METHOD FOR A RADIATOR EGS TO HARVEST GEOTHERMAL ENERGY

Abstract

An embodiment in accordance with the present invention includes an EGS configured to allow the commercial production of electrical energy. One criteria of an EGS according to the present invention is that the temperature and volume of the fluids extracted are sufficiently high and large enough as to allow the commercial production of electrical energy. The system is able to operate for at least N years before the extracted fluid falls below the minimum temperature needed for energy production. Additionally, fractures are separated from each other by a sufficiently large volume of rock (V.sub.crit) relative to the fractures surface area such that the ratio of the rate of heat extraction to the rate of heat supply controlled by the thermal conductivity of the rock is such that the intervening rock is cooled at a rate that is sufficiently slow to be economic.

Claims

1-20. (canceled)

21. A method, comprising: generating a manufactured hydrothermal fracture zone located in a plane defined by an injector well of a geothermal system and a production well of the geothermal system, wherein the manufactured hydrothermal fracture zone comprises a plurality of fractures generated by successive controlled permeability enhancement methodologies.

22. The method of claim 21, wherein the successive controlled permeability enhancement methodologies comprise energetics methodologies that directionally enhance a permeability of the manufactured hydrothermal fracture zone.

23. The method of claim 21, further comprising generating the plurality of fractures by administering a propellant based fracking agent in successively higher laterals to directionally form a zone of continuous fractured rock in each of the plurality of fractures.

24. The method of claim 21, wherein an orientation of the plurality of fractures is about vertical.

25. The method of claim 24, wherein the orientation of the plurality of fractures is within about forty-five degrees from a normal vector that is perpendicular to a horizontal plane.

26. The method of claim 21, wherein the plurality of fractures is configured to emulate a geometry of a radiator vane.

27. The method of claim 21, wherein: the injector well defines a first vertical pilot hole and a first lateral drilled to parallel a first maximum horizontal stress of the injector well; and the production well defines a second vertical pilot hole and a second lateral drilled to parallel a second maximum horizontal stress of the production well.

28. The method of claim 27, wherein the plurality of fractures extend from the first lateral of the injector well to the second lateral of the production well with no intermediary injection strings between the first lateral and the second lateral.

29. The method of claim 27, wherein the successively higher laterals are parallel to the first lateral of the injector well and the second lateral of the production well.

30. The method of claim 21, wherein the generating the manufactured hydrothermal fracture zone comprises generating the manufactured hydrothermal fracture zone to emulate a natural transmissive fracture system.

31. A system, comprising: a manufactured hydrothermal fracture zone located in a plane defined by an injector well of a geothermal system and a production well of the geothermal system, wherein the manufactured hydrothermal fracture zone comprises a plurality of fractures generated by successive controlled permeability enhancement methodologies.

32. The system of claim 31, wherein the successive controlled permeability enhancement methodologies comprise energetics methodologies that directionally enhance a permeability of the manufactured hydrothermal fracture zone.

33. The system of claim 31, wherein the plurality of fractures are generated by an administration of a propellant based fracking agent in successively higher laterals to directionally form a zone of continuous fractured rock in each of the plurality of fractures.

34. The system of claim 31, wherein the plurality of fractures is configured to emulate a geometry of a radiator vane.

35. The system of claim 31, wherein: the injector well defines a first vertical pilot hole and a first lateral drilled to parallel a first maximum horizontal stress of the injector well; and the production well defines a second vertical pilot hole and a second lateral drilled to parallel a second maximum horizontal stress of the production well.

36. The system of claim 31, wherein the manufactured hydrothermal fracture zone is formed to emulate a natural transmissive fracture system.

37. A system, comprising: an injector well defining a first vertical pilot hole and a first lateral drilled to parallel a first maximum horizontal stress of the injector well; a production well defining a second vertical pilot hole and a second lateral drilled to parallel a second maximum horizontal stress of the production well; and a manufactured hydrothermal fracture zone located in a plane defined by the injector well and the production well, wherein the manufactured hydrothermal fracture zone comprises a plurality of fractures generated by successive controlled manufactured hydrothermal fracture zone.

38. The system of claim 37, wherein the successive controlled permeability enhancement methodologies comprise energetics methodologies that directionally enhance a permeability of the manufactured hydrothermal fracture zone.

39. The system of claim 37, wherein the plurality of fractures are generated by an administration of a propellant based fracking agent in successively higher laterals to directionally form a zone of continuous fractured rock in each of the plurality of fractures.

40. The system of claim 37, wherein the plurality of fractures extend from the first lateral of the injector well to the second lateral of the production well with no intermediary injection strings between the first lateral and the second lateral.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings provide visual representations, which will be used to more fully describe the representative embodiments disclosed herein and can be used by those skilled in the art to better understand them and their inherent advantages. In these drawings, like reference numerals identify corresponding elements and:

[0014] FIG. 1 illustrates a schematic diagram of a Single “vane” unit of a Radiator EGS. A vane is a vertical manufactured fracture system.

