Adiabatic Welded Joints for Pipe-in-Pipe Systems.

Abstract

An improved insulated pipe-in-pipe system and method is provided, particularly one that is capable of withstanding significant bending and straightening forces, minimizing heat loss across joints between pipe-in-pipe segments, and allowing for simplified assembly. [Solution] An insulated joint pipe-in-pipe system including a weld connecting two inner pipes, with each outer pipe surrounding the inner pipe and terminating at a location distal to the weld. Each ring is coupled to the inner pipe at a distal location and the outer pipe is welded to the ring. Joint insulation covers the welds and a sleeve segment covers the welds and joint insulation. Preferably, the sleeve segment is formed from two half-pipe sections and welded to the ring to secure the sleeve segment to the connected pipe-in-pipe segments. Contemplated pipe-in-pipe systems exhibit significantly reduced heat loss and provide sufficient strength for pipe-laying processes including pipe bending and pipe straightening.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This invention claims priority to our co-pending U.S. Provisional Application No. 63 / 228,301, filed 8 / 2 / 2021, which is incorporated herein by reference. [Technical field]

[0002] The field of the invention is devices and methods for connecting insulated pipe-in-pipe systems. [Background technology]

[0003] The background description includes information that may be useful in understanding the present invention. No admission is made 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 in this specification are incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. In the event that a definition or usage of a term in an incorporated reference is inconsistent or contradictory with a definition of the term provided herein, the definition of the term provided herein applies and the definition of the term in the reference does not apply.

[0005] There are many methods of connecting pipes known in the art, such as, for example, threads, flanges or welding. In many cases, however, conventional pipe connections are not suitable in the case of insulated pipe-in-pipe systems, where an inner pipe is placed inside an outer pipe, and the space between the pipes must be insulated to avoid heat or cooling losses. To be able to connect such pipe-in-pipe systems, the ends of the insulating space of each insulated pipe-in-pipe segment can be capped to enclose an annular insulating space, and each capped end can be connected by welding or sleeves. Although such connections are relatively easy to perform on site, many drawbacks remain. Most notably, the end caps of the annular insulating space form a thermal conduction path, which leads to significant heat or cooling losses. Such losses are particularly undesirable when the pipe-in-pipe system has a significant length and requires a relatively large number of joints.

[0006] To reduce heat loss and thermal stress, a partition can be employed between two pipe-in-pipe segments, as described in US Patent US8,998,267. Here, the partition in the cryogenic pipe-in-pipe system includes an inner transition element, and separate first and second outer transition elements that are coupled to the inner transition element and at least partially surround the inner transition element. The partition can then be welded to each end of the inner and outer transition pipes of the adjacent pipe-in-pipe segments. Such a system advantageously reduces the heat transfer path, thereby reducing heat or cooling loss. Furthermore, thermal stress (e.g., due to contraction upon receiving cryogenic liquid) can be transferred from the inner to the outer pipe. However, due to the relatively complicated configuration, a relatively large number of welds and welding procedures are required, thus requiring a lot of assembly time and cost.

[0007] Additionally, pipe-in-pipe systems with capped insulated annular spaces or bulkheads are prone to mechanical failure due to exposure to forces that would be encountered if the pipe-in-pipe system were subjected to pipe installations requiring significant mechanical forces and pipe bending and pipe straightening steps. Summary of the Invention [Problem to be solved by the invention]

[0008] Thus, while various systems and methods for insulating pipe-in-pipe systems are known, all or nearly all suffer from certain drawbacks. Thus, there is a need for an improved insulating pipe-in-pipe system, and in particular a configuration and method that can withstand significant bending and straightening forces, minimize heat loss across joints between pipe-in-pipe segments, and allow for easy assembly. [Means for solving the problem]

[0009] Summary of the Invention The subject matter of the invention is directed to pipe-in-pipe systems and methods in which the inner and outer pipes of various pipe-in-pipe systems are bonded and insulated to one another via a ring bonded to the surface of the inner pipe. Most typically, the outer pipe is placed inside the inner pipe and terminates in a ring, and once the ends of the inner pipes of the two pipe-in-pipe segments are welded together, a sleeve segment is formed and joint insulation is bonded to the weld joint and then to the ring, thereby increasing the mechanical strength of the joint while minimizing thermal conductivity.

[0010] In one aspect of the inventive subject matter, the inventors contemplate an insulated joint in a pipe-in-pipe system including a first pipe-in-pipe segment and a second pipe-in-pipe segment, each of the pipe-in-pipe segments having an outer pipe surrounding an inner pipe, and each of the pipe-in-pipe segments having insulation in the annular space between the outer pipe and the inner pipe. Further, each of the pipe-in-pipe segments has a ring between the outer and inner pipes where the outer pipe terminates and to which the outer pipe is joined and to which the inner pipe is joined and beyond which the inner pipe extends. A weld joint connects each end of the inner pipe of the first and second pipe-in-pipe segments, and first and second half-pipe sleeves are connected via longitudinal welds to form a sleeve segment. The sleeve segments are disposed in the rings of the first and second pipe-in-pipe segments, (a) welds at the rings connect the outer pipes through the sleeves of the first and second pipe-in-pipe segments, and (b) welds at the rings connect the outer pipes of the first and second pipe-in-pipe segments to the inner pipes of the first and second pipe-in-pipe segments. Finally, joint insulation is disposed between the rings of the first and second pipe-in-pipe segments and the sleeve weld joints.

