CA3201901A1 - Electricity generation from post-blowdown steam assisted gravity drainage - Google Patents

Abstract

In an aspect, the present disclosures provides methods and systems for harvesting thermal energy, including for example, harvesting thermal energy from a spent oil well having an injection well borehole (IWB), comprising disposing a conduit system within the IWB
having an inner conduit within an outer conduit; connecting a first end of an inflow conduit to a proximal end of the inner conduit; connecting a second end of the inflow conduit to a cool water output of a heat exchanger (HX) system; connecting a first end of an outflow conduit to a proximal end of the outer conduit; connecting a second end of the outflow circuit to a hot water input of the HX system;
circulating water in a closed loop to harvest thermal energy from an environment surrounding the closed loop; and extracting heat from the water circulating through the HX
system.

Description

Electricity Generation from post-blowdown Steam Assisted Gravity Drainage FIELD OF THE INVENTION
[0001] The present disclosure relates generally to recovering heat from post-blowdown reservoirs from which oil was extracted through Steam Assisted Gravity Drainage (SAGD).
Further, the present disclosure relates to the conversion of the recovered heat energy into electrical energy.
BACKGROUND OF THE INVENTION

[0002] Large quantities of thermal energy remain in the ground after the blowdown of reservoirs from which oil was extracted through Steam Assisted Gravity Drainage (SAGD).
Attempts at efficiently harvesting this thermal energy have been made, but challenges remain.
Improvements are desirable.
SUMMARY OF THE INVENTION

[0003] The present disclosure relates to recovering heat from the post-blowdown Steam Assisted Gravity Drainage (SAGD) reservoirs and to the generation of electricity from that heat without fuel usage.

[0004] In the present disclosure, water is circulated in a closed loop, extracting heat from the reservoir and transporting it over into a heat exchanger to provide the heat source of an Organic Rankine Cycle (ORC) engine. The ORC engine converts thermal energy into mechanical power to generate electricity.

[0005] Several alternative wellbore configurations for heat recovery are introduced herein.
The presented systems and methods use a closed-loop circuit for water circulation for heat recovery and an ORC power plant. Some of the alternatives can maximize heat extraction but involve new drilling. One configuration utilizes the existing wells solely, and while the current well location may not be the best for heat extraction, it has the advantage of avoiding the cost of the new well drilling. While all these alternate configurations are introduced in the present disclosure, the inventors currently believe the solution that utilizes the existing wells is the most economical solution for most applications.

[0006] Nevertheless, mathematical modelling is required to simulate alternate configurations to choose the optimum solution for each specific case. All the calculations and simulations herein use a concentric conduit arrangement located in an existing steam injection well. As will be understood by the skilled worker, other conduit arrangements are to be considered within the scope of the present disclosure. For example, arrangements where conduits that are Date Recue/Date Received 2023-05-17 not concentrically centred with each other may be used. Further, arrangements such as conduits with non-circular cross-sections may also be used.

[0007] Embodiments in accordance with the present disclosure as described herein for SAGD may be used in other thermal projects, such as Cyclic Steam Stimulation (CSS) and steam flood projects after the completion of their life cycle to recover heat and produce electricity.

[0008] In the present disclosure, water (or any other suitable fluid) is circulated in a closed loop, extracting heat from the reservoir and transporting the extracted heat to a heat exchanger that can be connected, in some embodiments, to an Organic Rankine Cycle (ORC) engine. The water (or other fluid) containing the extracted heat acts as the heat source for the ORC engine.
The ORC converts thermal energy into mechanical energy, which is used to turn a generator that generates electricity.
BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:

[0010] Fig. 1A shows a side view of an embodiment of a heat recovery system in accordance with the present disclosure.

[0011] Fig. 1B shows a side view of a concentric conduit arrangement in accordance with the present disclosure.

[0012] Fig. 1C shows a cross-section view of the concentric conduit arrangement of Fig.
1B.

[0013] Fig. 2 shows another embodiment of the present disclosure where several concentric conduit arrangements located at several boreholes are operationally connected to a heat exchanger, ORC engine and electrical generator.

[0014] Fig. 3 shows schematics of alternatives of heat recovery configurations in accordance with the present disclosure.

[0015] Fig. 4 shows an example of a pie chart representing the percentage of the heat produced, lost and remaining in a reservoir example, upon completing the SAGD
blowdown.

[0016] Fig. 5A shows an example of a percentage pie chart of the heat loss to the surrounding strata, recoverable heat and the heat remaining in a reservoir, after the heat recovery for a specific case.

[0017] Fig. 5B shows an example of an energy pie chart representing the total heat remaining after the completion of the SAGD blowdown.

[0018] Fig. 6A shows an example of the inflowing water temperature profile along the inner conduit and the water temperature profile along the outer conduit.

Date Recue/Date Received 2023-05-17

[0019] Fig. 6B shows an example of a concentric conduit arrangement.

[0020] Figs. 7A and 7B shows two examples of vacuum-insulated tubing used for an outflow conduit, an inflow conduit, and an inner conduit, in accordance with the present disclosure.

[0021] Figs. 8A-8G show different examples of branch connections in accordance with the present disclosure.

[0022] Figs. 9A and 9B show Y connections in accordance with the present disclosure.

[0023] Fig. 10 shows an example of a flowchart of a method in accordance with the present disclosure.

[0024] Fig. 11A and 11B show plots of a system average temperature over time as well as a water inflow-outflow temperature for two different lengths of Vacuum Insulated Tubing, for a typical SAGD, based on numerical simulation.

[0025] Figs. 12A and 12B show graphs of a payback period in accordance with an embodiment of the present disclosure.

[0026] Fig. 13 shows an example graph of the cost per MWh based on average data from BNEF, IRENA, and Lazard [6-8].
DETAILED DESCRIPTION

[0027] According to an aspect, the present disclosure provides a method of harvesting thermal energy from a spent oil well, the spent oil well having an injection well borehole (IWB), the method comprising: forming a conduit system in the IWB, the forming of the conduit system comprising: disposing a conduit-in-conduit arrangement in the IWB, the conduit-in-conduit arrangement having an inner conduit and an outer conduit, the inner conduit being in the outer conduit, the outer conduit having an open proximal end and a sealed distal end, the inner conduit having an open proximal end and an open distal end; connecting a first end of an inflow conduit to the proximal end of the inner conduit; connecting a second end of the inflow conduit to a cool water output of a heat exchanger (HX) system; connecting a first end of an outflow conduit to the proximal end of the outer conduit; connecting a second end of the outflow circuit to a hot water input of the HX system, the inflow conduit and the outflow conduit being outside of each other;
circulating water in a closed loop, the closed loop comprising, in sequence, the cool water output of the HX system, the inflow conduit, the inner conduit, the outer conduit, the outflow conduit, the hot water input of the HX system and the HX system, the water circulating in the closed loop to harvest thermal energy from an environment surrounding the closed loop; and extracting heat from the water circulating through the HX system.

