Patent Grant
9423158
Not applicable.
Not applicable.
The present invention relates generally to the field of converting geothermal energy into electricity. More specifically, the present invention relates to capturing geothermal heat from deep within a drilled well and bringing this geothermal heat to the Earth's surface to generate electricity in an environmentally friendly process.
Wells that have been drilled for oil and gas exploration that are either depleted, or have never produced oil or gas, usually remain abandoned and/or unused and may eventually be filled. Such wells were created at a large cost and create an environmental issue when no longer needed for their initial use.
Wells may also be drilled specifically to produce heat. While there are known geothermal heat/electrical methods and systems for using the geothermal heat/energy from deep within a well (in order to produce a heated fluid (liquid or gas) and generate electricity therefrom), these methods have significant environmental drawbacks and are usually inefficient in oil and gas wells due to the depth of such wells.
More specifically, geothermal heat pump (GHP) systems and enhanced geothermal systems (EGS) are well known systems in the prior art for recovering energy from the Earth. In GHP systems, geothermal heat from the Earth is used to heat a fluid, such as water, which is then used for heating and cooling. The fluid, usually water, is actually heated to a point where it is converted into steam in a process called flash steam conversion, which is then used to generate electricity. These systems use existing or man made water reservoirs to carry the heat from deep wells to the surface. The water used for these systems is extremely harmful to the environment, as it is full of minerals, is caustic and can pollute water aquifers. Such deep-well implementations require that a brine reservoir exists or that a reservoir is built by injecting huge quantities of water into an injection well, effectively requiring the use of at least two wells. Both methods require that polluted dirty water is brought to the surface. In the case of EGS systems, water injected into a well permeates the Earth as it travels over rock and other material under the Earth's surface, becoming polluted, caustic, and dangerous.
A water-based system for generating heat from a well presents significant and specific issues. For example, extremely large quantities of water are often injected into a well. This water is heated and flows around the inside of the well to become heated and is then extracted from the well to generate electricity. This water becomes polluted with minerals and other harmful substances, often is very caustic, and causes problems such as seismic instability and disturbance of natural hydrothermal manifestations. Additionally, there is a high potential for pollution of surrounding aquifers. This polluted water causes additional problems, such as depositing minerals and severely scaling pipes.
Geothermal energy is present everywhere beneath the Earth's surface. In general, the temperature of the Earth increases with increasing depth, from 400°-1800° F. at the base of the Earth's crust to an estimated temperature of 6300°-8100° F. at the center of the Earth. However, in order to be useful as a source of energy, it must be accessible to drilled wells. This increases the cost of drilling associated with geothermal systems, and the cost increases with increasing depth.
In a conventional geothermal system, such as for example and enhanced geothermal system (EGS), water or a fluid (a liquid or gas), is pumped into a well using a pump and piping system. The water then travels over hot rock to a production well and the hot, dirty water or fluid is transferred to the surface to generate electricity.
As mentioned earlier herein, the fluid (water) may actually be heated to the point where it is converted into gas/steam. The heated fluid or gas/steam then travels to the surface up and out of the well. When it reaches the surface, the heated water and/or the gas/steam is used to power a thermal engine (electric turbine and generator) which converts the thermal energy from the heated water or gas/steam into electricity.
This type of conventional geothermal system is highly inefficient in very deep wells for several of reasons. First, in order to generate a heated fluid required to efficiently operate several thermal engines (electric turbines and generators), the fluid must be heated to degrees of anywhere between 190° F. and 1000° F. Therefore the fluid must obtain heat from the surrounding hot rock. As it picks up heat it also picks up minerals, salt, and acidity, causing it to very caustic. In order to reach such desired temperatures in areas that lack a shallow-depth geothermal heat source (i.e. in order to heat the fluid to this desired temperature), the well used must be very deep. In this type of prior art system, the geologies that can be used because of the need for large quantities of water are very limited.