[0015] FIG. 2 illustrates a schematic diagram of two “vane” units defining the intervening rock volume as V.sub.crit=l.sub.1×l.sub.2×l.sub.3.

[0016] FIG. 3 illustrates a schematic diagram of temperature distribution due to injection of fluid at a depth where rock temperature is >T.sub.min.

[0017] FIG. 4 illustrates a schematic diagram of a strike section to schematically illustrate how cooling will be slowed due to increasing temperature of fluid as it moves along the injector lateral.

[0018] FIG. 5 illustrates a schematic diagram of a multi-cell radiator unit to allow permanent continuous generation of electrical energy.

DETAILED DESCRIPTION

[0019] The presently disclosed subject matter now will be described more fully hereinafter with reference to the accompanying Drawings, in which some, but not all embodiments of the inventions are shown. Like numbers refer to like elements throughout. The presently disclosed subject matter may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Indeed, many modifications and other embodiments of the presently disclosed subject matter set forth herein will come to mind to one skilled in the art to which the presently disclosed subject matter pertains having the benefit of the teachings presented in the foregoing descriptions and the associated Drawings. Therefore, it is to be understood that the presently disclosed subject matter is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.

[0020] An embodiment in accordance with the present invention includes an enhanced geothermal system (EGS) configured to allow the commercial production of electrical energy. One criteria of an EGS according to the present invention is that the temperature and volume of the fluids extracted are of sufficiently high temperatures and large enough volumes as to allow the commercial production of electrical energy. The system is able to operate for at least N years before the extracted fluid falls below the minimum temperature needed for energy production. Additionally, fractures are separated from each other by a sufficiently large volume of rock (V.sub.crit) relative to the fractures' surface area, such that ratio of the rate of heat extraction to the rate of heat supply controlled by the thermal conductivity of the rock is such that the intervening rock is cooled at a rate that is sufficiently slow to be economic.

[0021] The basic structure of the proposed EGS is to create a set of “manufactured” vertical fractures that can circulate fluids through a rock volume such that the final fluid temperature is sufficient for commercial energy production. The key to creating such fractures is to essentially imitate the way that natural transmissive fracture systems are created, but to do so in a fashion that emulates the geometry of radiator vanes, so as to allow control of the system temperature. The geometry and orientation of the “Radiator” systems fractures is controlled by the ambient stress field including S.sub.1, the maximum stress, and S.sub.Hmax, the horizontal stress component. Below about 700 m, and depending on the specific geologic area, S.sub.1 is vertical and the average strike of transmissive fractures parallels S.sub.Hmax.

[0022] Creating fractures that include S.sub.1 and S.sub.Hmax requires drilling laterals that parallel S.sub.Hmax. This is normal to the direction typically chosen for exploiting unconventional Oil and Gas which are drilled normal to S.sub.Hmax. Fracking to “manufacture” the transmissive fracture system will require a highly controllable fracking tool such as energetics which can directionally enhance the rock permeability. For example, propellant based fracking could be used to manufacture the transmissive fracture system. Because S.sub.1 is vertical, fracture orientations will tend towards Mode 1 which tends to limit permeability. However, there should be sufficient variability in orientation of fragment surfaces such that most will have a significant shear component and therefore provide permeability.

[0023] FIG. 1 illustrates a schematic view of a set of two wells including of an injector and production well. The system 10 includes the injector well 12 and the production well 14 as a vane unit. Each well includes a vertical pilot hole 16 and a lateral 18 with each well 12, 14 connected to a pumping unit (not illustrated). While one set of injector well 12 and production well 14 are illustrated in FIG. 1 any number of wells can be used, as is known to or conceivable by one of skill in the art. Additionally, examples of expanding the number of wells are also included herein, below. The wells 12, 14 are oriented to parallel the maximum horizontal stress (S.sub.Hmax) 20 with both drilled to depths where the principal stress axis (S.sub.1) 22 is vertical. In general this will be depths >700 m. The production lateral is drilled to parallel the isotherm whose temperature T.sub.min, is greater than the minimum temperature required for commercial energy production (T.sub.e). While Tmin is > that required for commercial production we can allow the cell to go to Te, where Te is <Tmin. FIG. 1 illustrates a plane 24 parallel to the isotherm whose temperature is T.sub.max. The injector well lateral is drilled to a depth > the depth of the T.sub.min isotherm to a depth of an isotherm T.sub.max. FIG. 1 also illustrates a plane 26 that is parallel to the isotherm whose temperature is T.sub.max. The length (l.sub.3) of the injector below the T.sub.min isotherm plane 25 and the length (l.sub.2) of the lateral 34 are determined by the relationship V.sub.crit=l.sub.1×l.sub.2×l.sub.3, where l.sub.1 is the distance between successive vanes. Here V.sub.crit is the volume necessary to maintain a temperature of the heated fluid produced at the production well ≥T.sub.e for a sufficient amount of time that it will meet the economic criteria for commercial power generation (T.sub.e). The volume V.sub.crit is defined as a single “Radiator” cell.

