US20110232858A1

US20110232858A1 - Geothermal well using graphite as solid conductor

Info

Publication number: US20110232858A1
Application number: US12/946,104
Authority: US
Inventors: Hiroaki Hara
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-03-25
Filing date: 2010-11-15
Publication date: 2011-09-29

Abstract

A closed loop geothermal system and apparatus is provided comprising a piping system inside a main well to create a closed circulation of thermal fluid to a target temperature zone underground. The piping system may have an inner pipe is inserted inside an outer pipe/casing in a concentric arrangement to allow thermal fluid to flow downward between inner pipe and outer pipe/casing and upward inside inner pipe by entering inner pipe near the bottom of the well. A heat conducting filler comprising graphite may be packed in a space between the well and piping system in the target temperature zone. The system and apparatus may further include an extended portion of the main well and/or heat conducting channels each comprising graphite converging on a heat exchange zone of the well, which may further include a heat exchanger. Methods for constructing and operating the apparatus are also provided

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of priority to U.S. Provisional Patent Application Ser. No. 61/317,501 filed Mar. 25, 2010, the contents and disclosure of which are hereby incorporated by reference in their entirety.

BACKGROUND

1. Field of the Invention
This invention relates generally to geothermal power generation system and wells used to harness geothermal energy.
2. Related Art
Geothermal Power is one of the most low cost, non-intermittent, renewable energy sources available. However, geothermal projects are not yet ubiquitously present. The projects still carry the risk of not finding subsurface hydrothermal resources, and for various reasons, geothermal sites may become increasingly less productive over time even when subsurface hydrothermal resources are initially found. Subsurface hydrothermal resources are currently the only means to harvest geothermal energy for power production and remain a limiting factor for geothermal development. What is needed in the art are improved systems and methods for harnessing geothermal resources in a manner that is efficient at collecting heat from the earth without depleting the source of the subsurface thermal energy.

SUMMARY

According to a first broad aspect of the present invention, a closed loop geothermal apparatus is provided comprising: a main well comprising a hole in the earth; an inner pipe and an outer pipe; and a heat conducting filler, wherein the inner pipe is inside the outer pipe in a concentric arrangement, wherein the inner pipe and the outer pipe are inside the main well, such that a bottom portion of the inner pipe and the outer pipe reach a target temperature zone underground, wherein the inner pipe and the outer pipe are configured such that a thermal fluid traveling downward in the space between the inner pipe and the outer pipe can enter the inner pipe at or near the bottom of the outer pipe and travel upward within the inner pipe, and wherein the heat conducting filler consisting essentially of graphite packed in a space between the main well and the outer pipe in the target temperature zone. The first broad aspect may further comprise one or more heat conducting channels each comprising a wellbore filled and packed with graphite, wherein the one or more heat conducting channels converge to contact a heat exchange zone of the main well at or near the bottom of the outer and inner pipes.
According to a second broad aspect of the present invention, a closed loop geothermal apparatus is provided comprising: a main well comprising a hole in the earth; an inner pipe; an outer casing; and a heat conducting filler, wherein the inner pipe is inside the outer casing in a concentric arrangement, wherein the inner pipe and the outer casing are inside the main well, such that a bottom portion of the inner pipe reaches a target temperature zone underground, wherein the inner pipe and the outer casing are configured such that a thermal fluid traveling downward in the space between the inner pipe and the outer casing can enter the bottom of the inner pipe and travel upward within the inner pipe, and wherein the heat conducting filler consisting essentially of graphite packed in a space between the main well and the outer casing in the target temperature zone. The second broad aspect may further comprise one or more heat conducting channels each comprising a wellbore filled and packed with graphite, wherein the one or more heat conducting channels converge to contact a heat exchange zone of the main well at or near the bottom of the inner pipe.
According to a third broad aspect of the present invention, a closed loop geothermal apparatus is provided comprising: a main well comprising a hole in the earth; a piping system; and a heat conducting filler, wherein the piping system is inside the main well, such that a bottom portion of the piping system reaches a target temperature zone underground, wherein the piping system is configured such that a thermal fluid travels downward toward the bottom portion of the piping system before traveling upward toward the surface of the earth, wherein the heat conducting filler is packed in a space between the main well and the piping system in the target temperature zone, and wherein the heat conducting filler packed in the space between the main well and the piping system is pure or nearly pure graphite.
According to a fourth broad aspect of the present invention, a method is provided comprising: (a) providing a closed loop geothermal apparatus comprising a main well having a hole in the earth, an inner pipe and an outer pipe, and a heat conducting filler, wherein the inner pipe is inside the outer pipe in a concentric arrangement, wherein the inner pipe and the outer pipe are inside the main well, such that a bottom portion of the inner pipe and the outer pipe reach a target temperature zone underground, wherein the inner pipe and the outer pipe are configured such that a thermal fluid traveling downward in the space between the inner pipe and the outer pipe can enter the inner pipe at or near the bottom of the outer pipe and travel upward within the inner pipe, and wherein the heat conducting filler consisting essentially of graphite packed in a space between the main well and the outer pipe in the target temperature zone; and (b) causing a thermal fluid to flow downward in the space between the inner pipe and the outer pipe, enter the inner pipe at the bottom of the inner pipe, and flow upward inside the inner pipe. According to some embodiments, with or without the step of providing the geothermal apparatus or system of the present invention, the thermal fluid may be caused to flow through the geothermal apparatus or system in a first step and thermal energy may be harnessed from the thermal fluid at or near the surface of the earth.
According to a fifth broad aspect of the present invention, a method is provided comprising: (a) placing an inner pipe and an outer pipe in a main well to make a closed loop geothermal apparatus, such that a bottom portion of the inner pipe and the outer pipe reach a target temperature zone underground; and (b) packing a heat conducting filler consisting essentially of graphite in a space between the main well and the outer pipe in the target temperature zone.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate exemplary embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain the features of the invention.

FIG. 1 is a conceptual schematic drawing of a well head and main well having concentric fluid flow;

FIG. 2 is a conceptual schematic drawing of the flow of thermal fluid at the bottom of a main well at a heat exchange zone;

FIG. 3 is a diagram showing a Single Well Closed Loop Geothermal (SWCLG) according to some embodiments having a concentric fluid flow with outer and inner pipes;

FIG. 4 is diagram showing a bottom of a main well according to some embodiments filled with graphite filler up to a target temperature zone;

FIG. 5 is a diagram of a well with multiple graphite filled heat conducting channels and a close-up view of the heat exchange zone where heat conducting channels meet the main well;

FIG. 6 is a vertical cross-sectional view of a heat exchanger at the target temperature zone of a main well;

FIG. 7 is a horizontal cross-sectional view of a heat exchanger at the target temperature zone of a main well;

FIG. 8 is a conceptual schematic drawing of a heat exchanger at the target temperature zone of a well with well casing used as outer pipe;

FIG. 9 is a thermal gradient drawing for a closed loop geothermal well with isotherms drawn as lines;

FIG. 10 is a thermal gradient drawing for a closed loop geothermal well with isotherms drawn as lines wherein the isotherms shift as heat is continuously extracted;

FIG. 11 is thermal gradient drawing for a single well closed loop geothermal system with horizontal heat conducting channel;

FIG. 12 is a drawing of a single well closed loop geothermal system with horizontal heat conducting channels;

FIG. 13 is a drawing of a single well closed loop geothermal system with inclined horizontal heat conducting channels;

FIG. 14 is a top view of a set of horizontal heat conducting channels in a heat collection zone within a sediment layer;

FIG. 15 is a top view of a conceptual drawing of a possible pattern of heat collection channels each with a main well and horizontal heat conducting channels in a horizontal plane;