[0028] In an example embodiment, disposing the conduit-in-conduit arrangement in the IWB includes disposing of a conduit-in-conduit arrangement that includes thermal insulation Date Recue/Date Received 2023-05-17 surrounding the inner conduit for at least a portion of a length of the inner conduit, starting from the proximal end of the inner conduit.

[0029] In an example embodiment, at least one of the inner conduits and the outer conduit is a thermally insulated conduit.

[0030] In an example embodiment, connecting the first end of the inflow conduit to the proximal end of the inner conduit and connecting the first end of the outflow conduit to the outer conduit, includes using a wye connector or a Y connector to connect the first end of the inflow conduit to the proximal end of the inner conduit and connect the first end of the outflow conduit to outer conduit.

[0031] In an example embodiment, the Y connector or the wye connector may be installed at: a heel of the conduit-in-conduit arrangement, or at a higher level within a vertical well portion of the spent oil well, or at a ground surface level.

[0032] In an example embodiment, the method may further include incorporating thermal insulation in at least one of the inner conduit and the outer conduit, the thermal insulation selected from a group consisting of foam insulation, vacuum insulation, insulation by coating material or any combination thereof.

[0033] In an example embodiment, the method may further include determining a number of injection well boreholes for use in harvesting thermal energy, the determination based on: a total number of wells in a well-pad used for heat recovery, dimensions of the well-pad, left-over heat from post-blowdown reservoirs, and an economic factor.

[0034] In an example embodiment, the conduit-in-conduit arrangement comprises a concentric conduit arrangement.

[0035] According to an aspect, the present disclosure provides a power plant or system to harvest thermal energy from a spent oil well, the spent oil well having an injection well borehole (IWB), the power plant or system comprising: a heat exchanger (HX) having a hot water input and a cool water output; a conduit system formed in the IWB, the conduit system comprising a conduit-in-conduit arrangement, the conduit-in-conduit arrangement having an inner conduit and an outer conduit, the inner conduit being in the outer conduit, the outer conduit having an open proximal end and a sealed distal end, the inner conduit having a proximal end and a distal end; an inflow conduit having a first end and a second end, the first end of the inflow conduit being connected to the proximal end of the inner conduit, the second end of the inflow conduit being connected to the cool water output of the HX; and an outflow conduit having a first end and a second end, the first end of the outflow conduit being connected to the open proximal end of the outer conduit, the second end of the outflow conduit being connected to the hot water input of the HX, wherein: the Date Recue/Date Received 2023-05-17 HX, the conduit system, the inflow conduit and the outflow conduit define a closed loop configured to have, in operation, water circulating therein from, in sequence, the cool water output of the HX, the inflow conduit, the inner conduit, the outer conduit, the outflow conduit, the hot water input of the HX and the HX, the water circulating in the closed loop to harvest thermal energy from an environment surrounding the closed loop and to provide the harvested thermal energy to the HX.

[0036] In an example embodiment, the power plant or system may further include a pump configured to pump the water in the closed loop.

[0037] In an example embodiment, the inflow conduit and the outflow conduit include thermal insulation.

[0038] In an example embodiment, the inner conduit includes thermal insulation formed along a portion of a length of the inner conduit, beginning at the proximal end of the inner conduit.

[0039] In an example embodiment, the conduit-in-conduit arrangement is a concentric conduit arrangement.

[0040] In an example embodiment, the power plant or system may further include a wye connector or a Y connector connecting the inflow conduit to the inner conduit and connecting the outflow conduit to the outer conduit.

[0041] In an example embodiment, the power plant or system may further include an electricity generator system operationally connected to the HX.

[0042] In an example embodiment, the electricity generator system comprises an Organic Rankine cycle (ORC) engine configured to receive thermal energy from the HX
and to convert the thermal energy into mechanical energy.

[0043] In an example embodiment, the electricity generator system further comprises a generator coupled to the ORC engine to receive the mechanical energy and to generate electricity.

[0044] In an aspect, the systems and methods disclosed herein provide for recovering heat from post-blowdown SAGD reservoirs for use in generating electricity, in particular without using fuel. The system and methods disclosed herein, for example, implement a closed loop system, providing advantages over open-loop systems [14, 15]. Such open-loop systems generally invite additional complexity for treating water in order to separate bitumen/emulsion before re-injection, inducing additional costs and adverse environmental effects. Conversely, embodiments of a closed loop system as disclosed herein do not suffer from such drawbacks, and rather provide lower cost and more environmentally friendly solutions that may be easily rearranged to return to SAGD or combined with other processes and technologies.

[0045] Heat Recovery Using Existing Wells Date Recue/Date Received 2023-05-17

[0046] In the following example, water is circulated within a double tube installed inside the SAGD injection well screen. Hot water flows out from the annulus, defined by the space between the inner tube (inner conduit) and the outer tube (outer conduit) and enters a heat exchanger providing the ORC's heat source. After the heat transfer in the heat exchanger, cooled water returns to the well through the inner conduit. The inner tubing (inner conduit) extends towards the toe of the horizontal well and is connected to the annulus to form the closed circulation circuit. The water in the annular flow receives enough heat to raise its temperature close to the reservoir temperature before returning to the heat exchanger.

[0047] Fig. 1A shows a side view of an embodiment of a heat recovery system 100 in accordance with the present disclosure. The heat recovery system 100 has a concentric conduit arrangement 102 located (formed) in a borehole 104 previously used for steam injection.
Referring to Figs. 1B and 1C, the concentric conduit arrangement 102 has an inner conduit 20 and an outer conduit 22. A well screen 24 separates the concentric conduit arrangement from the borehole 104. The borehole 104 is formed in oil sand 26.

[0048] Referring back to Fig. 1A and to Figs. 1B and 1C, the concentric conduit arrangement 102 has a toe or toe section 106 defined by the end 108 of the outer conduit 22. The end 108 includes a stop that seals the outer conduit 22 from its outside environment. The inner conduit 22 has an open end 110 spaced apart from the end 108 of the outer conduit 22. The concentric conduit arrangement 102 also has a heel or heel section 112.

[0049] As shown in Fig. 1A, the inner conduit 20 is connected to an inflow conduit 28, and the outer conduit 22 is connected to an outflow conduit 30. The inflow conduit 28 is connected to pump 32, which is connected to an output of the heat exchanger 34. The outflow conduit 30 is connected to an input of heat exchanger 34.

