EP3911833A1

EP3911833A1 - A rock drilling system for geothermal drilling, a method and use of such a rock drilling system

Info

Publication number: EP3911833A1
Application number: EP20701410.1A
Authority: EP
Inventors: Petri Laukkanen
Original assignee: Pml Energy AB
Current assignee: Pml Energy AB
Priority date: 2019-01-15
Filing date: 2020-01-15
Publication date: 2021-11-24
Anticipated expiration: 2040-01-15
Also published as: SE1950045A1; WO2020148333A1; EP3911833B1; ES2933402T3; SE543090C2

Abstract

The invention relates to a rock drilling system (10) for geothermal drilling. The rock drilling system (10) comprises a drilling rig (2) with a drill string (22) and a drilling hammer (4) for drilling a borehole (9); at least one air compressor (1) configured for driving the drilling hammer (4) and supplying compressed air into the borehole (9) via the drill string (22); a conveying chamber arrangement (3) configured to be arranged at a ground surface (12), wherein the conveying chamber arrangement (3) is configured to encircle the drill string (22) and to be connected to a borehole casing (44). The rock drilling system (10) further comprises an extraction device (5) connected to the conveying chamber arrangement (3) to draw air containing drill cuttings from the borehole (9), thereby controlling the flow of air upwards through the borehole (9). The invention also relates to a use of such a rock drilling system (10) for generation of geothermal energy and a method for geothermal drilling with such a rock drilling system (10).

Description

A rock drilling system for geothermal drilling, a method and use of such a rock drilling system

TECHNICAL FIELD

The present invention relates to a rock drilling system for geothermal drilling and a method for geothermal drilling with such a rock drilling system. The invention also relates to a use of such a rock drilling system for generation of geothermal energy.

BACKGROUND

Geothermal energy is thermal energy generated and stored in the Earth. It is a clean and sustainable source of energy. Many regions of the world are already tapping geothermal energy as an affordable and sustainable solution to reducing dependence on fossil fuels. Thereby, global warming and public health risks that result from the use of fossil fuels are also reduced. Hence, geothermal energy is becoming more and more important in the global environment as the supply of fossil fuels diminish and the demand for energy increases. The Earth's geothermal resources are theoretically more than adequate to supply humanity's energy needs. Still, only a very small fraction is profitably exploited, since drilling for deep resources is very expensive and technically demanding.

Shallow geothermal boreholes, 50 - 200 meters, are commonly used as heat source or sink for heat pumping systems for heating of for example smaller residential buildings. When drilling deeper, the temperature increases and more geothermal energy can be extracted. However, drilling to greater depths, such as 2000-3000 metres or more, to reach high-temperature geothermal resources, becomes a challenge due to increasing pressure and temperature.

Thus, geothermal energy has great potential as an environmentally friendly source of energy in many parts of the world, but expansion has been constrained by technical difficulties and high costs related to drilling deep in hard rock.

One known solution for drilling deep boreholes is disclosed in document US 4653593 A. The document discloses a method for controlling the operation of a compressed air operated down-the-hole percussive rock drill when drilling deep boreholes.

SUMMARY OF THE INVENTION

An object of the present invention is to achieve an advantageous rock drilling system for enabling extraction of high-temperature geothermal resources.

Another object of the invention is to reduce the cost of investment in geothermal energy.

The herein mentioned objects are achieved by:

- a rock drilling system for geothermal drilling,

- a use of such a rock drilling system for generation of geothermal energy, and

- a method for geothermal drilling with such a rock drilling system,

according to the appended independent claims.

Hence, according to an aspect of the present disclosure a rock drilling system for geothermal drilling is provided. The rock drilling system comprises: a drilling rig with a drill string and a drilling hammer for drilling a borehole; at least one air compressor configured for driving the drilling hammer and supplying compressed air into the borehole via the drill string; and a conveying chamber arrangement configured to be arranged at a ground surface, wherein the conveying chamber arrangement is configured to encircle the drill string and to be connected to a borehole casing. The rock drilling system further comprises an extraction device connected to the conveying chamber arrangement to draw air containing drill cuttings from the borehole, thereby controlling the flow of air upwards through the borehole.

According to another aspect of the present disclosure a use of a rock drilling system as disclosed herein is provided for generation of geothermal energy.

According to another aspect of the present disclosure, a method for geothermal drilling with a rock drilling system as disclosed herein is provided. The method comprises the steps of: driving the drilling hammer and supplying compressed air into a borehole via the drill string by means of the at least one air compressor; and drawing air containing drill cuttings from the borehole via the conveying chamber arrangement, by means of the extraction device.

Thus, by means of supplying compressed air down the borehole by at least one air compressor and drawing air up from the borehole by means of the extraction device, the flow of air upwards through the borehole may be controlled. By controlling and maintaining an efficient flow of air upwards in the borehole, an efficient penetration rate of drilling, cooling of the drilling equipment and removal of drill cuttings is achieved, despite high temperatures and increasing pressure in the earth's interior. Thereby, an advantageous rock drilling system is achieved, which enables deep drilling such that high-temperature geothermal resources may be extracted. Thus, green energy may be harvest in a time- and cost-efficient manner.

In conventional borehole drilling, a drilling fluid is generally pumped downward through a drill string or outside the drill string along the borehole annulus. The fluid is then circulated upward to the surface with cuttings along the borehole annulus or inside the drill string. Common drilling fluids may be water, a mix of air and water, or others. When using water or other viscous fluid, the fluid has to be transported to and from the drilling site, which has a negative impact on the environment in the form of emissions and consumption of fossil fuels. In addition, in some part of the world, water is scarce. In these regions, drinking water must be prioritized, not drilling fluid.

In the present disclosure, compressed air is used as drilling fluid. Air is a strategic choice of fluid as it is cheap, always available in all part of the world, and there is no need for transportation of air to or from the drilling site. Accordingly, air is a cost- efficient and advantageous drilling fluid for environmental reasons.

In rock drilling systems, the removal of drill cuttings from the borehole is crucial. A constant removal of boring debris from the bottom of the borehole as drilling progresses is utterly important as the drill bit will get jammed and the flow in the borehole get clogged, without an efficient removal of drill cuttings. If the flow in the borehole is obstructed, the penetration rate of drilling will be reduced and the drilling equipment may also be damaged due to blockage. The penetration rate, or drill rate, is the speed at which a drill bit breaks the rock under it to deepen the borehole. In addition to functioning as flushing means, the drilling fluid also operates as cooling means. Thus, if the removal of drill cuttings does not function properly, the drilling equipment may be damaged due to overheating. The drilling fluid also ensures the stability of the borehole, i.e. the drilling fluid prevents that the borehole collapses.

