EP4224087A1 - Method for obtaining geothermal energy - Google Patents

Abstract

Method for extracting geothermal energy from an underground reservoir (2), comprising the following steps:- analyzing the stresses in the ground;- preparing a map showing the directions of the stresses in the ground;- creating injection wells ( 4) arranged along the direction (13) of maximum stress (8); - creating injection well cracks (12) in the soil by injecting high pressure liquid into the injection wells (4); - flowing the injections - wells (4) with a fluid; - allowing the fluid to absorb heat from the underground reservoir (2) and thereby increase the heat content of the fluid; - creating production wells (5) along the direction (13) of the maximum stress (8);- creating production well fractures (11) in the soil by injecting fluid under high pressure into the production wells (5);- removing at least part of the fluid with an increased heat content from the underground reservoir via the production wells (5) and- extracting heat from that part of the fluid which has an increased heat content.

Description

The invention relates to a method for extracting geothermal energy from an underground reservoir. The invention can also be used to utilize geothermal energy from an underground reservoir.

Renewable energy systems such as wind, solar and geothermal systems are increasingly being researched and developed. In a geothermal system, the heat of the earth is used. Geothermal energy is used to generate electrical energy, for example. Geothermal energy is an important renewable energy.

In a geothermal power plant, a fluid is pumped into an injection well in the ground and pumped back through a production well, with the heated fluid being used to generate energy. Water is often used as the fluid. However, it has been shown that the use of supercritical CO ₂ (other name: supercritical carbon dioxide) as a fluid results in advantages. Here, supercritical carbon dioxide is considered more closely as a fluid within the meaning of the invention.

Essentially, two concepts of CO ₂ -based geothermal power plants are described. On the one hand, there are so-called Enhanced Geothermal Systems (EGS) or Hot Dry Rock (HDR). Both methods are based on either widening existing fissures in solid rock at depths of more than 3,000 m or creating new fissures in weak zones. To do this, a process called hydrofracturing is used. In this case, a fluid is pressed or injected at high pressure into the ground or into the reservoir. Crystalline rock is often processed using this method, with sedimentary rock also being examined within the meaning of the invention.

In hydrofracturing, a fracture event occurs in a rock surrounding a well as a result of the hydraulic action of liquid or gas pressure through a fluid. The fluid is pumped under pressure into the layer to be fractured or fractured in order to separate or fracture the subterranean formation. As a result, existing fissures and fissures, which were formed when the geological formation was formed and subsequent tectonic movements, are widened and new fissures, fissures and fissures are created. The alignment of the induced fissures, fissures and fissures is primarily dependent on the prevailing stress state of the subterranean formation. The level of pressure with which the fluid is pumped into the formation depends on the properties of the rock and the stress fields in the subterranean formation.

On the other hand, systems are described which also use supercritical CO ₂ as a heat transfer medium, whereby hydrofracturing is deliberately avoided. If possible, supercritical CO ₂ should flow over a large area through naturally permeable sedimentary layers.

The advantage of these systems is that the reservoir is comparatively evenly flowed through both in terms of area and volume, so that the heat capacity of the rocks can be utilized to the maximum extent. This is particularly important in the case of sedimentary reservoirs, since the heat conduction of sedimentary rocks is low compared to crystalline rocks (e.g. granite, etc.) and the heat flowing in from the earth's core is comparatively low.

Sedimentary reservoirs exist worldwide (former oil and gas deposits) and sometimes extend over many kilometers, sometimes over an area of 100km x 100km.

So far, the output of a geothermal power plant has been determined by the flow resistance in the wells and the reservoir. Especially in the case of a reservoir permeability of less than 100mD, the flow resistance in the reservoir is dominant. This can be compensated for with an increased number of bores, which, however, is very expensive.

The invention has set itself the task of specifying a cost-effective method for obtaining geothermal energy.