FIG. 16 is a top view of a conceptual drawing of a possible intertwined pattern of horizontal heat conducting channels for collection of heat in a horizontal plane;

FIG. 17 is a top view of a conceptual drawing showing another possible placement of horizontal heat conducting channels for collection of heat in a horizontal plane with multiple main wells;

FIG. 18 is a diagram of a main well configured to collect heat escaping from below with an extended portion of main well formed along a fault plane; and

FIG. 19 is a diagram of a main well with a heat resistant thermal conductor, such as a high temperature pipe lowered into the magma.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There are a variety of technologies that may be used to harness geothermal energy. In general, the idea behind geothermal technology can be quite simple. Basically, a geothermal plant may be created by drilling into a hot water spring underground having a high enough temperature. For example, a spewing geyser can be harnessed to power a turbine of a geothermal generating plant. However, finding such underground resources at locations suitable to geyser quality steam output may be difficult. The temperature must be hot enough to make an effective amount of steam to power a turbine, and if the steam production is finite, it may eventually wane. These risks have limited the proliferation of geothermal projects.
One technology, referred to as a binary system, may utilize the energy of hot water at lower temperatures than dry steam by using a secondary fluid with a lower boiling temperature, such as pentane, anmonium or other fluids. For example, ORMAT Technologies Inc. has developed an Organic Rankine Cycle binary thermal engine system. This advancement has expanded opportunities to utilize underground reservoirs of hot water other than dry steam in a manner that is still effective for power generation.
There has been growing evidence that geothermal wells are a finite resource. By harnessing geothermal energy from steam, a water reservoir underground may become consumed, and the production of power from the reservoir may accordingly decrease. This has prompted some to pump water back into the ground for replenishment of the reservoir to make a more renewable source of energy. Theoretically, pumping water into a heat source reservoir rock will perpetuate the geothermal power generation cycle. Indeed, Enhanced Geothermal System (EGS) has been considered an energy technology for the future, and successful results have been documented. For example, some towns have implemented a program to inject their gray water into the underground reservoir to enhance recovery.
A related technology called Hot Dry Rock (HDR) Geothermal, utilizes the porous rock layer underground as a heat exchange channel for receiving pumped-in water, and steam recovered from the layer under the non-permeable cap rock may be used for energy production. There is hope that this technique may eliminate the need to prospect fault and volcanic structures. Since the earth's mantle is naturally hot, if one drills deep enough, suitable subterranean hot dry rock should be available to heat up the water pumped in and to create the cycle of geothermal heat exchange. However, results from feasibility studies have been mixed, and the recovery rate from the water pumped in was sometimes insignificant, thus requiring much more water to be pumped into the ground to yield adequate steam/hot water. In fact, some experimental projects, in which a deep well was drilled to take advantage of the heat of the subterranean earth's crust, such as one in Basel, Switzerland, produced numerous minor earthquakes at the stimulating phase or micro fracturing stage of the rock layer. Even though the magnitude was small, it was large enough to alarm area residents. As a result, the project has been suspended indefinitely and has posed a major setback for HDR proponents.
Another approach called a Down Hole Heat Exchanger (DHE) is to put a heat exchanger in a well to extract subsurface heat, which has been the subject of studies and experiments conducted since the 1970's. Successful application using a DHE for the purpose of direct heat is in use in various European and US towns. No deep well is drilled to extract high temperature for power generation purposes. In essence, this is a large scale Geothermal Heat Pump technology.
A Bore Hole Heat Exchanger (BHE) is similar to the DHE, except that the wellbore itself may be used for the heat exchanging surface, and most likely, concentric pipes are inserted directly into the wellbore. A thermally conductive grout may be used to make the inserted pipe thermally contacted with the wellbore and surrounding rocks. See, e.g., U.S. Pat. No. 6,251,179, the contents and disclosure of which are hereby incorporated by reference in their entirety. Graphite may also be used as an additive to improve the thermal conductivity of the grout for geothermal heat pump applications. See, e.g., U.S. Patent App. Pub. No. 2007/0125274, the contents and disclosure of which are hereby incorporated by reference in their entirety. However, as explained below, it is not the thermal conductivity of the grout that ultimately limits the harnessing of heat energy, power or output; rather the limitation is the thermal conductivity of the rocks surrounding the well, which is too low to supply heat continuously to the well.
Recent modeling studies have shown that due to the general lack of thermal conductivity of rocks surrounding the well, a simple Single Wellbore EGS (SWEGS) does not produce enough power generation and is not sustainable. However, these studies have also shown that if there is enough flow rate of fluid, SWEGS may actually produce better economy than EGS using paired wells at a geothermal depth of 5 km and a thermal gradient of 40° C./km.
Although, the above-mentioned U.S. Patent App. Pub. No. 2007/0125274 claims to rely on the grout and an electrically conducting material including graphite, it does not disclose data showing any improvement in conductivity. However, U.S. Patent App. Pub. No. 2008/0251755, the contents and disclosure of which are hereby incorporated by reference in their entirety, discloses thermal conductivity improvement of grout by adding graphite flakes to a cement clay. Premixed clay shows conductivity improvement up to 2.7 W/mK (1.6 BTU/hr·ft·° F.). However, while the grout's conductivity may increase, mixing with cement clay actually reduces graphite's thermal conductivity dramatically from its compressed pure powder or solid form. This is probably due to the fact that mixing creates graphite inter-particle distance separated by the clay, a thermal insulator.
Currently, there is a dependence on hydrothermal resources since most of the geothermal power generation is limited by the presence of subsurface hydrothermal reservoirs or by creating such reservoirs underground. The requirement for a hot water reservoir makes geothermal exploration additionally challenging and potentially much riskier in comparison to simply finding an underground heat source and harnessing its energy to produce electricity, if such a system were achievable.
In addition to finding a reliable subsurface hydrothermal reservoir, there are other costs and challenges. The cost of drilling a geothermal well is expensive primarily due to the time required to drill through hard rocks. Therefore, it is very important to control exploration to reduce the risk of drilling dry wells. Current geothermal sites require drilling of at least a pair of wells: one for injection, and the other for extraction. However, a Single Well Closed Loop Geothermal (SWCLG) system for generating power eliminates the need for paired wells.
There may also be significant operations and maintenance (O&M) costs with utilizing subsurface hydrothermal reservoirs. For example, water or flash steam can create grime deposits in the pipe. Such solid impurities could possibly damage the thermal engine. On the other hand, Closed Loop geothermal systems will be separated from any build-up of grime deposits in the pipe for long term viability of the system.
There are also substantial risks with harnessing geothermal energy. For instance, the subsurface geologic structure is often unknown. Even with extensive seismic investigation, and with other tools available, there remains significant number of unknowns with regard to the flow, size and temperature of hydrothermal resources. Even at high temperature zones, conventional geothermal power generation requires a reservoir. However, SWCLG will eliminate the need for hydrothermal resources.
Increasingly, clean surface water resources as well as subsurface aquifers for power generation are becoming scarce. Even though hydrothermal resources are a separate resource from surface water, EGS systems have increasingly required pumping of surface water. For example, surface gray water is sometimes used to inject into the production zone. However, none of the existing EGS systems recover 100% of the injected water thus indicating a fundamental lack of knowledge and control. Migration of water also poses a risk to environmental contamination.
Fundamentally, Single Well Geothermal Power Systems have been discouraged or prevented due to the poor thermal conductance of rocks and soil that surround the wells. They generally have a conductance that is lower than 2 W/mK, sometimes one order of magnitude less, compared to metal, such as copper having a conductance of 350 W/mK. Poor conductivity is not only due to the rock-to-well contact, but also the low conductance of the rock itself, which may be insufficient to provide a continuous heat supply from the underground heat source to the thermal fluid. Overcoming the poor conductivity of the earth and the rock-to-well contact is a primary challenge standing in the way of conceiving and designing efficient closed loop geothermal systems. This problem relates to the long-term heat transfer equilibrium from the underground heat source to the above ground heat engine.
