[0001] This application claims priority to our copending US Provisional patent application with the serial number 63/179088, which was filed April 23, 2021, and which is incorporated by reference herein.

Field of the Invention

[0002] The field of the invention is fluid conduits, particularly as it relates to nested conduits for transport of working fluids in geothermic power generation.

Background of the Invention

[0003] The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0004] All publications and patent applications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

[0005] Fixed spacer elements to maintain position and distance of an inner tube within an outer tube are well known, and exemplary fixed spacer elements are shown in US 4607665 and US 5803127. In further known devices, a drill collar is shown in US 3306378 where single spacer fins stabilize a drill string in operation. In still further known devices, multiple radially arranged spacers are used to allow for a sliding motion such as with a polymeric rod guide for a sucker rod as is described in US 9010418. Additional spacer devices for coaxially sheathed fuel pipes are disclosed in WO 2005/106306 and GB 722689, and minimal contact spacers as can be seen from JP 2016-138644.

[0006] US 5803127 discloses a pipe-in-pipe system in which a hazardous gas is transported in an inner conduit that is surrounded by an outer conduit in which a purge gas can be moved. The inner and outer conduits in such system are held apart at a fixed distance using symmetric spacer elements that advantageously permit bending of the coaxial pipes without crimping and that reduce stress fractures caused by vibrations. While such and other devices are desirable in selected use scenarios, currently known spacers are typically not suitable for relatively long nested conduits where the inner conduit must be advanced through an outer conduit for placement and operation. Moreover, and especially where such nested conduits have significant length ( e.g ., more than 1,000 meters), currently known spacers will present significant resistance to flow of a fluid in the annular space. Such resistance is particularly undesirable where the fluid is a working fluid for power generation as power generation efficiency will dramatically decrease with increased flow resistance of the working fluid.

[0007] Thus, even though various systems and methods of spacers for nested conduits are known in the art, all or almost all of them suffer from several drawbacks. Therefore, there remains a need for compositions and methods for improved spacers in nested conduits.

Summary of The Invention

[0008] The inventive subject matter is directed to various devices, systems, and methods of gliders in a pipe-in-pipe assembly for long range transport of a working fluid. Advantageously, contemplated gliders will not only facilitate advancement of an inner tubular conduit through an outer tubular casing, but also minimize inefficiencies and stabilize positioning of the tubular pipe within the tubular casing.

[0009] In one aspect of the inventive subject matter, the inventors contemplate a conduit that includes a tubular pipe having an inner surface and an outer surface, and a plurality of gliders coupled to the outer surface. Most typically, the at least a first and a second of the gliders have a longitudinal and a radial offset relative to each other with regard to a hypothetical central axis extending along a length of the tubular pipe, and each of the gliders comprise first and second materials, wherein the first material is coupled to the outer surface of the tubular pipe and wherein the second material forms an outer surface of the glider. In further preferred embodiments, the conduit will also include a third glider that has a longitudinal and a radial offset relative to the first and second gliders and relative to a hypothetical central axis extending along a length of the tubular pipe.

[0010] Additionally, it is contemplated that the tubular pipe may comprise an insulation material disposed between the inner and outer surfaces. Typically, but not necessarily, the gliders are welded to the outer surface of the tubular pipe. In some embodiments, the longitudinal offset between the first and second gliders is at least 30 inches, and/or the radial offset between the first and second gliders is at least 45 degrees. Among other suitable choices, the first material of the gliders may comprise steel, while the second material of the gliders may comprise an alloy having a hardness that is less than the hardness of the first material. Viewed form a different perspective, the second material of the gliders will typically have a lubricity that is greater than the lubricity of the first material. While not limiting the inventive subject matter, the first material of the gliders is preferably clad with the second material.

[0011] In further typical embodiments, the first and the second gliders may have an elongated shape extending along the hypothetical central axis and further have rounded terminal portions. Moreover, it is contemplated that the first and the second gliders may have a thickness that is sufficient to force the tubular pipe out of concentricity with respect to a hypothetical central axis of a tubular casing surrounding the tubular pipe. In still further contemplated embodiments, the tubular pipe has a strength sufficient to convey a fluid at a pressure of at least 2,000 psi and a temperature of at least 250 °F, and/or the tubular pipe has a length of at least 2,000 meters.