In known apparatus for drilling deep boreholes into the earth, the drilling mechanisms may comprise a drill bit and a pressure fluid motor that directly drives the drill bit, which motor is located at the bottom of the borehole being drilled. The pressurized fluid may be fed to the motor through a tubular shaft or duct inside a drill string that is supported from the surface of the earth at the mouth of the borehole. When deep holes are to be drilled, in particular holes that are several hundred meters deep, the pressure in the ground will be so high that it must be compensated for. To compensate for the increasing pressure, the supply of pressurized fluid fed to the apparatus may be varied in accordance with various rules of thumb. If the supply of pressurized fluid fed to the apparatus is too small, the penetration rate becomes very low and there is risk that the drill bit and borehole get jammed. On the other hand, if the supply of pressurized fluid is too high, there is risk that the impact velocity may damage the drilling equipment, or at least drastically reduce the life span of the drilling equipment.

Increasing the supply of pressurized fluid significantly increases the cost of drilling. In order to achieve an increase of the supply of pressurized fluid, more powerful and/or multiple sources of pressurized fluids are required. These types of sources are very expensive, and also consume fossil fuels in order to produce the pressurized fluid. Thus, an increase in power output also entails an increase of fossil fuel. Fossil fuels, such as diesel or petrol, is expensive and not an environmentally friendly choice. It is also difficult to get a hold of fossil fuels in many parts of the world. By means of supplying compressed air down the borehole by at least one air compressor and drawing air up from the borehole by means of the extraction device according to the present disclosure, less power is required to achieve an efficient flow of air in the borehole. Fewer air compressors, and/or less powerful air compressors may be needed, which save initial investment costs, reduce fuel consumption and are favourable in view of transport and logistics. The extraction device is relatively cheap and consumes a lot less power compared to attempts to obtain an efficient flow upward by adding additional, or extra powerful, air compressors. Thus, the solution of using an extraction device drawing air upwards in combination with the at least one air compressor forcing air downwards according to the present disclosure is superior in many ways compared to conventional methods, wherein only air compressors are used to force air down the borehole.

By means of the rock drilling system according to the present disclosure, the cost of investment in geothermal energy is reduced, in respect to both financial and environmental assets. Thus, by the present disclosure, an advantageous and sustainable way of achieving green and clean energy in the form of geothermal energy is obtained.

Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following details, and also by putting the invention into practice. Whereas the invention is described below, it should be noted that it is not restricted to the specific details described. Specialists having access to the teachings herein will recognise further applications, modifications and incorporations within other fields, which are within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For fuller understanding of the present invention and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various drawings, and in which: Figure 1 schematically illustrates a rock drilling system according to an example of the present disclosure;

Figure 2 schematically illustrates a conveying chamber

arrangement according to an example of the present disclosure;

Figure 3 schematically illustrates a conveying chamber

arrangement according to an example of the present disclosure; and

Figures 4 and 5 schematically illustrate block diagrams of methods

according to examples of the present disclosure.

DETAILED DESCRIPTION

The rock drilling system will be described in further detail below. It is understood that all the various examples of the rock drilling system also applies for the use of such a rock drilling system for generation of geothermal energy and methods for geothermal drilling with such a rock drilling system.

According to an aspect of the present disclosure, a rock drilling system for geothermal drilling is provided. The rock drilling system comprises: a drilling rig with a drill string and a drilling hammer for drilling a borehole; at least one air compressor configured for driving the drilling hammer and supplying compressed air into the borehole via the drill string; and a conveying chamber arrangement configurd to be arranged at a ground surface, wherein the conveying chamber arrangement is configured to encircle the drill string and to be connected to a borehole casing. The rock drilling system further comprises an extraction device connected to the conveying chamber arrangement to draw air containing drill cuttings from the borehole, thereby controlling the flow of air upwards through the borehole.

The rock drilling system as disclosed is adapted for geothermal drilling. This means that the rock drilling system is designed for drilling deep boreholes. The trajectory of the borehole may be straight, as for vertical drilling. However, the present disclosure is also suitable for directional drilling, which is the practise of drilling non vertical boreholes. The rock drilling system comprises a drilling rig with a drill string and a drilling hammer for drilling a borehole. The drilling rig may be a conventional drill rig with a feed beam or mast. The drill string may comprise multiple drill pipes which are screwed together or joined in some other way. The drilling hammer may be a conventional drilling hammer, driven by compressed air. The drilling hammer may be driven by compressed air only. It may be favorable to use a drilling hammer driven merely by compressed air at greater depth, as no electronics etc. may be needed in such drilling hammers. Other types of drilling hammers comprising sensitive material such as plastic or electronic components may be damaged due to the increase of temperature in deep boreholes.

The drilling hammer may be a pneumatically powered rock hammer. The drilling hammer may be a pneumatic percussion rock drill. The drilling hammer may be mounted to the lower end of the drill string. The drilling hammer may be a down-the- hole (DTH) pneumatic hammer. A down-the-hole drill, usually called DTH, is a pneumatic powered rock or ground drill, in which the percussive hammer is located directly behind the drill bit, so the percussion mechanism follows the drill bit down into the borehole. Compared to other geothermal drilling methods, down-the-hole hammers may have an increased penetration rate. Thus, the drilling procedure may be relatively quick.

The drill string may transfer the necessary feed force and rotation to the drilling hammer and drill bit, as well as compressed air for driving the drilling hammer. Drill pipes may be added to the top of the drill string as the borehole gets deeper. The drilling hammer may have a piston hammer that delivers impact to the drill bit either directly or through an anvil block. The piston hammer may directly strike the impact surface of the drill bit, while a hammer casing gives guidance to the drill bit. The drilling hammer impact may break hard rock into small particles, i.e. drilling cuttings, which may be blown upwards in the borehole by the air exhaust from the drill hammer.

The rock drilling system comprises at least one air compressor configured for driving the drilling hammer and supplying compressed air into the borehole via the drill string. The at least one air compressor may be of any type, driven by for example a diesel, gasoline or electric motor. The at least one air compressor forces, by means of the motor, more and more air into a storage tank, increasing the pressure. The pressurized air, i.e. the compressed air, may be used to drive the drilling hammer. Compressed air may be supplied from the air compressor to the drilling hammer through the drill string via an air duct. Such air ducts may comprise hoses, pipes, tubes etc. The compressed air may also be used to flush the borehole. The compressed air may remove drill cuttings from the borehole. A constant removal of boring debris from the bottom of the borehole as drilling progresses is very important as the drill bit will get jammed and the flow in the borehole get clogged, without an efficient removal of drill cuttings. In addition, the compressed air cools down the drilling equipment. The compressed air also ensures the stability of the borehole. By means of the at least one air compressor, the flow of air downwards through the drill string may be controlled. For example, by adjusting the supply of compressed air, the airflow and/or the air pressure in the channel in the drill string may be adjusted. By adjusting the airflow and/or air pressure in the channel, the drive of the drill hammer and the amount of exhaust air from the drill hammer may be adjusted. Thereby may for example the penetration rate and the amount of flushing air in the borehole be adjusted.