For SWEGS, continual supply of energy may be limited and eventually interrupted unless there is fluid flowing through the formation. Even still, once the heat energy is used and drained from surrounding rocks, its replenishment from the heat source perhaps down below is limited by the poor heat conductance of the rock layers.
According to a first broad aspect of the present invention, a closed loop geothermal system and apparatus for tapping into higher temperature sources underground is provided comprising a main well in a single bore hole having higher thermal efficiency and lower electric cost, while relieving the risk of not finding underground water. Generally speaking, the main well will have a mostly vertical orientation or arrangement descending from an opening at the earth's surface. The closed loop system and apparatus can use high temperatures underground without a need for hydrothermal resources. The closed loop system and apparatus may utilize one or more heat conducting channels filled and packed with an optimal thermally conducting material, which is most likely graphite, to bring geothermal energy to a heat exchange zone of the main well. According to some embodiments, a plurality of such heat conducting channels may converge to the same section or portion of the main well at the heat exchange zone at a target temperature zone or depth underground to provide a flow of heat to the main well that may be transferred to a thermal fluid flowing through the main well. According to some embodiments, a target temperature zone or depth may be a range of depths underground where the geothermal temperature is at least about the same or higher than the specific temperature of the thermal fluid desired for the thermal engine above ground.
According to embodiments of the present invention, a closed loop geothermal system and apparatus comprising a piping system inside a main well is provided such that a bottom portion of the piping system reaches a target temperature zone underground. A heat conducting filler comprising an optimal thermally conducting material, such as graphite or pure or nearly pure graphite, is packed in a space between the main well and the piping system in the target temperature zone to improve conductivity. The piping system itself may have a variety of configurations, but the piping system will generally be configured such that a thermal fluid will flow or travel downward toward the bottom portion of the main well for heat exchange before flowing or travelling upward toward the surface of the earth. The piping system will further be enclosed such that the thermal fluid remains fully contained within the piping system at least while flowing through the piping system underground.
According to embodiments of the present invention, the closed loop geothermal system and apparatus may comprise a main well having a piping system with a concentric arrangement of an outer pipe and an inner pipe to enclose the flow of a thermal fluid in a closed loop within a single well. The outer and inner pipes may be heat and/or pressure resistant. According to these embodiments, the inner pipe is inserted into the outer pipe such that there is a gap at the bottom of the inner pipe to allow a thermal fluid flowing between outer and inner pipe to enter and flow into inner pipe. As shown in FIGS. 1 and 2, the flow of a thermal fluid 109 in the main well 101 may be used to carry heat from a subterranean target temperature zone or depth underground to the surface where it can be harnessed or used. The outer pipe 105 (i.e., the space between the outer pipe 105 and the inner pipe 107) may be used to carry the relatively cooler thermal fluid 109 from at or near the surface downward toward the target temperature zone and/or heat exchange zone 117, and the thermal fluid 109 becomes increasingly heated as it flows downward. Therefore, the bottom portion of the inner pipe 107 and the outer pipe 105 should be deep enough to reach and overlap with a target temperature zone or depth to form a heat exchange zone 117. The heat exchange zone 117 is the physical portion of the well 101 within the target temperature zone where heat exchange primarily occurs. The target temperature zone is a sufficient depth under ground having a temperature at or above a desired target temperature as defined by a geothermal value. The thermal fluid 109 may conceivably include a variety of fluid types, but may preferably be water, steam, or supercritical CO₂(ScCO₂). ScCO₂may be suitable for temperatures, for example, over 370° C. The thermal fluid 109 flows downward in the space between outer pipe 105 and inner pipe 107 to a heat exchange zone 117 where the downward flowing thermal fluid 109 reverses direction at the bottom of the main well 101, and the warmer/hotter thermal fluid 109 turns and begins to flow upward through inner pipe 107. In addition, the outer pipe 105 may be contained within an outer well casing, or alternatively, the well casing may be used in place of outer pipe 105 (not shown).
Above or near the surface, the thermal fluid 109 may be used to generate power or electricity. Generally, use of a secondary fluid is not preferred. Indeed, the thermal fluid 109 itself may be used directly to power the engine or turbine at or near ground level. Alternatively, a second phase of the thermal fluid 109 may be utilized, such as steam as opposed to liquid water. Based on the temperature and type of fluid, a particular type of surface power engine or thermal engine may be most appropriate, and vice versa. For example, a high-pressure steam turbine may be used, or a turbine powered by supercritical CO₂or another fluid may instead be used. By harnessing the heat from the thermal fluid 109 at or near the surface, the thermal fluid 109 will become cooled and may then be recycled down the main well along the space between the inner pipe 107 and outer pipe 105. According to some embodiments, however, there may be an appropriate means for exchanging heat with a second fluid to operate a turbine to generate electricity. For example, the temperature of such a second fluid may be up to about 200° C., or about 200° C. or higher, or may be as high as 500° C., but these temperatures are not considered limiting.
According to some embodiments, the heat collected by the thermal fluid of the apparatus and system of the present invention may be used to provide energy for a large-scale heat pump, such as a community heat pump. The closed loop geothermal system with heat conducting channels may also be used in a reverse process for heat storage underground, such as to provide a heat sink for cooling operations and systems, such as heat pumps, operating above ground.
Embodiments of the present invention enable harvesting of geothermal energy using a single well closed loop geothermal system or apparatus, which may be used without the presence of hydrothermal resources. There are several advantages of using a single well bore with a concentric design of pipes for cycling the thermal fluid to the target temperature zone underground. One advantage is that a single well design may reduce cost. Drilling of a single well is likely to be cheaper in cost per Watt even though installation costs per well may be higher with the single well design. Yet another advantage of using a single well design is that existing dry wells that do not have hydrothermal resources present at the target temperature zone may be used. Such dry wells may be deep EGS wells or dry oil wells. Temperatures at the bottom of these wells at the sedimentary layer have been shown to be within the range or higher than the flush steam temperature even though they are dry. Thus, these wells are candidates for conversion to SWCLG. The cost of modifying a dry well to a CLG may be the cost of building heat conducting channels, the cost of graphite and its placement and packing in the well and channels, and the cost of installing the concentric pipes and facilities above ground as specified above. Instead of leaving dry wells dormant, the single well CLG according to present embodiments may recover investment and may produce energy over a longer time, even compared to a useful EGS. Further, the cost of graphite is relatively inexpensive. In fact, the cost of graphite powder is less than $10 per liter (net), and covering a 10 hectare of area with 10 centimeter material thickness would require about 10 cubic meters of the powder presently at a cost of no more than $100,000. Actual filling and packing of the material using additional equipment and operation may cost significantly more, but considering the cost of drilling, which may cost more than $20,000/day and take several months, the cost of CLG installation is minimal in comparison to drilling the paired geothermal wells.
The closed loop geothermal system according to embodiments of the present invention may eliminate maintenance expenses and replacement costs associated with pipe corrosion, turbine damage, etc. Further, the closed loop system eliminates many geological variables, uncertainties and risks associated with EGS.
According to some embodiments, when above ground power generation uses air-cooled systems, the requirement of running surface water may be eliminated or reduced. Further, when no injection means are used, there is no need for flowing water. In addition, graphite is very stable, inert, and non-soluble in water. The use of a closed loop system should not cause earthquakes, and does not generally pose a serious risk for the contamination of ground water or other conceivable environmental ill effects.
A challenge for geothermal systems is overcoming the heat insulating properties of the earth. The rocks and earth around a wellbore may work as an insulator, rather than a conductor. This may aid in the containment of heat within the warmer thermal fluid 109 flowing upward inside the inner pipe 107 but may counteract the flow of heat from the earth to the thermal fluid 109 at the target temperature zone or depth. To contain the heat of the warmer thermal fluid 109 flowing up the inner pipe 107, the inner pipe 107 according to some embodiments may itself be insulated from the colder thermal fluid 109 flowing downward around the inner pipe 107 using an insulating material (not shown) to help preserve the temperature of the heated thermal fluid 109 until it reaches near the surface where it can be harnessed or utilized. In addition, the concentric design of the present invention allows the thermal fluid 109 flowing down the space between the inner pipe 107 and outer pipe 105 to act as an additional insulator for the heated thermal fluid 109 flowing up the inner pipe 107, which may also allow the heated thermal fluid 109 to avoid becoming overly exposed or contacted to the surrounding rocks.