[0050] The pump 32 pumps water down the inflow conduit 28. The water propagates through the inflow conduit 28 and into and through the inner conduit 20. The water subsequently exits the inner conduit 20 and then flows through the outer conduit 22 and into and through the outflow conduit 30 to subsequently flow into the heat exchanger 34.

[0051] As the water propagates through the inflow conduit 28, the inner conduit 20, the outer conduit 20 and the outflow conduit 30, it exchanges heat with its surrounding environment.
As the oil sand 26 contains heat left there by a previously conducted SAGD
process, the water propagating through the outer conduit 22 will be heated by the surrounding oil sand 26.

[0052] The heat exchanger 34 provides the heat extracted from the heated water to an ORC engine 36, which powers a generator 38.

Date Recue/Date Received 2023-05-17

[0053] Embodiments in accordance with the present disclosure may include operationally connecting the pump 32, the heat exchanger 34, the ORC engine 36 and the generator 38 to more than one concentric conduit arrangement 102 located in one borehole 104.
Fig. 2 shows another embodiment of the present disclosure where several concentric conduit arrangements 102 located in several boreholes 104 are operationally connected to the same heat exchanger 34, ORC engine 36 and generator 38.

[0054] Heat Recovery Using New Wells

[0055] Fig. 3 shows the schematics of alternatives of heat recovery configurations from a well pad that may be applicable depending on the well-pad dimensions and the number of well pairs. The alternatives can be divided into three different categories:
1. Tubing is installed inside the current injection well that is extended to the surface to form a recirculation loop ABCDEF as shown in Fig. 3. To form such a tubing loop, it is required to drill a vertical well to extend the toe of the injection well to the surface.
2. Several new wells are drilled parallel to and above the injection wells, close to the centroid of the heating chamber, to maximize the extracted fluid temperature. The tubing is installed inside these new wells. Tubing may either be concentric, as described before, such that the inflow and outflow are accomplished from one side of the well or be simple tubing extended to the surface to form a loop like the AiBiCiDiEiFi loop, as shown in Fig.
3.
3. Several new wells are drilled perpendicular to and above the injection wells, close to the centroid of the heat chamber, to maximize the extracted fluid temperature. The tubing is installed inside these wells and may either be concentric, as described before, such that the inflow and outflow are accomplished from one side of the well, or it can be simple tubing. In the latter case, the well is extended to the surface from the toe to form a loop similar to the A2B2C2D2E2F2 loop in Fig. 3.

[0056] In some scenarios, it may be easier to drill such wells together with the SAGD wells before the SAGD process is started to reduce cost. These wells may be used during the SAGD
process for monitoring purposes and then be used to accommodate the tubing required for the recirculation of fluid in the post-SAGD heat recovery for electricity generation.

[0057] Power Plant Technology

[0058] Organic Rankine Cycle technology seems advantageous since the heat recovered from the post-blowdown SAGD is not sufficient to run a steam water-based Rankine Vapour Cycle. The ORC can be an excellent solution to recover waste heat energy from thermal Date Recue/Date Received 2023-05-17 processes for electricity generation [1]. The low-temperature heat is converted into useful work using the ORC, and the work is converted into electricity by an electrical generator.

[0059] Another possible waste heat recovery technology for electricity generation is the thermoelectric generation (TEG). However, this technology is currently too expensive and still requires further advancement. Studies have shown that the instantaneous efficiency of the TEG
system could reach about 6.5%. [2]. Therefore, ORC is the preferred technology at the moment as it is a more efficient and low-cost technology. However, TEG or other technologies may be developed in the future which can be used for electricity generation from thermal well heat recovery.

[0060] Selection of the most suitable working fluid is an important step when designing an ORC. Fluids with high critical temperatures or high boiling points, such as toluene and silicone oils, are adapted for high-temperature heat sources. Hydrocarbons such as Pentanes, benzene, butanes and cryogens are good candidates for moderate and low temperatures.
Fluids with a high density in the vapour phase are advisable to reduce vapour turbine and heat exchanger sizes.

[0061] Recoverable Thermal Energy from SAGD

[0062] Numerical and analytical calculations were carried out for a specific representative case for an existing SAGD well. The estimates indicate that over 2.3 million GJ of heat energy is injected per well pair over 10 years of SAGD operation. Out of this amount, over 700,000 GJ heat remains inside the reservoir after completing the SAGD blowdown for each well pair. For a SAGD
pad consisting of 10 well pairs, the post-SAGD stored energy is greater than 7 million GJ. Fig. 4 is a pie chart representing the percentage of the heat produced, lost and remaining in the reservoir upon completing the SAGD blowdown.

[0063] Fig. 5A shows the percentage of the heat loss to the surrounding strata, recoverable heat and the heat remaining in the reservoir after the heat recovery for the specific case we studied. As will be described below, and as shown in Fig. 5B, from the total heat remaining in the reservoir after the completion of SAGD blowdown, about 33 percent of the heat (about 2.31 million GJ) can be extracted in ten years before the produced water temperature falls below 80 degrees. One pad recoverable electrical energy (ORC, average thermal efficiency 10%) =230,000 GJ or 64,100 MWh. One well pad equivalent electrical energy revenue (considering 18% heat loss in the wellbore) at a rate of $0.13/kWh is about CAD 6.83 million.

[0064] Fig. 6A shows the inflowing water temperature profile (Ta) along the inner conduit 20 and the water temperature profile (Tt) along the outer conduit 22, in the annulus defined by the space between the inner conduit 20 and the outer conduit 22.

Date Recue/Date Received 2023-05-17

[0065] Fig. 6B relates to the variation of water temperature in the concentric conduit arrangement 102. The performance of the concentric conduit arrangement 102 in the horizontal well can be seen as satisfactory as the temperature is nearly uniform along the well. The reservoir temperature was assumed to be 185 C. Results indicate a quick temperature increase near the heel and a constant temperature farther away. The results are only shown in the first 140 meters of the well, as the temperature beyond this point is nearly constant. Fig. 6A
shows a quick temperature rise within the first 60 meters of the well. The return annular flow temperature drops about 30 degrees when exposed to the cooler inflow at the heel. However, the drop in temperature of the water is undesirable from the ORC engine performance perspective.