[0011] In some embodiments, each of the pipe-in-pipe segments has a length of about 10-20 m, the inner pipe of the first and second pipe-in-pipe segments has a diameter of about 10-20 cm, the outer pipe of the first and second pipe-in-pipe segments has a diameter of about 15-25 cm, and / or the sleeve segment has a length of about 20-50 cm.

[0012] With respect to the ring, it is contemplated that the ring has a radial width of about 3-10 cm and a thickness of about 2-5 cm. It is therefore contemplated that the distance between the inner pipe and the outer pipe is equal to the radial width of the ring. Most typically, the ring is welded to the inner pipe of each of the first and second pipe-in-pipe segments.

[0013] In a further embodiment, the first and / or second half-pipe sleeve includes a support bar (on the inside of the half-pipe) along the longitudinal weld. It is further contemplated that the sleeve segment and the outer pipe of the first and second pipe-in-pipe segments have the same outer diameter. Preferably, joint insulation is wrapped around the weld joint, and it is especially preferred that the welds, rings, and sleeve segments of the connected pipe-in-pipe segments have sufficient strength for the pipe-laying process, including pipe bending and straightening.

[0014] The present invention then contemplates a method of connecting a first pipe-in-pipe segment to a second pipe-in-pipe segment, where each of the pipe-in-pipe segments has an outer pipe surrounding an inner pipe that extends beyond the outer pipe, and each of the pipe-in-pipe segments has insulation in the annular space between the outer pipe and the inner pipe. The method typically includes forming a weld joint between each end of the inner pipe of the first and second pipe-in-pipe segments, and further covering the weld joint with joint insulation. Yet another step is to weld the first and second half-pipe sleeves together via a longitudinal weld, form a sleeve segment above the weld joint, and then weld the sleeve segment onto each ring on the first and second pipe-in-pipe segments such that (a) the welds of the rings connect the outer pipes of the first and second pipe-in-pipe segments via the sleeve, and (b) the welds of the rings connect the outer pipes to the respective inner pipes via the rings of the outer pipes of the first and second pipe-in-pipe segments.

[0015] Preferably, but not necessarily, the weld joint is covered by wrapping the joint insulation material around the weld joint. Furthermore, it is typically preferred that the first and second half-pipe sleeves include support bars along the longitudinal welds and / or that each ring on the first and second pipe-in-pipe segments is welded to the inner pipe of the first and second pipe-in-pipe segments. Additionally, it is preferred that the sleeve segment and the outer pipe of the first and second pipe-in-pipe segments have the same outer diameter.

[0016] In some examples, at least 20 pipe-in-pipe segments are connected in series, each of the pipe-in-pipe segments having a length of about 10-20 m and the sleeve segment having a length of about 20-50 cm. In further examples, the inner pipe of the first and second pipe-in-pipe segments has a diameter of about 10-20 cm and the outer pipe of the first and second pipe-in-pipe segments has a diameter of about 15-25 cm. Most preferably, the welds, rings, and sleeve segment of the connected pipe-in-pipe segments have sufficient strength for the pipelaying process, including bending and straightening the pipe.

[0017] Thus, in one example of the use of the contemplated method, the inventors contemplate a method of installing an insulated return pipe in a geothermal heat recovery plant, the method including the steps of providing a plurality of pipe-in-pipe segments, each having an outer pipe surrounding an inner pipe, and each of the pipe-in-pipe segments having insulating material in the annular space between the outer pipe and the inner pipe. In another step, the pipe-in-pipe segments are horizontally welded together such that (1) the ends of the inner pipes are welded together; (2) the ends of the outer pipes are welded to respective rings on the inner pipes of the pipe segments; and (3) sleeve segments are placed between the rings of the pipe segments, welded to the rings, and further welded to the ends of the outer pipes, thereby forming an outer pipe that is continuous and surrounds the welds connecting the inner pipes. In yet another step, the connected pipe-in-pipe segments are advanced from horizontal to vertical using bending and straightening devices into a wellbore into the formation.

[0018] In such methods, each of the pipe-in-pipe segments has a length of about 10-20 m, the inner pipe of the first and second pipe-in-pipe segments has a diameter of about 10-20 cm, the outer pipe of the first and second pipe-in-pipe segments has a diameter of about 15-25 cm, and / or the sleeve segment has a length of about 20-50 cm. Most typically, the ring has a radial width of about 3-10 cm and a thickness of about 2-5 cm. In some embodiments, the connected pipe-in-pipe segments are advanced into a casing in the earth formation and / or the earth formation is at a depth of at least 500 m.