An additional advantage of the concentric design is that to the extent heat from the warmer thermal fluid 109 does escape or radiate out of the inner pipe 107, it may be captured and retained to some extent by the relatively colder thermal fluid 109 flowing downward between the inner pipe 107 and the outer pipe 105 and recycled for use by the closed loop system. According to some embodiments, the diameter of the inner pipe 107 may become gradually reduced as the thermal fluid 109 ascends, thereby the pressure and the speed of the ascending thermal fluid 109 increases while the surface area in contact with cold fluid outside of the annulus is smaller.
In general, when there is no heat loss from a conductive material or fluid, heat may pass through the material or fluid very quickly from a source to a heat sink at another location. Therefore, the closed loop system according to embodiments of the present invention should be insulated by or in relation to the surrounding earth and rock where no heat transfer is intended to occur, but heat conducting at a heat exchange zone at a target temperature zone or depth to allow the heat to be collected and transferred to the thermal fluid. Dry rocks are expected to work as insulators rather than conductors. Therefore, above or shallower than the target temperature zone, a heat insulating filler, layer or material 121, such as a cement or grout, may be used according to some embodiments between the outer pipe 105 or casing of the main well 101 and the surrounding rock or earth of the hole or well bore. The heat insulating filler 121 may help to control or minimize heat loss from the thermal fluid 109 and closed loop system along portions of the main well 101 surrounded by rock or sedimentary layers of the earth that does not have a high enough temperature for heat exchange. As an example, regular concrete may be used as the heat insulating filler. On the other hand, a heat conducting filler, layer or material 119 made of an optimal thermally conducting material, such as graphite, may be used in tight contact between the outer pipe 105 or casing of the main well 101 and the surrounding rock or earth of the hole or well bore along the target temperature zone or depths. As mentioned below, graphite may also be packed along an extended portion of the well and/or heat conducting channels. The heat conducting filler 119 allows for exchange of heat with the surrounding earth and rock at the target temperature zone and/or heat exchange zone where there is a sufficient amount of heat to warm or heat the thermal fluid 109.
According to some embodiments, there may also be a seal between the borehole and casing, (or the borehole and the outer pipe if a casing is not used) so that there shall be no leakage of geologically pressured gas or fluid to escape through the space and possibly blow out to the well head. This technique is well known among those skilled in the art of well drilling. According to embodiments of the present invention, the main well or well bore may be extended further down or beyond the target temperature zone or well bottom used for heat exchange with the thermal fluid. As shown for example in FIG. 4, this extended portion 150 of the main well or well bore may be filled and packed with an optimal thermally conducting material 113, such as graphite, up to the level or depth of the target temperature zone and/or heat exchange zone 117, which may contact the outer pipe 105 if bottom of outer pipe 105 is closed or a plug 129 below the bottom of the outer pipe 105. Between the packed portion of the main well 101 and the casing (or outer pipe 105) containing the thermal fluid 109, a high pressure sealed plug 129 may be used to seal and separate the optimal thermally conducting material 113 from the thermal fluid 109. Alternatively, there may be no plug 129 between the packed portion of the main well 101 and the casing (or outer pipe 105), and the optimal thermally conducting material may be in more direct contact with the casing (or outer pipe 105). By having a column of optimal thermally conducting material placed into the extended portion 150 of the main well 101, heat may be brought up to the heat exchange zone 117 to heat the thermal fluid 109. In addition, the heat conducting filler or layer 119 may also be extended down along the extended portion 150 to make a tight contact between the surrounding earth and the casing or outer pipe 105 of the extended portion 150.
According to some embodiments, graphite powder placed into the extended portion 150 by gravity may have the tendency to settle the powder in an orientation having the basal direction horizontal. In other words, it places a flat layer over the other flaked particles. Since graphite does not have isotropic thermal conductance, care must be taken to properly orient the crystal structure in the desirable direction if it is necessary, or at least make them settle in the isotropic direction in aggregate under pressure. The conductivity under pressure is expected to be very high. Experiments may be conducted to confirm the optimal methods and the resulting thermal conductivity of a powder aggregate. According to embodiments of the present invention, an optimal thermally conducting material, such as graphite with a thermal conductivity over 100 W/m·K, in contact with the main well may be used to efficiently conduct heat from the surrounding earth to outer casing, outer pipe, and/or the main well at the heat exchange zone to effectively transfer heat to the thermal fluid. As described below, an optimal thermally conducting material may also be used in the heat conducting channels to conduct, carry or bring thermal energy to a heat exchange zone of the main well. Diamond is known to have extremely high thermal conductivity, though its cost is prohibitive for this application. See, e.g., Wei, L. et al., “Thermal conductivity of isotopically modified single crystal diamond,” Physical Review Letters 70: 3764 (1993), the contents and disclosure of which are hereby incorporated by reference in their entirety. However, graphite offers an economical alternative with relatively high thermal conductivities from 25-450 W/m·K at ambient pressure, but graphite conductivity is not isotropic. Therefore, the optimal thermally conducting material according to embodiments of the present invention will generally comprise a graphite material, such as graphite rods, graphite powder, graphite flakes, extruded shapes of graphite and/or graphite slurry. Graphite slurry may be used for the purpose of delivery by injection into the earth and may then settle or form a sediment in place. The optimal thermally conducting material may generally be tightly packed and/or under pressure to ensure close contact among the graphite particles and molecules of the optimal thermally conducting material thus producing higher conductivity.
According to some embodiments, the optimal thermally conducting material may have a conductivity of about 100 W/m·K or greater. As further discussed below, for example, the graphene structure may have a conductivity as high as 5780 W/m·K and provides an upper limit for the conductivity of the optimal thermally conducting material. Thus, the optimal thermally conducting material may have a conductivity of from about 100 W/m·K to 5780 W/m·K. As further discussed herein, for example, extruded graphite rods may alternatively have a conductivity from about 100 W/m·K to about 450 W/m·K, or 120 W/m·K to about 450 W/m·K, or from about 120 W/m·K to about 300 W/m·K. Such an optimal thermally conductive material comprising graphite will generally have a high percentage of at or near 100%, near purity, or purity of graphite material, such as in the form of extruded graphite rods, graphite powder, graphite flakes and/or graphite slurry.
Graphite is essentially a carbon allotrope with a graphene structure stacked over one another. Bonding within the graphene plane is extremely strong, and thermal conductivity within the plane is extremely high and has been reported to be twice as high as that of diamond. Graphene, which is a basal plane crystalline formation of graphite crystal, shows even higher conductivity (i.e., 4840±440 to 5300±480). See, e.g., Saito, K. et al., “Ballistic thermal conductance of a graphene sheet,” Physical Review B76:115409 (2007), the contents and disclosure of which are hereby incorporated by reference in their entirety. It is one substance with the highest thermal conductivity known within the graphene plane. However, the c-axis bond is rather weak, and the atomic distance is long. Along this c-axis direction, therefore, the thermal as well as electron conductance is relatively low (15 W/m·K).
The aggregate bulk conductivity of graphite powder or solid graphite is dependent on how tightly it is packed. The inter-particle voids and distance are an important determining factor of aggregate conductance. Graphene planes can easily be dissociated from one another and slide, which makes graphite one of the most lubricious solid materials. With underground pressure compression, when packed tight, the inter-particle gap should be reduced, and its conductivity may be expected to be higher than under ambient pressure.