The rock drilling system comprises a conveying chamber arrangement configured to be arranged at a ground surface, wherein the conveying chamber arrangement is configured to encircle the drill string and to be connected to a borehole casing. The conveying chamber may facilitate connection of different parts in the rock drilling system. The configuration of the conveying chamber arrangement may separate and guide airflows in, out and within the mouth of the borehole at the ground surface. By means of the conveying chamber arrangement, the airflow in the borehole may be controlled. The configuration of the conveying chamber arrangement enables the drill string with compressed air to enter the borehole, and air and drill cutting to exit the borehole, while maintaining the flow in the borehole. The configuration of the conveying chamber arrangement counteract air leaks and unfavourable airflows. The configuration of the conveying chamber arrangement also impedes contamination of the surroundings around the borehole, as air and drill cuttings may be prevented from leaking out to the ambient air or at the ground surface.

The conveying chamber arrangement is configured to be connected to a borehole casing. A borehole casing is a large diameter pipe that is lowered and usually cemented in place in order to line the borehole of an open well. The borehole casing may be strategically sized and placed into the borehole so that drilling operations can reach desired depths. The borehole may extend from the ground surface through a top layer of softer material, such as soil or gravel, to a rock layer. The borehole casing may line the borehole from the ground surface into the rock layer. The borehole casing may thus ensure the stability of borehole, i.e. prevent that the upper part of the borehole collapses. The borehole casing also supports the flow of air upwards through the borehole.

The rock drilling system further comprises an extraction device connected to the conveying chamber arrangement to draw air containing drill cuttings from the borehole. The extraction device may be any type of suction device, suitable for extracting air and drill cuttings. The extraction device may be a tank comprising an inlet, an outlet and a pump. The extraction device may be a vacuum truck or vacuum tanker. By means of the extraction device, air and drill cuttings may efficiently be removed from the borehole. By means of the extraction device, the flow of air upwards through the borehole may be controlled. For example, by adjusting the force of suction of the extracting device, the airflow in the passage between the drill string and the inner circumference of the borehole may be adjusted. By keeping the air flowing fast enough upwards in the passage between the the drill string and the inner circumference of the borehole, an air curtain may be created. The air curtain may comprise air moving at increased velocity, i.e. accelerated air. The air curtain may be beneficial for the transportation of drill cuttings up to the ground surface.

Thus, by means of the supply of compressed air down the borehole by at least one air compressor, the configuration of the conveying chamber arrangement and the drawing of air from the borehole by means of the extraction device, the flow of air upwards through the borehole may be controlled. The airflow in the borehole may be further controlled by adjusting at least one of the following two parameters: the supply of air from the at least one air compressor and the suction force of the extraction device. By altering and optimizing these two parameters for different applications, an efficient penetration rate and removal of drill cuttings may be achieved.

By controlling and maintaining an efficient flow of air upwards in the borehole, an efficient penetration rate of drilling, cooling of the drilling equipment and removal of drill cuttings is achieved, despite high temperatures and increasing pressure in the ground. Thereby, an advantageous rock drilling system is achieved, which enables deep drilling such that high-temperature geothermal resources may be extracted.

According to an example, the rock drilling system may be configured so that the air flows in a direction towards the bottom of the borehole in a channel inside the drill string and in a direction towards the ground surface in a passage formed between the drill string and an inner circumference of the borehole. This configuration of airflow in the borehole is advantageous, as the supply of compressed air driving the drilling hammer may be efficiently distributed to the drilling hammer through the drill string, while the removal of drill cuttings may simultaneously be efficiently removed through the passage between the drill string and the inner circumference of the borehole.

According to an example, the rock drilling system may further comprise air jetting means with at least one nozzle arranged along the drill string above the drilling hammer, wherein the at least one nozzle is configured to eject air from a channel inside the drill string to a passage formed between the drill string and an inner circumference of the borehole.

The at least one nozzle may be arranged along the drill string to forward air flowing from the bottom of the borehole. The at least one nozzle may thus assist in drill cutting removal up the borehole. The at least one nozzle may be arranged to eject air in in direction upwards towards the ground surface. The at least one nozzle may alternatively be arranged to eject air in a radial direction of the borehole. The at least one nozzle may be arranged above the drilling hammer. This mean that the at least one nozzle may be arranged along the drill string between the drilling hammer and the ground surface. The at least one nozzle may be arranged directly above the drilling hammer.

The air jetting means allow large volumes of compressed air to be sent down the drill string for flushing, channeling no more air to the drilling hammer than is needed for efficient operation. Multiple nozzles placed throughout the drill string allow excess air at various points to assist evacuation of drill cuttings in the borehole. This is especially important in for example turns or horizontal drilling situations. Use of air jetting means also prevent over-pressuring of the hammer environment in deep rock applications. Even when large volumes of compressed air is supplied to the drill string in order to achieve an efficient removal of drill cuttings, only the amount of air needed to drive the drilling hammer is transferred to the drilling hammer. The excess air, which may have negative impact on the operation of the drilling hammer, may be discharged by the nozzles into the passage between the drill string and the inner circumference of the borehole, before reaching the drilling hammer. The excess air may form a curtain of air in the passage, which may enhance the speed of the airflow moving upwards the borehole.

The air jetting means may be passively controlled by the airflow and/or the air pressure in the channel inside the drill string. The air jetting means may be passively controlled by the difference in air pressure between the air pressure in the channel inside the drill string and the air pressure in the passage formed between the drill string and the inner circumference of the borehole. The term“passively controlled” means that the air jetting means may act without the need of any external power supply. The passive control of the air jetting means may be achieved by means of mechanically actuated valves, such as check valves or similar devices. The ejection by the air jetting means may be adjusted by e.g. changing the type or number of nozzles, altering the size, shape and/or angle of the discharge opening, the positioning of the nozzles along the drill string, and the configuration of when and where in the drilling process the nozzles are opened and closed etc. The air jetting means may be manually actuated and/or adjusted by an operator. It may be suitable to perform such manual procedures, such as actuating and/or adjusting the air jetting means, in conjunction with changing or sharping the drill bit. Alternatively, the air jetting means may be electronically controllable.