The deeper the well, the more challenging it is to implement a water-based system. Moreover, as the well becomes deeper the gas or fluid must travel further to reach the surface, allowing more heat to dissipate. Therefore, using conventional geothermal electricity-generating systems can be highly inefficient because long lengths between the bottom of a well and the surface results in the loss of heat more quickly. This heat loss impacts the efficacy and economics of generating electricity from these types of systems. Even more water is required in such deep wells, making geothermal electricity-generating systems challenging in deep wells.
Accordingly, prior art geothermal systems include a pump, a piping system buried in the ground, an above ground heat transfer device and tremendous quantities of water that circulates through the Earth to pick up heat from the Earth's hot rock. The ground is used as a heat source to heat the circulating water. An important factor in determining the feasibility of such a prior art geothermal system is the depth of wellbore, which affects the drilling costs, the cost of the pipe and the size of the pump. If the wellbore has to be drilled to too great a depth, a water-based geothermal system may not be a practical alternative energy source. Furthermore, these water-based systems often fail due to a lack of permeability of hot rock within the Earth, as water injected into the well never reaches the production well that retrieves the water.
The present invention discloses a geothermal method of harvesting heat energy so it can be turned into electricity. Typically a drilled well's bore diameter reduces in diameter from as much 30 inches on the top to six to eight inches at the bottom of the well. The bottom of the well from the start of the Heat Zone 10 to the Bottom of the Well 11 (Heat Nest) is the target area for extraction of heat. This invention is an approach to maximize the amount of heat that can be transferred form the earth (surface of hot rock) to a heat exchanging element in the Heat Nest 12 by using modelling techniques and proper designs and materials to implement an effective heat extraction system. The heat exchanging Mechanism is a combination of a fluid heat Exchanging Element 5, heat conductive material 6 and heat conductive grout 6 placed in the bottom of a well that has been designed and constructed for heat flow. The heat conductive material and grout conducts the heat from the hot rock surface to the fluid heat exchanging element. The fluid heat exchanging element transfers heat from the heat conducting material and grout to a heat conductive fluid that is flowing through the element. The ratio of temperature and gallons of fluid pumped per minute versus the amount of hot rock surface and the conductivity of the hot rock is critical to creating a system that reaches heat equilibrium, these ratios and the proper implementation of the system needs to be modelled to predict the proper design. Heat equilibrium is the point at which the amount of heat extracted from the bottom of the well is equal to the rate at which the surface of the hot rock is able to replace its heat. A model that helps achieve the proper design of a heat nest 12 that will maximize the value of the heat equilibrium will provide for optimum results. A predictive model that takes into account the design choices and other parameters is used to optimize the performance of the heat extraction.
Wells that have been drilled for oil and gas exploration that are either depleted, or have never produced oil or gas, can now be used to generate electricity. Wells can also be drilled specifically for the purpose of generating electricity. The only requirement is that the wells are deep enough to generate heat from the bottom of the well. The invention is a process for maximizing the heat transfer from the earth (surface of hot rock) to a heat exchanging mechanism at the bottom of a well constructed with a Heat Nest 12. The heat exchanging mechanism is a combination of a fluid heat exchanging element 5, heat conductive material and heat conducting grout 6 properly placed in a well bottom where a Heat Nest has been implemented to exchange heat. The mating and proliferation of the heat conductive material and grout to the surrounding geothermic designed and constructed Heat Nest environment is a fundamental element for the optimization of heat flow. The parametric characteristics (length, width, quantity, heat conductivity, placement, etc) will impact the efficiency of the Heat Nest and the transfer of heat.
The surface of the hot rock exposed in the heat nest is the source of the heat for the generation of power. The hot rock has a capacity to deliver heat that is dependent on its ability to replenish the heat it transfers to the heat conductive material and grout. The heat that can be delivered from the hot rock surface on a continuous basis is the heat equilibrium of the heat nest. The predictive model computes the hot rock surface and the positioning of the creation of the hot rock surface in order to maximize heat flow.
An optimized system uses the proper materials and components in the proper design. The design and components are characterized in a model that will guide the design and implementation. The model can be used for each of the different embodiments described herein. The following chart lists the data used and generated by model, other data inputs and outputs can be added when needed.
