Method for sinking a borehole

Abstract

Method for sinking a borehole (2) in the rock, in which -the rock at the bottom of the borehole (2a) is thermally melted and is removed upwards from the borehole (2) with the aid of a gaseous medium, - the heat required to melt the rock is provided by at least one electric plasma generator (8) associated with a propulsion device (4) located at the front of a feed and supply rod (3) that can be inserted into the borehole (2), an annular space remaining between the propulsion device (4) and the borehole wall (2b) for the removal of the loosened rock, - the propulsion device (4) has a heat shield (5) at the front, which covers the borehole bottom (2a) except for a peripheral gap between the outer edge of the heat shield (5) and the borehole wall (2b) and forms a dynamic pressure chamber (7) with the borehole bottom (2a), - the gaseous medium is divided into a first partial flow (19a) for plasma generation and a second partial flow (19b) for cooling the propulsion device (4), the feed and supply rods (3) and the borehole wall (2b), - the first partial flow (19a) is injected into the dynamic pressure chamber (7) and is converted there into a high-pressure plasma with the aid of the electric plasma generators (8), which heats the rock at the bottom of the borehole (2a) to at least above its liquidus temperature and carries the loosened rock out of the dynamic pressure chamber (7) into the annular space between the propulsion device (4) and the borehole wall (2b) via the peripheral annular gap between the heat shield (5) and the borehole wall (2b), - the second partial flow (19b) is injected into the annular space between the propulsion device and the borehole wall and there cools the part of the propulsion device (4) located above the heat shield (5), the first partial flow loaded with loosened rock and the borehole wall (2b) to below the solidus temperature of the rock, - and a heat-affected zone (21) is formed in the borehole wall (2b) around the borehole (3), at the inner boundary of which the rock is heated at least to the liquidus temperature during the sinking process and at the outer boundary of which the rock does not reach the solidus temperature during the sinking process, characterized in that the material composition of the molten rock in each case is continuously determined and in that the advance speed of the propulsion device (4), the energy supply to the plasma generator (8) and the pressure and temperature of the two partial flows (19a, 19b) of the gaseous medium are controlled as a function of the material composition of the rock in each case determined in such a way that the heat-affected zone (21) forming in the region of the borehole wall (2b) has a thickness of at least one borehole diameter.

Description

[0001] The invention relates to a method for drilling a borehole in the rock, in which -the rock at the bottom of the borehole is thermally melted and removed upwards from the borehole with the aid of a gaseous medium, - the heat required to melt the rock is provided by at least one electric plasma generator associated with a propulsion device located at the front of a feed and supply rod that can be inserted into the borehole, with an annular space remaining between the propulsion device and the borehole wall for the removal of the loosened rock, - the propulsion device has a heat shield at the front, which covers the borehole floor except for a peripheral gap between the outer edge of the heat shield and the borehole wall and forms a dynamic pressure chamber with the borehole floor, - the gaseous medium is divided into a first partial flow for plasma generation and a second partial flow for the provision of cooling and conveying gas, - the first partial flow is injected into the dynamic pressure chamber and there, with the aid of the electric plasma generators, is converted into a high-pressure plasma, which heats the rock at the bottom of the borehole to at least above its liquidus temperature and carries the loosened rock out of the dynamic pressure chamber into the annular space between the propulsion system and the borehole wall via the peripheral annular gap between the heat shield and the borehole wall, - the second partial flow is introduced into the annular space between the propulsion system and the borehole wall, where it cools the part of the propulsion system located above the heat shield, the first partial flow loaded with loosened rock, and the borehole wall to below the solidus temperature of the rock, - and a heat-affected zone is formed in the borehole wall around the borehole, at the inner boundary of which the rock is heated to at least the liquidus temperature during the drilling process and at the outer boundary of which the rock does not reach the solidus temperature during the drilling process.

[0002] Such a method is known, for example, from WO 2013 / 135391 A2 or WO 2015 / 140344 A2.

[0003] Furthermore, WO2014 / 100 255 A1 discloses a rock drill using a plasma generator, in which the material composition of the molten rock is determined by means of sensors.

[0004] A key advantage of the method described above is that it uses non-contact rock destruction, meaning that the drilling tools used rarely or never need to be replaced, which is particularly important for extremely deep drilling. Another advantage is that no liquid drilling fluid is required to transport the loosened rock from the bottom of the borehole to the earth's surface; instead, a gaseous medium is used, which is used as a high-pressure plasma gas to melt the rock and also as a cooling and conveying medium. Finally, it is advantageous that the energy required for rock destruction can be supplied to the bottom of the borehole neither mechanically nor hydraulically, but essentially electrically.