Thus, the airflow in the borehole may be controlled not only by adjusting the supply of air from the at least one air compressor and the suction force of the extraction device. The ejection by the air jetting means is a third parameter, which may be used to control the airflow in the borehole. Hence, by altering and optimizing these three parameters for different applications, an efficient penetration rate and removal of drill cuttings may be achieved.

According to an example, the rock drilling system may further comprise a drill cuttings separator for separating the drill cuttings from the air containing drill cuttings.

The drill cutting separator may be of any sort that separate drill cuttings from the air. The drill cutting separator may collect the drill cuttings and release the air into the atmosphere. The air may be cleaned before the air is released into the atmosphere by means of an air filter. The air filter may for example comprise a stainless steel mesh and/or HEPA-f liters (high-efficiency particulate air filters). The drill cutting separator may comprise a tank with an inlet for air and drill cuttings, an air outlet and a filter element arranged between the inlet and the outlet. Alternatively, the drill cutting separator may be a cyclone separator. The drill cutting separator may be a separate unit or integrated with for example the extraction device. The drill cutting separator may be movable. The drill cutting separator may be arranged on a vehicle.

According to an example of the present disclosure, the rock drilling system may be configured for drilling boreholes that are at least 1500 meters deep. According to an example, the rock drilling system may be configured for drilling boreholes that are at least 2000 meters deep, or at least 3000 meters deep. Due to the configuration of the rock drilling system according to the present disclosure, drilling very deep boreholes into the earth to depths, greater than 1500 meters, 2000 meters and/or 3000 meters, may be accomplished. By means of a simple and efficient rock drilling system, a more efficient airflow in the borehole is achieved. Thereby, deep drilling may be accomplished quickly and at low cost.

According to an example, the drilling rig, the at least one air compressor and the extraction device may be mobile. By means of the equipment being mobile, the equipment may be easily transported to the drilling site. This enables drilling at places hard to reach, far from railroads and other types of infrastructure. This may be useful especially for sustainable development in countries suffering from severe structural impediments. The drilling rig, the at least one air compressor and the extraction device may be arranged on vehicles. The different units may be arranged on different vehicles, or one or more units may share the same vehicle. The vehicles may comprise wheels or continuous tracks (i.e. tank or caterpillar treads).

According to an example, the conveying chamber arrangement may be configured to be airtight, in order to maintain the flow of air upwards through the borehole. That the conveying chamber arrangement may be configured to be airtight means that the borehole is sealed for pressurization by means of the at least one air compressor and the extraction device. By means of the conveying chamber being airtight, the airflow directed downwards through the drill string may efficiently be separated from the airflow directed upwards through the borehole. The configuration of the conveying chamber arrangement to be airtight, also impedes air leaks in and out of the convening chamber arrangement. It is important that the extraction device draws air from the borehole, and not ambient air from the outside of the conveying chamber arrangement. Air leaks of ambient air may affect the airflow upwards in the borehole negatively. The configuration of the conveying chamber arrangement to be airtight, also impedes contamination of the surroundings around the borehole, as air and drill cuttings may be prevented to leak out in the ambient air or at the ground surface.

By means of an airtight conveying chamber arrangement, the airflow in the borehole may be properly controlled. The airtight configuration of the conveying chamber arrangement enables the drill string with compressed air to enter the borehole, and air and drill cutting to exit the borehole, while maintaining an efficient airflow in the borehole. According to an example, the conveying chamber arrangement may comprise: a top cover with an opening for the drill string; a drill string sleeve connected to the top cover and arranged to encircle the drill string; chamber walls connected to the top cover and encircling the drill string sleeve, wherein the chamber walls are configured to be connected to the borehole casing at a bottom end; and an extraction opening configured to be connected to the extraction device. By means of this configuration, the conveying chamber arrangement may facilitate connection of different parts in the rock drilling system.

The drill string may be slidingly engaged with the opening in the top cover. The drill string sleeve may be fixedly connected to the top cover by welding. Alternatively, the drill string sleeve may be connected to the top cover by attachment means, such as threaded parts, bayonet connectors or any other suitable type of coupling or connector. The chamber walls may be connected to the top cover and the borehole casing by means of bolts, screws and nuts or other types of durable engagement part, suitable for engagement and disengagement. The extraction opening may be formed in the chamber walls of the conveying chamber arrangement. The extraction opening is configured to be connected to the extraction device by means of clamping jaws, claw couplings, bayonet connectors, quick coupling or other types of suitable coupling for connecting a suction hose, pipe or similar to the extraction opening.

According to an example, the conveying chamber arrangement may comprise sealing elements between the top cover and the chamber walls and/or at the opening for the drill string, and/or at the extraction opening, and/or at the bottom end of the chamber walls.

The sealing elements may be of any type suitable for sealing the different components to each other, such that an airtight conveying chamber arrangement is achieved. The sealing elements may comprise gaskets, O-rings or other elastic parts. The sealing elements may comprise clamping plates, sealing flanges etc. By means of these sealings, the air pressure and airflow within the borehole may be controlled. By means of the sealing means, air leaks in and out of the conveying chamber arrangement may be impeded. Air leaks of ambient air may affect the airflow upwards in the borehole negatively.

The conveying chamber arrangement may comprise sealing elements between the top cover and the chamber walls. The sealing elements may comprise gaskets, O- rings or other elastic parts. The top cover may be connected to the chamber walls by means of fastening means. The fastening means may comprise clamping bolts and nuts, or other types of durable engagement part, suitable for engagement and disengagement.

The conveying chamber arrangement may comprise sealing elements at the opening for the drill string. These sealing elements may comprise gaskets, O-rings or other elastic parts and clamping plates, sealing flanges etc. These sealing members may be arranged above the top cover. These sealing members may comprise at least one flat gasket, covering the entire top cover. The flat gasket may tightly seal any small gap between the drill string and the drill string sleeve, about the opening in the top cover. The drill string may be slidingly engaged with a flat gasket and the opening in the top cover. By means of the flat gasket, the entrance of the drill string into the drill string sleeve may be airtight. The at least one flat gasket may be clamped between the top cover and for example a clamping plate by means of fastening means. The fastening means may comprise clamping bolts and nuts, or other similar fastening devices. The fastening means may be the same as mentioned above.

The conveying chamber arrangement may comprise sealing elements at the extraction opening, and/or at the bottom end of the chamber walls. The sealing elements may comprise gaskets, O-rings or other elastic parts. The sealing element arranged at the extraction opening, may be arranged between the extraction opening of the conveying chamber arrangement and a suction hose, connecting the conveying chamber arrangement to the extraction device. The sealing elements may be clamped between the extraction opening and the suction hose by means of clamping jaws, claw couplings, bayonet connectors, quick coupling or other types of suitable coupling for connecting a suction hose or similar to the extraction opening. The sealing element at the bottom end, may be arranged between the bottom end and the borehole casing. The sealing element arranged between the bottom end and the borehole casing may be clamped by means of fastening means. The fastening means may comprise clamping bolts and nuts, or other types of durable engagement part, suitable for engagement and disengagement.

