Method and arrangements for thermal insulation, including downhole monitoring and control for a subsurface well work-string for geothermal and petroleum energy exploration and production

Abstract

A nested pipe string (100) for use in a well includes at least one nested pipe joint comprising an inner tube (10B) nested within an outer tube (10A) so as to define an annular space therebetween. The inner tube and the outer tube each comprises a connector (10A1, 10A2, 10B1, 10B2) at each longitudinal end. At least one centralizer (12) is disposed in the annular space and arranged to separate the inner tube from contact with the outer tube. The string comprises a sub (30) connectable to the at least one nested pipe joint. The sub has a first connector mateable with the connector at one longitudinal end of the outer tube, and a second connector mateable with the connector at a corresponding longitudinal end of the inner tube. The first and second connectors are longitudinally offset from each other whereby the inner tube and the outer tube are separately accessible at a longitudinal end opposed to the sub for separately assembling the inner tube and the outer tube to the sub.

Description

METHOD AND ARRANGEMENTS FOR THERMAL INSULATION, INCLUDING DOWNHOLE MONITORING AND CONTROL FOR A SUBSURFACE WELL WORK-STRING FOR GEOTHERMAL AND PETROLEUM ENERGY EXPLORATION AND PRODUCTIONBackground

[0001] This disclosure relates to the field of completion of subsurface wells for extracting geothermal energy contained in the Earth’s crust and for drilling and completion strings used for petroleum exploration and production. More particularly, the disclosure relates to the tools and arrangements used for such energy extraction.

[0002] FIG. 1 shows a known well structure for geothermal energy production, i.e., to drill and complete two substantially vertical wells P, I into such a formation F. The wells P, I are spaced apart a predetermined lateral distance L from each other. Fluid, e.g., water, is pumped down through one of the wells, termed the injector well I, and heated fluid is produced from the formation F from the other well, termed the producing well P. The fluid is heated by the rock at depth when flowing through the formation F between the injector well I and the producing well P. There are various challenges with this structure for geothermal heat extraction.It is necessary to have a permeable, hot formation layer F to heat the subsurface liquid (water) flow. This limits the use of the above structure to locations where such formations exist underground, and suitable places having such formations may be far from locations where the geothermal heat energy is needed.In order to provide sufficient permeability to the formation F, in some cases, it may be necessary to fracture treat the formation F, which can increase the risk of groundwater pollution, seismicity and environmental degradation.The fluid, mainly limited to water, may dissolve and absorb minerals from the formation F that may cause problems such as scaling and corrosion, which may substantially increase well maintenance and pumping costs.There is considerable thermal energy loss in the producing well P as the heated fluid moves to surface.

[0003] A known solution to reduce the foregoing problems using spaced apart vertical wells is to drill and complete one or several inclined or horizontal well sections, which in some instances may intersect to connect two or more wells at depth and thereby construct one or more downhole closed circulation loops, but such solution represents a well completion challenge. Closed circulation loops using one well with fluid return inside the completion pipe string is also common, however, the foregoing has shown to be difficult to implement efficiently for deep hot wells.

[0004] FIG. 2 shows another example of a closed circulation loop structure, e.g., to install a thermally insulated completion tubing string T or a nested conduit in a long- reach horizontal well. A casing C may be used to line the drilled portion of the well, and an insulated tubing T may be nested within the casing C to transport the heated fluid to the surface. The geothermal heat is in this case extracted from the formation F, especially in the horizontal well section. The construction of such a well is challenging, due to high requirements for the tubular strength and due to the high cost and risk involved in the installation process.

[0005] US Pat. No. 5,862,866 issued to Springer discloses a nested pipe string that comprises an outer pipe string and an inner pipe string nested within the outer pipe string. The nested pipe strings are assembled by first assembling the outer pipe string in a conventional manner, e.g., coupling joints and / or stands of such joints together end to end. After the outer pipe string is completely assembled, the inner pipe string is assembled in a similar manner, specifically by inserting the inner pipe string during assembly into the interior of the outer pipe string. In addition to possible difficulties in correctly locating and sealing the bottom of the inner pipe string during assembly in highly inclined or horizontal well sections, the amount of time for assembly of the nested pipe strings may be substantially greater than for assembling a single pipe string or the dual, nested pipe string disclosed in International Application Publication No. WO 2023 / 017485 A1, in which individual segments (“joints”) of pipe comprises nested pipe segments whereby the nested pipe string is assembled joint by joint or stand by stand similarly to assembly of a single pipe string.

[0006] In-situ downhole monitoring and control of the wells represent an additional challenge by use of cables and control lines, especially for horizontal well sections of the well.

[0007] Similar challenges for downhole monitoring and control are present for petroleum exploration and production. Current solutions are based on the use of electric or hydraulic cables or on acoustic-or electromagnetic telemetry. These are all vulnerable and associated with risks.

[0008] Lack of effective solutions for thermal insulation of the production tubing also leads to significant scaling problems, reduced production and high costs for workover operations related to scaling of the wells.

[0009] Proper thermal insulation of the well pipe (work-string) is also important for the drilling of deep and hot wells for both geothermal and petroleum energy production. Thermal insulation of the work-string enables improved lifetime for downhole electronic components and thereby deeper drilling depths and improved energy recovery.

[0010] There is therefore a need for improved arrangements and procedures for the drilling and completion of geothermal and petroleum wells.Summary

[0011] One aspect of the present disclosure is a nested pipe string for use in a well. A pipe string according to this aspect includes at least one nested pipe joint comprising an inner tube nested within an outer tube so as to define an annular space therebetween. The inner tube and the outer tube each comprises a connector at each longitudinal end. At least one centralizer is disposed in the annular space and arranged to separate the inner tube from contact with the outer tube. The string comprises a sub connectable to the at least one nested pipe j oint. The sub has a first connector mateable with the connector at one longitudinal end of the outer tube, and a second connector mateable with the connector at a corresponding longitudinal end of the inner tube. The first and second connectors are longitudinally offset from each other whereby the inner tube and the outer tube are separately accessible at a longitudinal end opposed to the sub for separately assembling the inner tube and the outer tube to the sub.

[0012] In some implementations, the connector at at least one longitudinal end of the inner tube or the outer tube comprises a threaded connector.