Most other thermally conductive substances, such as metals, are prohibitively expensive and are limited in their thermal conductivity. On the other hand, high quality graphite is commercially available at a fraction of cost of copper at relative volumes. High purity extruded graphite rods of various diameters and lengths are also commercially available. These products have specified thermal conductivities and normally have higher conductivity lengthwise (e.g., as high as 195-300 W/m·K). The cost of such graphite rods is presently about $20/net liter. However, graphite powder may offer a cheaper alternative compared to graphite rods. There are also many grades of natural and synthetic graphite powder available. The highest grades may cost about $10/net liter at present. The exact conductivity of packed bulk graphite powder at ambient and elevated pressure is currently under investigation. Graphite is chemically very stable and inert making it safe for use in the environment. Graphite is also not soluble in either water or organic solvents and thus will not be easily dissolved or carried away. Therefore, graphite is expected to perform predictable heat conduction over a long time.
SGL Carbon's XM0906 extruded graphite rods of 6″ diameter and 72″ length have 195 W/m·K thermal conductance along the grain, which is longitudinal, and 128 W/m·K against the grain, which is cross directional. It is one of the thermally conductive extruded graphites commercially available. The 32 inch diameter 96 inches long electrode grade graphite rod has 300 W/mK of thermal conductivity along the length. The volume cost of these rods is less than 12.5% of the cost of copper ore per equal volume. The cost of powder graphite is less than half of the costs of these rods. In the deep well, the high pressure is expected reduce the inter-particle distances of packed powder and thus its thermal resistance. At a depth of 100 meters, the column of graphite provides little over twice the weight of water, and thus, it is about 11 atm or 1.1 MPa pressure. At 1 km depth, the fluid pressure is theoretically 11 MPa. Therefore, it is expected to improve thermal conductivity dramatically.
Without improved heat conductivity, heat may not be sufficiently supplied to the main well due in part to the low thermal conductivity of the earth at about 1-2 W/mK (nowhere near the conductivity of the optimal thermally conductive material, which may be as high as 195 W/mK to 300 W/mK). Indeed, the conductivity of the heat conducting layer or filler 119 and heat exchange zone 117 of the main well 101 may quench the heat source without additional volume and surface area in contact with the heat source.
Therefore, according to embodiments of the present invention, one or more heat conducting channel(s) or extensions is provided to carry or conduct heat from a larger volume of the earth to the heat exchange zone of the main well. The major axis of each heat conducting channel may be theoretically at any angle transverse the vertical axis of the main well including at a right angle to the vertical axis of the main well as long as the heat conducting channel intersects the main well. Generally, the major axis of each heat conducting channel will not be parallel to the vertical axis of the main well. As shown in FIG. 5, one or more heat conducting channel(s) 115 may be used and filled or packed with an optimal thermally conducting material 113, such as graphite, to conduct and/or carry heat from one or more heat source(s) or zones present in the earth to the thermal exchange zone 117 of the main well 101. A portion 131 of the heat conducting channel(s) 115 may be in direct contact with the outer casing or outer pipe 105 of the main well 101 and/or the heat conducting filler 119 at or near the thermal exchange zone 117. The one or more heat conducting channel(s) 115 may be arranged such that they converge to contact a single heat exchange zone 117 of the main well 101.
According to embodiments, the one or more heat conducting channel(s) 115 may provide much greater efficiency as a result of the greatly increased surface area of the optimal thermally conductive material 113 of the heat conducting channel(s) 115 being in contact with the larger volume and/or number of heat sources present in the earth. For example, the heat source may be a superheated gas or fluid. By placing the heat conducting channel(s) 115 in the earth and connected to the heat exchange zone 117 of the main well 101, the problems associated with poor heat conductivity of the earth's crust may be reduced or overcome. For example, a heat conducting channel 115 may comprise graphite rods and graphite powder filler to interface and contact the surrounding earth. The direction of such heat conducting channels should be based on the geology of specific locations.
According to embodiments of the present invention, the graphite may be injected from and placed within the heat conducting channels using any method or technique known in the art for injection and placement of fluids and solids underground. Even though graphite is not soluble in either water or many organic solvents, small graphite powder particles can be suspended in turbulent fluid, such as hot water, steam or supercritical CO₂. Together with the injected fluid, graphite powder may permeate porous material surrounding the channel and may become trapped in the pores. The turbulent fluid may pulverize the heated sedimentary rock, such that graphite may penetrate the pores and settle within the soil to form a solid channel. The sedimentary layer may be relatively soft and porous and may contain convecting fluid. Thus, it may be easier to drill through and inject graphite into the sedimentary layer. Graphene layers may slide and line up along the vector of the fluid flows. As a result of such alignment of grapheme layers, the conductivity of the sedimentary layers may become much higher than normal for rock, which generally has conductivities of 2 W/m·K or less. Simply mixing soil and graphite may also improve conductivity of the surrounding soil, albeit to a lesser extent than packed pure graphite. The altered conductivity of the soil is expected to be one or two orders of magnitude higher around and along such channels. A thermal gradient may be created within the horizontal layer between soil near the channel and soil away from it. The applicability of this type of heat collection is not limited to shallow high temperature zones. Thermal equilibrium simulations and calculations should be conducted for each well design based on specific geothermal information and estimation, along with the target thermodynamic calculation of the engine. In general, the thermal equilibrium modeling must be conducted to find the target temperature.
According to embodiments of the present invention, the surface area of the main well 101 in contact with the thermal fluid 109 at the heat exchange zone 117 may be increased through the use of additional heat conducting materials. As shown in FIGS. 6 and 7, for example, the surface area in contact with the thermal fluid 109 may be increased using a heat exchanger 123 at heat exchanging zone 117 comprising (in the case of the concentric design) additional supporting sections 125 made of a heat conducting material placed between casing 103 or outer pipe 105 and inner pipe 107 and perhaps touching or resting on the bottom of heat exchanger 123. (FIG. 6 provides a vertical cross-section of the heat exchanger 123, and FIG. 7 provides a horizontal cross-section of a heat exchanger in a well without an outer casing unlike FIG. 6.) Such supporting sections 125 may be made of any thermally conducting material and may also function to support and align the inner and outer pipes. The supporting sections 125 may have any shape as long as it fits between inner pipe 107 and outer pipe 105 and will have slots, openings, or gaps between individual supporting sections 125 to allow thermal fluid 109 to flow through slots, openings, or gaps between supporting sections 125. Preferably, the supporting sections 125 should contact the outer surface of the inner pipe 107 and the inner surface of the outer pipe 105. In FIG. 6, under the bottom of heat exchanger 123 and bottom of outer pipe 105 and in contact with heat exchanger 123 and outer pipe 105 are graphite rods 116 stacked within the optimal thermally conducting material 113, such as packed graphite powder and flakes, of extended portion 150 of main well 101. FIG. 8 provides another example of a heat exchanger 123 at heat exchange zone 117 with plug 129 separating thermal fluid 109 within casing 103 from optimal thermally conducting material 113 of extended portion 150 of main well 101.
The heat exchanger may further comprise a thermally conducting object 127 inside inner pipe 107 in contact with inner pipe 107, such as a finned or star-shaped thermal conductor or rod, which may also touch or rest on the bottom of outer pipe 105. Preferably, the thermally conducting object 127 should contact the inner surface of the inner pipe 107. However, thermally conducting object 127 may have a variety of shapes and dimensions as long as it contacts inner pipe 107 and provides sufficient slots, openings, or gaps for thermal fluid 109 to flow into and/or through the heat exchange zone 117 of inner pipe 107. According to embodiments, the supporting sections 125 and thermally conducting object 127 may be arranged so that slots, openings, or gaps formed by each are aligned at least enough to allow the thermal fluid 109 flowing downward from through slots, openings, or gaps of supporting sections 125 between inner pipe 107 and outer pipe 105 to enter slots, openings, or gaps formed by the thermally conducting object 127 inside the inner pipe 107.
The addition of the heat exchanger 123, which may comprise either or both of the supporting sections 125 and the thermally conducting object 127, should increase or improve the heat transfer with the thermal fluid 109 at the heat exchange zone 117 by increasing the heated surface area in contact with the thermal fluid 109. To further improve efficiency of heat transfer at the heat exchange zone 117, either or both of the inner pipe 107 and outer pipe 105 may be made thermally conducting, and the inner pipe 107 may lack the additional insulating material which may be present above the target temperature zone. The combination of the contacting heat conducting outer and inner pipes 105, 107, heat conducting filler or layer 119, and heat exchanger 123 with supporting sections 125 and/or the thermally conducting object 127, may create a continuous flow of thermal energy into the heat exchange zone 117 of the main well 101 with greatly increased heated surface area in contact with the thermal fluid 109 as it flows through the heat exchanger 123. The length of the heat exchange zone 117 and the thicknesses of the supporting sections 125 between inner pipe 107 and the outer pipe 105 and the thermally conducting object 127 within the inner pipe 107 may be optimized by the parameters derived from the desired heat exchange and the specific geology and target temperature.