According to an example, the drilling hammer may be configured to be arranged at the bottom of the borehole at an end of the drill string. Arranging the drilling hammer to the lower end of the drill string may be advantageous in many different ways as previously described. For example, a down-the-hole hammer may have an increased penetration rate compared to for example pneumatic top hammers. Also, at deeper levels, the weight of the drill string becomes highly significant and the number of joints between drill pipes numerous. As an example, a 2000 meters long drill string may weigh 45 tons, i.e. 45 000 kg. Consequently, the drill string may collapse if, for example, a pneumatic top hammer drill is used. In top hammer drilling, the hammer produces a percussive force on top of the drill string, which is transferred to the drill bit through the drill string. Thus, by using a drilling hammer arranged at the bottom of the borehole at the end of the drill string, a more efficient and robust configuration is achieved for drilling of deep holes.

According to an example, the rock drilling system may further comprise a control device configured to control the drilling rig and/or the at least one air compressor and/or the extraction device and/or the air jetting means. The control device may be implemented as a separate entity or distributed in two or more physical entities. The control device may comprise one or more control units and/or computers. The control device may thus comprise control units comprised in the at least one air compressor, the drilling rig and/or the extraction device. The control device may be implemented or realised by the control device comprising a processor and a memory. The memory may comprise instructions, which when executed by the processor causes the control device to perform method steps.

By means of the control device controlling the drilling rig, the drill rig may transfer the necessary feed force and rotation to the drill string. The drill string may then transfer the feed force and rotation to the drilling hammer and drill bit. By means of the control device controlling the at least one air compressor, the driving of the drilling hammer and supply of compressed air into the borehole may be controlled. By means of the control device controlling the extraction device, the drawing of air containing drill cuttings from the borehole may be controlled. Thereby, the flow of air upwards through the borehole may be controlled. By means of the control device controlling the air jetting means, the ejection of air by means of air jetting means may be controlled. The air jetting means may assist the flow of air and drill cuttings upwards through the borehole. Thereby, the flow of air upwards through the borehole may be controlled.

By means of the control device, the airflow in the borehole may be controlled by adjusting at least some of the following three parameters: the supply of air from the at least one air compressor, the suction force of the extraction device and/or the ejection by the air jetting means. By altering and optimizing these parameters for different applications, an efficient penetration rate and removal of drill cuttings may be achieved.

According to an example, suitable air filters and shielding elements may be provided at the air inlets and air outlets of the rock drilling system. Air filters and shielding elements may keep dust and dirt out of the pneumatic mechanisms. According to an example, guarding elements, in the form of grids, mesh, nets etc., may be arranged at the top of the borehole to protect the drilling equipment in the borehole from falling stones and the like. The guarding arrangement may be arranged in the borehole casing.

According to an aspect of the present disclosure, use of a rock drilling system as disclosed herein is provided, for generation of geothermal energy.

By the use of the rock drilling system for generation of geothermal energy, the cost of investment in geothermal energy is reduced, in respect to both financial and environmental assets. By the use of the rock drilling system for generation of geothermal energy, an advantageous and sustainable way of achieving green and clean energy is obtained.

According to an aspect of the present disclosure, a method for geothermal drilling with a rock drilling system as disclosed herein is provided.

The method comprises the steps of: driving the drilling hammer and supplying compressed air into a borehole via the drill string by means of the at least one air compressor; and drawing air containing drill cuttings from the borehole via the conveying chamber arrangement, by means of the extraction device.

By means of steps of driving the drilling hammer and supplying compressed air into a borehole via the drill string by means of the at least one air compressor; and drawing air containing drill cuttings from the borehole via the conveying chamber arrangement, by means of the extraction device, the flow of air upwards through the borehole may be controlled. By controlling and maintaining an efficient flow of air upwards in the borehole, an efficient penetration rate of drilling, cooling of the drilling equipment and removal of drill cuttings is achieved, despite high temperatures and increasing pressure in the ground. Thereby, an advantageous rock drilling system is achieved, which enables deep drilling such that high-temperature geothermal resources may be extracted.

The step of drawing of air containing drill cuttings by means of the extraction device may be initiated when reaching a depth of about 200-300 meters, i.e. when the air pressure in the borehole increases. At smaller depth, a sufficient flow of air upwards through the borehole may be achieved by means of the at least one air compressor only.

According to an example, the method as disclosed above further comprising the step of ejecting air by means of air jetting means to assist the flow of air and drill cuttings upwards through the borehole. By means of the step of ejecting air by means of air jetting means, larger volumes of compressed air may be sent down the drill string for flushing, without affecting the operation of the drill hammer negatively. Excess air, not needed to operate the drill hammer, may be ejected by the air jetting means and improve the flow of air in the passage between the drill string and the inner circumference of the borehole. Consequently, the flow of air in the passage may be controlled and the removal of drill residuals from the borehole may be improved.

According to an aspect of the disclosure, a conveying chamber arrangement for a rock drilling system is provided. The conveying chamber arrangement is configured to be arranged at a ground surface, wherein the conveying chamber arrangement is configured to encircle a drill string and to be connected to a borehole casing. The conveying chamber arrangement comprises: a top cover with an opening for the drill string; a drill string sleeve connected to the top cover and encircling the drill string; chamber walls connected to the top cover and encircling the drill string and the drill string sleeve; wherein the chamber walls are configured to be connected to a borehole casing at a bottom end; and an extraction opening configured to be connected to an extraction device.

The conveying chamber arrangement may facilitate connection of different parts in a rock drilling system. The configuration of the conveying chamber arrangement may separate and guide airflows in, out and within the mouth of a borehole at the ground surface. By means of the conveying chamber arrangement, the airflow in the borehole may be controlled. The configuration of the conveying chamber arrangement enables a drill string with compresses air to enter the borehole, air and drill cutting to exit the borehole, while maintaining the flow in the borehole. The configuration of the conveying chamber also impedes contamination of the surroundings around the borehole, as air and drill cuttings may be prevented to leak out in the ambient air or at the ground surface.

According to an example, the conveying chamber arrangement as disclosed herein, comprises sealing elements between the top cover and the chamber walls and/or at the opening for the drill string, and/or the extraction opening, and/or the bottom end of the chamber walls. The sealing elements may be of any type suitable for sealing the different components to each other such an airtight conveying chamber arrangement is achieved. The sealing elements may comprise gasket, O-rings or other elastic parts. The sealing elements may comprise clamping plates, sealing flanges etc. By means of these sealings, the conveying chamber arrangement may be connected airtight to the drill string, borehole casing and the extracting device. Thereby, air pressure and airflows within the borehole may be controlled.