[0019] Most preferably, bending forces during bending and straightening are transferred from the outer pipe to the inner pipe through the rings. It is further contemplated that the rings are spaced apart a distance that prevents compression of the insulation within the annular space due to reduction in the annular space. Additionally, the inner pipe within each pipe-in-pipe segment has sufficient strength to carry fluids at a pressure of at least 2,000 psi and a temperature of at least 200° C.

[0020] Accordingly, the inventors also contemplate a geothermal heat recovery plant that includes a casing within the formation that surrounds a pipe-in-pipe system having a plurality of serially connected pipe-in-pipe segments, each having an outer pipe surrounding an inner pipe, and each of the pipe-in-pipe segments having insulation in the annular space between the outer and inner pipes. Most preferably, the pipe-in-pipe segments are coupled together such that (1) the ends of the inner pipes are welded together; (2) the ends of the outer pipes are welded to respective rings on the inner pipes of the pipe segments; and (3) sleeve segments are placed between the rings of the pipe segments, welded to the rings, and further welded to the ends of the outer pipes, thereby forming an outer pipe that is continuous and surrounds the welds connecting the inner pipes. Most typically, the casing, the pipe-in-pipe system, and the heat exchanger are fluidly coupled to form a closed loop working fluid circuit for heat recovery and power generation.

[0021] Other suitable options are that the formation may be at a depth of at least 500 m and that the formation may have a temperature of at least 200° C. In some embodiments, the series connected pipe-in-pipe segments have a length of at least 1,000 m. Preferably, the closed loop working fluid circuit is thermally coupled to an electric generator. Effect of the Invention

[0022] Various objects, features, aspects and advantages of the present subject matter will become more apparent from the following detailed description of preferred embodiments. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic diagram illustrating an example longitudinal cross-section of a pipe-in-pipe segment in accordance with the present inventive subject matter.

[0024] [Diagram 2]FIG. 2 is a schematic diagram showing an example of a longitudinal cross-section of a first pipe-in-pipe segment in accordance with the present subject matter, welded with an inner pipe to a second pipe-in-pipe segment (ring and outer pipe not shown for the second segment).

[0025] [Diagram 3] FIG. 3 is a schematic diagram showing an example of a longitudinal cross section of the joined segments of FIG. 2 with joint insulation.

[0026] [Figure 4] FIG. 4 is a schematic diagram illustrating an example of a longitudinal cross section of two joined pipe-in-pipe segments having joint insulation and a sleeve welded to a ring in accordance with the inventive subject matter.

[0027] [Diagram 5] FIG. 5 is a schematic diagram illustrating an example of a longitudinal cross section of a sleeve segment and two joined pipe-in-pipe segments welded to a ring (joint insulation not shown) in accordance with the inventive subject matter.

[0028] [Figure 6] FIG. 6 is an example of a cross-sectional schematic of two half-pipe sleeves, one of which has a support bar.

[0029] [Figure 7] FIG. 7 is an example of a schematic longitudinal cross-sectional view of two joined pipe-in-pipe segments with a sleeve segment in accordance with the inventive subject matter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Detailed Description The inventors have discovered various pipe-in-pipe systems and methods for joining multiple pipe-in-pipe segments such that the resulting pipe-in-pipe system has reduced heat loss between the joints joining the pipe-in-pipe segments, and the pipe-in-pipe system has sufficient mechanical strength / resistance to bending and straightening operations to facilitate substantially horizontal creation in-situ and substantially vertical installation in a geothermal well.

[0031] In one example, a pipe-in-pipe system is constructed from multiple pipe-in-pipe segments, each segment having an outer pipe surrounding an inner pipe, and each segment including insulation in the annular space between the outer pipe and the inner pipe. A ring is placed between the inner and outer pipes, typically by welding the ring to the outer surface of the inner pipe. Preferably, but not necessarily, the ring has a width that allows the outer pipe to be welded to one part of it, and another part of the ring to be used to weld a sleeve to the ring and / or the outer pipe. During construction, which is usually done on-site, generally in a horizontal orientation (i.e., near a vertical well through which the generated pipe-in-pipe system will be advanced), the inner pipe of one pipe-in-pipe segment is welded to the inner pipe of the other pipe-in-pipe segment. Once the weld joints are completed at each end of the inner pipes of the first and second pipe-in-pipe segments, joint insulation material is applied (e.g., as a wrap from sheet stock) between the rings of the first and second pipe-in-pipe segments to cover the weld joints, and preferably to cover most or all of the space between the rings of the first and second pipe-in-pipe segments. In such an embodiment, the gap between the recessed outer pipes terminating in each ring is then covered with a sleeve, preferably formed from two half-pipe sleeves. As will be readily understood, the two half-pipe sleeves are welded together and to the rings to complete the insulating joint of the pipe-in-pipe system.