As shown in FIG. 9, the thermal gradient isotherms of the vertical closed loop geothermal well 100 generally show that the rocks surrounding the well 101 do not initially transfer heat as fast as the thermal convection inside the well 101 takes away the heat as indicated by the sharp temperature drop horizontally around the well 101. The concept of using an optimal thermally conducting material 113, such as graphite is to augment the heat supply from hotter rocks below more quickly. Generally, the surrounding rocks will act to insulate the well 101 as the optimal thermally conducting material 113 or graphite gets heated, and a column of heat will be formed around the main well 101 including the extended portion 150 of the main well 101, provided that there is enough of a temperature difference between the top of the main well 101 and the target temperature zone (shaded) where the heat exchanger 123 may be placed. Thus, progressively cooler isotherms may be formed along the column above the target temperature zone, while an inverted set of progressively hotter isotherms may be formed in the column at and below the target temperature zone.
As shown in FIG. 10, however, the pattern of isotherms shifts as the heat is extracted by the heat exchange zone 117 over time. The isotherms at and below the target temperature zone become more flat as the heat is pulled up the main well 101 and carried out by the thermal fluid 109. FIG. 11 further shows how the pattern of isotherms with a CLG system may be altered with the presence of horizontal heat conducting channel(s) 115. The horizontal plane of the heat conducting channel(s) 115 cools as the heat is extracted. The heat supply is coming from the earth underneath as the horizontal plane takes away heat from the entire plane. The isotherm gradient may become less steep, indicating less saturation.
According to embodiments of the present invention, one or more horizontal heat conducting channels may be created and used to improve and increase the collection of heat slowly rising vertically through the rock over a larger area than with only the vertical well. Heat transfer through the horizontal heat conducting channels, which are filled and packed with graphite rod and powder will likely be very fast. When filling or packing the horizontal wellbore or channel with powder and/or solid graphite, care must be taken to ensure that the graphite is tightly packed with no inter-particle, nor inter-solid void, and the wellbore must be compressed with graphite upon completion.
Although drilling the horizontal heat conducting channel(s) for heat collection may add cost, it is relatively fast to drill through the horizontal layers of sedimentary rock, and the drilling cost may be controlled the number of wells drilled. At a target temperature depth according to some embodiments, one or more horizontal heat conducting channel(s) may be drilled from the main vertical well through a sedimentary layer(s). Porous sedimentary layer drilling is generally faster, easier, and less expensive.
As shown in FIG. 12, horizontal heat conducting channels are drilled through the target temperature zone sedimentary layer, graphite powder or slurry is injected strategically, then the horizontal well is filled and packed by graphite, the layer becomes a heat collection zone. The graphite channels may become heat conducting channels, which may penetrate through fractures and cracks to further extend the reach of these heat conducting channels. The heat exchange zone of the main well may be located at about the same depth as or slightly shallower than these heat collection channels.
As shown in FIG. 13, the horizontal heat conducting channels may alternatively be inclined, angled, or curved upward toward the main well in the direction of heat flow up the main well. The curvature of the inclined or curved heat conducting channels may be at an angle commonly used in the art of drilling wells. This may enable graphite rods to slide and be gravity fed into the inclined or curved heat conducting channels due to the incline and there being very little friction.
The horizontal heat conducting channels may be drilled along and within the sedimentary layer in all directions. They can be drilled using waterjet or another conventional drilling technique. The purpose of the drill is to create a channel around the single hole of the main well to later inject graphite powder and pack it with the powder using turbulent fluid. Water may be sufficient; however, supercritical CO₂as the fluid may be particularly well suited due to its permeability and possible affinity to this solid conductor. The amount of CO₂required is nowhere near the amount used for carbon sequestration, nor CO₂injection for enhanced oil recovery. The intent with drilling the heat conducting channels is not to sequester, but to permeate through the sedimentary layer. As soon as the graphite is packed tight, the fluid injection is complete.
The heat conducting channels to be drilled do not have to be of large diameter. Six inch diameter at the borehole may be sufficient. After such channels are drilled, graphite may be injected into each hole through the borehole entrance using turbulent fluid to push them through the channel. The fluid may be steam, pressured water, or supercritical CO₂. Each well shall be injected with the graphite until it is packed tight. This enables graphite powder of microns in diameter to migrate into the pores of the sedimentary rocks with the injection fluid and alter the thermal conductivity of such sedimentary rocks to be significantly increased throughout the range of the channels. Along with solid particles and channels, any fluid remaining that was used to inject the graphite powder may also convect within the sedimentary layer, which may further increase the effective conductivity of the heat collection zone. Solid conductance of the graphite channel near the borehole may be higher using graphite rods to ensure even higher conductivity of collected heat to the borehole.
The possibility exists that the sedimentary layer may contain fluids, such as water. The temperature balance between the heat collecting channels and the rest of the rocks may create convection within the formation, and the presence of fluids may generally improve the thermal conductivity and overall horizontal thermal transfer within the sedimentary layer within the heat collection zone. The extent of thermal conductivity increase resulting from the presence of fluid in the layer as well as the optimization of injection methods should be the subject of further study.
According to some embodiments, a plurality of horizontal heat conducting channels may be arranged to cover a large area within a horizontal plane. Ideally, the horizontal heat conducting channels may be drilled at a thermal layer to cover an area of about 200-300 meters in radius. Such an area of heat conducting channels may supply sufficient heat to the heat exchange zone of a vertical main well to ultimately generate electricity above ground by collecting heat rising through such area from underneath. Depending on the thermal conductance modeling, a staggered arrangement of heat conducting channels in a single layer may preferably be drilled. A number of different arrangements of channels are possible. For example, FIG. 14 shows a top view of a heat collection zone comprising a spoke-like pattern of horizontal heat conducting channels in a sedimentary layer. FIG. 15 shows an example of a pattern of heat collection zones with each composed of a plurality of horizontal heat conducting channels in a spoke-like pattern feeding into a main well. FIG. 16 shows another exemplary arrangement of horizontal heat conducting channels that are intertwined in the sedimentary layer and feeding into several main wells. FIG. 17 provides yet another example of an arrangement of heat conducting channels with each feeding into separate main wells.
Current drilling technology is capable of drilling wells at significantly higher temperatures above 300° C. and also allows for directional drilling. According to embodiments of the present invention, as shown in FIG. 18, the direction of an extended portion of a well or heat collecting channel may be drilled along a fault plane 160 where superheated thermal vents may be found. Heat rises though the fault plane from a heat source below that may be greater than 500° C. and may exit at the surface through vents. The presence of such superheated vents are observable by satellite thermal imagery above ground as its vent exits. According to some embodiments, a vertical main well 101 may be drilled downward toward a hot target zone(s) or heat source(s) by drilling from a somewhat distant point on the surface away from the vent exits, and directional drilling may then be employed to form an extended portion of the main well or a heat conducting channel 170, which may be formed on an incline along the fault plane 160. The extended portion of the main well or heat conducting channel 170 may consist of a wellbore filled and packed with an optimal thermally conducting material, such as graphite powder and/or solid graphite shapes. The closed loop geothermal system or apparatus may then be placed in the main well 101.