[0012] In another aspect of the inventive subject matter, the inventors contemplate a pipe assembly that includes the conduits presented herein, wherein a tubular casing surrounds the tubular pipe, and wherein the gliders maintain a distance between the outer surface of the tubular pipe and an inner surface of the tubular casing.

[0013] For example, the distance between the outer surface of the tubular pipe and the inner surface of the tubular casing may be between 0.25 inch and 1.50 inches or more. It is still further contemplated that the tubular casing and the tubular pipe are coupled to each other to form a closed circuit for circulation of a working fluid, and that the closed circuit may further comprise a heat exchanger and/or a power generator. Consequently, the inventors also contemplate a geo heat power and/or heat plant comprising the pipe assemblies presented herein.

[0014] In a still further aspect of the inventive subject matter, the inventors contemplate glider for a tube-in-tube pipe assembly that is constructed from a first material and a second material that are coupled to each other and configured such that, upon installation into a space between two tubes in the tube assembly, the first material contacts an outer surface of an inner pipe and the second material contacts an inner surface of an outer pipe. Most typically, the glider has an elongated shape with at least one rounded terminal portion, for example, having a length- to-width ratio of at least 5 : 1 and/or a width-to-height ratio of at least 1:1.

[0015] Preferably, but not necessarily, the first and second materials are coupled to each other by cladding. For example, the first material may comprise steel and the second material may comprise a copper and/or aluminum alloy. In further examples, it is contemplated that the elongated shape has a length of between 8 and 16 inches, a width of between 1 and 2 inches, and/or a thickness of between 0.5 and 1.0 inches. Where desired, the elongated shape may have side portions that are parallel to each other, and/or the rounded terminal portion may have a spherical or parabolic shape.

[0016] In yet another aspect of the inventive subject matter, the inventors contemplate a method of moving a tubular pipe within a tubular casing that includes a step of advancing the tubular pipe through the tubular casing while maintaining a distance between the tubular pipe and tubular casing. Most typically, the distance is maintained by a plurality of gliders, wherein the gliders have a longitudinal and a radial offset relative to each other with regard to a hypothetical central axis extending along a length of the tubular pipe, and at least 90% of total friction forces between the tubular pipe and the tubular casing during the step of advancing is borne by the plurality of gliders.

[0017] In further contemplated embodiments, at least some of the advancing is in a vertical direction, and/or the kinetic friction coefficient of the gliders with respect to the tubular casing is equal or less than 0.5. It is further contemplated that the gliders may have a thickness that is sufficient to force the tubular pipe out of concentricity with respect to a hypothetical central axis of the tubular casing surrounding the tubular pipe. Typically, the tubular pipe will comprise an insulation material disposed between an inner and an outer surface of the tubular pipe. With respect to suitable gliders, the same considerations as noted above apply.

[0018] Therefore, and viewed form a different perspective, the inventors also contemplate a method of reducing power loss in a geo heat plant that includes a step of moving a working fluid in an annular space formed by a tubular pipe disposed within a tubular casing, wherein the annular space is maintained by a plurality of gliders between the tubular pipe and tubular casing. Most typically, each of the plurality of gliders has an elongated shape with at least one rounded terminal portion, and at least a first and a second of the gliders have a longitudinal and a radial offset relative to each other with regard to a hypothetical central axis extending along a length of the tubular pipe.

[0019] While numerous working fluids are deemed suitable to be the heat carrying working fluid, it is preferred that the tubular casing and the tubular pipe are coupled to each other to form a closed circuit for circulation of the working fluid, and/or that the tubular pipe and tubular casing have a length of at least 2,000 meters.

[0020] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

Brief Description of The Drawing

[0021] FIG.l is an exemplary schematic longitudinal view along a central axis of a return pipe with gliders according to the inventive subject matter.

[0022] FIG.2 is an exemplary schematic cross-sectional view of the return pipe of FIG.l.

[0023] FIG.3 is an exemplary schematic side view of the return pipe of FIG.l.

[0024] FIG.4 depicts exemplary glider shapes according to the inventive subject matter.

[0025] FIG.5 is an exemplary perspective view of the return pipe of FIG.l.

[0026] FIG.6 is an exemplary schematic longitudinal view along a central axis of the return pipe of FIG.1 in a tubular casing.