[0024] FIG. 2 illustrates a schematic diagram of two “vane” units defining the intervening rock volume as V.sub.crit=l.sub.1×l.sub.2×l.sub.3. FIG. 2 also illustrates a second vane unit. The second vane unit includes a second injection well 28 and a second production well 30. l.sub.1, 32 is defined as a distance between the laterals 18 of the production wells 14 and 30. l.sub.2, 34 is defined as a length of the lateral 18 of the injection well 28. l.sub.3, 36 is defined as a height between the lateral of the injection well 12 and the production well 14. V.sub.crit is then the volume defined by l.sub.1×l.sub.2×l.sub.3.

[0025] The “Radiator Vane” or “manufactured” fracture, is created by successive controlled fracs, one above the other in successively higher laterals located in the plane defined by the injector and production wells. The pressures created by the fracking agent, must be sufficient and rapid enough to exceed the fundamental strength of the rock and thereby open up fractures in the rock. Rocket propellant is an example of such an agent. Because the production and injection wells are directly above and parallel to one another and because the plane they so define includes both S.sub.1 22 and S.sub.hmax 20 with S.sub.hmin 27 normal to this plane, the successive lateral fracs will form a vertical zone of fractured rock.

[0026] FIG. 3 illustrates a schematic diagram of temperature distribution due to injection of fluid at a depth where rock temperature is >T.sub.min, and FIG. 4 illustrates a schematic diagram of a strike section to schematically illustrate how cooling will be slowed due to increasing temperature of fluid as it moves along the injector lateral. FIGS. 3 and 4 show how the system functions to solve the problem of the low thermal conductivity of rock resulting in the too rapid cooling of the surrounding rock. The basic concept is to inject fluid at some depth l.sub.3, 36, below the isotherm surface 24 whose temperature T.sub.min is the minimum required for producing commercial quantities of electrical energy. By doing so as the fluid rises at some point its temperature will be greater than that of the surrounding rock, thus instead of cooling the rock through which it is now passing, it will heat it, as illustrated in FIG. 3. Because the temperature of the surrounding rock through which the fluid is rising is >T.sub.min, the fluid emerging above the T.sub.min isosurface 24 and available for energy production, will be >T.sub.min for some period of time. The critical parameter l.sub.3 36 is a function of the vertical temperature gradient, dT/dz. The fluid temperature can be maintained to the surface by insulating the casing above the T.sub.min isosurface. The direction of fluid flow in FIG. 3 is vertical.

[0027] A similar effect will occur for the “Manufactured” fracture along its strike, as illustrated in FIG. 4. As the fluid enters the fracture at the beginning of the injector lateral, it cools the surrounding rock but itself is gradually heated as it moves along the injector lateral. The result is that as the fluid at the end of the lateral rises its temperature will be closer to the ambient temperature at the depth of the T.sub.max isotherm 26. Consequently there will be even less and therefore slower cooling of the surrounding rock above the lateral “toe” as fluid rises towards the production well. As illustrated in FIGS. 3 and 4, color scale shows relative temperatures. Dark is hottest and light is coolest. T.sub.min isotherm 24 is at a depth where the ambient rock temperature is higher than the one required for commercial energy production. The direction of fluid flow in FIG. 4 is lateral.

[0028] In order to keep the “Radiator” cells size reasonable it is necessary to make their heat production transitory, i.e. yield commercial quantities of heat for a fixed period rather than steady state. However, if the entire EGS, including of multiple cells, is to be commercial it must be able to generate heat for what amounts to a steady state. This is done by having a set of radiator cells which are successively harvested. The individual cells must be of sufficient size to be able to provide the required energy for commercial production for a period of years. To meet this condition the “Radiator” EGS unit must cycle production among a set of “radiator” cells. A schematic of this system is shown in FIG. 5 and described by the following.

[0029] FIG. 5 illustrates a schematic diagram of a multi-cell radiator unit to allow permanent continuous generation of electrical energy. Continuous energy production is maintained by cycling through the radiator cell system 50 in the following fashion. Energy production is from one cell at a time, e.g. Cell 1, 52. When the temperature of the produced fluid drops below the minimum temperature required for commercial energy production, the cell is shut in and moved to a fully restored cell, e.g. Cell 3, 54. Cell 1 then is allowed to re-equilibrate to the ambient geothermal gradient, e.g. Cell 2, 56.

[0030] The number of cells required and their size, is set by the number of years for a complete cycle through all of the cells as to allow the i.sup.th cell to return to its initial thermal state. Thus each volume would be allowed to recover for the duration of each cycle; e.g. Volume i produces for N years, then is left to recover while heat extraction shifts to Volume j for N years, etc. The number of volumes (n) being set by the amount of time to “draw down” each successive volume such that the total cycle time T.sub.total=N, is sufficient to allow each Volume i harvested to recover completely.

[0031] The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention, which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.