature increases with an increased depth, a maximum depth may be used to prevent having to form the borehole through underground sections possibly containing hydrocarbons such as oil or gas. Any method disclosed herein may thus be defined in that the borehole does not pass through underground sections containing hydrocarbons such as oil or gas. This may provide the advantage that the drilling equipment does not have to be suitable for drilling through such underground sections.

[0084] Instead of drilling the borehole deeper to increase the temperature to which fluid can be exposed, the present methods and system allow for the length of the borehole to be increased when at least part of the borehole is oriented at an angle relative to the vertical, for example essentially horizontal, to increase transfer of geothermal energy into the fluid flowing through the tubular element. The maximum depth for any system herein may for example be 1000 metres of less, or even 500 metres or less.

[0085] In another aspect, the present disclosure contemplates a method of retrieving water from an underground reservoir, the method comprising forming a borehole towards the underground reservoir, lining the borehole with an expanded tubular section formed by radially expanding an unexpanded tubular section inside the borehole, and transporting water from the underground reservoir through the tubular element to the Earth’s surface.

[0086] Optionally, a filter may be positioned in the tubular element, for example in the unexpanded tubular section, or conceivable in the expanded tubular section, in particular in case the unexpanded tubular section is removed. Preferably, the filter is positioned at or near a distal end of the tubular section, at or near the underground source. The filter may be arranged to prevent or reduce solid matter from being transported with the water through the tubular element.

[0087] Figs. 7A-7B show a well 100 for production of water from an underground source 600. In Fig. 7 A, a situation is depicted wherein a borehole 102 is being formed, for example using a drill 700. The drill 700 is connected to a drill string 702 for providing fluid and / or torque to the drill 700. When the bending zone 206 of the tubular element 200 is approximately at a halfway distance towards the underground source 600, an interface 270 can be connected to the unexpanded tubular section 204. The interface 270 has a passage 272 to allow the drill string 702, and conceivable the drill 700, for example in a retracted state, to pass through the interface 270. A similar interface may be used to position a seal 220, for example the seal 220 disclosed in conjunction with Figs. 2A-2B, in the unexpanded tubular section 204.

[0088] In Fig. 7B, the well 100 of Fig. 7A is depicted with the tubular element 200 in fluid communication with the underground source 600, such that water can be retrieved from the underground source 600 through the tubular element 200, in particular through the unexpanded tubular section 204.

[0089] As a particular option to position a filter or a seal in any unexpanded tubular section 204 of the present disclosure, the filter 274 or seal can be connected to the interface 270, after the interface 270 has been moved into the borehole 102 together with the unexpanded tubular section 204. The filter 274 or seal can be lowered into the unexpanded tubular section 204, in particular after the drill string 702 has been removed from the unexpanded tubular section 204, and subsequently connected to the interface 270, for example using a clamped connection, threaded connection, adhesive, weld, magnetic connection, any other connection, or any combination thereof.

[0090] The water retrieved from any underground reservoir may be used as drinking water, and / or depending on the temperature of the water, for cooling purposes or heating purposes.

[0091] Any feature or features disclosed in conjunction with the borehole, tubular element, unexpanded tubular section, and / or expanded tubular section of any of the examples and embodiments disclosed herein, for example in conjunction with Figs. 1-6, may be readily applied to any well for production of water from an underground source, in any combination.

[0092] In any method and system of the present disclosure, prior to transporting the fluid flow through the tubular element, an unexpanded tubular section may be removed from the expanded tubular section. In particular, the unexpanded tubular section was previously connected to the expanded tubular section via a bending zone.

[0093] Additionally, or alternatively, for any method and system of the present disclosure, the expanded tubular section has been permanently expanded. Permanently expanded implies that while extracting geothermal energy, the shape of the expanded tubular section essentially remains the same. Any expanded tubular section may thus in use act as a rigid tubular section.

Claims

Claims1. Method of extracting geothermal energy from the Earth’s crust, comprising: transporting a relatively cold fluid flow downstream into the Earth’s crust through a borehole with a tubular element positioned therein, the tubular element comprising an expanded tubular section formed by radially expanding an unexpanded tubular section inside the borehole; allowing geothermal energy to be transferred into the relatively cold fluid flow transported through the tubular element to increase the temperature of fluid in the fluid flow, such that the relatively cold fluid flow becomes a heated fluid flow; and transporting the heated fluid flow up towards the Earth’s surface through the same tubular element.

2. Method according to claim 1, wherein the tubular element further comprises an unexpanded tubular section inside the expanded tubular section.

3. Method according to claim 1, wherein prior to transporting the fluid flow through the tubular element, an unexpanded tubular section is removed from the expanded tubular section.

4. Method according to claim 2, wherein the unexpanded tubular section transitions into the expanded tubular section via a bending zone.