[0027] FIG.7 is an exemplary schematic of multiple return tubes of FIG.6 deployed in a dry geo heat plant.

[0028] FIG.8 is a photograph showing an exemplary tubular casing enclosing a tubular pipe with insulation material between an inner and outer surface of the tubular pipe.

Detailed Description

[0029] The inventors have developed a glider that can advantageously be used to accommodate a sliding motion between a tubular pipe and a tubular casing, for example in a closed-loop geothermic application. Notably, the gliders presented herein will not only carry the weight of the tubular pipe, but also provide support to centralize the tubular pipe, and provide lubricity when the tube slides along the casing during installation and due to thermal axial length changes. Moreover, the gliders presented herein have a streamlined shape to so prevent or reduce impedance of flow of a working fluid in the annular gap between the tubular pipe and a casing surrounding the tubular pipe. In most typical uses, multiple gliders are mounted along the tube in offset orientations to allow the pipe to flex in a deviated well, and to adapt to any machining irregularities, such as casing ovality, encountered while the tube is sliding along the casing surface. In still further embodiments, at least some of the gliders will be somewhat oversized to so generate compression between the glider and the casing via mild deflection of the tubular pipe to prevent pipe motion while being subjected to forces from fluid flow.

[0030] In one exemplary configuration, as is shown in the axial view of FIG.l, a tubular pipe 100 has an inner wall 112 and an outer wall 114, which may or may not enclose an insulation material 116. Coupled to the outer wall 114 are three gliders 120A, 120B, and 120C with an equidistant radial and longitudinal offset. In the example of FIG.l, the radial offset is equidistant at an angle of 120 degrees. FIG.2 depicts a cross-sectional view at a location with a glider and with an outer tubular casing. Here, the tubular pipe having an inner wall 212, an outer wall 214, and an insulation material 216 therebetween is located within a tubular casing 230. A glider is welded via welds 226 to the outer surface 214 of the tubular pipe. It should be particularly appreciated that the glider in this example is constructed from two distinct materials, a first backer material 224 that is welded to the outer surface 214 of the tubular pipe and a second clad material 222 that contacts the inner surface tubular casing 230. It should be recognized that such choice of distinct materials is particularly beneficial from at least two perspectives: The first backer material can be selected to facilitate welding to the outer surface of the tubular pipe, while the second clad material can be selected to reduce friction (and to provide lubricity) between the glider outer surface and the inner surface of the tubular casing. Viewed from a different perspective, the first material is preferably similar to the material of the outer wall of the inner pipe to so allow direct welding of the first material to the outer wall of the inner pipe. On the other hand, the second material is preferably selected such as to obtain a low coefficient of friction between the second material and the inner wall of the tubular casing as is described in more detail below. FIG.3 depicts the tubular pipe of FIG.l in a side view for enhanced clarity with respect to the longitudinal and radial offset of the gliders. As can be seen in this example, each spacer has a radial and longitudinal offset such that at any given point along the longitudinal axis of the tubular pipe only a single glider is present.

[0031] With respect to the tubular pipe and the tubular casing it should be appreciated that the specific sizes and dimensions are not limiting to the inventive subject matter. Therefore, suitable tubular pipes may or may not have an insulation material and may have the same or different diameter throughout their lengths. Likewise, the specific inner and outer diameter may vary considerably. However, it is generally preferred that the inner diameter is at least 1.0 inch, or at least 1.5 inches, or at least 2.0 inches, or at least 2.5 inches, or at least 3.0 inches, or at least 3.5 inches, or at least 4.0 inches, or at least 4.5 inches, or at least 5.0 inches, or at least 6.0 inches, or at least 7.0 inches, or at least 8.0 inches, or at least 9.0 inches, or at least 10 inches, or even larger. Therefore, the outer diameter of the tubular pipe may have a diameter of at least 3.0 inches, or at least 3.5 inches, or at least 4.0 inches, or at least 4.5 inches, or at least 5.0 inches, or at least 5.5 inches, or at least 6.0 inches, or at least 7.0 inches, or at least 8.0 inches, or at least 10.0 inches, or at least 12.0 inches, or at least 15.0 inches, or at least 20.0 inches, or even larger.