• Analyse der Spannungen im Boden;
• Erstellen einer Übersicht, in der die Richtungen der Spannungen im Boden zu entnehmen sind;
• Erzeugen von Injektionsbohrungen, die entlang der Richtung der maximalen Spannung angeordnet werden;
• Erzeugen von Injektionsbohrungs-Rissen im Boden durch Injizieren von Flüssigkeit unter hohem Druck in die Injektionsbohrungen;
• Beströmen der Injektionsbohrungen mit einem Fluid;
• Ermöglichen, dass das Fluid Wärme aus dem unterirdischen Reservoir absorbiert und dadurch der Wärmeinhalt des Fluids erhöht wird;
• Erzeugen von Produktionsbohrungen, die entlang der Richtung der maximalen Spannung angeordnet werden;
• Erzeugen von Produktionsbohrungs-Rissen im Boden durch Injizieren von Flüssigkeit unter hohem Druck in die Produktionsbohrungen;
• Entfernen von mindestens einem Teil des Fluids mit einem erhöhten Wärmeinhaltes aus dem unterirdischen Reservoir über die Produktionsleitungen und
• Entziehen von Wärme aus dem Teil des Fluids, der einen erhöhten Wärmeinhalt aufweist.

This task is solved by a method for extracting geothermal energy from an underground reservoir, which includes the following steps:

• Analysis of soil stresses;
• Creation of an overview showing the directions of the stresses in the soil;
• creating injection holes arranged along the direction of maximum stress;
• creating injection well fractures in the ground by injecting high pressure fluid into the injection wells;
• Flowing the injection wells with a fluid;
• allowing the fluid to absorb heat from the subterranean reservoir thereby increasing the heat content of the fluid;
• creating production wells located along the direction of maximum stress;
• creating production well fractures in the ground by injecting high pressure fluid into the production wells;
• removing at least a portion of the elevated heat content fluid from the underground reservoir via the production lines; and
• Extracting heat from the part of the fluid that has an increased heat content.

Advantageous developments are specified in the dependent claims.

It is thus proposed to specify a method for obtaining geothermal energy in which stimulation, also referred to as hydrofracture, is used, with the method preferably being used in sedimentary reservoirs. Especially when the vertical permeability, also known as permeability, is very low, such as in shale rock, cracks are to be created by injecting liquid under very high pressure. It has been recognized that these cracks are in the plane of the two highest stresses; i.e. mostly in the plane of the vertical stress and the maximum horizontal stress.

In a step of the method according to the invention, an analysis is carried out to find out in which horizontal direction the stress is greatest.

In a first approximation, the direction of the highest horizontal stress also corresponds to the direction of the global plate movement, in particular the continental plate movement. In a closest approximation, the highest horizontal stress points from the south-west to the north-east at a central European location.

An essential idea of the invention is to take this prognosis about the crack growth into account.

By arranging the injection wells and the production wells in the direction of maximum horizontal stress, cracks are generated between the injection wells and between the production wells. As a result, the supercritical CO ₂ flows into the reservoir with less resistance and pressure losses during flow through the reservoir are reduced. This allows the flow rate to be increased.

In a first approximation, the pressure losses across the reservoir are reduced by a factor of approx. 2.4. Assuming that the total pressure losses are divided equally between the injection wells, the reservoir flow and the production wells, the performance of the system according to the invention can be increased by up to approximately 30%.

The properties, features and advantages of this invention described above, and the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the exemplary embodiments, which are explained in more detail in connection with the drawings.

Identical components or components with the same function are identified with the same reference symbols.

Exemplary embodiments of the invention are described below with reference to the drawings. These are not intended to represent the exemplary embodiments to scale, rather the drawing, where useful for explanation, is in schematic and/or slightly distorted form. With regard to additions to the teachings that can be seen directly in the drawing, reference is made to the relevant state of the art.

Figur 1

eine sehr vereinfachte schematische Darstellung einer Geothermie-Anlage

Figure 2

eine schematische Darstellung einer herkömmlichen Bohrung

Figur 3

eine schematische Darstellung einer Bohrung mit Darstellung eines induzierten Risses

Figur 4

eine schematische Darstellung der räumlichen Spannungen

Figur 5

eine schematische Darstellung einer Rissanordnung

Figur 6

eine schematische Darstellung einer Verteilung der Injektionsbohrung und Produktionsbohrung

Show it:

figure 1

a very simplified schematic representation of a geothermal plant

Figure 2

a schematic representation of a conventional well

figure 3

a schematic representation of a bore showing an induced crack

figure 4

a schematic representation of spatial tensions

figure 5

a schematic representation of a crack arrangement

figure 6

a schematic representation of a distribution of the injection well and production well

The figure 1 shows a very simplified representation of a geothermal system 1. Such geothermal systems 1 use the thermal energy present in the earth, which is converted into electrical energy, among other things. Geothermal plants have often been described in the literature. At this point, such a geothermal plant 1 is only to be presented in simplified form.