[0032] FIG. 1 illustrates a longitudinal cross-section of an end portion of a pipe-in-pipe segment 100 having an inner pipe 110 and an outer pipe 120. A ring 130 is welded to the outer surface of the inner pipe 110, and the outer pipe 120 rests on a certain position of the ring. If desired, the end portion of the outer pipe 120 can be welded to the ring. The annular space 115 between the outer and inner pipes contains an insulating material (not shown). During assembly of the pipe-in-pipe system, the ends of the two inner pipes of each of the pipe-in-pipe segments are placed adjacent to each other and welded together at a weld joint 112 (the outer pipe and the ring of the second pipe-in-pipe segment are not shown) as shown in FIG. 2. As shown in FIG. 3, a joint insulating material 140 is then applied in the space between the rings of the weld, and the weld joint and the joint insulating material are covered with a sleeve 150 formed from two half-pipe sleeves. In the example of FIG. 4, each end of the sleeve is welded to each ring. Here, welds 152 connect the sleeve to the ring and also connect the ends of the sleeve to each end of the outer pipe of the pipe-in-pipe segment. Welds 154 connect the two half-pipe sleeves. Such a connection is particularly advantageous because loads are transferred between the outer and inner pipes through the ring, and between the outer pipe through the ring and sleeve.

[0033] FIG. 5 is a diagram of another example of an insulating joint for a pipe-in-pipe system. As can be seen, the joint weld 112 connects the inner pipe, while the outer pipe 120 terminates in a welded ring 130 with a ring weld 132 welded to the outer surface of the inner pipe. The ring weld 132 also connects the end of the sleeve 150 to the outer pipe. The insulating material in the annular space and the joint insulating material covering the joint weld are not shown. FIG. 6 illustrates first and second half-pipe sleeves, which may further have a support bar 156. Once the half-pipe sleeves are placed around the weld joint, they may be welded together longitudinally along the support bar 156 (see weld 154 in FIG. 4) to form a sleeve (see weld 152 in FIG. 4). Note that in this way, the outer surface of the sleeve and the outer pipe are at the same level and continuous, thereby making it very easy to run the pipe-in-pipe system through a tensioning, bending and straightening device.

[0034] However, in another embodiment shown in FIG. 7, one or more sleeves can also be configured as sleeves 750, which are placed over and around the weld joint 712 connecting the inner pipe 710, the joint insulation material (not shown), and the ring 730 such that the inner surface of the sleeve is adjacent to the outer surface of the outer pipe 720. In such a case, the ring is only joined (typically welded) to the inner and outer pipes, but is not welded to the sleeve. As can be easily seen, such a sleeve can be made from a half pipe as described above, which may be a closed pipe segment that slidingly engages with the outer pipe. The use of such an "outer" sleeve advantageously simplifies and speeds up the assembly. Moreover, such an assembly allows for telescoping / articulation, which enhances the flexibility required for bending and straightening operations. If desired, the sleeve can be welded to the outer pipe, or joined to the outer pipe by friction, friction material, or friction structure between the sleeve and the outer pipe.

[0035] It should be appreciated that the systems and methods presented herein provide various benefits and advantages. In particular, it should be appreciated that the ring supports significant tensile and compressive loads, and particularly as loads are generated during installation and bending of the insulated pipe-in-pipe system, which allows the ring and sleeve to share the loads between the inner and outer pipes. In that regard, it should be noted that bending and straightening forces (leading to plastic deformation) are primarily applied to the outer pipe, which is then transferred to the inner pipe via the support ring. Such improved stability / toughness allows for thinner walls of the inner and outer pipes than conventional designs, which advantageously reduces overall weight. Such reduced weight is particularly preferred when the pipe-in-pipe system has a significant length. Additionally, the systems and methods presented herein significantly reduce, or more typically eliminate, buckling of the outer pipe, which leads to loss of stability and structural integrity and compression of the insulating material in the annular space and / or in the space above the weld joint.

[0036] With respect to the pipe-in-pipe segments presented herein, it is contemplated that the particular configuration and dimensions of the pipe-in-pipe segments can vary considerably, and that the particular configuration and dimensions are dictated by the particular application and environmental parameters. However, particularly preferred pipe-in-pipe segments include those used as return pipes in geothermal recovery / harvesting operations where multiple pipe-in-pipe segments are connected (welded) together at locations into a wellbore. Thus, contemplated pipe-in-pipe segments are typically between 5-20 m, or between 20-40 m, and even longer, such as between 7-15 m, or between 10-20 m, or between 20-30 m, or between 30-40 m, and even longer.

[0037] With regard to the outer diameter of the inner and outer pipes, it is contemplated that the inner pipe has a smaller outer diameter than the outer pipe since the inner pipe is housed within the outer pipe. Furthermore, since the pipe-in-pipe assembly also includes an insulating material, the difference in diameter must take into account the presence of the insulating material in the annular space. For example, suitable outer diameters of the inner pipe include at least 7 cm, or at least 9 cm, or at least 11 cm, or at least 13 cm, or at least 15 cm, or at least 20 cm, and even more, while suitable outer diameters of the outer pipe include at least 10 cm, or at least 12 cm, or at least 14 cm, or at least 16 cm, or at least 18 cm, or at least 20 cm, or even at least 25 cm, or even more. Thus, the distance between the walls of the inner and outer pipes in the annular space may be, for example, between 1.0-2.0 cm, or 2.0-3.0 cm, or between 3.0-4.0 cm, or even between 4.0-5.0 cm, or even more.