[0066] To mitigate annular flow temperature drops due to the cooler inflow at the heel, a length Lo (for example, Lo = 100 m or more) of the inflow tube (inner conduit 20) can be insulated using any suitable insulation material 40 such as, for example, Vacuum Insulated Tubing (VIT), as shown in Figs. 7A and 7B. Also shown in Fig. 7A is the inflow conduit 28 and the outflow conduit 30 within the vertical well are separated as well as insulated to minimize heat loss. In this arrangement, the return annular flow temperature drops due to the cooler inflow when travelling from A to B, i.e., before approaching the insulated part of the inner tube.
Then its temperature will increase to about the reservoir temperature within the distance B to C. In conditions where installing a Y or Wye pipe fitting due to well geometry, constraint is not applicable at the heel, a Y
or Wye pipe fitting can be used at a higher elevation within the vertical well or at the ground surface, as shown in Fig 7B. In that case, to mitigate annular flow temperature drops in the vertical well, the outer conduit can be insulated using any suitable material

[0067] Considering a typical SAGD well and using CMG STARS software, many simulation results are collected to evaluate the role of the circulated water rate, inflow water temperature and the inner conduit insulated length on inflow and outflow water temperature profile as well as the reservoir temperature and pressure change. The simulation results revealed that the insulated length Lo has a substantial effect on both the temperature variation along the well, as well as the outflow water temperature and hence the heat recovery for power generation out of the well pad. The longer insulated length provides a more uniform temperature distribution within the reservoir along the well and hence a longer well-pad lifespan for power generation.
Taking Lo equal to about the total length of the horizontal well yields the best heat flow, as the reservoir cooling starts from the toe and gradually proceeds to the heel. Such an arrangement makes it possible to maximize the overall efficiency of the process as well as the well-pad heat lifespan for electricity generation. However, by increasing the length Lo, the cost will also increase, hence, requiring optimization work to determine the best length for the project at hand. Therefore, Date Recue/Date Received 2023-05-17 the piping system can be designed to maximize the ORC heat source temperature during the lifespan of the well pad while also enhancing the thermal efficiency of the power plant.

[0068] Tubing Material

[0069] There are several options for materials to balance cost and performance. The following describes some of these options.

[0070] Hot-dip Galvanized Steel

[0071] According to American Galvanizers Association [3], galvanized coatings perform well under continuous exposure to temperatures up to 392 F (200 C). Exposure to temperatures above this level can cause the outer free zinc layer to peel from the underlying zinc-iron alloy layer. However, the remaining zinc-iron alloy layer will provide good corrosion resistance and will continue to protect the steel for a long time, depending on its thickness.
Hydronic heating or cooling systems employ corrosion inhibitors and perhaps biocides. It seems using corrosion inhibitors in the flow stream for this technology is cost-effective as the system is a closed loop;
hence, small inhibitor replenishment over time should suffice.

[0072] Aluminized Steel

[0073] Aluminized steel ensures a tight metallurgical bond between the steel sheet and its aluminum coating, producing a material with a unique combination of properties possessed neither by steel nor by aluminum alone. Aluminized steel shows better behavior against corrosion [4, 5] and protects the base steel properties for temperatures lower than 800 C (1,470 F).

[0074] At low temperatures and good water treatment, galvanized steel and aluminized steel pipes have an average life expectancy of 40 to 50 years. It is expected that the galvanized/
aluminized steel pipes at 200 C and proper water treatment can last for over 20 years. The combination of steel pipe and aluminum heat exchangers requires a very narrow pH range in hydronic systems, typically 8 to 8.5.

[0075] Water De-airing and Treatment

[0076] In some embodiments, the system can be a typical closed-loop heat transfer system with continuous water circulation sealed from the atmosphere. The mineral content and dissolved air can accumulate if not properly treated. An air separator may be installed in the hydraulic circuit to remove all of the air that may be in the water. Further, any minor loss of water over time is made up with new water. The corrosion of iron should be a self-limiting reaction proceeding to equilibrium and then slowing down to an almost immeasurable rate. This slowing down of the corrosion rate is why closed-loop heating and cooling systems can be constructed of steel and iron and have a good service life. However, in heat transfer systems, the corrosion problem is Date Recue/Date Received 2023-05-17 worse in the presence of oxygen because the hotter the system, the more rapid the oxidation process.

[0077] Beyond selecting metal alloy system components that resist oxidation, various treatments can slow the corrosion process. These include, for example, coatings on wetted elements of the conduits (pipes) to create an oxide barrier, placement of a corrosion-resistant lining and use of a "sacrificial element" such as a zinc rod. Some water treatments are designed to accelerate an oxide layer buildup to protect the metal surfaces from corrosion.

[0078] Tubing Insulation

[0079] It is essential to insulate the inflow conduit 28 and 20 and the outflow conduit 30 to prevent heat loss from the heated water when travelling in the wellbore towards the surface. This is to ensure the vast majority of the recovered heat is delivered to the power plant. There are two insulation solutions: (1) foam insulation, (2) vacuum insulation, and (3) insulation by coating material. Instead of using insulation, composite tubing with low thermal conductivity could be used for inflow conduit 20.

[0080] Foam Insulation

[0081] For a pipe (conduit) having an outer diameter of 4 inches, a fluid temperature at the entry of 150 C, an ambient temperature of 10 C and an insulation thermal conductivity of 0.04 W m-1 K-1, table 1 shows the temperature versus distance (m) for different insulation thicknesses:
Table 1: Temperature loss in the return water Insulation n ThichneN-5 " 50 100 150 200 250 300 2 inch 150.0000 149.6713 149.3427 149.0140 148_6E153 148_3587 148.0280 linch 150.0000 149.3989 148.7978 148.1966 147.5955 1469944 146.3933 0.5 inch 150.0000 148 7482 147_4964 146_2447 144_9929 143.741.1 142_4893

[0082] Vacuum Insulated Tubing

[0083] Vacuum Insulated Tubing (VIT) is a possible solution to maintaining an insulation system to control heat flux to the vertical well. The VIT substantially improves thermal performance by having conductivity values in a range much lower than most insulation materials.

[0084] K-values expressed W/m K units are rated into different categories, for example:
dependent on their insulation values:
= "A" = 0.035 ¨ 0.046, = "B" = 0.023 ¨ 0.035, = "C" = 0.012 ¨ 0.023, Date Recue/Date Received 2023-05-17 = "D" = 0.0035 ¨ 0.0116, = "E" = 0.0012 ¨ 0.0035.

[0085] It is possible to purchase tubes and weld them to provide the tubing and then apply a vacuum to the annulus region at a specified level (for example, categories A
¨ E above). To achieve higher categories/ levels, more powerful equipment (vacuum pump and better sealing) is needed. In addition, it takes a longer time to achieve higher levels/categories of insulation. The "A" category/ level is much easier to achieve than the category "D" or "E".

[0086] Insulation by coating material

[0087] Since VIT is expensive, coating tubes with low thermal conductivity materials are a possible solution. The most important parameter to consider here is the working temperature of the material as well as its lifespan. For example, PTFE
(PolyTetraFluoroEthylene) is a good candidate for this application as PTFE has a high operating temperature (260 C/500 F), very low coefficient of friction, good abrasion and chemical resistance.