The present invention discloses, generally, a system and method of economically conducting geothermal heat from a well to the Earth's surface and then using this heat to generate electricity in a closed-loop, solid state system. This system and method, known as GTherm, is environmentally responsible because there is no fluid flow from the Earth. It is entirely based on heat flow from rock deep within a well through solid materials to heat contents of pipes pumped in a closed loop from and to the Earth's surface.
The present invention discloses a system for generating electricity using geothermal heat from within a drilled well, comprising a heat harnessing component having a closed-loop solid state heat extraction system. The closed-loop solid state heat extraction system includes a heat exchanging element positioned within a heat nest in a well and a heat conductive material inserted into the well to conduct geothermal heat from the rock surrounding the heat nest to the heat exchanging element. The rock surrounding the heat nest heats the heat conductive material to an equilibrium temperature determined by a surface area of the rock surrounding the heat nest, the equilibrium temperature being a temperature at which the rock surrounding the heat nest and generating the geothermal heat continually recoups the geothermal heat it is conducting to the heat conductive material and above which the geothermal heat generated by the rock surrounding the heat nest dissipates as the heat conductive material conducts heat from the rock surrounding the heat nest to the heat exchanging element. The system also includes an electricity generating component that includes a thermal engine, the electricity generating component receiving geothermal heat from contents of a piping component coupling the heat harnessing component to the electricity generating component, the piping component including a set of downward-flowing pipes and a set of upward-flowing pipes, the upward-flowing pipes conveying contents of the piping component heated by the heat exchanging element to a surface of the well and into the electricity generating component. The system further includes insulation inserted into the well and substantially surrounding at least the upward-flowing pipes at least one position between the heat nest and the surface of the well to maintain a temperature of the contents of the piping system substantially constant as the contents of the piping system are pumped to the surface of the well. The closed-loop, solid state heat extraction system extracts geothermal heat from the well without exposing the rock surrounding the heat nest to a liquid flow.
In another embodiment, the present invention discloses a heat extraction system for generating geothermal heat from within a drilled well. The heat extraction system comprises a heat conductive material injected into an area within a heat nest near a bottom of a drilled well between a heat exchanging element and rock surrounding the heat nest to form a closed-loop, solid state heat exchange to heat contents of a piping system flowing into and out of the heat exchanging element at an equilibrium temperature at which the rock surrounding the heat nest and generating the geothermal heat continually recoups the geothermal heat it is conducting to the heat conductive material and above which the geothermal heat generated by the rock surrounding the heat nest dissipates as the heat conductive material conducts heat from the rock surrounding the heat nest to the heat exchanging element. The heat conductive material solidifies to substantially fill the area within the heat nest to transfer heat from the rock surrounding the heat nest and the heat exchanging element, the piping system bringing the contents of the piping system from a surface of the well into the heat nest and carrying heated contents to the surface of the well from the heat nest. The closed-loop solid state heat extraction system extracts geothermal heat from the well without exposing the rock surrounding the heat nest to a liquid flow.
In another embodiment, the present invention discloses a method of generating electricity using geothermal heat from within a drilled well. The method comprises extracting geothermal heat from rock surrounding a heat nest positioned at a location within a well by injecting a heat conductive material into the heat nest to surround a heat exchanging element to form a closed-loop, solid-state heat extraction system, the heat conductive material exchanging geothermal heat from the rock surrounding the heat nest to the heat exchanging element to heat contents of a piping system, the contents heated within the heat nest at an equilibrium temperature at which the rock surrounding the heat nest and generating the geothermal heat continually recoups the geothermal heat it is exchanging with the heat conductive material and above which the geothermal heat generated by the rock surrounding the heat nest dissipates as the heat conductive material exchanges heat from the rock surrounding the heat nest to the heat exchanging element. The method also comprises insulating the piping system at least one point between the heat nest and the surface of the well to maintain a temperature of the contents of the piping system substantially constant as the contents of the piping system are pumped to the surface of the well. The method further comprises pumping the heated contents of the piping system into an electricity generating component after the heated contents of the piping system reaches the surface of the well. The closed-loop solid state heat extraction system extracts geothermal heat from the well without exposing the rock surrounding the heat nest to a liquid flow.