[0038] Most typically, the wall thickness of the inner and outer pipes is constant. For example, the wall thickness of the inner pipe may be between 0.2-2.0 cm, and more typically between about 0.2-0.5 cm, or between 0.5-0.75 cm, between 0.75-1.0 cm, and even more typically between 1.0-1.5 cm, or between 1.5-2.0 cm, or even thicker. Since the outer pipe is less exposed to the pressure of the heated working fluid, the wall thickness is generally thinner than the inner pipe. Thus, a typical wall thickness of the outer pipe may be between about 0.1-1.5 cm, and more typically between about 0.1-0.25 cm, or between 0.25-0.40 cm, or between 0.40-0.65 cm, and even more typically between 0.5-0.8 cm, or between 0.65-1.0 cm, or even thicker.

[0039] As will be readily apparent, the materials of the inner and outer pipes are preferably selected to withstand the significant temperatures and pressures encountered in geothermal harvesting. The materials of the inner and outer pipes may be very different, and the appropriate selection of materials will be obvious to one skilled in the art in view of the intended purpose. For example, suitable materials include various metals and alloys, polymers, and all reasonable combinations thereof. However, and especially when the inner pipe carries a liquid and / or gaseous phase working fluid at elevated pressure temperatures, it is preferred that the material of the inner and outer pipes is iron, and in particular steel (e.g., soft carbon steel or its alloys). Among other parameters, the material may be such that the pressure of the working fluid in the inner and outer pipes is 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 may be such that the working fluid in the tubular pipe has 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, or even higher.

[0040] In this regard, and particularly when pipe-in-pipe systems are used in geothermal applications, the finished and deployed pipe-in-pipe system may be 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. Steel pipes are therefore particularly preferred, and especially higher grade steels having relatively high tensile strength and. For example, suitable steels include P110 grade steel and those having similar physical properties. As will be readily apparent, the welding follows well-known protocols for the materials used.

[0041] With respect to the rings used in the systems and methods presented herein, it should be understood that the rings perform several important functions. Among other things, it should be understood that the rings significantly reduce heat conduction (and the associated heat loss) between the inner and outer pipes and provide a mechanism for transmitting substantial bending forces therealong. To that end, it is contemplated that the material of the rings is preferably a medium carbon low alloy steel that has significant strength, toughness, while having excellent weldability and corrosion resistance. For example, suitable ring materials are 4130 and 4140 steels.

[0042] In a further embodiment, it is contemplated that the rings, once welded to the inner and outer pipes, act as the main support for the connecting sleeve, and allow the transmission of bending forces, once welded to the inner and outer pipes and sleeves. The rings must therefore have a minimum size to accommodate these functions. However, due to their connection to the inner pipe, the rings also provide a limited thermal conduction, with heat passing through the ring from the inner to the outer pipe. Thus, a given thickness of the ring contributes to the overall thermal conduction, since there is a direct thermal conduction path from the hot inner fluid to the cold outer fluid, and it is generally preferred to minimize the contact surface to the inner flow passage while maintaining its mechanical function. Thus, depending on the size of the inner and outer pipes, the size of the rings may vary, at least to a certain extent.

[0043] For example, suitable rings may have a thickness between 1.0-1.5 cm, or between 1.5-2.0 cm, or between 2.5-3.0 cm, or between 3.0-3.5 cm, or between 3.5-4.0, or between 4.0-4.5 cm, or between 4.5-5.0 cm, and thicker. Similarly, and depending on the size of the inner and outer pipes, the rings may have a radial thickness (i.e., width from inner edge to outer edge measured radially) between 2-4 cm, or between 4-6 cm, or between 6-8 cm, or between 8-10 cm, or between 10-12 cm, or between 12-15 cm, or even thicker. Most typically, the rings of a single pipe-in-pipe segment have the same dimensions, but it should be appreciated that different dimensions are also suitable for use herein. Furthermore, it is preferred that each of the pipe-in-pipe segments has at least two rings, one located at each end of the outer pipe, as shown, for example, in FIG. 1. When more than one ring is disposed in a contemplated pipe-in-pipe system, it is preferred that the rings are equally spaced. Similarly, it is typically preferred that the distance between the inner and outer pipes is the same as the radial width of the rings. In a more preferred aspect, the spacing between the rings is small enough to allow the transfer of bending forces from the outer pipe to the inner pipe and to minimize or completely eliminate localized reduction in the annular space between the inner and outer pipes. In this manner, the rings also serve as a means of protection for the insulating material between the inner and outer pipes, since even moderate compression of the insulating material between the outer and inner pipes can result in loss of insulating capacity (and therefore thermal efficiency). In a further contemplated aspect, the rings may have holes extending vertically through the rings to maintain stability but reduce the thermal conduction path. Additionally, it is contemplated that the shape / profile of the pipes may be modified, for example, the wall thickness of the outer pipe may be increased to improve compression capability.