The geothermal plant 1 is used to extract geothermal energy from an underground reservoir 2 . In this case, one or more injection holes 4 is attached to a surface of the earth 3, wherein in the figure 1 only one injection hole is shown. The injection well 4 leads to a fluidic connection between the earth's surface 3 and the underground reservoir 2, where the thermal energy is stored.

A fluid flows through the injection wells, in particular supercritical CO ₂ . The fluid effluent from the injection well 4 flows to an entrance of a production well 5. On the way from the injection well 4 to the production well 5, the fluid is allowed to absorb heat from the underground reservoir 2 and thereby the Heat content of the fluid is increased. The fluid thus heated flows through the production bore 5 to a local plant 6, where the thermal energy of the fluid is processed.

• Analyse der Spannungen im Boden;
• Erstellen einer Übersicht, in der die Richtungen der Spannungen im Boden zu entnehmen sind;
• Erzeugen von Injektionsbohrungen 4, die entlang der Richtung 13 der maximalen Spannung 8 angeordnet werden;
• Erzeugen von Injektionsbohrungs-Rissen 12 im Boden durch Injizieren von Flüssigkeit unter hohem Druck in die Injektionsbohrungen 4;
• Beströmen der Injektionsbohrungen 4 mit einem Fluid;
• Ermöglichen, dass das Fluid Wärme aus dem unterirdischen Reservoir 2 absorbiert und dadurch der Wärmeinhalt des Fluids erhöht wird;
• Erzeugen von Produktionsbohrungen 5, die entlang der Richtung 13 der maximalen Spannung 8 angeordnet werden;
• Erzeugen von Produktionsbohrungs-Rissen 11 im Boden durch Injizieren von Flüssigkeit unter hohem Druck in die Produktionsbohrungen 5;
• Entfernen von mindestens einem Teil des Fluids mit einem erhöhten Wärmeinhaltes aus dem unterirdischen Reservoir 2 über die Produktionsleitungen 5 und
• Entziehen von Wärme aus dem Teil des Fluids, der einen erhöhten Wärmeinhalt aufweist.

The method according to the invention for obtaining geothermal energy from the underground reservoir 2 is characterized by the following steps:

• Analysis of soil stresses;
• Creation of an overview showing the directions of the stresses in the soil;
• creating injection wells 4 arranged along the direction 13 of maximum stress 8;
• creating injection well cracks 12 in the ground by injecting high pressure liquid into the injection wells 4;
• Flowing through the injection wells 4 with a fluid;
• allowing the fluid to absorb heat from the underground reservoir 2, thereby increasing the heat content of the fluid;
• creating production wells 5 arranged along the direction 13 of maximum stress 8;
• creating production well fractures 11 in the ground by injecting high pressure fluid into the production wells 5;
• Removing at least part of the fluid with an increased heat content from the underground reservoir 2 via the production lines 5 and
• Extracting heat from the part of the fluid that has an increased heat content.

In a first step, the stresses in the soil are analyzed. The figure 4 shows an example of the stresses that can occur. Accordingly, a vertical stress σ _v 7 occurs that is orthogonal to two horizontal stresses, whereby the horizontal stresses, which are aligned approximately parallel to the earth's surface, are divided in a first approximation into a maximum horizontal stress σ _H,max 8 and a minimum aligned orthogonally to it horizontal voltage σ _H,min 9. σ _v > σ _H,max > σ _H,min applies.

In a further approximation, the direction of the highest or maximum horizontal stress σ _H,max 8 also corresponds to the direction of the global plate movement, in particular the continental plate movement. In a closest approximation, the highest or maximum horizontal stress ( σ _h,max 8) shows from south-west to north-east at a central European location.