[0013] In some implementations, the first connector or the second connector on the sub each comprises a threaded connector.

[0014] In some implementations, the connector at each longitudinal end of the inner tube or the outer tube comprises a threaded connector.

[0015] In some implementations, the at least one centralizer comprises circumferentially spaced apart spheres or buttons disposed in a frame, the frame comprising an attachment to lockably engage an interior surface of the outer tube or an exterior surface of the inner tube and openings to retain the spheres or buttons, the spheres or buttons sized to fill the annular space to prevent lateral contact between the inner tube and the outer tube proximate the at least one centralizer.

[0016] In some implementations, the frame comprises openings for set screws to lock the fame to the inner tube or the outer tube.

[0017] In some implementations, the spheres or buttons comprise a thermally and electrically insulating material.

[0018] In some implementations, the thermally and electrically insulating material comprises ceramic.

[0019] In some implementations, the sub is arranged to sealingly close the annular space when assembled to the inner tube and the outer tube of the at least one nested pipe joint.

[0020] In some implementations, the sub comprises an electrical insulator disposed radially between the first connector and the second connector, whereby electrical isolation is maintained between the inner tube and the outer tube.

[0021] Some implementations further comprise at least one tension anchor disposed in at least one of a plurality of nested pipe joints. The at least one tension anchor comprises a plurality of longitudinally and circumferentially locking pins disposed on either an interior surface of the outer tube or an exterior surface of the inner tube, and a plurality of locking receivers disposed on either the exterior surface of the inner tube or the interior surface of the outer tube. A circumferential and longitudinal spacing between adjacent locking pins and locking receivers is chosen to enable longitudinal pass through of the locking pins with respect to the locking receivers and lockingengagement between the locking pins and locking receivers when the inner tube is rotated with respect to the outer tube.

[0022] Some implementations further comprise electrically and thermally insulating material disposed between contact surfaces of the locking pins and the locking receivers.

[0023] Some implementations further comprise at least one tension anchor disposed in at least one of a plurality of nested pipe joints. The at least one tension anchor comprises a plurality of circumferentially spaced apart locking slips disposed between an interior surface of the outer tube and an exterior surface of the inner tube. A circumferential spacing between adjacent locking slips is chosen to enable fluid flow through the tension anchor between the inner tube and the outer tube.

[0024] Some implementations further comprise electrically and thermally insulating material disposed between contact surfaces of the locking slipsSome implementations further comprise electrically and thermally insulating material disposed for the locking slips.

[0025] Some implementations further comprise a tubing hanger assembled to an opposed longitudinal end of the at least one nested pipe joint than the sub, the tubing hanger comprising an adapter engageable with the connector at the opposed longitudinal end of the inner tube and the outer tube, the adapter arranged to close the annular space and comprising a fluid port in fluid communication with the annular space to enable evacuation of the annular space from a side of the tubing hanger opposed to a side coupled to the adapter.

[0026] In some implementations, the adapter comprises an electrical insulator arranged to electrically insulate the inner tube from the outer tube, the adapter further comprising an electrical contact making insulated electrical connection to the inner tube to enable electrical communication with the inner tube from the side of the tubing hanger opposed to the side coupled to the adapter.

[0027] Some implementations further comprise a pipe protector engageable with one longitudinal end of the at least one nested tube joint. The pipe protector comprises an outer connector engageable with the connector at one longitudinal end of the outer tube and an inner connector engageable with the connector at a same one longitudinalend of the inner tube. The pipe protector comprises a rod disposed through the outer connector and the inner connector. The rod is lockably movable through the inner connector to enable the inner tube to move through the outer tube such that an opposed longitudinal end of the inner tube protrudes from a corresponding longitudinal end of the outer tube in one position.

[0028] Some implementations further comprise a telescoping joint comprising an inner telescoping joint tube nested within an outer telescoping joint tube. The telescoping joint is arranged to enable change in length of the inner tube. The telescoping joint comprises connectors on longitudinal ends of the inner and outer telescoping joint tubes arranged to connect to the connectors on a longitudinal end of the nested pipe joint.

[0029] A method according to another aspect of the present disclosure for deploying a nested pipe string in a well comprises the following. A sub is suspended proximate a top of the well. The sub has a first connector mateable with a connector at one longitudinal end of an outer tube and a second connector mateable with a connector at a corresponding longitudinal end of an inner tube nested within the outer tube in a nested pipe joint. The first and second connectors are longitudinally offset from each other whereby the inner tube and the outer tube are separately accessible at a longitudinal end opposed to the sub for separately assembling the inner tube and the outer tube to the sub. The inner tube and the outer tube are separated from each other in an annular space by at least one centralizer. The outer tube is assembled to the sub. The inner tube is assembled to the sub, and the assembled inner tube, outer tube and sub are moved into the well to enable assembly to a longitudinal end of the nested pipe joint of a subsequent nested pipe joint.

[0030] Some implementations further comprise assembling a tension anchor to a longitudinal end of the nested pipe joint opposed to the longitudinal end thereof connected to the sub. The tension anchor comprises a plurality of longitudinally and circumferentially locking pins disposed on one of either an interior surface of an outer anchor tube, or on an exterior surface of an inner anchor tube nested within the outer anchor tube. A plurality of locking receivers is disposed on the other of either the exterior surface of the inner tube or the outer surface of the inner tube. A circumferential and longitudinal spacing between adjacent locking pins and lockingreceivers is chosen to enable longitudinal pass through of the locking pins with respect to the locking receivers, and locking engagement between the locking pins and locking receivers when the inner anchor tube is rotated with respect to the outer anchor tube.

[0031] Some implementations further comprise setting the tension anchor by rotating the inner tube such that the locking pins are circumferentially oriented between circumferential spaces separating adjacent locking receivers. The inner tube is lifted and rotated such that the locking pins are in circumferential alignment with the locking receivers. The inner tube is lowered until the locking pins engage the locking receivers.

[0032] Some implementations further comprise setting of the tension anchor by inserting slips in the annular space between the inner and outer tubes, so that the anchoring is performed just by pulling the inner pipe, inserting the slips and releasing the tension on the inner pipe. In this case no rotation is required, since the slips, that can be assisted by spring elements, will automatically perform the locking between the pipes just by releasing the lifting tension in the inner tube.