[0044] The contemplated sleeve is typically dimensioned and sized such that, once installed, it covers the weld joints and joint insulation material, thereby completing the thermal insulation layer between the inner and outer pipes. Of course, and as already mentioned above, the sleeve mechanically connects the outer pipes to each other, and the sleeve is mechanically connected to the ring. For ease of implementation, the sleeve typically consists of a half-pipe (or smaller section), with support bars along the longitudinal welds. Thus, once installed, the outer surface of the sleeve is continuous with the outer surface of the outer pipe. From a different perspective, the sleeve seals the annular space between the inner pipe, the ring, and the outer pipe, forming a continuous pipe-in-pipe system with reduced heat loss and increased mechanical strength.

[0045] With regard to suitable insulation materials for the weld joint and annular space, it is contemplated that all insulation materials are suitable for use herein, including insulating foam, aerogel, mineral / fiberglass mats, etc. As will be readily appreciated, the insulation material need not be the same between the material in the annular space in the pipe-in-pipe segment and the space above the weld joint. For example, the annular space insulation material may be preformed and sized as a half-pipe foam inset, while the joint insulation material may be wrapped around the weld joint from a tape or blanket.

[0046] As can be readily appreciated, when such an arrangement is used in a geothermal plant, the tubular casing is subject to heat transfer from the geological formations to the working fluid. In this regard, it is noted that the term "geothermal" as used herein refers to a heat source found in hot rocks, often at great depths, that can be extracted for industrial power and heat generation. Most typically, the heat source is a "dry" source from which heat can be extracted without the concomitant extraction of fluids (e.g., brine (part line) from the formation or treated injection water). For example, the tubular pipes and casing may be part of a closed loop system through which a working fluid circulates. Most typically, such a closed system further includes a heat exchanger and a turbine and generator to generate electrical energy, as exemplified in U.S. Pat. No. 8,020,382, the entire contents of which are incorporated herein by reference.

[0047] In this regard, closed loop geothermal technology should be understood to involve harvesting heat from rock into a working fluid that circulates in a completely closed environment. Most typically, a closed loop well includes a larger casing pipe thermally coupled to the rock by a thermally conductive grout and an inner insulated pipe to return the heated fluid to the surface. The working fluid flows down through the annular space between the casing and the insulated return pipe, picking up heat from the rock through the casing wall, and then flows up the insulated return pipe to provide energy for multiple purposes, including power generation. Most preferably, the formation has a sufficient temperature to convert the liquid working fluid (e.g., water) to a gaseous fluid (steam) that is transported to the topside and expanded and cooled in an expansion turbine or fed to a heat exchanger that heats a second working fluid of a generator. Examples of closed loop geothermal systems are described in U.S. Patent US 8201409 and U.S. Patent Publication US 2018 / 0274524, which are incorporated herein by reference in their entireties.

[0048] As a result, the inventors also contemplate a method of installing an insulated return pipe in a geothermal heat recovery plant, in which a plurality of pipe-in-pipe segments are provided and optionally stored for later use. Each segment has an outer pipe surrounding an inner pipe, and each pipe-in-pipe segment has insulating material in the annular space between the outer pipe and the inner pipe. During installation in a thermal well, the pipe-in-pipe segments are welded together in a continuous end-to-end manner, with (1) the ends of the inner pipes welded together; (2) the ends of the outer pipes welded (or pre-welded) to respective rings on the inner pipes of the pipe segments; (3) sleeve segments are placed between and welded to the rings of the pipe segments, and further welded to the ends of the outer pipes, thereby lying horizontally to form a continuous outer pipe surrounding the welded and connected inner pipes. The pipe-in-pipe segments thus joined are then advanced (typically with tensioners) from horizontal to vertical into the wellbore into the formation. As will be readily appreciated, the pipe-in-pipe segments connected in this manner may be passed through a bending device to reorient the connected pipe-in-pipe segments and through a straightening device to reverse the bend so that the connected pipe-in-pipe segments are vertically oriented. Of course, it should be appreciated that the connected pipe-in-pipe segments do not necessarily have to be horizontally oriented, but some angling may be implemented in the assembly. Similarly, other angles are contemplated if the well is not completely vertical. Furthermore, the well may be curved at some depth, and the connected pipe-in-pipe segments may accommodate the bend without mechanical failure. A further contemplated aspect is that the installation of the insulated pipe-in-pipe system within the casing may be made easier by the addition of one or more glider pieces, and specifically contemplated gliders are described in International Application PCT / US2022 / 025717, which is incorporated herein by reference.

[0049] Thus, also contemplated is a geothermal heat recovery power plant that includes a casing within the formation, the casing enclosing a pipe-in-pipe system that includes a plurality of serially connected pipe-in-pipe segments, each having an outer pipe surrounding an inner pipe, and each of the pipe-in-pipe segments having insulating material in the annular space between the outer pipe and the inner pipe. Most typically, the pipe-in-pipe segments are connected as described above, and the casing and pipe-in-pipe system are then fluidly connected to each other and to a heat exchanger to form a closed loop working fluid circuit for heat recovery and power generation.