[0032] Most typically, the material of the tubular pipe may vary considerably, and the appropriate choice of material will be readily apparent to the person of ordinary skill in the art in view of the intended purpose. Therefore, suitable materials include various metals and metal alloys, polymers, and all reasonable combinations thereof. However, and especially where the tubular pipe conveys a working fluid in liquid and/or vapor phase, it is preferred that the tubular pipe materials comprise iron, and especially a steel ( e.g ., mild carbon steel). Among other parameters, the material will be selected such that the working fluid in the tubular pipe may have a pressure of at least 500 psig, or at least 1,000 psig, or at least 1,500 psig, or at least 2,000 psig, or at least 2,500 psig, or at least 3,000 psig, or at least 4,000 psig, or at least 5,000 psig, and even higher. Similarly, the material will be selected such that the working fluid in the tubular pipe may have a temperature of at least 30 °C, or at least 50 °C, or at least 80 °C, or at least 100 °C, or at least 150 °C, or at least 200 °C, or at least 250 °C, or at least 300 °C, or at least 350 °C, or at least 400 °C, and even higher. Most typically, and particularly where the tubular pipe is used in geo heat applications, the length of the pipe is at least 500 meters, or at least 1,000 meters, or at least 2,000 meters, or at least 3,000 meters, or at least 4,000 meters, or at least 5,000 meters, or at least 6,000 meters, or even longer. [0033] Consequently, the tubular casing will have materials, sizes and dimensions that will match the parameters of the tubular pipe. Thus, and especially where the tubular casing conveys a working fluid in liquid and/or vapor phase, it is preferred that the tubular casing materials comprise iron, and especially a steel ( e.g ., mild carbon steel). Among other parameters, the material will be selected such that the working fluid in the tubular casing pipe may have a pressure of at least 500 psig, or at least 1,000 psig, or at least 1,500 psig, or at least 2,000 psig, or at least 2,500 psig, or at least 3,000 psig, or at least 4,000 psig, or at least 5,000 psig, and even higher. Similarly, the material will be selected such that the working fluid in the tubular casing may have a temperature of at least 30 °C, or at least 50 °C, or at least 80 °C, or at least 100 °C, or at least 150 °C, or at least 200 °C, or at least 250 °C, or at least 300 °C, or at least 350 °C, or at least 400 °C, and even higher. Most typically, and particularly where the tubular casing is used in geo heat applications, the length of the casing is at least 500 meters, or at least 1,000 meters, or at least 2,000 meters, or at least 3,000 meters, or at least 4,000 meters, or at least 5,000 meters, or at least 6,000 meters, or even longer.

[0034] With respect to contemplated glider shapes and arrangements of the gliders on the outer surface of the tubular pipe, it should be appreciated that numerous shapes and arrangements are deemed suitable so long as such arrangement provides for radial and longitudinal offset of at least two of the gliders. In at least some embodiments it is preferred that the glider is streamlined in shape to minimize the impedance of flow through the annular space. The streamlined shape also gives the glider sufficient contact area to bear the load of the insulated pipe. Moreover, it is generally preferred that the glider is contoured on the leading and trailing edge to accommodate smooth fluid flow past the surface. As will be appreciated, the wear surface of the glider must also be durable enough to withstand continuous wear during its design life. In further contemplated aspects, it should be noted that the thickness of the glider, along with the glider spacing, supports the insulated tubular pipe to prevent sag, which could create drag forces between the insulated tubular pipe and the casing and obstruct the nearly concentric installation of the return pipe within the casing.

[0035] Therefore, in at least some embodiments it is contemplated that the gliders are spaced apart in longitudinal direction (longitudinal offset), and most typically the longitudinal distance between at least two gliders will be space be at least twice, or at least three times the length of a glider, or even more. For example, where a glider has a length of between 10-15 inches, the distance between two (also typically radially offset) gliders will be at least 20 inches, or at least 30 inches, or at least 40 inches, or at least 50 inches, or even more. Thus, and especially where the gliders also have a radial offset, it should be appreciated that at any given location no more than two gliders, and most typically only one glider will be present as is exemplarily shown in FIG.3. Where two gliders are present at the same location, the gliders will typically not be on opposite sides of the insulated pipe to avoid compression where the casing is not perfectly circular.