[0005] A particular advantage of this known process is that the molten rock created at the bottom of the borehole comes into intensive contact with the rock at the borehole walls under very high pressure, so that the rock is heated to liquidus temperature and any pore spaces present there are closed. Liquidus temperature is understood here as the temperature at which all mineral components of the rock become completely liquid. When the rock, heated to liquidus temperature, cools down, a glass-like solidified inner layer forms directly at the borehole wall, which is absolutely dense and load-bearing in itself. Behind this glass-like solidified inner layer, a supporting layer forms in the remaining heat-affected zone. This layer consists of molten rock and solidified mineral deposits, depending on the temperature reached and is also largely dense, i.e.without any remaining pore spaces. This supporting layer is intimately interlocked with the surrounding rock, right up to the boundary of the heat-affected zone, where heating only reaches the solidus temperature, meaning no more liquid melt is formed. Overall, a dense and load-bearing layer forms on the borehole wall throughout the entire heat-affected zone, which—if thick enough—makes casing of the borehole unnecessary.

[0006] A problem with this known method, however, arises from the fact that the composition of the exposed rock layers is usually not consistent along the length of the borehole. This is especially true for drilling into sedimentary rock, which, due to its formation history, consists of minerals of different origins and can exhibit very different melting behavior depending on its mineral composition. A particularly pronounced reduction in the liquidus temperature occurs, for example, in the presence of feldspar, calcite, fluorite, or similar fluxes in the rock.When applying the method of the type mentioned above in low-melting rock, problems can arise from the fact that the corresponding rock layers are penetrated too quickly, so that there is not enough time for the formation of a sufficiently load-bearing heat-affected zone in the borehole wall, or from the fact that they are penetrated too slowly, so that cavities are created there unintentionally and uncontrollably.

[0007] It is therefore an object of the invention to further develop the method of the type mentioned at the outset in such a way that a sufficiently thick and load-bearing borehole wall is automatically produced everywhere over the entire borehole length while maintaining a constant borehole diameter.

[0008] To achieve this object, the invention proposes, based on the method of the type mentioned at the outset, that the material composition of the respective molten rock is continuously determined and that the feed rate of the propulsion device, the energy supply to the plasma generator as well as the pressure and temperature of the two partial flows of the gaseous medium are controlled as a function of the respective determined material composition of the rock in such a way that, with a constant borehole diameter, the heat-affected zone forming in the region of the borehole wall has a thickness of at least one borehole diameter everywhere.

[0009] The teaching of the invention is based on the knowledge that, in a fusion drilling process of the type according to the invention, a targeted and meaningful influence on the supporting layer forming in the area of ​​the borehole wall is fundamentally only possible if the material composition of the rock in question and thus its melting behavior are known with sufficient accuracy when controlling the fusion drilling process.Accordingly, according to the teaching of the invention, for the first time the usual control variables for the melting process - namely the feed rate of the propulsion device, the energy supply to the plasma torch as well as the pressure and temperature of the partial flows of the gaseous medium - are made dependent on the continuous monitoring of the material composition of the rock in question and thus on the melting behavior of the rock in question in such a way that, with a constant borehole diameter, a sufficiently thick solidified heat-affected zone is created everywhere in the area of ​​the borehole wall, with a thickness of at least one borehole diameter.

[0010] When drilling deep boreholes for geothermal energy (geothermal drilling), long borehole service lives are particularly important. In this case, it is recommended, according to the teachings of the invention, to create a heat-affected zone on the borehole wall with a thickness of one and a half to two and a half borehole diameters.

[0011] The continuous determination of the material composition of the rock molten at the bottom of the borehole is conveniently carried out using UV sensors, which detect the UV radiation emitted by the newly molten rock.

[0012] It is also advisable to continuously monitor the pressures and temperatures occurring in the dynamic pressure chamber. The pressures and temperatures prevailing there also influence the thickness and consistency of the heat-affected zones that develop.

[0013] Finally, it is advisable to continuously determine and monitor the thickness of the resulting heat-affected zone. This provides continuous quality control to determine whether the applied process measures have led to success.

[0014] An embodiment of the invention is explained in more detail below with reference to the drawing, which schematically shows a system which operates according to the method according to the invention.