[0050] In some embodiments, numerical values ​​expressing properties such as amounts of ingredients, concentrations, reaction conditions, and the like used to describe and claim certain embodiments of the invention are understood to be modified to some extent in some cases by the term "about". Accordingly, in some embodiments, the numerical parameters set forth in the specification and appended claims are approximations that may vary depending on the desired properties sought to be obtained by a particular embodiment. The specification of numerical ranges herein is merely intended to serve as a shorthand method of referring individually to each separate value within the range. Unless otherwise indicated, each separate value is incorporated herein as if it were individually recited.

[0051] All methods described herein can be performed in any suitable order unless otherwise noted or clearly contradicted by context. The use of any and all examples or illustrative language (such as "for example") with respect to certain embodiments herein is intended merely to better clarify the invention and not to limit the scope of the invention unless otherwise noted. No language in the specification should be construed as indicating anything non-claimed that is necessary to the practice of the invention.

[0052] As used throughout the description and claims of this specification, "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Also, as used in the description of this specification, "in" includes "in" and "on," unless the context clearly dictates otherwise. As used herein, and unless the context clearly dictates otherwise, the term "coupled to" is intended to include direct couplings (two elements are coupled to one another) and indirect couplings (at least one additional element is disposed between the two elements). Thus, the terms "coupled to" and "coupled with" are used interchangeably.

[0053] It will be apparent to those skilled in the art that many variations beyond those already described are possible without departing from the inventive concept herein. The subject matter of the present invention is therefore not limited except as set forth in the 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 "comprise" and "comprising" should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced element, component, or step may be present, used, or combined with other elements, components, or steps not expressly referenced. When the specification or claims refer to at least one selected from the group consisting of A, B, C, and N, it should be interpreted as requiring only one element from the group, not A+N or B+N, etc.

Claims

1. An insulating joint in a pipe-in-pipe system of a geothermal recovery plant, comprising: a first pipe-in-pipe segment and a second pipe-in-pipe segment, each pipe-in-pipe segment having an outer pipe surrounding an inner pipe, and each pipe-in-pipe segment having insulating material in an annular space between the outer pipe and the inner pipe; wherein each pipe-in-pipe segment has a ring between the outer and inner pipes where the outer pipe terminates and to which the outer pipe is joined and to which the inner pipe is joined and beyond which the inner pipe extends, the radial width of the ring being equal to the distance between the inner and outer pipes; a welded joint between each end of the inner pipe of the first and second pipe-in-pipe segments; first and second half-pipe sleeves joined together via longitudinal welds to form a sleeve segment; wherein the sleeve segment is welded to the rings of the first and second pipe-in-pipe segments such that (a) the welds of the rings connect the outer pipes of the first and second pipe-in-pipe segments via the sleeve, and (b) the welds of the rings connect the outer pipes of the first and second pipe-in-pipe segments via the rings to respective inner pipes of the first and second pipe-in-pipe segments to enable bending and straightening forces to be transmitted from the outside to the inner pipes; joint insulation material between the rings and between the weld joint and the sleeve of the first and second pipe-in-pipe segments; 13. An insulating joint in a pipe-in-pipe system comprising:

2. 2. The thermal insulation joint of claim 1, wherein each of said pipe-in-pipe segments has a length of about 10-20 m.

3. 2. The thermal insulation joint of claim 1, wherein the inner pipe of the first and second pipe-in-pipe segments has a diameter of about 10-20 cm, the outer pipe of the first and second pipe-in-pipe segments has a diameter of about 15-25 cm, and the sleeve segment has a length of about 20-50 cm.

4. 2. The thermal insulation joint of claim 1, wherein said ring has a radial width of about 3-10 cm and a thickness of about 2-5 cm.

5. 2. The thermal insulation joint of claim 1, wherein the ring is welded to the inner pipe of each of the first and second pipe-in-pipe segments.

6. 2. The thermal insulation joint of claim 1, wherein the first and / or second half-pipe sleeves include support bars along the longitudinal welds.

7. 2. The thermal insulation joint of claim 1, wherein said sleeve segment and said outer pipes of said first and said second pipe-in-pipe segments have the same outside diameter.

8. 2. The insulation joint of claim 1, wherein the joint insulation is wrapped around the weld joint.

9. 2. The insulating joint of claim 1, wherein the welds, the rings, and the sleeve segments of the connected pipe-in-pipe segments have sufficient strength for pipelaying processes including pipe bending and straightening.

10. A method of connecting a first pipe-in-pipe segment to a second pipe-in-pipe segment for use in a geothermal heat recovery plant, each of the pipe-in-pipe segments having an outer pipe surrounding an inner pipe extending beyond the outer pipe, and each of the pipe-in-pipe segments having insulation in an annular space between the outer pipe and the inner pipe, comprising: forming a weld joint between respective ends of the inner pipe of the first and second pipe-in-pipe segments; covering the welded joint with joint insulation; welding the first and second half-pipe sleeves together via a longitudinal weld to form a sleeve segment above the weld joint; and weld the sleeve segment onto each ring on the first and second pipe-in-pipe segments such that (a) the welds of the rings connect the outer pipes of the first and second pipe-in-pipe segments via the sleeve, and (b) the welds of the rings connect the outer pipes of the first and second pipe-in-pipe segments to the inner pipes of the first and second pipe-in-pipe segments via the ring to allow bending and straightening forces to be transmitted from the outside to the inner pipes, and a radial width of the ring is equal to the distance between the inner pipe and the outer pipe; The method includes:

11. The method of claim 10 , wherein the weld joint is covered by wrapping the joint insulation material around the weld joint.