In still another embodiment, the present invention discloses a method of extracting geothermal heat from within a drilled well. The method comprises determining a type of rock at a depth of a well, a surface area of the rock at the depth of the well, and a heat conductivity factor of the rock at the depth of the well, increasing the surface area of the rock at a desired point in the well between a heat point of the well and a bottom of the well, and forming a heat nest within the well beginning at the bottom of the well and ending at the heat point of the well. The method also includes injecting a heat conductive material between rock surrounding the heat nest and a heat exchanging element within the heat nest to form a closed-loop, solid-state heat extraction system to exchange heat from the rock surrounding the heat nest to the heat exchanging element to heat a contents of a piping system flowing into and out of the heat exchanging element at an equilibrium temperature at which the rock surrounding the heat nest and generating the geothermal heat continually recoups the geothermal heat it is exchanging with the heat conductive material and above which the geothermal heat generated by the rock surrounding the heat nest dissipates as the heat conductive material exchanges heat from the rock surrounding the heat nest to the heat exchanging element. The method further comprises insulating the piping system between the heat nest and a surface of the well. The closed-loop solid state heat extraction system extracts geothermal heat from the well without exposing the rock surrounding the heat nest to a liquid flow.
Other embodiments, features and advantages of the present invention will become more apparent from the following description of the embodiments, taken together with the accompanying several views of the drawings, which illustrate, by way of example, the principles of the invention.
In the following description of the present invention reference is made to the accompanying drawings which form a part thereof, and in which is shown, by way of illustration, exemplary embodiments illustrating the principles of the present invention and how it may be practiced. It is to be understood that other embodiments may be utilized to practice the present invention and structural and functional changes may be made thereto without departing from the scope of the present invention.
In the first embodiment (
In the second embodiment
In the third embodiment
In the fourth embodiment
The heat conductive material used 6 can be metal, plastic, ceramics or any other material that conducts heat well. It can take the form of rods, mesh, foam, particles and balls. The material should be environmentally inert and should resist the caustic environment of the well. In a preferred embodiment the conductive material is in the form of small balls. An example of a material that could be used is steal ball bearings. The balls can be specifically designed for this use. The ball shape is particularly useful for the balls will roll and fill in all the space between the hot rock and the fluid heat conductive exchange element 5. As the balls fill the space 6 they will touch each other and the hot rock and provide a conductive path for the heat. The balls are particularly effective in embodiments 3 and 4 (
The balls are delivered down to the heat nest by using a liquid filled pipe to control the flow and speed of the balls as they proceed down the well. As the liquid and balls arrive at the heat nest the liquid will evaporate because of the heat (could be turned to steam that escapes up the well) and the balls will then roll into the empty spaces.
Once the balls fill the heat nest the heat conductive gout is delivered in liquid form with a pipe. The grout flows around the balls (or other forms of solid heat conductive material) to fill all the empty spaces. As the grout hardens it creates a solid state heat conductive mechanism in the heat nest. The grout has been prepared to counteract the caustic environment of the well. If the environment of the heat nest is acidic the grout is prepared as an alkaline mixture to counter act the acidic environment. If the environment of the heat nest is alkaline the grout is prepared with an acidic mixture to counter act the alkaline environment.
The size of the balls and the materials used determine the heat conductivity of the heat exchange mechanism. The predictive model will compute the amount of heat that can be extracted based on the supplied data and materials.
Once the grout hardens the well bore from the grout to the surface is filled with insulation. This reduces heat loss from the well bottom to the electric generation equipment. Examples of insulation that can be used are “Therm-O-Case” and “Therm-O-Trol” manufactured by General Electric for use in the oil industry.