[0033] Some implementations further comprise assembling a tubing hanger to a longitudinal end of the nested pipe joint or a longitudinally endmost one of a plurality of assembled nested pipe joints using an adapter having a fluid port in fluid communication with an annular space between the inner tube and the outer tube. The fluid port has a fluid connection on a side of the tubing hanger opposed to a side thereof connected to the nested pipe joint or longitudinally endmost nested pipe joint. The annular space is evacuated through the tubing hanger.

[0034] In some implementations, the connecting the inner tube and the outer tube to the sub comprises suspending the inner tube and the outer tube over the sub. A pipe protector assembled to the inner tube and the outer tube is released. The pipe protector comprises an outer connector engageable with the connector at one longitudinal end of the outer tube, an inner connector engageable with the connector at a same one longitudinal end of the inner tube. The pipe protector further comprises a rod disposed through the outer connector and the inner connector. The rod is lockably movable through the inner connector to enable the inner tube to move through the outer tube such that an opposed longitudinal end of the inner tube protrudes from acorresponding longitudinal end of the outer tube in one position. The connector at the longitudinal end of the inner tube and the outer tube to is corresponding ones of the connectors on the sub.

[0035] In some implementations, assembling either or both the inner tube and the outer tube to the sub comprises assembling threaded connections.

[0036] Other aspects and possible advantages will be apparent from the description and claims that follow.Brief Description of the Drawings

[0037] FIG. 1 shows a geothermal energy production apparatus known in the art using two laterally spaced apart vertical wells.

[0038] FIG. 2 shows a geothermal energy production apparatus known in the art using a horizontal or extended reach well.

[0039] FIG. 3 shows an example of an assembly of a nested tubing string.

[0040] FIGS. 4 A through 4D show an example implementation of components of and an assembled joint of nested pipe according to the present disclosure.

[0041] FIGS. 5 A, 5B and 5C show an example of a centralizer.

[0042] FIGS. 6 A and 6B shows an example of a bottom hole sub.

[0043] FIG. 7 shows an example of a tension anchor.

[0044] FIGS. 7 A through 7D show operation of the tension anchor of FIG. 7.

[0045] FIG. 7E shows another implementation of the tension anchor.

[0046] FIGS. 8 A and 8B show an example of a bottom hole sub.

[0047] FIGS. 9 A through 9E show an example of a pipe handling protector being installed into a segment of nested pipe according to the present disclosure.

[0048] FIG. 10 shows an example of a pipe handling protector in operation during installation.

[0049] FIG. 11 shows an example of a bumper sub, to allow for flushing during installation.

[0050] FIG. 11 shows an example of a bumper sub, to allow for flushing during installation.Detailed Description

[0051] Reelwell AS, Sola, Norway, has developed a well drilling method based on a nested pipe or conduit (“work string”) that alleviates certain challenges occurring in long-reach horizontal or high inclination wells in relation to downhole torque, drag and formation pressure control. The foregoing method may allow a well to be drilled and completed beyond the attainable horizontal reach using conventional, single conduit drill string techniques, and thus may enable construction of closed loop horizontal geothermal wells with improved cost efficiency. The foregoing closed loop drilling and completion method is described in International Application Publication No. WO 2023 / 017485 Al. The structure and method set forth in this disclosure represent extensions to such nested pipe string technology to enable improved performance both for closed loop geothermal wells and for petroleum exploration and production.

[0052] FIG. 3 shows an example implementation of assembled components of a nested pipe string according to the present disclosure. In the present example implementation, the assembled nested pipe string 100 may comprise one or more segments (“joints”) 10 of nested tube or pipe assembled end to end. One longitudinal end of the nested pipe string 100 may be inserted into a well to a chosen depth. Such longitudinal end comprises a bottom hole sub 30 coupled to both an inner tube (FIG. 4B) and outer tube (FIG. 4A) of the longitudinal endmost nested pipe joint 10. The bottom hole sub 30 will be explained in more detail below with reference to FIGS. 6 A and 6B. The longitudinally opposed end of the nested pipe string 100 may comprise one or more tension anchor joints 20 and downhole communication subs (not shown), positioned at suitable places along the nested pipe string 100 string between the bottom hole sub 30 and a tubing hanger 40 at the longitudinally opposed end of the nested pipe string 100 to the bottom hole sub 30. The tubing hanger 40 suspends the nested pipe string 100 in a wellhead (not shown) or similar device at the surface end of a well.

[0053] The nested pipe joints 10 of the nested pipe string 100, to be explained further below with reference to FIGS. 4A through 4D, each may comprise an inner tube nested within an outer tube, and one or more centralizers 12 disposed within in an annular space between the inner tube and the outer tube to reduce contact therebetween such that the conductive heat transfer in the radial direction through the nested pipe joint 10 is minimized. In addition, the inner or outer surfaces of the inner pipe and the outer pipe can be coated with material layers to minimize the radiation heat transfer in the radial direction, for example by one or more layers of aluminum coating, which may be metallic aluminum, or for example one or more layers of composite coatings of fiberglass and metallic materials that may fill nearly all the space of the annular space between the inner tube and the outer tube.

[0054] Optionally the bottom hole sub 30, the tubing hanger 40 and the centralizers 12 all have arrangements comprising electrically insulating material included to allow electrical isolation between the inner tube string and the outer tube string. In such implementations, case, a modem sub or collar (not shown) can be included proximate the bottom hole sub 30, or positioned at suitable locations along the nested pipe string 100 by means of an electrical feed-thru cable to the inner tube in the tubing hanger 40 or in the wellhead. The modem sub (not shown) can have built in sensors for monitoring of, for example and without limitation, in-well temperature and fluid pressure, and may comprise actuators, such as, and without limitation, downhole valves, for possible control of fluid flow from the surface by means of electrical signals and power transmission through the nested pipe string 100. Such actuators, if used, could also comprise fluid heaters to reduce or eliminate scale deposits for petroleum production applications, or any other type of electric actuators and sensors for subsurface process or fluid influx control.