According to an aspect of the disclosure, a method performed by a control device, for geothermal drilling with a rock drilling system as disclosed herein is provided. The method comprising the steps of: controlling the at least one air compressor to drive the drilling hammer and supply compressed air into a borehole via the drill string; controlling the extraction device to draw air containing drill cuttings from the borehole via the conveying chamber arrangement. The control device performing the method is comprised in the rock drilling system.

It is to be understood that the control device may be implemented as a separate entity or distributed in two or more physical entities. The control device may comprise one or more control units and/or computers. The control device may thus be implemented or realised by the control device comprising a processor and a memory, the memory comprising instructions, which when executed by the processor causes the control device to perform the above disclosed method steps.

The control device may allow monitoring and controlling of the different units in the rock drilling system. By means of monitoring drilling processes during drilling of boreholes, data and parameters may collected and stored. The collected data may thus be analysed and used to control upcoming drilling procedures. The drilling procedure may thus be optimized, based on the collected data from previous drilling procedures. The control device may allow remote monitoring and controlling of the different units in the rock drilling system via Internet, Bluetooth, mobile phone network data service or similar.

According to an example, the method above may further comprise the step of controlling air jetting means to eject air in order to assist the flow of air and drill cuttings upwards through the borehole. In this event, the air jetting means may be electronically controllable. Alternatively, the air jetting means may be manually actuated and/or adjusted on the initiative of a signal given by the control device to an operator. Thus, an actuation procedure of the air jetting means as such may be manually operated, but monitored and controlled by the control device. Thus, the control device may notify the operator when a manual procedure is suitable to be carried out, e.g. when reaching a certain depth, or when the flow of air upwards in the borehole decreases. It may be suitable to perform such manual procedures, such as actuating and/or adjusting the air jetting means, in conjunction with changing or sharping the drill bit. By means of the control device controlling the air jetting means, the ejection of air by means of air jetting means may be controlled. The air jetting means may assist the flow of air and drill cuttings upwards through the borehole. Thereby, the flow of air upwards through the borehole may be controlled.

By means of the control device, the airflow in the borehole may be controlled by adjusting at least one of the following three parameters: the supply of air from the at least one air compressor, the suction force of the extraction device and, when applicable, the ejection by the air jetting means. By adjusting and optimizing these parameters for different applications, an efficient penetration rate and removal of drill cuttings may be achieved. Thereby, deep holes may be efficiently drilled.

The altering and optimizing of these parameters for different applications may be based on collected data from previously performed drilling processes. The altering and optimizing of these parameters for different applications may for example be based on the current drilling depth and/or the material being drilled (such as the type of rock) and other relevant parameters for the current application. When the drilling depth increases, so does the pressure inside the borehole. The supply of air from the at least one air compressor and the suction force of the extraction device, and the ejection by the air jetting means when applicable, may then be automatically increased by means of the control device. The method steps of controlling the at least one air compressor, controlling the extraction device and controlling the air jetting means may be performed continuously throughout the drilling process, in order to efficiently control and regulate the drilling process. According to an aspect of the disclosure, a computer program comprising instructions which, when the program is executed by a computer, causes the computer to perform the method as disclosed above is provided. By means of the computer program, an increased control of the drilling process may be obtained. The computer program causes the rock drilling system to perform the above methods steps when executed, with increased predictability and reproducibility compared to performing the method manually and/or in accordance with various rules of thumb.

According to an aspect of the disclosure, a computer-readable medium comprising instructions, which when executed by a computer causes the computer to carry out the method as disclosed above is provided. The computer-readable medium may be any tangible and/or non-transitory medium that may contain or store a program for execution by a processor.

The present disclosure will now be further illustrated with reference to the appended figures, wherein for the sake of clarity and understanding of the disclosure some details of no importance are deleted from the figures. Moreover, the figures shall not be considered drawn to scale as some features may be exaggerated in order to more clearly illustrate the invention.

Figure 1 schematically illustrates a side view of a rock drilling system 10 according to an example of the present disclosure. A deep, vertically extending borehole 9 of circular cross section is illustrated. However, the present disclosure is also suitable for directional drilling. The borehole 9 may extend from the ground surface 12 through a top layer 7 of softer material, such as soil or gravel, to a rock layer 8. A borehole casing 44 may line the borehole 9 from the ground surface 12 into the rock layer 8.

The rock drilling system 10 for geothermal drilling as schematically illustrated in Figure 1 comprises: a drilling rig 2 with a drill string 22 and a drilling hammer 4 for drilling a borehole 9; at least one air compressor 1 configured for driving the drilling hammer 4 and supplying compressed air into the borehole 9 via the drill string 22; a conveying chamber arrangement 3 arranged at the ground surface 12, wherein the conveying chamber arrangement 3 is configured to encircle the drill string 22 and to be connected to a borehole casing 44. An extraction device 5 is connected to the conveying chamber arrangement 3 to draw air containing drill cuttings from the borehole 9, thereby controlling the flow of air upwards through the borehole 9.

The drilling rig 2 has a feed beam or mast 21 and a drive unit 20 which may rotate and feed the drill string 22. The drive unit 20 may be a diesel, gasoline or electric motor. The drill string 22 may consist of multiple drill pipes which are screwed together or joined in some other way. The drill string 22 may transfer the necessary feed force and rotation to the drilling hammer 4 and a drill bit 42, as well as compressed air for driving the drilling hammer 4. The drilling hammer 4 may comprise the drill bit 42. Drill pipes are added to the top of the drill string 22 as the borehole 9 gets deeper. The drilling hammer 4 may comprise a piston hammer 41 that delivers impact to the drill bit 42 either directly or through an anvil block. The piston hammer 41 may directly strike the impact surface of the drill bit 42, while a hammer casing gives guidance to the drill bit. The drilling hammer 4 impact may break hard rock into small particles, i.e. drilling cuttings, which may be blown upwards in the borehole 9 by air exhaust from the drill hammer 4.

The drilling hammer 4 may be a conventional drilling hammer, driven by compressed air. According to an example, the drilling hammer 4 may be arranged at the bottom of the borehole 9 at an end of the drill string 22. According to an example, the drilling hammer 4 may be a pneumatic down-the-hole percussive rock drill. Compressed air may be supplied from the air compressor 1 to the drilling rig 2 via an air compressor hose 1 1 . From the drilling rig 2, the compressed air may be transported to the drilling hammer 4 through the drill string 22.