[0036] One particularly preferred mounting method of the gliders to the outer wall of the tubular pipe is welding. In this context it should be noted that instead of welding dissimilar metals directly to the pipe, the glider may be composed of two materials: a base plate of a steel material closely matching the steel material of the external pipe surface, and a softer plate material serving as a gliding surface, affixed to the glider steel plate by variety of techniques such as by cladding. The gliding surface reduces the static and kinematic friction which increases axial stress on the return pipe when sliding.

[0037] For example, and with respect to contemplated shapes, it should be appreciated that preferred shapes of the gliders will be elongated and include at least one rounded terminal portion to so reduce drag forces and/or turbulence of a fluid passing through the annular space. Therefore, contemplated glider shapes may have a rounded ( e.g ., spherical) or pointed (e.g. , parabolical) tip as is exemplarily shown in the three glider examples in FIG.4. Here, it should be noted that the particular dimensions provided are merely exemplary and should not be construed as limiting the inventive subject matter. Indeed, it should be noted that the size of the gliders will at least in part depend on the particular dimensions of the pipe and casing, but it is generally contemplated that the width of the glider will not exceed 20%, or 18%, or 16%, or 14%, or 12%, or 10%, or 8%, or 6%, or 4% of the circumference of the outer surface of the tubular pipe. With respect to the length of the glider, it is generally contemplated that the length will be at least 4 times, or at least 6 times, or at least 8 times, or at least 10 times, or at least 12 times the width of the glider. Regarding the thickness of the glider, it should be appreciated that the thickness will be such that the glider occupies at least 80%, or at least 85%, or at least 90% or at least 95%, or at least 100%, or at least 105%, or at least 110%, or at least 115%, or at least 120%, or at least 125%, or at least 130% of the distance between the outer surface of the tubular pipe and the inner surface of the tubular casing as measured when the pipe and casing are in concentric position relative to each other. Especially where the glider thickness exceeds 100%, it should be appreciated that such thickness will help to elastically deflect the inner pipe and so pre-tension the inner pipe, which advantageously reduces motion (and possibly also vibration) of the inner pipe while the inner pipe is subjected to fluid flow forces in an annular space. Therefore, and viewed form a different perspective, the glider may have an elongated shape with a length-to- width ratio of at least 5:1 and/or a width-to-height ratio of at least 1:1. Moreover, the gliders may have parallel side portions or curved side portions as can be taken from FIG.4.

[0038] For example, suitable glider dimensions for geo heat applications will include those where the glider has a length of at least 4 inches, or at least 6 inches, or at least 8 inches, or at least 10 inches, or at least 12 inches, or at least 14 inches, or at least 16 inches or at least 18 inches, or even more, and a width of at least 0.5 inches, or at least 1.0 inches, or at least 1.5 inches, or at least 2.0 inches, or at least 2.5 inches, or at least 3.0 inches, or even more. Likewise, suitable thicknesses include those of at least 0.2 inches, at least 0.4 inches, at least 0.6 inches, at least 0.8 inches, at least 1.0 inches, at least 1.2 inches, at least 1.4 inches, at least 1.6 inches, at least 1.8 inches, and even thicker.