[0088] Insulation by low thermal conductivity composite tubing

[0089] The composite pipes are being used in the oil and gas industry, and it is expected to grow in the coming years by increasing demand for cost-effective pipeline solutions in different industries. An alternative insulation is to use customized composite tubing with low thermal conductivity but suitable strength, stiffness, abrasion and chemical resistance within the expected working conditions.

[0090] Pump Specifications

[0091] There are different options for hot water recirculating pumps in the market. Hot-water Centrifugal Pumps are manufactured for various applications. Some pumps last for 10 to 15 years of continuous operation, as they are made of high-quality materials.
The most important parameter to consider in this technology is the sealing at high temperatures.
The quality pump manufacturer usually uses isolator technology combined with the heat exchanger, which allows the seal cavity to reach a maximum temperature of, say, 77 C. In contrast, the process temperature can go as high as 204 C. This lower seal temperature significantly increases the seal life, which means less downtime for the end user. The selection of the specific model will depend upon the pump characteristics (e.g., the impeller Trim) and available power supply. It is estimated that a high-quality pump for such an application (see Appendix A of the detailed description) costs less than CAD 8,000.

[0092] Y and Wye pipe fittings manufacturing processes

[0093] To enhance the thermal efficiency of the power plant, it is important to keep the heat source temperature as high as possible. To increase the heat source temperature (the Date Recue/Date Received 2023-05-17 temperature of the water as it reaches the heat exchanger/ORC engine), it is important to reduce the heat loss of the returning fluid to the surrounding environment. Referring to Figs. 7A and 7B, an effective solution to this problem is to convert concentric flow in the concentric conduit arrangement 102 to two flows in the two detached conduits (inflow conduit 28, outflow conduit 30) at the heel 112. This reduces the heat transfer between the hot outflow and the cooler inflow fluids, as well as the hot outflow fluid and the cooler environment. In addition, it is important to insulate a sufficient length of the inner tubing (inner conduit 20) near the heel portion 112 of the horizontal well, as shown in Figure 7. A proper fitting is required to connect the detached tubing (inflow conduit 28, outflow conduit 30) to the concentric tubing (concentric conduit arrangement 102).

[0094] Figs. 8A-G show different types of branch connections. Fig. 8A
shows a wye fitting, Fig. 8B a combination wye fitting, Fig. 8C an assembly using a wye fitting, Fig. 8D an assembly using a combination wye fitting, Fig. 8E an assembly using a wye fitting of unequal branch diameter, Fig. 8F a concentric tubing to concentric tubing arrangement wye, and Fig. 8G a concentric tubing to concentric tubing arrangement combination wye.

[0095] Fig. 9A shows a Y-fitting. Fig. 9B shows an assembly using a Y-fitting.

[0096] The piping/conduit separation can be carried out using a wye fitting, as shown in Figures 8A and 8B, or by fabricating a true Y, as shown in Figure 9A.

[0097] The branch line of the pipe wyes is angled to reduce friction, which could hamper the flow (Figs. 8A and 8C). The pipe connection angle can be selected to match the geometrical constraints. A combined wye fitting (Figs. 8B and 8D) is more desirable than the simple wye fitting due to less head loss and water hammer in this fitting. Figure 8E shows a special wye fitting where the branch pipe diameter is different from that of the main pipe (header) diameter. Concentric tubing to concentric tubing wye pipe fitting arrangement is also shown in Figures 8F and 8G.
These arrangements may be used for insulation purposes. This is done by welding one metal disc at the top section and one metal disc at the bottom section of each branch to isolate the space between the inner and outer tubing. The air inside the annular region is vacuumed to a desirable range by a vacuum pump. For example, a range that meets the vacuum category "E" defined above provides great insulation; however, achieving a vacuum that meets this category requires a powerful vacuum pump and will cost more. It is up to the design engineer to choose an optimum range. Similarly, by extending the two-outer tubing of the Y pipe fitting (see Figure 9B), two concentric tubings are formed, which makes them possible to be used for insulation purposes.

[0098] Various manufacturing processes can be used to manufacture wye pipe fittings.
The choice of the manufacturing process is guided by the specifications of the wye fittings, Date Recue/Date Received 2023-05-17 including the materials, sizes, shapes, standards and any special properties.
Similar to other pipe fittings, wye fittings may be welded or threaded to other components. As sizes and pressures increase, they are often welded in place by either butt-weld or socket-weld methods.

[0099] Cutting seamless tubing, joining by welding and heat treatment

[00100] For a low number of products, branch connections in equal-diameter pipes can easily be fabricated by cutting and joining seamless tubing. The cutting border can be determined by locating the centerline of the intersection on the header. The geometrical intersection of the branch and header can be obtained and implemented by accurate cutting of the branch and header (Figure 8A). The branch and header can be joined by welding.

[00101] Fabrication of combined wye fitting is more difficult due to the more complex cutting intersection of straight and bent pipes and joining the two parts by welding (Figure 8B).

[00102] For the fabrication of Y-fittings, a full-sized drawing of the intersection should be made (Figure 8A). Point "a" is the intersection of the center lines of the three pipes.
Connecting point "a" to the intersections of the pipe walls at "b," "c," and "d" will locate the cutting line. Suitable beveling is required for successful welding. It will be important to heat-treat the welded components in a controlled process in which a material that has been welded is reheated to a temperature below its lower critical transformation temperature. Then it is held at that temperature for a specified amount of time for optimum mechanical properties.

[00103] Hot or cold metal-forming processes

[00104] For smaller pipe diameters, pipe fittings, including Y pipe fittings, are usually hot forged. Hot forming is a plastic deformation of a metal at a temperature and strain rate such that recrystallization occurs simultaneously with deformation. Hot forging provides numerous advantages, including higher surface profile tolerance, reduced metal spring-back effect, optimum yield strength, low hardness and high ductility. Pipe fittings are often threaded to match threads on the ends of the pipe. For larger diameter pipe/fittings, other forming processes, such as hot extrusion forming for heavy wall thickness and hydraulic bulge forming for light wall thickness fittings, can be employed. Large steel pipe fittings are often extruded or drawn over a mandrel from a welded or seamless pipe. Hot forming results in a product that is stronger than cast or machined metal parts. Thus, hot forming technology has a special place in producing parts of superior mechanical properties with minimum waste of material. Cold forming in nature is limited by low values of deformation. However, this process would be able to deliver products which are precise in tolerances with minimal or no secondary processing. A high number of metal products employ a combination of hot and cold forming to ensure the consistency of the batch.