FIG. 18 depicts the way a well filled with solid conducting graphite may be configured for collecting heat in a fault zone or plane 160. Heated gas originating from a heat source, possibly from subsurface magma escapes along the fault plane 160. On the surface, superheated vents result in hot spots shown on thermal spectrum satellite images. The seismic analysis may reveal the corresponding fault structure. The vertical main well 101 may be drilled somewhat distant from the hot spots but over the fault plane such that the main well 101 may be drilled to target a subsurface cross section of the fault plane 160. The intersect of the main well 101 and the cross section of the fault plane 160 should be at least be at a target temperature zone or depth, but may be much higher. The temperature of the cross section or nearby area may be estimated by geological modeling by those skilled in the art. When the main well 101 reaches the fault plane 160, directional drilling may allow the extended portion of the main well or heat conducting channel 170 to be drilled along the fault plane 160 aiming toward the heat source to increase or maximize contact with the venting gas. When a sufficient extension of the well is drilled along the heated fault plane 160, then the extended portion of the main well or heat conducting channel 170 is filled with an optimal thermally conducting material, such as graphite powder and/or rods or shapes and packed tight for no gas leak. Then, the closed loop geothermal system of the vertical main well 101 including the piping system, which may include outer and inner pipes and/or heat exchanger, may be put in place at a heat exchange zone 117 directly above the extended portion of the main well or heat conducting channel 170 and surrounded in contact with an optimal thermally conducting material 113, such as graphite filler. According to some embodiments, multiple main wells 101 may be drilled to intersect with fault plane 160 that may each be accompanied by an extended portion of the main well or a heat conducting channel 170.
According to some embodiments, as shown for example in FIG. 19, it is envisioned that an extended portion 150 of a main well may in the future be filled with packed graphite and extended toward the magma chamber. In addition, a heat resistant thermal conductor, such as a closed end high temperature pipe 145 that may also be packed with graphite, may actually extend into the magma directly. For the high temperature pipe 145, an alloy may be used that is tolerant to high temperatures, such as an Inconel pipe, which can withstand the temperature well above 1200° C. Graphite itself is not combustible and is stable up to about 1800° C., which is higher than the magma temperature. The temperature of the main well near the heat exchange zone may be about 200° C., and the temperature near the bottom of the extended portion 150 of the main well 101 may be higher than about 300° C. The temperature of the magma may be greater than 500° C. It may be necessary for this type of system that the high temperature pipe 145 used to collect thermal energy from the magma to not cause solidification of the magma. As long as the magma remains fluid or liquid, a continuous supply of heat may be possible, but the conductivity of the magma rock is reduced if solidified. Thermal equilibrium must be carefully examined prior to determining its feasibility. Magma may solidify as water molecules are separated from molten rock.
According to another broad aspect of the present invention, methods are provided for the making/formation as well as the operation of the closed loop geothermal system and apparatus of the present invention. According to embodiments of the present invention, a method is provided comprising providing first providing or placing, setting, configuring, inserting, etc., a piping system comprising one or more pipes in a main well comprising a hole in the earth, wherein the piping system is inside the main well to make a closed loop geothermal apparatus, such that a bottom portion of the piping system reaches a target temperature zone underground, wherein one or more heat conducting channels each comprise a wellbore filled and packed with graphite, wherein the one or more heat conducting channels converge to contact a heat exchange zone of the main well at or near the bottom of the piping system, and wherein the heat conducting filler consisting essentially of graphite is packed in a space between the main well and the piping system in the target temperature zone.
According to some embodiments of the present invention, a method is provided for making an apparatus of the present invention comprising first placing, setting, configuring, inserting, etc., an inner pipe and an outer pipe in a main well to make a closed loop geothermal apparatus, such that the bottom portions of the inner pipe and the outer pipe reach a target temperature zone underground, and then filling and/or packing a heat conducting filler comprising an optimal thermally conducting material in a space between the main well and the outer pipe in the target temperature zone. According to some embodiments, the inner pipe and the outer pipe is placed, set, configured, inserted, etc., such that the inner pipe is inside the outer pipe in a concentric arrangement. The inner pipe and the outer pipe may be configured such that a thermal fluid traveling downward in the space between the inner pipe and the outer pipe can enter the inner pipe at or near the bottom of the outer pipe and travel upward within the inner pipe. Generally, the thermal fluid will be warmer or hotter inside the inner pipe relative to the thermal fluid between the inner and outer pipe as well as the surrounding earth.
According to some embodiments, such a method may further comprise the step of forming one or more heat conducting channels that converge to contact a heat exchange zone of the main well at or near the bottom of the piping system, or outer and inner pipes in the case of the concentric design. This step may be performed prior to placing, setting, configuring, inserting, etc., the piping system or the inner pipe and the outer pipe in a main well to make the closed loop geothermal apparatus. The method may further comprise the step of filling and/or packing the one or more heat conducting channels with an optimal thermally conducting material, such as graphite, again prior to the step of placing, setting, configuring, inserting, etc., the piping system or the inner pipe and the outer pipe in a main well. The method may yet further comprise the step of filling and/or packing a portion of each of the one or more heat conducting channels with an optimal thermally conducting material, which may then interfaces with the heat conducting filler to provide a continuous flow of thermal energy from the one or more heat conducting channels to the heat exchange zone of the main well through the optimal thermally conducting material of the one or more heat conducting channels and the heat conducting filler. According to some method embodiments, prior to placing, setting, configuring, inserting, etc., the piping system or the inner pipe and the outer pipe in a main well to make the closed loop geothermal apparatus, methods of the present invention may comprise a step of injecting graphite, such as graphite slurry which may be composed mainly of small graphite particles and a fluid carrying the particles, into the sedimentary rock layer(s) to form one or more heat conducting channels. Such step according to some method embodiments of the present invention may further comprise filling the pores and cracks of such rock layer(s) to increase contact with the one or more heat conducting channels.
According to embodiments of the present invention, a method is provided for the operation of an apparatus or system of the present invention comprising first providing a closed loop geothermal apparatus of the present invention; and then causing a thermal fluid to flow downward toward the bottom portion of the piping system and heated, before traveling upward toward the surface of the earth. According to embodiments having the concentric design of the piping system, such methods may include a step of causing a thermal fluid to flow downward in the space between an inner pipe and an outer pipe, enter the inner pipe at the bottom of the inner pipe, and flow upward inside the inner pipe. According to some embodiments, such methods may further or separately comprise a step of harnessing thermal energy from the thermal fluid at or near the surface of the earth, which may be performed in addition to the step of causing a thermal fluid to flow through a closed loop geothermal apparatus or system of the present invention.
According to some method embodiments, the apparatus provided in the first step may further comprise one or more heat conducting channels with each comprising a wellbore filled and packed with an optimal thermally conducting material as described herein. Alternatively, according to some embodiments, methods of the present invention may further comprise a step of injecting graphite, such as graphite slurry which may be composed mainly of small graphite particles and a fluid carrying the particles, into the sedimentary rock layer(s) to form one or more heat conducting channels. Such step according to some method embodiments of the present invention may further comprise filling the pores and cracks of such rock layer(s) to increase contact with the one or more heat conducting channels. Such step of injecting graphite may be performed before the providing step. The heat conducting channels may generally converge to contact a heat exchange zone of the main well at or near the bottom of the piping system. The apparatus provided in the first step may further comprise an optimal thermally conducting material filled and/or packed in a portion of each of the one or more heat conducting channels, which may interface with the heat conducting filler packed in a space between the main well and the piping system to provide a continuous flow of thermal energy from the one or more heat conducting channels to the heat exchange zone of the main well through the optimal thermally conducting material of the one or more heat conducting channels and the heat conducting filler.
While the present invention has been disclosed with references to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Furthermore, it should be appreciated that all examples in the present disclosure, while illustrating many embodiments of the invention, are provided as non-limiting examples and are, therefore, not to be taken as limiting the various aspects so illustrated. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof.