In a next step, injection well cracks 12 are generated in the ground by injecting liquid into the injection wells 4 under high pressure. Likewise, in a next step, production well cracks 11 are produced in the ground by injecting liquid under high pressure into the production wells 6 . This will be in the figure 5 shown schematically. At a location x, a crack 10 is generated by generating a high pressure in the injection well 4 or production well 5, which is in the figure 5 is shown in the form of a parabola. The crack 10 grows in the direction of the maximum horizontal stress 8.

The emergence of the crack 10 is based on the Figures 2 and 3 be explained in more detail. The figure 2 shows an injection well 4 or a production well 5 seen in cross section. The diameter is d _w . The figure 3 shows the state of the injection well 4 or a production well 5 in cross section after a production well crack 11 or injection well crack 12 has been produced by injecting liquid under high pressure into the production well 5 or injection well 4 . The crack 11, 12 propagates in both directions of the bore 2, 3. The in the Figures 2, 3 The arrows shown are intended to represent heat transfer. The space created by the crack 11, 12 leads to better flow through the bores 2, 3.

The figure 6 shows a plan view of a distribution of the injection wells 2 and production wells 3 of the invention Process for extracting geothermal energy from an underground reservoir. In an essential step, it is first analyzed and examined in which direction 13 the maximum horizontal stress σ _H,max 8 is. In a next step, the injection wells 2 and the production wells 3 are arranged along this direction. The distance between the individual injection wells 2 and production wells 3 depends on the size of the cracks 11, 12, which in turn depend on the nature of the ground. As the figure 6 12 shows the cracks 11, 12 aligned in such a way that they point in the direction 13 of the maximum horizontal stress ( σ _h,max 8). The cracks 11, 12 are therefore aligned essentially parallel to one another.

For reasons of clarity are in the figure 6 only a few cracks have been given the reference numbers 11 and 12. Also for reasons of clarity are in the figure 6 only a few injection wells 2 and production wells 3 are provided with the reference numerals 2 and 3.

The arrows 14 in figure 6 symbolize the flow of the fluid, in particular a flow of supercritical CO ₂ . On the way from the injection well 2 to the production well 3, the fluid absorbs heat from the underground reservoir. This increases the heat content of the fluid.

Claims (10)

Method for extracting geothermal energy from an underground reservoir (2), comprising the following steps: - Analysis of soil stresses; - Creation of an overview showing the directions of the stresses in the soil; - creating injection holes (4) arranged along the direction (13) of maximum stress (8); - creating injection well fractures (12) in the ground by injecting liquid under high pressure into the injection wells (4); - Flowing the injection bores (4) with a fluid; - allowing the fluid to absorb heat from the subterranean reservoir (2), thereby increasing the heat content of the fluid; - creating production bores (5) arranged along the direction (13) of maximum stress (8); - creating production well fractures (11) in the ground by injecting high pressure fluid into the production wells (5); - Removal of at least part of the fluid with an increased heat content from the underground reservoir (2) via the production wells (5) and - Extraction of heat from the part of the fluid that has an increased heat content. Method according to claim 1,
the soil comprising sedimentary rock. Method according to claim 1 or 2,
wherein the fluid is liquid carbon dioxide essentially comprising carbon dioxide fluid in the supercritical phase or carbon dioxide fluid in the supercritical phase is transformed by the hot underground reservoir. Method according to one of claims 1 to 3,
the fluid flowing through the injection wells (4) and through the injection well fractures (12). Method according to one of claims 1 to 4,
the fluid flowing through the production wells (5) and through the production well fractures (11). Method according to one of claims 1 to 5,
wherein the injection wells (4) are arranged essentially in rows of injection wells. Method according to one of claims 1 to 6,
wherein the production wells (5) are essentially arranged in production well rows. Method according to claim 6 or 7,
wherein the injection well rows are located between the production well rows. Method according to one of claims 1 to 8,
wherein the production wells (5) are located such that one production well (5) is located adjacent to four injection wells (4). Method according to claim 9,
the distances between the production well (5) and the respectively adjacent injection wells (4) being essentially the same.

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