During a drilling operation, the at least one air compressor 1 may drive the drilling hammer 4 and supply compressed air into the borehole 9 via the drill string 22. When reaching a depth of about 200-300 meters, when the air pressure in the borehole 9 increases, the drawing of air containing drill cuttings by means of the extraction device 5 may be initiated. At minor depths, a sufficient flow of air upwards through the borehole 9 may be achieved by means of the at least one air compressor 1 only.

According to an example, the rock drilling system 10 may be configured so that the air flows in a direction downwards towards the bottom of the borehole 9 in a channel 23 inside the drill string 22 and upwards in a direction towards the ground surface 12 in a passage 24 formed between the drill string 22 and an inner circumference of the borehole 9. The direction of the airflow is schematically illustrated by arrows in figure 1.

According to an example, the rock drilling system 10 may comprise air jetting means 6 with at least one nozzle arranged along the drill string 22 above the drilling hammer 4. The at least one nozzle may be configured to eject air from the channel 23 inside the drill string 22 to the passage 24 formed between the drill string 22 and the inner circumference of the borehole 9. The air jetting means 6 may assist the flow of air and drill cuttings upwards through the borehole 9.

According to an example, the rock drilling system 10 may comprise a drill cuttings separator 55 for separating the drill cuttings from the air containing drill cuttings. The drill cutting separator 55 may be a separate unit or integrated with for example the extraction device 5 as schematically illustrated in figure 1 . The drill cutting separator 55 may be movable. The drill cutting separator 55 may be arranged on a vehicle.

According to an example, the rock drilling system 10 may be configured for drilling boreholes 9 that are at least 1500 meters deep. According to an example, the rock drilling system is configured for drilling boreholes 9 that are at least 2000 meters deep, or at least 3000 meters deep. According to an example, the drilling rig 2, the at least one air compressor 1 and the extraction device 5 may be mobile. The different units 2, 1 ,5 may be arranged on different vehicles, or one or more units 2, 1 ,5 may share the same vehicle. The vehicles may comprise wheels or continuous tracks (i.e. tank or caterpillar treads). In figure 1 , the drilling rig 2, the at least one air compressor 1 and the extraction device 5 are illustrated as separate vehicles. The drilling rig 2 is schematically illustrated with continuous tracks. According to an example, the conveying chamber arrangement 3 may be configured to be airtight, in order to maintain the flow of air upwards through the borehole 9.

According to an example, the rock drilling system 10 may further comprise a control device 100 configured to control the drilling rig 2 and/or the at least one air compressor 1 and/or the extraction device 5 and/or the air jetting means 6. The control device 100 may allow remote monitoring and controlling of the different units in the rock drilling system 10 via Internet, Bluetooth, mobile phone network data service or similar. The control device 100 may be implemented as a separate entity or distributed in two or more physical entities. The control device 100 may comprise one or more control units and/or computers. The control device 100 may thus be implemented or realised by the control device 100 comprising a processor and a memory. The memory may comprise instructions, which when executed by the processor causes the control device 100 to perform method steps. According to an example, the controll device 100 may comprise a computer program P. The computer program P may comprise instructions which when the program is executed by a computer, causes the computer to perform method steps as disclosed herein.

According to an aspect of the present disclosure, the rock drilling system 10 as illustrated in figure 1 may be intended for use for generation of geothermal energy.

Figure 2 and figure 3 schematically illustrate details of the rock drilling system 10. Figure 2 and figure 3 illustrates examples of a conveying chamber arrangement 3. The conveying chamber arrangement 3 may comprise: a top cover 36a with an opening 31 for the drill string 22; a drill string sleeve 33 connected to the top cover 36a and encircling the drill string 22; chamber walls 38 connected to the top cover 36a and encircling the drill string 22 and the drill string sleeve 33, wherein the chamber walls 38 are configured to be connected to the borehole casing 44 at a bottom end 32; and an extraction opening 39 configured to be connected to the extraction device 5. The conveying chamber arrangement 3 may according to an example comprise sealing elements 34a, 34b, 34c, 34d, 36b between the top cover 36a and the chamber walls 38 and/or at the opening 31 for the drill string 22 and/or at the extraction opening 39, and/or at the bottom end 32 of the chamber walls 38.

The conveying chamber arrangement 10 may be configured as disclosed in figure 3. In figure 3, the drill string sleeve 33 is more elongated than in figure 2. When the drill string sleeve 33 is longer, a supporting structure 37 may be arranged to support the drill string sleeve 33. The supporting structure 37 may comprise struts, or some sort of supporting legs, attached to the chamber walls 38. A more elongated drill string sleeve 33 may be beneficial for achieving an airtight conveying chamber arrangement. In figure 3, it is schematically illustrated that the diameter of the borehole casing 44 varies. The diameter of the borehole casing 44 may be varied in order to obtain an efficient airflow upwards in the borehole 9.

As illustrated in figure 2 and figure 3, the conveying chamber arrangement 3 may comprise sealing elements 34b, 36b at the opening 31 for the drill string 22. These sealing elements 34b, 36b may comprise gaskets, O-rings or other elastic parts and clamping plates, sealing flanges etc. For example, the sealing elements 34b, 36b are arranged above (on top of) the top cover 36a and may comprise at least one flat gasket 34b. The at least one flat gasket 34b may have a similar shape and size as the top cover 36a. However, the opening in the at least one flat gasket 34b for the drill string may be smaller than the opening 31 of the top cover 36a. Due to this configuration, the at least one flat gasket 34b may tightly seal any small gap between the drill string 22 and the drill string sleeve 33 at the opening 31 in the top cover 36a. The drill string 22 may be slidingly engaged with the at least one flat gasket 34b and the opening 31 in the top cover 36a. By means of the at least one flat gasket 34b, the entrance of the drill string 22 into the drill string sleeve 33 may be airtight. The at least one flat gasket 34b may be clamped between the top cover 36a and for example a clamping plate 36b by means of fastening means 35a. The clamping plate 36b may comprise a flat circular plate with an opening for the drill string 22. According to an example, there may be two flat gaskets 34b between the top cover 36a and the clamping plate 36b. The fastening means 35a may comprise clamping bolts and nuts, or other similar fastening devices. The fastening means 35a may be the same as mentioned above.

The conveying chamber arrangement 3 may comprise sealing elements 34c, 34d at the extraction opening 39 and/or at the bottom end 32 of the chamber walls 38. The sealing elements 34c, 34d may comprise gaskets, O-rings or other elastic parts. The sealing element 34c arranged at the extraction opening 39, may be arranged between the extraction opening 39 of the conveying chamber arrangement 3 and a suction hose 51 , connecting the conveying chamber arrangement 3 to the extraction device 5. The sealing elements 34c may be clamped between the extraction opening 39 and the suction hose 51 by means of clamping jaws, claw couplings, bayonet connectors, quick coupling or other types of suitable coupling for connecting a suction hose or similar to the extraction opening 39. The sealing element 34d at the bottom end 32, may be arranged between the bottom end 32 and the borehole casing 44. The sealing element 34d arranged between the bottom end 32 and the borehole casing 44 may be clamped by means of fastening means 35b. The fastening means 35b may comprise clamping bolts and nuts, or other types of durable engagement part, suitable for engagement and disengagement.