[0039] Regardless of the particular size and geometry, and as already noted above, it should be appreciated that the glider may be composed of at least two different materials to accommodate various requirements. For example, it is contemplated that the first material is suitable for facile coupling of the glider to the outer surface of the tubular pipe. Among other suitable modes of coupling, welding is a particularly preferred manner and the choice of first material will therefore at least in part be determined by the similarity of the materials (e.g. , first material and outer surface are both mild carbon steel). On the other hand, the second material will be chosen such as to reduce friction of the second material with respect to the inner surface of the tubular casing (e.g, such as to achieve a kinetic friction coefficient of equal or less than 0.60, or equal or less than 0.55, or equal or less than 0.50, or equal or less than 0.45, or equal or less than 0.4). For example, suitable second materials include lubricious metal and non- metal containing materials such as aluminum and copper-based alloys, nickel coatings, nickel boron nitride coatings, fluoropolymeric coatings, etc. As will be readily appreciated, the two materials can be joined in a variety of manners, and the particular choice will depend on the specific materials chosen. For example, suitable manners of coupling include cladding, gluing, explosion welding, friction stir welding, etc. In less preferred aspects, it should be appreciated that alternate manners of coupling such as screwing, bolting, etc. are also deemed appropriate. [0040] Therefore, the inventors also contemplate a method of moving a tubular pipe within a tubular casing in which the tubular pipe is advanced through the tubular casing while maintaining a distance between the tubular pipe and tubular casing. As discussed above, the distance is maintained by a plurality of gliders, wherein the gliders have a longitudinal and a radial offset relative to each other with regard to a hypothetical central axis extending along a length of the tubular pipe, and at least 80%, or at least 85%, or at least 90%, or at least 95%of total friction forces between the tubular pipe and the tubular casing during the step of advancing are borne by the plurality of gliders. As will be readily appreciated position of the tubular pipe and casing may be strictly in a vertical orientation, or at an angled or curved orientation, or in a horizontal orientation relative to normal. Moreover, it is preferably preferred that the kinetic friction coefficient of the gliders with respect to the tubular casing is equal or less than 0.6, equal or less than 0.5, equal or less than 0.4, equal or less than 0.3, or even lower. Such low friction is particular advantageous where the gliders have a thickness that is sufficient to force the tubular pipe out of concentricity with respect to a hypothetical central axis of the tubular casing surrounding the tubular pipe.

[0041] With respect to the placement of the gliders it is generally preferred that the gliders are coupled to the tubular pipe such that at any given cross section of the tubular pipe no more than two, and more typically no more than one glider is present. Viewed from a different perspective, it is contemplated that at least two (and more typically most or all) of the gliders have a longitudinal offset of at least 1 inch, or at least 5 inches, or at least 10 inches, or at least 20 inches, or at least 30 inches, or at least 40 inches, or at least 50 inches, or at least 60 inches, or more. Similarly, with respect to radial offset it is contemplated that the radial offset between at least two (and more typically most or all) the gliders is at least 15 degrees, or at least 30 degrees, or at least 45 degrees, or at least 60 degrees, or at least 90 degrees, or at least 120 degrees, or at least 180 degrees. One exemplary configuration of radial and longitudinal offset is shown in FIG.5. and an end view of the tubular pipe of FIG.5 in a tubular casing is depicted in FIG.6

[0042] Since the glider provides a narrow point of contact between the insulated return pipe and the casing, the glider can also be contoured with a radius on the leading and/or trailing edge to slide over smaller surface defects it encounters (i.e., the thickness at a terminal portion of the glider is less than at a central portion of the glider). Such contouring can advantageously serve to protect the insulated return pipe from damage through rapid stress increase from forces transferred from/to the glider.

[0043] As will be readily appreciated, where such arrangement is used in a geo heat plant, the tubular casing will be subject to heat transfer from the geological formation to the working fluid. In this context, it is noted that the term “geo heat” as used herein refers to a heat resource found in high temperature rock, often at great depths, which can be extracted for industrial power and heat production. Most typically, that heat resource is a ‘dry’ resource where heat can be extracted without concomitant extraction of a fluid (such as brine from a formation or processed injected water) from the geological formation. For example, the tubular pipe and casing may be part of a closed-loop system in which a working fluid circulates. Most typically, such closed loop system will further comprise a heat exchanger and a turbine and generator to so generate electrical energy as is schematically depicted in FIG.7 and described in US 8020382, incorporated by refence herein in its entirety.

[0044] In this context, it should be appreciated that closed-loop geothermic technologies aim at collecting (harvesting) heat from hot rock into a working fluid, which circulates within a fully contained environment. Most typically, a closed-loop well comprises a larger casing pipe that is thermally connected to the rock by a thermally conductive grout, and an inner insulated tube to return the heated fluid to the surface. The working fluid flows down through the annular space between the casing and the insulated return tube, gaining heat drawn from the rock through the casing wall, and then flows up the insulated return pipe to supply energy to a multitude of purposes including power generation. Most preferably, the geological formation has a temperature sufficient to convert the liquid working fluid ( e.g ., water) into a gaseous fluid ( e.g ., steam) that is transported topside and expanded and cooled in an expansion turbine or fed into a heat exchanger that heats a secondary working fluid of a power generator. Examples of closed-loop geothermic systems are described in US 8201409 and US 2018/0274524, incorporated by refence herein in their entirety.