Date Recue/Date Received 2023-05-17

[00105] Die casting of Y pipe fitting

[00106] Steel pipefittings, including the Y pipefittings, can be produced in both casting and forging methods. Considering the high tooling cost of forging, casting is the preferred method when the required quantity is small. Steel casting could also be used to produce different types of pipefittings in low quantities. Stainless steel casting has the features of high corrosion and wear resistance. It also provides excellent machinability. Stainless steel casting is a cost-effective method for small volume production of complex parts, including Y
pipefittings.

[00107] Installation of the tubing arrangement

[00108] Example of a sequence of installation of the tubing arrangement as further illustrated in Fig. 10:
1. Run the concentric tubing assembly through the sand control screen (e.g., slotted liner) already installed in the horizontal well.
2. Locate the packer on the outer tubing before connecting the concentric tubing to the Y
pipe fitting.
3. Enter the inner tubing into the entry section of the Y pipe fitting and connect the outer pipe to that of the outer surface of the Y pipe fitting.
4. Locate Packers 1 and 2 as shown in Figures 8C-8G and 9B.
5. Continue assembling the two branches of the inflow and outflow simultaneously while pushing the whole tubing arrangement forward into the well.
6. After that, the whole assembly is located in the well, and the packer on the outer pipe at the heel is fixed.
7. The tubing assembly is installed in all the wells in the well pad.
8. The outflow tubing is connected to the inflow of Manifold 1 (hot manifold).
9. The inflow tubing is connected to the outflow of Manifold 2 (warm manifold).
10. The outflow from the hot manifold is connected to the inflow of the heat exchanger providing the ORC heat source.
11. The outflow from the heat exchanger is connected to the pump inlet, and the outlet of the pump is connected to the inflow of the warm manifold to form a hydraulic circuit, as shown in Figure 1.
12. The hydraulic circuit should also be equipped with a back-pressure regulator, safety relief valves and air bleeding equipment.

[00109] Appendix A: Mathematical System Analysis

[00110] This section contains the results of mathematical calculations to support the estimates presented in the previous section.
Date Recue/Date Received 2023-05-17

[00111] Post-SAGD Extractable Heat

[00112] The total extractable heat consists of the total heat remaining in the reservoir after the SAGD completion minus the heat loss from the reservoir boundaries during the heat recovery and the unrecoverable heat in the reservoir at low temperatures.

[00113] Fig. 11A shows an example of the system's average temperature overtime.
As seen, the reservoir temperature drops over time depending on the rate of heat extraction and is somewhat exponential.

[00114] Fig. 11B shows the water inflow-outflow temperature for two different lengths of Vacuum Insulated Tubing used for enhancing the outflow temperature (A- The total length of the inner tube = 900 m and B- partial length of the inner tube insulation =300 m) for a typical SAGD and 144 m3/day flow rate based on numerical simulation.
Extractable heat in 20 years of extraction with a rate of 216 m3/day is estimated to be about 19% of that of the total post-SAGD energy. The assessment considers a temperature difference of 40 deg C in water circulation, when using full-length VIT for the inner conduit before the reservoir temperature drop below 80 C.

[00115] Tubing Pressure Drops and Pump Power Calculations

[00116] Considering a typical SAGD horizontal well with a 1,000 m length at 300 m depth, the inner and outer tube length is estimated to be 1,350 m. Tables Al and A2 show the calculated pressure drops and the corresponding power consumption in the inner tubing and annulus for a flow rate of 6 m3/hr (per well), water viscosity of 0.15 cp at 180 C or 0.23 cp at 120 C, and an absolute roughness of 0.4 mm.

[00117] Table Al: Pipe pressure drops and power consumption in the inner tubing.
Diameter Flow Reynolds Pressure Power (mm) velocity number drops consumption m/s (kPa) kW
63.5 0.53 145037 98.31 0.164 69.8 0.43 131851 59.81 0.099 76.2 0.37 120547 37.53 0.0626 101.6 0.21 90648 8.11 0.0135

[00118] Table A2: Pipe pressure drops and power consumption in the annulus Diameter Reynolds Pressure Power (mm) number drops consumption Date Recue/Date Received 2023-05-17 Di Do Flow (kPa) kW
velocity m/s 63.5 101.6 0.34 85534 80.07 0.1334 76.2 101.6 0.47 79425 266.14 0.4436 69.5 114.3 0.26 76686 38.54 0.0643 82.5 127 0.23 67391 29.65 0.0494 101.6 152.4 0.16 55597 13.17 0.0219 Pump power consumption: Pp = 36-60130 Electrical motor power: Pm =
)173 77m For tube (D=76.2 mm), annulus (Di=82.5, Do=127 mm), the pump power to feed 10 wells (60 m3/hr per pad) is estimated to be Pp= 1.12 kW. The electrical motor power is estimated to be Pm=2 kW. This power to circulate 144 m3/hr of water in a pad of 10 wells is calculated to be about 10 kW.

[00119] Appendix B: Project Economics

[00120] A typical budget for SAGD heat recovery project for electricity generation is presented in Table B1.

[00121] Table B1: Estimated expenditure and depreciation for power generation from a pad for two different cases Type CASE A1:10 Years CASE B2: 20 Years heat extraction, 60 heat extraction, m3/hr from 10 wells 45 m3/hr from 5 per pad wells per pad Site preparation $10K $10K
Civil and Building structural construction Mechanical Hydraulic circuit $2200K/241100K $1100K
equipment components supplies (tubing etc.)3 Two 2MVVth-ORC 924K x (10/30) 924K x (20/30) generators 4308K 4586K

Date Recue/Date Received 2023-05-17 Capital (Lifespan 30 cost years) Electrical Included in the - -instrumentation generator price and control Engineering $20K $20K
Project indirect Labor and $140K $70K
costs material Start-up and $30K $20K
commissioning Preliminary $20K $20K
Other costs feasibility and engineering studies Insurance costs $40K $30K
Electrical $100K/5=20K $100K/5420K
interconnection to a nearby electrical transmission system4 Maintenance cost ORC module 20x$10K4200K 20x$20K4400K
(Per one pad lifespan "20 maintenance years") Other 10x$6K460K 20x$6K4120K
maintenance Operation cost5 Salary 10x280K/84350K 20x280K/104560K
(Per one pad lifespan "20 Vehicle 10x$30K/8438K
20x$30k/10460K
years") expenditure and depreciation Total $2336K $3046K
lestimated well-pad lifespan= 10 years 2estimated well-pad lifespan= 20 years 3 The number of wells in a well pad for heat recovery for case A is considered to be 10 out of 10 wells and for the case B this is 5 out of 10 wells.