Figure 4 schematically illustrates a block diagram of a method for geothermal drilling with a rock drilling system 10 according to an example. The method relates to the rock drilling system 10 as disclosed in figure 1 .

The method comprises the steps of: driving s10 the drilling hammer 4 and supplying compressed air into a borehole 9 via the drill string 22 by means of the at least one air compressor 1 ; and drawing s20 air containing drill cuttings from the borehole 9 via the conveying chamber arrangement 3, by means of the extraction device 5. The method may further comprise the step of: ejecting s30 air by means of air jetting means 6 to assist the flow of air and drill cuttings upwards through the borehole 9.

Figure 5 schematically illustrates a block diagram of a method performed by a control device 100, for geothermal drilling with a rock drilling system 10 according to an example. The method relates to the rock drilling system 10 as disclosed in figure 1 . The method may thus be performed by the control device 100 as disclosed in figure 1 .

The method comprising the steps of: controlling s1 10 the at least one air compressor 1 to drive the drilling hammer 4 and supply compressed air into a borehole 9 via the drill string 22; controlling s120 the extraction device 5 to draw air containing drill cuttings from the borehole 9 via the conveying chamber arrangement 3.

The method may optionally comprise the step of controlling s130 air jetting means 6 to eject air in order to assist the flow of air and drill cuttings upwards through the borehole 9.

It is to be understood that the control device 100 may be implemented as a separate entity or distributed in two or more physical entities. The control device 100 may comprise one or more control units and/or computers. The control device 100 may thus be implemented or realised by the control device 100 comprising a processor and a memory, the memory comprising instructions, which when executed by the processor causes the control device 100 to perform the above disclosed method steps.

According to an example, a computer program P comprising instructions which, when the program is executed by a computer, causes the computer to perform the method as disclosed above is provided. The computer program P is schematically illustrated in figure 1 . According to an example, a computer-readable medium comprising instructions, which when executed by a computer causes the computer to carry out the method as disclosed above is provided.

The foregoing description of the preferred examples of the present disclosure is provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to restrict the invention to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The examples of the present disclosure have been chosen and described in order best to explain the principles of the invention and its practical applications and hence make it possible for specialists to understand the invention for various embodiments and with the various modifications appropriate to the intended use.

Claims

1 . A rock drilling system (10) for geothermal drilling, the rock drilling system (10) comprising:

a drilling rig (2) with a drill string (22) and a drilling hammer (4) for drilling a borehole (9);

at least one air compressor (1 ) configured for driving the drilling hammer (4) and supplying compressed air into the borehole (9) via the drill string (22); a conveying chamber arrangement (3) configured to be arranged at a ground surface (12), wherein the conveying chamber arrangement (3) is configured to encircle the drill string (22) and to be connected to a borehole casing (44); characterized by that

an extraction device (5) is connected to the conveying chamber arrangement (3) to draw air containing drill cuttings from the borehole (9), thereby controlling the flow of air upwards through the borehole (9).

2. The rock drilling system (10) according to claim 1 ,

wherein the rock drilling system (10) is configured so that the air flows in a direction towards the bottom of the borehole (9) in a channel (23) inside the drill string (22) and in a direction towards the ground surface (12) in a passage (24) formed between the drill string (22) and an inner circumference of the borehole (9).

3. The rock drilling system (10) according to claim 1 or 2, further comprising:

air jetting means (6) with at least one nozzle arranged along the drill string (22) above the drilling hammer (4),

wherein the at least one nozzle is configured to eject air from a channel (23) inside the drill string (22) to a passage (24) formed between the drill string (22) and an inner circumference of the borehole (9).

4. The rock drilling system (10) according to any one of the preceding claims, further comprising:

a drill cuttings separator (55) for separating the drill cuttings from the air containing drill cuttings.

5. The rock drilling system (10) according to any one of the preceding claims, wherein the rock drilling system (10) is configured for drilling boreholes that are at least 1500 meters deep.

6. The rock drilling system (10) according to any one of the preceding claims,

wherein the drilling rig (2), the at least one air compressor (1 ) and the extraction device (5) are mobile.

7. The rock drilling system (10) according to any one of the preceding claims,

wherein the conveying chamber arrangement (3) is configured to be airtight, in order to maintain the flow of air upwards through the borehole (9).

8. The rock drilling system (10) according to any one of the preceding claims, wherein the conveying chamber arrangement (3) comprises:

a top cover (36a) with an opening (31 ) for the drill string (22);

a drill string sleeve (33) connected to the top cover (36a) and arranged to encircle the drill string (22);

chamber walls (38) connected to the top cover (36a) and encircling the drill string sleeve (33), wherein the chamber walls (38) are configured to be connected to the borehole casing (44) at a bottom end (32); and

an extraction opening (39) configured to be connected to the extraction device (5).

9. The rock drilling system (10) according to claim 8,

wherein the conveying chamber arrangement (3) comprises sealing elements (34a, 34b, 34c, 34d, 36b) between the top cover (36a) and the chamber walls (38) and/or at the opening (31 ) for the drill string (22) and/or at the extraction opening (39), and/or at the bottom end (32) of the chamber walls (38).

10. The rock drilling system (10) according to any one of the preceding claims, wherein the drilling hammer (4) is configured to be arranged at the bottom of the borehole (9) at an end of the drill string (22).

11. The rock drilling system (10) according to any one of the preceding claims, further comprising a control device (100) configured to control the drilling rig (2) and/or the at least one air compressor (1 ) and/or the extraction device (5) and/or the air jetting means (6).

12. Use of a rock drilling system (10) according to any one of claims 1 -11 ,

for generation of geothermal energy.

13. A method for geothermal drilling with a rock drilling system (10) according to any of claims 1 -11 ,

wherein the method comprises the steps of:

- driving (s10) the drilling hammer (4) and supplying compressed air into a borehole (9) via the drill string (22) by means of the at least one air compressor (1 ); and

- drawing (s20) air containing drill cuttings from the borehole (9) via the conveying chamber arrangement (3), by means of the extraction device (5).

14. The method according to claim 13 further comprising the step of:

- ejecting (s30) air by means of air jetting means (6) to assist the flow of air and drill cuttings upwards through the borehole (9).