[0055] FIGS. 4 A through 4D show an example implementation of components of and an assembled joint of nested pipe according to the present disclosure. The assembled nested pipe string (100 in FIG. 3) must be able to withstand high downhole pressure, i.e., the outer pipe requires high collapse pressure rating, whereas the inner pipe must have high burst pressure rating. Each nested pipe joint 10 may comprise an inner tube (FIG. 4B) and an outer tube (FIG. 4A) in which the inner tube is nested. The outer tube and inner tube can be made of steel or other suitable strong and heat resistantmaterial, such as aluminum alloys or high performance composite materials. The selection of materials, dimensions, type of connectors on each longitudinal end, etc., is subject to individual considerations for each well, based on, e.g., cost and performance. It is not required according to the present disclosure, but in the following description it is assumed that the inner and outer pipe joints have approximately equal lengths. Centralizers may be attached to the inner pipe joints before insertion into the outer pipe.

[0056] FIG. 4A shows a segment or joint of outer tube 10A. In some implementations, the dimensions and the type of connections at each end of the joint of the outer tube 10A may comprise oil and gas industry standards for the foregoing. The outer tube joint 10A may comprise a threaded connector at each longitudinal end. In the present example implementation, a male or “pin” threaded connector may be disposed at one longitudinal end of the and is shown at 10A1. A female of “box” threaded connector 10A2 may be disposed at the other longitudinal end of the outer tube joint 10A. The pin 10A1 and box 10A2 connectors in some implementations, may be such that the exterior profde of the assembled outer tube joints 10A and thereby the nested pipe string (100 in FIG. 3) is smooth, e.g., “flush joint” tubing. In some implementations, the box end 10A2 may comprise an enlarged exterior diameter with reference to the remainder of the outer tube joint 10A, e.g., “external upset” tube. While the present example implementation of the outer tube joint 10A comprises a male connector at one end and a female connector at the other end, it is to be clearly understood that the disclosed connectors are a matter of discretion for the user or designer and are not intended to limit the scope of the present disclosure. Pin / pin end pipe segments or box / box end pipe segments are equally within the scope of the present disclosure, it being understood that adapters, collars or similar devices may be used when each pipe segment has the same gender of threaded connector at both ends.

[0057] FIG. 4B shows a segment or joint of inner tube 10B, which when assembled is nested inside one of the outer tube joints shown in FIG. 4A. The inner tube joint 10B may comprise a threaded connector 10B1, 10B2 at each longitudinal end corresponding to the threaded connectors\ at each longitudinal end of each joint of the outer tube joint (10A in FIG. 4A). In some implementations, it is possible to have connectors at each longitudinal end of each inner and outer tube that are not based onthe use of threads for the application, as long as the particular connectors used have sufficient strength and hydraulic sealing capability. As is the case for the outer tube joints, the type of connector on the inner tube joint 10B is not a limitation on the scope of the present disclosure.

[0058] FIG. 4C shows an assembled nested tube joint 10A. When assembled inside the outer tube joint 10A, the inner tube joint 10B is disposed within the interior of the outer tube joint 10A so as to define an annular space 10C therebetween. The annular space 10C may have disposed therein at one or more selected locations along the length of the annular space 10C a centralizer 12. The centralizer(s) 12 provide positive separation between the inner tube joint 10B and the outer tube joint 10A. The number of centralizers and their placement in any one or more nested pipe joints 10 may depend on, for example, the relative diameters and wall thicknesses of the inner tube joint 10B and outer tube joint 10A, the depth of and the trajectory of the well into which the nested pipe string (100 in FIG. 3) is to be disposed. The nested pipe joint 10 may be arranged such that there is a predetermined longitudinal offset L between the inner tube joint 10B and the outer tube joint 10A. The offset L facilitates assembly of the nested pipe joints 10 into a complete nested pipe string (100 in FIG. 3). The offset L may be obtained when the nested pipe joint 10 is assembled to the bottom hole sub (30 in FIG. 3) and when further nested pipe joints are assembled to the foregoing.

[0059] FIG. 4D shows a side view of an example implementation of one of the centralizers 12. The centralizers 12, to be explained in more detail with reference to FIGS. 5 A through 5C may comprise a retaining sleeve and several, circumferentially spaced apart thermal (and in some implementations electrical) insulators, such as, and without limitation, ceramic spheres or buttons.

[0060] FIGS. 5 A and 5B show an example implementation of the centralizers 12. An oblique view in FIG. 5A illustrates that the centralizers 12 may comprise a frame 12A such as may be made from steel or other high strength material to be attached to the inner tube, at intervals determined by the position and operation among other considerations. The frame 12A may be generally circular in shape and traverse a principal diameter D (FIG. 5B) chosen to fit about the exterior surface of the inner tube (10B in FIG. 4B) and may comprise a plurality of upsets 12C that can retain oneormore spacers 12B. The spacers 12B may have size selected to fit within the annular space (IOC in FIG. 4C) so as to maintain the diameter of the annular space under variable well conditions to which the nested pipe string (100 in FIG. 3) is subjected. In some implementations, the spacers 12C may comprise high strength, low thermal conductivity and low electrical conductivity material (e.g., ceramic) spheres, which may provide the properties of minimum contact surface between the spacers 12C and the inner and outer tubes, and may provide that the inner tube may move relative to the outer tube. In some embodiments the spacers 12C are free to rotate to minimize the friction due to relative movement between the surfaces. The frame 12A may comprise openings 12D, e.g., for set screws to lock the frame 12A into position along the inner tube. The manner of securing the frame 12A to the inner tube 10B is not a limitation on the scope of the present disclosure. Other manner of attachment, for example and without limitation may include spot welding, adhesive and interference fit.

[0061] A side view of one of the centralizers 12 is shown in FIG. 5B, wherein may be observed the upsets 12C and spacers 12B about the circumference of the frame 12A. The number of and circumferential spacing of the upsets 12A and spacers 12B is not a limitation on the scope of the present disclosure, however considerations is choosing the foregoing may include, without limitation, the inclination of the well into which the nested pipe string (100 in FIG. 3) is to be disposed and the relative diameters of the inner tube and the outer tube. To minimize their associated heat loss and costs, it is desirable to use as few centralizers 12 as possible.