Claims

1. A closed loop geothermal apparatus comprising:

a. a main well comprising a hole in the earth;

b. a piping system comprising one or more pipes;

c. one or more heat conducting channels; and

d. a heat conducting filler,

wherein the piping system is inside the main well, such that a bottom portion of the piping system reaches a target temperature zone underground,

wherein the one or more heat conducting channels each comprise a wellbore filled and packed with graphite,

wherein the one or more heat conducting channels converge to contact a heat exchange zone of the main well at or near the bottom of the piping system;

and

wherein the heat conducting filler consisting essentially of graphite is packed in a space between the main well and the piping system in the target temperature zone.

2. The apparatus of claim 1, wherein the piping system comprises an inner pipe and an outer pipe in a concentric arrangement.

3. The apparatus of claim 2, wherein the inner pipe and the outer pipe are configured such that a thermal fluid traveling downward in the space between the inner pipe and the outer pipe can enter the inner pipe at or near the bottom of the outer pipe and travel upward within the inner pipe.

4. The apparatus of claim 2, wherein the inner pipe is made of a heat conducting material in the target temperature zone.

5. The apparatus of claim 2, wherein the outer pipe is made of a heat conducting material in the target temperature zone.

6. The apparatus of claim 1, wherein the heat conducting filler packed in the space between the main well and the outer pipe comprises graphite rods, graphite powder, and/or graphite flakes.

7. The apparatus of claim 1, wherein the heat conducting filler packed in the space between the main well and the outer pipe is pure or nearly pure graphite.

8. The apparatus of claim 1, wherein the heat conducting filler has a thermal conductivity in a range from about 100 W/m·K to about 5780 W/m·K.

9. The apparatus of claim 10, wherein the heat conducting filler comprising graphite has a thermal conductivity from about 100 W/m·K to about 450 W/m·K.

10. The apparatus of claim 1, wherein the heat conducting filler comprising graphite has a thermal conductivity from about 120 W/m·K to about 300 W/m·K.

11. The apparatus of claim 1, further comprising an extended portion of the main well below the bottom of the piping system, wherein the extended portion of the main well is filled and packed with graphite.

12. The apparatus of claim 11, wherein the graphite of the extended portion of the main well is pure or nearly pure graphite.

13. The apparatus of claim 11, wherein the piping system has a closed bottom, and wherein the graphite in the extended portion of the main well contacts the closed bottom of the piping system.

14. The apparatus of claim 11, wherein the graphite in the extended portion of the main well includes multiple graphite rods stacked in the extended portion of the main well, wherein the graphite rods contact the closed bottom of the piping system.

15. The apparatus of claim 1, wherein a portion of each of the one or more heat conducting channels comprises graphite that interfaces and contacts the graphite of the heat conducting filler to provide a continuous flow of thermal energy from the one or more heat conducting channels to the heat exchange zone of the main well through the graphite of the one or more heat conducting channels and the heat conducting filler.

16. The apparatus of claim 15, wherein the graphite filled and packed in the one or more heat conducting channels comprises graphite rods, graphite powder, and/or graphite flakes.

17. The apparatus of claim 15, wherein the graphite filled and packed in the one or more heat conducting channels is pure or nearly pure graphite.

18. The apparatus of claim 15, wherein the one or more heat conducting channels extend horizontally through a sedimentary layer of the earth.

19. The apparatus of claim 1, further comprising an outer casing positioned between the main well and the piping system, wherein the heat conducting filler is packed in a space between the main well and the outer casing in the target temperature zone.

20. The apparatus of claim 3, further comprising a heat exchanger positioned in a heat exchange zone of the main well at or near the bottom of the inner and outer pipes.

21. The apparatus of claim 20, wherein the heat exchanger comprises one or more supporting sections between the inner and outer pipes.

22. The apparatus of claim 20, wherein the heat exchanger comprises a thermally conducting object inside the inner pipe.

23. The apparatus of claim 1, wherein the piping system is configured such that a thermal fluid travels downward toward the bottom portion of the piping system and heated, before traveling upward toward the surface of the earth.

24. A closed loop geothermal apparatus comprising:

a. a main well comprising a hole in the earth;

b. a piping system comprising one or more pipes;

c. an extended portion of the main well below the bottom of the piping system; and

d. a heat conducting filler,

wherein the piping system is configured such that a thermal fluid traveling downward toward the bottom of the piping system and heated before traveling upward toward the surface of the earth,

wherein the heat conducting filler consisting essentially of graphite is packed in a space between the main well and the piping system in the target temperature zone, and

wherein the extended portion of the main well is filled and packed with graphite.

25. The apparatus of claim 24, wherein the graphite of the extended portion of the main well is pure or nearly pure graphite.

26. The apparatus of claim 24, wherein the piping system has a closed bottom, and wherein the graphite in the extended portion of the main well contacts the closed bottom of the piping system.

27. The apparatus of claim 24, wherein the graphite in the extended portion of the main well includes multiple graphite rods stacked in the extended portion of the main well, wherein the graphite rods contact the closed bottom of the piping system.

28. A method comprising:

(a) providing a closed loop geothermal apparatus comprising a main well having a hole in the earth, a piping system having one or more pipes, one or more heat conducting channels; and a heat conducting filler;

wherein the piping system is inside the main well, such that a bottom portion of the piping system reaches a target temperature zone underground, wherein the one or more heat conducting channels each comprise a wellbore filled and packed with graphite, wherein the one or more heat conducting channels converge to contact a heat exchange zone of the main well at or near the bottom of the piping system; and wherein the heat conducting filler consisting essentially of graphite is packed in a space between the main well and the piping system in the target temperature zone; and (b) causing a thermal fluid to flow downward toward the bottom portion of the piping system and heated, before traveling upward toward the surface of the earth.