Crude oil moving through 800 miles trans-Alaska pipeline must be kept at relatively high temperature approximately 180 degrees Fahrenheit to maintain fluidity of oil in arctic weather. GE provided a product called Therm-O-Trol which is metal bonded polyurethane foam especially formulated for arctic insulation. Another problem was solved using Therm-O-Case which is a double walled oil well casing with multi-layered insulation which provides a protective barrier against heat transfer. Evolving from Gemini and Apollo, this product solved problem involving bringing in hot crude oil from 2,000 foot deep wells to surface without transferring oil heat to the surrounding permafrost soil; heat transfer could melt the frozen terrain and cause dislocation that might destroy expensive well casings.
A second preferred embodiment is the use of a highly conductive foam that can be pumped into the space between the hot rock and the fluid heat conductive exchange element 5. This foam can be pumped done into the heat nest space with a pipe. Once the foam has been piped into the space and hardens it can be capped with the heat conductive grout and then insulation can be installed between the grout cap and the top of the well.
Carbon foams were first developed by researchers in the late 60's as a reticulated vitreous (glassy) carbon foam. Ford (1) reported on carbon foams produced by carbonizing thermosetting organic polymer foams through a simple heat treatment. Then, Googin et al. 2 at the Oak Ridge Atomic Energy Commission Laboratory reported the first process dedicated to controlling the structure and material properties of carbon and graphitic foams by varying the precursor material (partially cured urethane polymer). In the several decades following these initial discoveries, many researchers explored a variety of applications for these materials ranging from electrodes to insulating liners for temperatures up to 2500° C. In fact, reticulated carbon foams have been used as the template for many of the metal and ceramic foams currently used in industry. In the 1970's, research focused primarily on producing carbon foams from alternative precursors. For example, Klett, R. (6) at the Sandia National Laboratories produced the first carbon foams from cork, a natural cellular precursor. Others worked on various processing and precursor changes in an attempt to modify properties and reduce cost. The majority of these carbon foams were used for thermal insulation, although some structural applications were found.
In the early 1990's, researchers at the Wright Patterson Air Force Base Materials Lab pioneered mesophase-derived graphitic foams, specifically for replacing expensive 3-D woven fiber performs in polymer composites and as replacements for honeycomb materials. Their work was centered on developing a highly structural material that was lightweight, and to date, exhibits the highest specific strength of carbon foams. Concurrently, Ultramet Corp, performed research on RVC foam and used chemical vapor deposition (CVD) as a technique to place pyrolytic graphite on the glassy carbon ligaments of RVC, producing 3-D carbon structures with high-modulus ligaments.
With the goal of producing very inexpensive carbon foams, researchers at West Virginia University developed a method that used coal as a precursor for high strength foams with excellent thermal insulation properties. In 1997, Klett, J. at the Oak Ridge National Laboratory (ORNL) reported the first graphitic foams with bulk thermal conductivities greater than 40 W/m·K (recently, conductivities up to 180 W/m·K have been measured). By combining an open cellular structure with a thermal conductivity to weight ratio of greater than 200 (compared to 45 for copper), this material presents a unique opportunity to radically change the approach to solving many heat transfer problems. This graphite material has been examined for the core of heat transfer devices such as radiators and heat sinks, evaporative cooling and phase change devices. Furthermore, the ability of the graphite foam to intercalate lithium and absorb acoustic energy makes them candidates for several applications beyond thermal management. The following table outlines the thermal capacity of the foam.
It is to be understood that other embodiments may be utilized and structural and functional changes be made without departing from the scope of the present invention. The foregoing descriptions of the embodiments of the invention have been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Accordingly, many modifications and variations are possible in light of the above teachings. It is therefore intended that the scope of the invention not be limited by this detailed description.
This application is a continuation-in-part of U.S. Non-Provisional patent application Ser. No. 12/456,434 filed on Jun. 15, 2009. This application also claims priority to 1) U.S. Provisional Application No. 61/137,956, filed on Aug. 5, 2008; 2) U.S. Provisional Application No. 61/137,974, filed on Aug. 5, 2008; 3) U.S. Provisional Application No. 61/137,955, filed on Aug. 5, 2008; and 4) U.S. Provisional Application No. 61/137,975, filed on Aug. 5, 2008, the contents of all of which are hereby incorporated in their entirety.
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 12456434 | Jun 2009 | US |
| Child | 12462657 | US |