[0062] FIG. 5C shows the centralizer 12 attached to the inner tube 10B and providing standoff within the annular space 10C between the inner tube 10B and the outer tube 10A. The centralizers 12 may provide the assembled nested pipe joint 10 with the following:Give minimum radial conductive heat flow between the inner and outer tubes.Sustain the high contact forces between the inner and outer tubes, in bends, etc.Avoid direct metal to metal contact between the inner and outer tubes.

[0063] FIGS. 6 A and 6B show example implementations of the bottom hole sub 30. The bottom hole sub 30 provides the lower end connection between the inner tube(10B in FIG. 4B) and the outer tube (10A in FIG. 4A) of the nested pipe string (100 in FIG. 3). The bottom hole sub 30 may comprise an inner tube adapter 31 having a threaded connector 31A adapted to receive the longitudinal end connector of the lowermost one of the inner tube joints. In some implementations, and as explained with reference to FIG. 4B, the longitudinal end connector (10B1 in FIG. 4B) may be a pin or male threaded connector. In such implementations, the inner tube adapter 31 may therefore comprise a box connector as the threaded connector 31 A. The inner tube adapter 31 may be connected within and sealed, by sealing elements 33A to the interior of an outer tube adapter 32. The outer tube adapter 32 may comprise a threaded connector 32A to receive the longitudinal end threaded connector (10A1 in FIG. 4A) from the lowermost outer tube joint. In some implementations, the bottom hole sub 30 may comprise a lower nut 33 to engage further devices such as an extension pipe 34 and internal insulating pipe 35. In some implementations, and with reference to FIG. 6B, the bottom hole sub 30 may comprise, at 36, an optional telemetry modem sub with sensors and actuators, as may be needed, for downhole telemetry and electric power supply through the nested pipe string (100 in FIG. 3).

[0064] It will be appreciated that in some implementations, by electrically insulating the inner tube from the outer tube, the bottom hole sub 30 may thereby enable using the nested pipe string (100 in FIG. 3) as an electrical power and signal telemetry channel in the manner of a two conductor electrical cable. In such implementations, the use of insulated spacers (see 12C in FIGS. 5A and 5C) may help to maintain electrical insulation along the entire length of the nested pipe string (100 in FIG. 3). Such electrical power and signal channel capability may enable operating the various sensors (not shown separately) and actuators (not shown separately) in the bottom hole sub 30 and in any connected devices below.

[0065] During assembly of the nested pipe string (100 in FIG. 3), as an initial step, the bottom hole sub 30 may be suspended in slips (FIG. 10) through the drill floor on a drilling rig or workover rig of types known in the art. A joint of nested pipe (10 in FIG. 4) may be assembled to the bottom hole sub 30 by individually rotating both the outer tube joint (10A in FIG. 4A) and the inner tube joint (10B in FIG. 4B) to engage the respective threaded connectors to the corresponding threaded connectors in the bottom hole sub 30. Final make up torque may be applied to the outer tube (10A inFIG. 4A) on its tool joint surface and then to the inner tube (10B in FIG. 4B) on its tool joint surface, each of the foregoing usually longitudinally coincident with or proximate to the threaded connectors (10A1, 10A2). Because the inner tube is longitudinally offset from the outer tube as shown in FIG. 4C, it is possible to apply make up torque, or any other mechanical action required to assemble the connection (e.g., when non-threaded connectors are used), separately to each of the inner tube and the outer tube. The assembled bottom hole sub 30 and nested pipe joint 10 may be lowered through the drill floor until the next make up point is reached. At such point a successive nested pipe joint may be assembled to the uppermost nested pipe joint suspended in the slips. The foregoing may be repeated until a longitudinal position within the nested pipe string (100 in FIG. 3) or at the upper longitudinal end of the nested pipe string where a tension anchor (20 in FIG. 3) may be assembled to the part of the nested pipe string suspended in the slips.

[0066] Referring to FIG. 7, an example implementation of a tension anchor 20 is shown. The tension anchor 20 may comprise locking receivers 10B3 disposed along the exterior surface of an inner tube joint 10B. The locking receivers 10B3 may be arranged in one or more circumferentially spaced apart lines, wherein a total number of the locking receivers 10B3 is sufficient to suspend safely the entire weight of the assembled inner tube joints along the entire nested pipe string. Locking pins 10A3 may be disposed along the interior surface of the outer tube joint 10A. The locking pins 10A3 may be arranged in corresponding circumferentially spaced apart lines, whereby the inner tube 10B may be lifted and rotated while the outer tube 10A is hung in the slips. The inner tube 10B may be released longitudinally when the lines of locking pins 10A3 and locking receivers 10B3 are aligned longitudinally. After lowering, the weight of the inner tube will be transferred to the outer tube, whereby the inner tube may be maintained in tension. In some implementations, the locking receivers 10B3 or locking pins 10A3 may comprise electrically / thermally insulating inserts, at their respective contact surfaces, whereby electrical / thermal insulation between the inner tube and the outer tube is maintained through the tension anchor 20. It is within the scope of the present disclosure to assemble more than one such tension anchor in any particular nested pipe string, depending on, for example, the total depth of the well, the well trajectory, the respective well, inner tube and outer tube diameters and expected fluid pressures. Where any particular tension anchor isto be intermediate the bottom hole sub (30 in FIG. 6A) and the tubing hanger (40 in FIG. 3), further nested tube joints (10 in FIG. 4C) may be assembled to and above the intermediate tension anchor as explained elsewhere herein.

[0067] For improved flexibility on the nested pipe string design and its optimization, the string will contain one or several tension anchors. The level of pre-tension of each string element can be estimated based on the expected temperature variations for the string section during the operations. For example, if the temperature variation of the string section is expected to reach 50 degrees Celsius, a pre-tension of the inner string that gives the same length variation is suggested, to avoid unwanted mechanical hazards or failures. Since the lower horizontal section of the well would normally experience less variations in temperature of the inner and outer string than for the vertical section of the well, the pre-tension for the lower section can be accepted to be lower than the pre-tension in the upper vertical section. The thermal expansion levels are calculated from the thermal expansion coefficients of the materials of the strings. The stress levels can be calculated from Hookes law for elastic materials.