[0045] It should also be noted that for the geo heat harvesting methods contemplated herein the clearances between the casing wall and the insulated return pipe are relatively small (e.g., between 0.2 and 0.4 inches, or between 0.4 and 0.6 inches, or between 0.6 and 0.8 inches, or between 0.8 and 1.0 inches, or between 1.0 and 2.0 inches). Consequently, contact between the two components during the installation of the return pipe would be inevitable without the use of a glider. FIG.8 is a photograph showing an exemplary tubular casing enclosing a tubular pipe with partially exposed insulation material between an inner and outer surface of the tubular pipe. The gliders (not shown in FIG.8) as presented herein provide a lubricating surface to reduce the possibility of galling between the components. Additionally, the gliders will minimize damage to the casing surface finish, which is preferably smooth after installation to minimize disruption to fluid flow during the many years of operation of the well.

[0046] It should further be recognized that contemplated gliders also accommodate a sliding motion due to thermal expansion and contraction during well operation. A closed-loop geo heat well is often subject to large swings in temperature, and contemplated gliders will allow for differential movement between the casing and the return tube caused by temperature changes over at least some of the life of the system. In addition, for reasons of operational optimization or maintenance, the flow in the closed loop system may be temporarily stopped, thus resulting in a temperature transient leading to differential movement between the external casing and the return pipe. The gliders will be instrumental in preventing excessive axial stress build-up in the return pipe under these circumstances.

[0047] Finally, it is noted that unlike prior configurations, multiple gliders are not mounted in radial symmetry around the pipe at a given location. Rather, the gliders are mounted with an offset along the length of the pipe. Because the glider will only have a single point of contact along a local length of pipe, the pipe can flex away from any irregularities encountered on the surface of the casing. This allows the glider to accommodate bends, machining tolerance irregularities and defects on the casing surface.

[0048] It should further be appreciated that while the accommodating installation and periodic sliding motion in a closed-loop geothermic well is somewhat analogous to the role of a centralizer used in rotary drilling, numerous unique distinctions exist.

[0049] First, the loads borne by the gliders presented herein are expected to be modest compared to those observed in rotary drilling. Indeed, both the return pipe installation and the periodic thermal sliding will occur at low speeds, with primarily axial (forward and backward) rather than rotational motion. As such, multiple gliders mounted in radial symmetry at multiple points around the insulated tubing would not only be excessively redundant but would also create potential for high stress build up with an ovalized or otherwise deformed cross section of the casing. Moreover, fewer components will advantageously reduce cost and string weight. [0050] Second, unlike conventional rotary drilling equipment, the insulated return pipe will remain in place for extended periods of time. The insulated return pipe, and its supporting components such as the gliders, are not expected to be withdrawn for maintenance or replacement. As such, minimization of tubing and casing damage during the tube installation and operation is necessary to ensure the longevity of the component. The current systems and methods provide a small additional cost to create a designed, tailored, or fit-for-purpose contact point to improve the expected life time of the insulated return pipe as compared to typical industry -used centralizer system allowing the return pipe to slide against the casing.

[0051] Third, minimization of flow impedance within the annular gap is an important design goal due to the need to maximize withdrawn power. Unlike conventional drilling operations where the use of large amounts of power can be justified in pursuing high density hydrocarbons, energy losses in power generation should be reduced wherever possible. As such, a glider optimized to minimize flow impedance is a significant feature of energy efficiency.

[0052] Finally, similar to the function of a traditional centralizer, the glider allows the insulated return pipe to be nearly concentric with the casing. While perfect concentricity is not a requirement for the insulated return pipe to function properly, using the glider to create standoff distance between the insulated return pipe and the casing allows flow around the full circumference of the casing, and so allows radial heat withdrawal from the rock from all directions. Moreover, the concentricity of the tube, and the relatively small flow disturbance caused by the gliders help to ensure smooth flow of the heat carrying liquid, thus preventing cavitation, whirl, and/or wake erosion of the tubing.

[0053] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. [0054] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[0055] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. As also used herein, and unless the context dictates otherwise, the term "coupled to" is intended to include both direct coupling (in which two elements that are coupled to each other contact each other), and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms "coupled to" and "coupled with" are used synonymously.

[0056] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the scope of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification or claims refer to at least one of something selected from the group consisting of A, B, C .... and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.