[0015] In the drawing, a sinking frame arranged at the surface is designated by reference numeral 1. This sinking frame 1 is positioned above a borehole 2 to be sunk, comprising a borehole bottom 2a and a borehole wall 2b, and is provided with the usual devices (not shown in detail) for inserting and operating a feed and supply rod 3, which serves to advance and supply a propulsion device 4 arranged in the borehole 2.

[0016] This propulsion device 4 is provided on its side facing the borehole bottom 2a with a heat shield 5, which covers the borehole bottom 2a except for a gap 6 located at its periphery between the borehole wall 2b and the heat shield 5 and forms a dynamic pressure chamber 7 above the borehole bottom 2a.

[0017] In or on the heat shield 5, several electrical plasma generators 8 are arranged, which generate a high-pressure plasma gas which is introduced into the dynamic pressure chamber 7 in the direction of the borehole bottom 2a and whose heat causes the rock at the borehole bottom 2a to melt or evaporate.

[0018] The rock melted and / or vaporized at the borehole bottom 2a is discharged from the pressure chamber 7 by the overpressure prevailing in the pressure chamber 7 via the gap 6 located at the periphery of the heat shield 5, introduced into a gaseous production stream indicated by arrows 9, conveyed by this to the surface and there separated from the production stream 9 in a suitable separator 10.

[0019] The propulsion device 4 has, on its side facing away from the borehole bottom 2a, an adapter 11 connected to the aforementioned feed and supply rod assembly 3. The feed and supply rod assembly 3 can be raised and lowered within the sinking frame using the equipment commonly used in deep drilling technology. It contains, in particular, a thermally insulated liquid gas line 12 for supplying liquid nitrogen from a nitrogen tank 13, electrically insulated lines 14 for supplying the required electrical power from a generator 15, and suitable signal lines 16 for transmitting measurement and control data to a control and regulation unit 17 assigned to the sinking frame 1.

[0020] In the adapter 11 there is a controlled distribution valve 18 which divides the liquid nitrogen flow 19 arriving via the liquid gas line 12 into a first partial flow 19a for plasma generation and a second partial flow 19b for the provision of cooling and conveying gas.

[0021] The first partial flow 19a is evaporated and heated in an electrically heated evaporator 20, then fed to the plasma generators 8 of the propulsion device 4 and converted there into a high-pressure plasma gas, which is fed to the dynamic pressure chamber 7.

[0022] The second partial flow, in contrast, is guided for cooling purposes through the adapter 11 into the area immediately above the heating elements 5 and is injected there via injection nozzles oriented upwards in the flow direction above the gap 6 into the annular space between the borehole wall 2b, on the one hand, and the adapter 11, on the other. Thus, this second partial flow 19b initially cools all parts of the mechanical equipment potentially at risk of overheating, and subsequently cools the borehole wall 2b and the molten and / or vaporized rock detached from the borehole bottom 2a and discharged via the gap 6, so that the rock can solidify and / or condense and be discharged as dust with the conveying flow 9.

[0023] The active cooling of the borehole wall 2b described above creates a glass-like solidified inner layer on its inside that is absolutely dense and load-bearing in itself. Behind this glass-like solidified inner layer, a supporting layer forms in the remaining heat-affected zone 21. This supporting layer consists of molten rock and solidified mineral deposits depending on the temperature reached and is also largely dense, i.e., has no remaining pore spaces. This supporting layer is intimately interlocked with the surrounding rock right up to the outer boundary region of the heat-affected zone 21, in which only solidus temperature is reached during heating, i.e., no liquid melt is formed. The thickness of the heat-affected zone 21 depends on various factors, in particular the material composition of the rock and the duration and intensity of the heating process during drilling.

[0024] To carry out the method according to the invention, a large number of sensors are assigned to the propulsion device 4, all of which are connected via the signal line 16 to the control and regulation unit 17, in which the data measured by the sensors is compiled and evaluated using suitable control and regulation software. During the drilling process, this control and regulation software controls the propulsion speed of the propulsion device 4, the electrical power of the plasma generators 8, as well as the pressure, temperature, and distribution of the supplied liquid nitrogen in such a way that a vitrified inner layer is formed throughout the borehole wall 2a and a stabilizing heat-affected zone 21 is formed towards the outside, which has a thickness at least corresponding to the borehole diameter everywhere. If necessary, the thickness of this heat-affected zone 21 can also be adjusted to one and a half to two and a half borehole diameters. About the sensors in detail:

[0025] The propulsion device 4 is equipped with two UV spectrometers 22 on its side facing the dynamic pressure chamber 7. These spectrometers continuously measure the UV radiation emitted by the vaporized or vitrified rock at the borehole bottom 2a, which can be used to determine the material composition of the rock present at the borehole bottom 2a. Another UV spectrometer 22 is located on the adapter 11 and is directed toward the area where the two partial streams 19a and 19b mix.