[0068] FIGS. 7A through 7D show an example implementation of engaging the tension anchor 20 illustrated in FIG. 7. In FIG. 7A, initially, the inner tube 10B may be rotated, such as by a top drive (not shown) on the rig (not shown) such that the locking receivers 10B3 are circumferentially aligned with circumferential spaces 10A4 between circumferentially adjacent locking pins 10A3. When such alignment is obtained, and referring to FIG. 7B, the inner tube 10B may be lifted axially such that the locking receivers 10B3 move through the circumferential spaces 10A4 and are disposed within axial spaces 10A5 between axially spaced apart, circumferentially aligned ones of the locking pins 10A3. In FIG. 7C, the inner tube 10B may be rotated such that the locking receivers 10B3 and the locking pins 10A3 are in circumferential alignment. When such circumferential alignment is obtained, the inner tube 10B may be lowered to engage the locking receivers 10B3 with the locking pins 10A3. In this way, weight of the inner tube 10B is transferred to the outer tube 10A through the engaged locking pins 10A3 and locking receivers 10B3. FIG. 7D shows the inner tube 10B and the outer tube as fully engaged.

[0069] FIG. 7E shows another example implementation of a tension anchor 20. This alternative tension anchor 20 may comprise sets of internal anchor slips 10C disposedalong the exterior surface of an inner tube joint 10B. The internal anchor slips IOC may be arranged in one or more circumferentially spaced apart lines, wherein a total number of internal anchor slips is sufficient to suspend safely the entire weight of the assembled inner tube joints along the entire nested pipe string. These internal anchor slips IOC on the inner tube 10B allows the inner tube string to be locked in tension after lifting the inner tube string while the outer tube 10A is hung in external slips (e.g., on a hoist unit of a well servicing apparatus or rig) for the string in the rotary table. The inner tube 10B may be released longitudinally, and the internal anchor slips IOC will be engaged to prevent movement between the inner string and outer string, and thereby to lock the tension in the inner string below the anchor slips IOC.. After lowering, the weight of the inner tube 10B will be transferred to the outer tube 10A, whereby the inner tube 10B may be maintained in tension. In some implementations, the engagement of the internal anchor slips IOC may assisted by spring elements 10D, as indicated in FIG. 10E. In some implementations, the internal anchor slips IOC may comprise electrically / thermally insulating material, or at their respective contact surfaces, whereby electrical / thermal insulation between the inner tube 10B and the outer tube 10A is maintained through the tension anchor 20. It is within the scope of the present disclosure to assemble more than one such tension anchor in any particular nested pipe string, depending on, for example, the total depth of the well, the well trajectory, the respective well, inner tube and outer tube diameters and expected fluid pressures. Where any particular tension anchor is to be intermediate the bottom hole sub (30 in FIG. 6A) and the tubing hanger (40 in FIG. 3), further nested tube joints (10 in FIG. 4C) may be assembled to and above the intermediate tension anchor as explained elsewhere herein.

[0070] FIG. 8A and FIG. 8B show an oblique and cut away view, respectively, of an example implementation of the tubing hanger 40. An adapter 42 may make mechanical connection between the longitudinal end of the nested pipe string (100 in FIG. 3) and the tubing hanger 40. The tubing hanger 40, which in addition to transferring the nested pipe string (100 in FIG. 3) weight load to the wellhead (not shown) may provide the well completion with one or more of the following properties:Provide a fluid channel to enable evacuation of the annular space (10C in FIG. 5C) in the nested pipe string (100 in FIG. 3).Provide a channel for an electrical cable for electric power and signal transmission through the nested pipe string (100 in FIG. 3).

[0071] To enable the electric signal transmission the tubing hanger 40 may be provided with an electrically insulated pipe insert 44, that both will provide sealing in the annular space between the nested pipes, to allow the downhole evacuation of this annular space (10C in FIG. 5C), and at the same time prevent electrical contact between the tubing hanger 40 and nested inner pipe string below the tubing hanger 40. After the tubing hanger 40 is installed in the wellhead, the tubing hanger 40 allows access to evacuate the annular space (10C in FIG. 4C) through a fluid line 41. A connector 43 may be provided to attach an electrical cable (not shown) from surface for downhole electric power and telemetry.

[0072] FIGS. 9A through 9E show an example implementation of a nested pipe handling protector (“pipe protector”) 50. The pipe protector 50 serves as a tool-joint (threaded connector) protection device for one longitudinal end, e.g., the surface, female thread end ofthe nested tubing joint 10. The pipe protector 50 may be installed in the longitudinal end of the nested pipe joint 10 according to the present disclosure by threading or otherwise locking an inner tube thread protector 51 into the threaded connector (10B2 in FIG. 4B) at the longitudinal end of the inner tube 10B. The foregoing is shown in FIG. 9B. The inner tube thread protector 51 may be disposed on a protector rod 52. The protector rod 52 may be movable longitudinally through the inner tube thread protector 51. After the inner tube protector 51 is locked into position in the longitudinal end of the inner tube 10B, an outer tube thread protector, shown at 53, may be moved into place, e.g., by sliding it along the rod 52 through the inner tube protector 51, as shown in FIG. 9C. As shown in FIG. 9D, the outer tube thread protector 53 may then be engaged, e.g., by threading, into the longitudinal end of the outer tube 10A. In FIG. 9E, the outer tube thread protector 53 is engaged with the end ofthe outer tube 10A, and the inner tube 10B is locked in place longitudinally by locking the outer tube protector 53 in place longitudinally along the rod 52.

[0073] After installation of the pipe protector 50 as shown in FIGS. 9 A through 9E, and during transport to the well site, the pipe protector 50 will be in the locked position, i.e., it locks longitudinally and prevents movement of the inner tube 10B within the outer tube 10A during transport. The lock is disengaged during theinstallation of the nested pipe joint 10 to a nested pipe string (e.g., 100 in FIG. 3). After the lock is disengaged, and referring to FIG. 10, when the nested pipe joint 10 is lifted in vertical position for insertion at the top of the string by the pipe -elevator, top-drive or other pipe lifting arrangement, the pipe protector 50 allows the inner tube 10B to slide longitudinally by a pre -determined distance D to provide a suitable longitudinal offset D2 of the inner tube 10B below the lower end of the outer tube 10A. Thread protectors 17 of any conventional type may be already affixed to the opposed longitudinal ends of the inner tube 10B and the outer tube 10A.