5. Method according to any of the preceding claims, further comprising radially expanding the tubular element in the borehole, prior to transporting the fluid flow through the tubular element, wherein radially expanding the tubular element in the borehole comprises steps of:bending the tubular element radially outward and in axially reverse direction so as to form an expanded tubular section extending around an unexpanded tubular section, wherein the bending occurs in a bending zone; and increasing the length of the expanded tubular section by pushing the unexpanded tubular section in axial direction relative to the expanded tubular section further into the borehole.

6. Method according to any of the preceding claims, wherein part of the unexpanded tubular section is thermally insulated, in particular part of the unexpanded tubular section in an upper section of the tubular element.

7. Method according to any of the preceding claims, wherein part of the expanded tubular section is thermally insulated, in particular part of the expanded tubular section in an upper section of the tubular element.

8. Method according to any of the preceding claims 1, 2, 4-7, wherein the unexpanded tubular section is of a different material composition than the expanded tubular section.

9. Method according to any of the preceding claims, the method further comprising: placing a seal or seal interface in the unexpanded tubular section; and providing one or more openings in the unexpanded tubular section upstream of the seal or seal interface, such that a passage through the unexpanded tubular section is in fluid communication with an annular space between the unexpanded tubular section and the expanded tubular section.

10. Method according to claim 9, wherein the seal or seal interface is placed in the unexpanded tubular section at or near an entry into theborehole, and the seal or seal interface is transported into the borehole together with the unexpanded tubular section.

11. Method according to claim 9 or 10, wherein transporting the fluid flow through the tubular element comprises transporting the fluid flow through the unexpanded tubular section in a downstream direction, transporting the fluid flow subsequently through the one or more openings in the unexpanded tubular section, and transporting the fluid flow as the heated fluid flow through the annular space between the unexpanded tubular section and the expanded tubular section towards the Earth’s surface.

12. Method according to claim 9 or 10, wherein transporting the fluid flow through the tubular element comprises transporting the fluid flow through the annular space between the unexpanded tubular section and the expanded tubular section in a downstream direction, transporting the fluid flow subsequently through the one or more openings in the unexpanded tubular section, and transporting the fluid flow through the unexpanded tubular section as the heated fluid flow towards the Earth’s surface.

13. Method according to any of the claims 9-12, further comprising a step of connecting a seal to the seal interface after the seal interface is positioned in the borehole by pushing the unexpanded tubular section in axial direction relative to the expanded tubular section further into the borehole.

14. Method according to any of the preceding claims, wherein the borehole is oriented essentially vertically.

15. Method according to any of the claims 1-14, wherein at least part of the borehole is oriented generally horizontally, or at least at an angle of 20 degrees relative to the vertical.

16. Method according to any of the claims 1-8, wherein the borehole in which the tubular element is positioned enters the Earth’s surface at a first entry, and exits the Earth’s surface at a first exit at a distance from the first entry.

17. Method according to claim 16, wherein the fluid flow is transported from the first entry to the first exit.

18. Method according to claim 17, further comprising: providing a second tubular element, which second tubular element is positioned in a second borehole and comprises an expanded tubular section formed by radially expanding an unexpanded tubular section inside the second borehole, which second borehole enters the Earth’s surface at a second entry, and exits the Earth’s surface at a second exit at a distance from the second entry, wherein the fluid flow is transported through the first tubular element from the first entry to the first exit, and subsequently through the second tubular element from the second entry to the second exit.

19. Method according to claim 18, wherein the first exit and the second entry are positioned adjacent to each other, and the method further comprises extracting thermal energy from the fluid flow between the first exit and the second entry.

20. Method according to claim 18 or 19, wherein the second exit and the first entry are positioned adjacent to each other, and the method further comprises extracting thermal energy from the fluid flow between the second exit and the first entry.

21. Method according to any of the preceding claims, wherein the fluid flow essentially consists of water.

22. System for extracting geothermal energy, the system comprising: a first tubular element positioned in a first borehole, the first tubular element comprising an expanded tubular section formed by radially expanding an unexpanded tubular section; a first pumping device for pumping a fluid through the first tubular element between a first entry and a first exit; and a first heat exchanger for extracting thermal energy from fluid at the first exit.

23. System according to claim 22, further comprising: a second tubular element positioned in a second borehole, the second tubular element comprising an expanded tubular section formed by radially expanding an unexpanded tubular section, wherein the second tubular element is arranged for transporting a flow of fluid from a second entry to a second exit; wherein the second tubular element is in fluid communication with the first tubular element.

24. System according to claim 23, wherein the first tubular element and the second tubular element form a closed loop through which fluid can be circulated.

25. System according to claim 23 or 24, further comprising a second heat exchanger for extracting thermal energy from fluid at the second exit.

26. System according to claim 22, wherein the first tubular element further comprises an unexpanded tubular section positioned inside the expanded tubular section.

27. System according to claim 26, further comprising a seal sealing the unexpanded tubular section and one or more openings through the unexpanded tubular section positioned upstream of the seal.

28. Method according to any of the claims 1-21, wherein the expanded tubular section has been permanently expanded.

29. Method according to claim 3, wherein the unexpanded tubular section was previously connected to the expanded tubular section via a bending zone.

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