Date Recue/Date Received 2023-05-17 4Electricity generated from 5 pads uses one transformer for interconnection 50ne operator and one qualified engineer operate 8 to10 sites

[00122] Tubing Cost Estimates

[00123] Below are estimated costs in today's market.

[00124] Considering galvanized steel pipe, the total pipe price per well pad is estimated to be about $1,100K.

[00125] As mentioned, the galvanized/ aluminized steel pipes at 200 C and proper water treatment last over 20 years. For a flow rate of 9 m3/hr, this time roughly corresponds to a post-SAGD reservoir heat recovery lifespan. Hence such types of steel pipes are favourable for the proposed technology.

[00126] Power-plant Cost

[00127] Currently, ORCs are the best technical solution for generating electricity from low-medium temperature heat sources of limited capacity. An average price of a 4MW
thermal power plant with a lifespan of 30 years in today's price considering a 5% duty rate for import to Canada, is about $924k.

[00128] Investigators working in ORC have considered many different working fluids.
Depending on the working fluid, a higher degree of superheat may increase isentropic efficiency.
When superheat is increased, the pressure ratio increases slightly for most fluids. The results showed that when the heat source temperature is between 80-200 C, the system efficiency varies somewhat linearly between 6.5 to 15 percent [11-13]. In this analysis, two 2 MWth-ORC
power plant (one high temperature module and one low temperature module) considered to be appropriate that can be used in series such that the outflow water from the first power plant heat exchanger flow into the second power plant heat exchanger. In this case a value of (9+6=15) %
is approximated for the overall efficiency of the two power plants.

[00129] Table B1 includes the capital cost estimates for a flow rates of 60 m3/hr (Case A) and a flow rates of 45 m3/hr per pad (Case B).

[00130] Payback Period

[00131] The estimated electricity power generated using two 2MW thermal module is estimated and are given in Table C. The total electricity generated from one pad in its lifespan, considering 10 days of overhaul each year, as well as the equivalent total electricity prices ($0.13/
kWh) from one pad for each case also calculated and presented in table C.

[00132] The payback period of the two cases A and B are represented in Fig.
12A and 12B
respectively. Referring to Table C and Fig. 12A and 12B it is concluded that although the case A
has a shorter payback period its cost per MVVh and its total income compared to case B are lower.

Date Recue/Date Received 2023-05-17

[00133] Table C: Economic comparison of Case A and Case B
Case study Estimated total Total heat Power Cost per Total income cost per well- extracted generated MWh CAD
pad lifespan (GJ) (MWh) (USD/MWh) A1 $2,336K 867,600 36,150 48.6 $4,639K
B2 $3,046K 1,300,000 54,000 42.4 $7,020K
lestimated well-pad lifespan= 10 years 2estimated well-pad lifespan= 20 years

[00134] Generation Cost Comparison with other Energy Sources

[00135] The Levelized Cost Of Energy (LCOE) is a measure of a power source that allows comparing different electricity generation methods consistently. The costs include the initial capital, the costs of continuous operation, fuel, maintenance, and the costs of decommissioning and remediating any environmental damage.
ves _________________________________________________________ = sum of costs over lifetime (1+r)1 LCOE
sum of electrical energy produced over lifetime vn Et X-itu=1.
It investment expenditures in the year t F4 electrical energy generated in the year t Mt operations and maintenance expenditures in the year t r discount rate Ft fuel expenditures in the year t n expected lifetime of system or power station

[00136] Cost per MWh based on average data from BNEF, IRENA, and Lazard

[00137] Figure 13 presents the cost per MWh based on average data from BNEF, IRENA, and Lazard [6-8]. The current technology's cost per MWh without considering any carbon credit for this technology is also shown in the same figure. It is seen that the electricity generation using LCOE analysis from a post-SAGD cost less than any other technologies.
Generating electricity from post-SAGD using the current technology is done without incurring any fuel usage. It is a clean technology, i.e. no emission and no environmental harm.

[00138] Carbon Pricing

[00139] In Canada, the federal carbon tax is set to increase from $65 per tonne to $170 per tonne of CO2 in 2030 [9]. Provinces are free to determine their equivalent climate policies as long as the federal government determines that the provinces meet the same threshold as the established federal minimum carbon price.

[00140] The Alberta benchmark is set using a "good-as-best-gas" concept, at 0.370 tonCO2 per MWh (Carbon Competitiveness Incentive Regulation, 2017) [10]. Therefore, facilities with emissions intensities above the benchmark will have extra costs. In contrast, facilities with Date Regue/Date Received 2023-05-17 emissions intensities below the benchmark receive offset credits with a nominal value equal to the carbon price.

[00141] Table D: Comparison of carbon price credits for case A and case B
Case study Total power Total carbon price in Yearly carbon price generated (MWh) well-pad lifespan per well-pad Case A 36,150 $870K $87K
Case B 54,000 $1,300K $65K

[00142] Receiving such offset credit as the carbon price, reduces the payback period as shown in Fig. 12A and 12B, making this technology even more attractive as an electricity-generating technology.

[00143] The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be affected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.
References 1. Tchanche B. F., Quoilin S., Declaye S., Papadakis G., and Lemort V. 2010.
Economic Feasibility Study of a Small-Scale Organic Rankine Cycle System in Waste Heat Recovery Application, 10th Biennial Conference on Engineering Systems Design and Analysis, Paper #ESDA2010-24828, ASME, Istanbul, Turkey.
2. Jinlong C., Kewen L., Changwei L., Mao L., Youchang L., Lin J., and Shanshan J. 2017.
Enhanced Efficiency of Thermoelectric Generator by Optimizing Mechanical and Electrical Structures, Energies, 10, 1329; Do1:10.3390/en10091329 3. https://www.zi I larac.com/Portals/O/Docu ments/PDF/HDGCorrProtection.pdf 4. "Aluminized Steel Offers Attractive Physical Characteristics for Use in Industrial Duct Construction". Sheet Metal and Air Conditioning Contractors' National Association. Retrieved 26 February 2011". Archived from the original on 2011-02-20. Retrieved 2011-02-26.
5. Zaba K., Nowosielski M., Kita P., Kwiatkowski M., Tokarski T., Puchlerska, S. 2015. Effect of Heat Treatment on The Corrosion Resistance of Aluminized Steel Strips", ARCHIVES OF
METALLURGY AND MATERIALS, 60(3): 1825-1832.
6. BNEF Executive Fact-book. 2 March 2021. Retrieved 3 March 2021.
7. Renewable Power Generation Costs in 2019. Abu Dhabi: International Renewable Energy Agency (I RENA). June 2020. ISBN 978-92-9260-244-4. Retrieved 6 June 2020.
8. Levelized Cost of Energy and Levelized Cost of Storage 2020, 19 October 2020. Retrieved 24 October 2020.