[0074] The inner tube 10B is disposed at a position with reference to the outer tube 10A where its connector 10B1 is lower than the connector 10A1 for the outer tube 10A when the joint 10 is either hung off in the slips S, or lifted in vertical position by the pipe elevator or any other pipe lifting device. This arrangement allows the inner tube 10B to be connected to the inner tube already installed in the well below the drill floor. After connection of the inner tube, the outer tube 10A may be lowered for the outer tube to connect to the string below the drill floor. After the string is lowered into the well with the present nested tube joint connected to the prior existing pipe string, the pipe protector 50 is removed from the nested pipe joint 10, to make the nested pipe joint 10 ready for installation of another nested pipe joint.

[0075] Because there will be some variations in the lengths of the inner and outer pipe, and because the inner and outer string have different stress levels, the offset of the inner tube will vary during the installation process of the nested pipe string. In case the offset length should become short for the convenient operation window for the connection tools for the inner tube, short segment (“pup-joints”) for the inner pipe, readily available at the installation site, may be connected to the inner tube to bring the offset length of the inner tube back into a convenient operation window. Similarly, if the offset length would become too long for the convenient operation window for connection tools for the inner string, pup-joints for the outer pipe, readily available pup joints at the installation site, should be connected to the outer pipe to bring the offset length of the inner tube back into a convenient operation window.

[0076] FIG. 11 shows an example telescopic joint 60, which can be used in different ways, both during installation and during operation. The telescopic joint 60 can optionally be used in connection with the installation and operation.The telescopic joint 60 may be connected to the top-drive (or kelly) of a drilling or workover rig inside a suitable length of outer pipe joint / tube. The telescopic joint 60 may be used if rotation or flushing / pumping through the nested pipe string (100 in FIG. 3) would be required during the operations, in order to remove debris or to release the nester pipe string Kelly friction during installation in, for example, deep horizontal wells. The telescopic joint 60 can also be inserted as a joint of the inner tube to allow expansion and contraction of the inner tube caused by temperature variations during operation. For this purpose the telescopic joint 60 may reduce or eliminate the need for tension anchors (e.g., 20 in FIG. 3), for improved flexibility for the string design.

[0077] In light of the principles and example implementations described and illustrated herein, it will be recognized that the example implementations can be modified in arrangement and detail without departing from such principles. The foregoing discussion has focused on specific implementations, but other configurations are also contemplated. In particular, even though expressions such as in “an implementation," or the like are used herein, these phrases are meant to generally reference implementation possibilities, and are not intended to limit the disclosure to particular implementation configurations. As used herein, these terms may reference the same or different implementations that are combinable into other implementations. As a rule, any implementation referenced herein is freely combinable with any one or more of the other implementations referenced herein, and any number of features of different implementations are combinable with one another, unless indicated otherwise. Although only a few examples have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible within the scope of the described examples. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

1. A nested pipe string for use in a well, comprising:at least one nested pipe joint comprising an inner tube nested within an outer tube so as to define an annular space therebetween, the inner tube and the outer tube each comprising a connector at each longitudinal end;at least one centralizer disposed in the annular space and arranged to separate the inner tube from contact with the outer tube; anda sub connectable to the at least one nested pipe joint, the sub comprising a first connector mateable with the connector at one longitudinal end of the outer tube and a second connector mateable with the connector at a corresponding longitudinal end of the inner tube, the first and second connectors longitudinally offset from each other whereby the inner tube and the outer tube are separately accessible at a longitudinal end opposed to the sub for separately assembling the inner tube and the outer tube to the sub.

2. The string of claim 1 wherein the connector at at least one longitudinal end of the inner tube or the outer tube comprises a threaded connector.

3. The string of claim 2 wherein the first connector or the second connector on the sub each comprises a threaded connector.

4. The string of claim 1 wherein the connector at each longitudinal end of the inner tube or outer tube comprises a threaded connector.

5. The string of claim 1 wherein the inner tube and the outer tube pin and box connectos have a chemical dry surface coating to enhance the vacuum seal ability between the inner tube and the outer tube over a prolonged period of time under high temperature.

6. The string of claim 1 wherein the at least one centralizer comprises circumferentially spaced apart spheres or buttons disposed in a frame, the frame comprising an attachment to lockably engage an interior surface of the outer tube or an exterior surface of the inner tube and openings to retain the spheres or buttons, the spheres or buttons sized to fill the annular space to prevent lateral contact between the inner tube and the outer tube proximate the at least one centralizer.

7. The string of claim 6 wherein the frame comprises means for attaching the frame to the inner tube or the outer tube.

8. The string of claim 6 wherein the spheres or buttons comprise a thermally and electrically insulating material.

9. The string of claim 6 wherein the spheres or buttons can freely rotate within the containment of the frame .

10. The string of claim 1 wherein the inner tube and / or the outer tube have a surface coating to minimize radiation heat transfer between the inner tube and the outer tube. 11. The string of claim 1 wherein the annular space between the inner tube and the outer tube contains one or several layers of metal or composite materials to minimize radiation heat transfer between the inner tube and the outer tube.

12. The string of claim 10 wherein the thermally and electrically insulating material comprises ceramic.

13. The string of claim 1 wherein the sub is arranged to sealing close the annular space when assembled to the inner tube and the outer tube of the at least one nested pipe joint.

14. The string of claim 13 wherein the sub comprises an electrical insulator disposed radially between the first connector and the second connector, whereby electrical isolation is maintained between the inner tube and the outer tube.

15. The string of claim 1 further comprising at least one tension anchor disposed in at least one of a plurality of nested pipe joints, the at least one tension anchor comprising a plurality of longitudinally and circumferentially spaced apart locking pins disposed on one of either an interior surface of an outer anchor tube or an exterior surface of an inner anchor tube nested within the outer anchor tube, and a plurality of locking receivers disposed on the other of either the exterior surface of the inner anchor tube or the outer surface of the inner anchor tube, a circumferential and longitudinal spacing between adjacent locking pins and locking receivers chosen to enable longitudinal pass through of the locking pins with respect to the locking receivers and locking engagement between the locking pins and locking receivers when the inner anchor tube is rotated with respect to the outer anchor tube.