12. The method of claim 10 , wherein the first and second half-pipe sleeves include support bars along the longitudinal welds.

13. The method of claim 10, wherein each of the rings on the first and second pipe-in-pipe segments is welded to the inner pipe of the first and second pipe-in-pipe segments.

14. The method of claim 10, wherein the sleeve segment and the outer pipe of the first and second pipe-in-pipe segments have the same outer diameter.

15. The method of claim 10, wherein the sleeve segment and the outer pipe of the first and second pipe-in-pipe segments are welded together to the respective rings.

16. The method of claim 10, wherein at least 20 pipe-in-pipe segments are connected in series.

17. The method of claim 10, wherein each of the pipe-in-pipe segments has a length of about 10-20 m and the sleeve segment has a length of about 20-50 cm.

18. 11. The method of claim 10, wherein the inner pipe of the first and second pipe-in-pipe segments has a diameter of about 10-20 cm, and the outer pipe of the first and second pipe-in-pipe segments has a diameter of about 15-25 cm.

19. 11. The method of claim 10, wherein the welds, the rings, and the sleeve segments of the connected pipe-in-pipe segments have sufficient strength for pipelaying processes including pipe bending and straightening.

20. 1. A method of installing an insulated return pipe in a geothermal heat recovery plant, comprising the steps of: providing a plurality of pipe-in-pipe segments, each having an outer pipe surrounding an inner pipe, and each of the pipe-in-pipe segments having insulating material in an annular space between the outer pipe and the inner pipe; The pipe-in-pipe segment is (1) the ends of the inner pipe are welded together; (2) each end of the outer pipe is welded to a respective ring on the inner pipe of the pipe segment, the radial width of the ring being equal to the distance between the inner pipe and the outer pipe; (3) sleeve segments are placed between the rings of the pipe segments and welded to the rings, and further welded to each end of the outer pipe, thereby forming a continuous outer pipe surrounding the welds connecting the inner pipes and allowing the transmission of bending and straightening forces from the outside to the inner pipe; and advancing the connected pipe-in-pipe segments from a horizontal to a vertical direction using bending and straightening devices into a wellbore into an earth formation, the earth formation having a temperature of at least 200°C; The method includes:

21. The method of claim 20, wherein each of the pipe-in-pipe segments has a length of about 10-20 m.

22. 21. The method of claim 20, wherein the inner pipe of the first and second pipe-in-pipe segments has a diameter of about 10-20 cm, and the outer pipe of the first and second pipe-in-pipe segments has a diameter of about 15-25 cm, and the sleeve segment has a length of about 20-50 cm.

23. 21. The method of claim 20, wherein the ring has a radial width of about 3-10 cm and a thickness of about 2-5 cm.

24. The method of claim 20, wherein the connected pipe-in-pipe segments are advanced into a casing in the earth formation.

25. 21. The method of claim 20, wherein the formation is at a depth of at least 500 m.

26. The method of claim 20, wherein the welded pipe-in-pipe segment eliminates buckling of the outer pipe.

27. 21. The method of claim 20, wherein the rings are spaced apart a distance that prevents compression of the insulation within the annular space due to reduction in the annular space.

28. 21. The method of claim 20, wherein each of the inner pipes in the pipe-in-pipe segment has sufficient strength to carry a fluid at a pressure of at least 13,700 kPa and a temperature of at least 200.degree.

29. 1. A geothermal heat recovery plant comprising: a casing within the formation enclosing a pipe-in-pipe system including a plurality of serially connected pipe-in-pipe segments, each having an outer pipe surrounding an inner pipe, and each having insulation in an annular space between the outer pipe and the inner pipe; the formation is at a depth of at least 500 m and / or has a temperature of at least 200° C.; The pipe-in-pipe segment comprises: (1) the ends of the inner pipe are welded together; (2) each end of the outer pipe is welded to a respective ring on the inner pipe of the pipe segment, the radial width of the ring being equal to the distance between the inner pipe and the outer pipe; (3) a sleeve segment is placed between the rings of the pipe segments, welded to the rings, and further welded to each end of the outer pipe, thereby forming a continuous outer pipe surrounding the welds connecting the inner pipes, and allowing bending and straightening forces to be transmitted from the outer pipe to the inner pipe. are connected to each other like this, and A geothermal heat recovery plant, wherein the casing, the pipe-in-pipe system and the heat exchanger are fluidly coupled to form a closed-loop working fluid circuit for heat recovery and power generation.

30. 30. The plant of claim 29, wherein the series connected pipe-in-pipe segments have a length of at least 1,000 m.

31. 30. The plant of claim 29, wherein the closed loop working fluid circuit is thermally coupled to an electrical generator.

32. A pipe assembly comprising a plurality of serially connected pipe-in-pipe segments of claim 1.

33. 33. A geothermal plant including the pipe assembly of claim 32.

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