Date Recue/Date Received 2023-05-17 9. Government of Canada. The federal carbon pollution pricing benchmark.
10. Carbon Competitiveness Incentive Regulation, Pub. L. No. Alta Reg 255/2017 (2017).
Retrieved from http://www.qp.alberta.ca/1266.cfm?page=2017 255.cfm&leci type=Reqs&isbncln=9780779 11. Kamyar D., Mehdi A. E., Farideh A., and Marc A. R. 2015. Selection of Optimum Working Fluid for Organic Rankine Cycles by Exergy and Exergy-Economic Analyses, Sustainability, 7: 15362-15383; doi:10.3390/su71115362 12. Xiaojun Z., Lijun W., Xiaoliu W., Guidong J. 2016, Comparative Study of Waste Heat Steam SRC, ORC and S-ORC Power Generation Systems in Medium-low Temperature, Applied Thermal Engineering 106: 1427-1439 13. Herfurth S., Kuhn D., Wiemer, H. 2015. Performance Optimization of ORC
Power Plants, Proceedings World Geothermal Congress 2015 Melbourne, Australia, 19-25 ApriL
14. Bilozir et al. Waste Heat Recovery from Depleted Reservoir: US
2015/0144345 Al, 28 May 2015.
15. Beentjes, I, Bogatkov, D. 2023. Heavy Oil Late Life Energy Recovery¨Maximizing the Value of Mature Thermal Assets, Society of Petroleum Engineers DO! 10.2118/212820-MS, SPE
international.

Date Recue/Date Received 2023-05-17

Claims (17)

What is claimed is:

1. A method of harvesting thermal energy from a spent oil well, the spent oil well having an injection well borehole (IWB), the method comprising:
forming a conduit system in the IWB, the forming of the conduit system comprising:
disposing a conduit-in-conduit arrangement in the IWB, the conduit-in-conduit arrangement having an inner conduit and an outer conduit, the inner conduit being in the outer conduit, the outer conduit having an open proximal end and a sealed distal end, the inner conduit having an open proximal end and an open distal end;
connecting a first end of an inflow conduit to the proximal end of the inner conduit;
connecting a second end of the inflow conduit to a cool water output of a heat exchanger (HX) system;
connecting a first end of an outflow conduit to the proximal end of the outer conduit;
connecting a second end of the outflow circuit to a hot water input of the HX
system, the inflow conduit and the outflow conduit being outside of each other;
circulating water in a closed loop, the closed loop comprising, in sequence, the cool water output of the HX system, the inflow conduit, the inner conduit, the outer conduit, the outflow conduit, the hot water input of the HX system and the HX system, the water circulating in the closed loop to harvest thermal energy from an environment surrounding the closed loop; and extracting heat from the water circulating through the HX system.

2. The method of claim 1, wherein disposing the conduit-in-conduit arrangement in the IWB
includes disposing of a conduit-in-conduit arrangement that includes thermal insulation surrounding the inner conduit for at least a portion of a length of the inner conduit, starting from the proximal end of the inner conduit.

3. The method of claim 1, wherein at least one of the inner conduits and the outer conduit is a thermally insulated conduit.

4. The method of claim 1, wherein connecting the first end of the inflow conduit to the proximal end of the inner conduit and connecting the first end of the outflow conduit to the outer conduit, includes using a wye connector or a Y connector to connect the first end of the inflow conduit to the proximal end of the inner conduit and connect the first end of the outflow conduit to outer conduit.

5. The method of claim 4, wherein the Y connector or the wye connector may be installed at:
a heel of the conduit-in-conduit arrangement, or at a higher level within a vertical well portion of the spent oil well, or at a ground surface level.

6. The method of claim 3, further comprising incorporating thermal insulation in at least one of the inner conduit and the outer conduit, the thermal insulation selected from a group consisting of foam insulation, vacuum insulation, insulation by coating material or any combination thereof.

7. The method of claim 1, further comprising determining a number of injection well boreholes for use in harvesting thermal energy, the determination based on: a total number of wells in a well-pad used for heat recovery, dimensions of the well-pad, left-over heat from post-blowdown reservoirs, and an economic factor.

8. The method of claim 1, wherein the conduit-in-conduit arrangement comprises a concentric conduit arrangement.

9. A power plant to harvest thermal energy from a spent oil well, the spent oil well having an injection well borehole (IWB), the power plant comprising:
a heat exchanger (HX) having a hot water input and a cool water output;
a conduit system formed in the IWB, the conduit system comprising a conduit-in-conduit arrangement, the conduit-in-conduit arrangement having an inner conduit and an outer conduit, the inner conduit being in the outer conduit, the outer conduit having an open proximal end and a sealed distal end, the inner conduit having a proximal end and a distal end;
an inflow conduit having a first end and a second end, the first end of the inflow conduit being connected to the proximal end of the inner conduit, the second end of the inflow conduit being connected to the cool water output of the HX; and an outflow conduit having a first end and a second end, the first end of the outflow conduit being connected to the open proximal end of the outer conduit, the second end of the outflow conduit being connected to the hot water input of the HX, wherein:

the HX, the conduit system, the inflow conduit and the outflow conduit define a closed loop configured to have, in operation, water circulating therein from, in sequence, the cool water output of the HX, the inflow conduit, the inner conduit, the outer conduit, the outflow conduit, the hot water input of the HX and the HX, the water circulating in the closed loop to harvest thermal energy from an environment surrounding the closed loop and to provide the harvested thermal energy to the HX.

10. The power plant of claim 9 further comprising a pump configured to pump the water in the closed loop.

11. The power plant of claim 9, wherein the inflow conduit and the outflow conduit include thermal insulation.

12. The power plant of claim 9, wherein the inner conduit includes thermal insulation formed along a portion of a length of the inner conduit, beginning at the proximal end of the inner conduit.

13. The power plant of claim 9, wherein the conduit-in-conduit arrangement is a concentric conduit arrangement.

14. The power plant of claim 13, further comprising a wye connector or a Y
connector connecting the inflow conduit to the inner conduit and connecting the outflow conduit to the outer conduit.

15. The power plant of claim 9, further comprising an electricity generator system operationally connected to the HX.

16. The power plant of claim 15, wherein the electricity generator system comprises an Organic Rankine cycle (ORC) engine configured to receive thermal energy from the HX and to convert the thermal energy into mechanical energy.

17. The power plant of claim 16, wherein the electricity generator system further comprises a generator coupled to the ORC engine to receive the mechanical energy and to generate electricity.