16. The string of claim 15 further comprising electrically and thermally insulating material disposed between contact surfaces of the locking pins and the locking receivers.

17. The string of claim 1 further comprising at least one tension anchor disposed in at least one of a plurality of nested pipe joints, the at least one tension anchor comprising a plurality of locking slips disposed between an interior surface of an outer anchor tube and an exterior surface of an inner anchor tube nested within the outer anchor tube wherein locking engagement between the inner and outer anchor tube occurs when the inner anchor tube is released from a controlled axial tension with respect to the outer anchor tube.

18. The string of claim 17 further comprising electrically and thermally insulating material disposed in the locking slips and / or between contact surfaces of the locking slips.

19. The string of claim 17 further comprising one or several spring element to assist engagement of thelocking slips.

20. The string of claim 17 wherein the plurality of locking slips are circumferentially spaced apart from each other to enable fluid movement between the inner anchor tube and the outer anchor tube.

21. The string of claim 1 further comprising a tubing hanger assembled to an opposed longitudinal end of the at least one nested pipe joint than the sub, the tubing hanger comprising an adapter engageable with the connector at the opposed longitudinal end of the inner tube and the outer tube, the adapter arranged to close the annular space and comprising a fluid port in fluid communication with the annular space to enable evacuation of the annular space from a side of the tubing hanger opposed to a side coupled to the adapter.

22. The string of claim 21 wherein the adapter comprises an electrical insulator arranged to electrically insulate the inner tube from the outer tube, the adapter further comprising an electrical contact making insulated electrical connection to the inner tube to enable electrical communication with the inner tube from the side of the tubing hanger opposed to the side coupled to the adapter.

23. The string of claim 1 further comprising a pipe protector engageable with one longitudinal end of the at least one nested tube joint, the pipe protector comprising an outer connector engageable with the connector at one longitudinal end of the outer tube an inner connector engageable with the connector at a same one longitudinal end of the inner tube, the pipe protector comprising a rod disposed through the outer connector and the inner connector, the rod lockably movable through the inner connector to enable the inner tube to move through the outer tube such that an opposed longitudinal end of the inner tube protrudes from a corresponding longitudinal end of the outer tube in one position.

24. The string of claim 1 further comprising a telescoping joint comprising an inner telescoping joint tube nested within an outer telescoping joint tube, the telescoping joint arranged to enable change in length of the inner tube, the telescoping joint comprising connectors on longitudinal ends of the inner and outer telescoping joint tubes arranged to connect to the connectors on a longitudinal end of the nested pipe joint.

25. A method for deploying a nested pipe string in a well, comprising:suspending a sub proximate a top of the well, the sub comprising a first connector mateable with a connector at one longitudinal end of an outer tube and a second connector mateable with a connector at a corresponding longitudinal end of an inner tube nested within the outer tube in a nested pipe joint, the first and second connectors longitudinally offset from each other whereby the inner tube and the outer tube are separately accessible at a longitudinal end opposed to the sub for separately assembling the inner tube and the outer tube to the sub, the inner tube and the outer tube separated from each other in an annular space by at least one centralizer;assembling the inner tube to the sub;assembling the outer tube to the sub; andmoving the assembled inner tube, outer tube and sub to enable assembly to a longitudinal end of the nested pipe joint of a subsequent nested pipe joint.

26. The method of claim 25 further comprising assembling a tension anchor to a longitudinal end of the nested pipe joint opposed to the longitudinal end thereof connected to the sub, the tension anchor comprising a plurality of longitudinally and circumferentially locking pins disposed on one of either an interior surface of an outer anchor tube or an exterior surface of an inner anchor tube nested within the outer anchor tube, and a plurality of locking receivers disposed on the other of either the exterior surface of the inner tube or the outer surface of the inner tube, a circumferential and longitudinal spacing between adjacent locking pins and locking receivers chosen to enable longitudinal pass through of the locking pins with respect to the locking receivers and locking engagement between the locking pins and locking receivers when the inner anchor tube is rotated with respect to the outer anchor tube.

27. The method of claim 26 further comprising setting the tension anchor by rotating the inner tube such that the locking pins are circumferentially oriented between circumferential spaces separating adjacent locking receivers, lifting the inner tube, rotating the inner tube such that the locking pins are in circumferential alignment with the locking receivers, and lowering the inner tube until the locking pins engage the locking receivers.

28. The method of claim 25 further comprising assembling a tension anchor to a longitudinal end of the nested pipe joint opposed to the longitudinal end thereof connected to the sub, the tension anchor comprising a plurality of circumferentially spaced apart locking slips to enable longitudinal pass through of the locking slips and locking engagement between the inner and outer anchor tube when the inner anchor tube is lowered with respect to the outer anchor tube.

29. The method of claim 28 further comprising setting the tension anchor by lowering the inner tube such that the locking is obtained by lifting the inner tube and lowering the inner tube until the locking slips engage between the inner and outer tubes.

30. The method of claim 25 further comprising: assembling a tubing hanger to a longitudinal end of the nested pipe joint or a longitudinally endmost one of a plurality if assembled nested pipe joints using an adapter having a fluid port in fluid communication with an annular space between the inner tube and the outer tube, the fluid port having a fluid connection on a side of the tubing hanger opposed to a side thereof connected to the nested pipe joint or longitudinally endmost nested pipe joint; and evacuating the annular space through the tubing hanger.

31. The method of claim 25 wherein the connecting the inner tube and the outer tube to the sub comprises:suspending the inner tube and the outer tube over the sub;releasing a pipe protector assembled to the inner tube and the outer tube, the pipe protector, the pipe protector comprising an outer connector engageable with the connector at one longitudinal end of the outer tube an inner connector engageable with the connector at a same one longitudinal end of the inner tube, the pipe protector comprising a rod disposed through the outer connector and the inner connector, the rod lockably movable through the inner connector to enable the inner tube to move through the outer tube such that an opposed longitudinal end of the inner tube protrudes from a corresponding longitudinal end of the outer tube in one position; andengaging the connector at the longitudinal end of the inner tube and the outer tube to corresponding ones of the connectors on the sub.

32. The method of claim 25 wherein the assembling the inner tube to the sub or the assembling the outer tube to the sub comprises making up threaded connections. 

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