[0026] Furthermore, the propulsion device 4 has two distance sensors 23 on its side facing the dynamic pressure chamber 7, which operate with sonar detection or with ultrasonic detection and continuously determine the respective distance between the heat shield 5 and the borehole bottom 2a.

[0027] In addition, a plurality of further sensors are arranged on the outer circumference of the adapter 11, namely: - a temperature sensor 24 for monitoring the temperature reached, - a pressure sensor 25 for monitoring the pressure, - a moisture sensor 26 for detecting any water present in the rock, - a gas sensor 27 for detecting combustible gases present in the rock, - an oxygen sensor 28 for detecting any oxygen present in the rock, - a flow sensor 29 for determining and monitoring the flow velocities in the ascending gas stream, and - a temperature difference sensor 30 for determining the temperature difference between adapter 11 and borehole wall 2a.

[0028] For continuous monitoring of the heat-affected zone 21 forming behind the borehole wall 2a, a GPR radar device 31 is provided at the top of the adapter 11. This device provides information about the depth and physical properties of the rock layer adjacent to the borehole wall 2a. Furthermore, another radar device 32 is provided at the bottom of the adapter 11, which monitors the inside of the developing borehole wall for cracks or other irregularities.

[0029] To monitor the nitrogen supply and material distribution, an ultrasonic flow meter 33 and a level meter 34 are arranged at the lower end of the liquid gas line 12.

[0030] To monitor the production gas stream 9 discharged from the borehole and laden with the loosened rock, a measuring station 35 is provided immediately upstream of the separator 10. This measuring station determines the temperature, pressure, and mass flow of the production gas stream 9 at this point. The data determined here are also sent to the control unit 17. Finally, the outlet of the separator 10 is assigned a controllable outlet valve 36, which is also connected to the control unit 17 and can be used to influence the pressure in the production gas stream 9.

[0031] It is essential that all measuring and control devices with the reference numerals 22 to 36 are connected to the control and regulation unit 17 and together provide the technical information necessary or useful for the method according to the invention. List of reference symbols 1 sinking frame 2 boreholes 2a Borehole bottom 2b borehole wall 3 Feed and supply rods 4 Propulsion equipment 5 Heat shield 6 gap 7 Dynamic pressure chamber 8 plasma generators 9 Flow rate 10 separators 11 adapters 12 LPG pipeline 13 Nitrogen tank 14 insulated cables 15 Generator 16 signal lines 17 Control unit 18 distribution valve 19 Liquid nitrogen stream 19a first partial stream 19b second partial stream 20 evaporators 21 Heat-affected zone 22 UV spectrometers 23 distance sensors 24 Temperature sensor 25 Pressure sensor 26 Humidity sensor 27 Gas sensor 28 Oxygen sensor 29 Flow sensor 30 Temperature difference sensor 31 GPR radar device 32 radar device 33 ultrasonic flow meters 34 level gauges 35 measuring stations 36 Exhaust valve

Claims

[1] Method for sinking a borehole (2) in the rock, in which -the rock at the bottom of the borehole (2a) is thermally melted and is removed upwards from the borehole (2) with the aid of a gaseous medium, - the heat required to melt the rock is provided by at least one electric plasma generator (8) associated with a propulsion device (4) located at the front of a feed and supply rod (3) that can be inserted into the borehole (2), an annular space remaining between the propulsion device (4) and the borehole wall (2b) for the removal of the loosened rock, - the propulsion device (4) has a heat shield (5) at the front, which covers the borehole bottom (2a) except for a peripheral gap between the outer edge of the heat shield (5) and the borehole wall (2b) and forms a dynamic pressure chamber (7) with the borehole bottom (2a), - the gaseous medium is divided into a first partial flow (19a) for plasma generation and a second partial flow (19b) for cooling the propulsion device (4), the feed and supply rods (3) and the borehole wall (2b), - the first partial flow (19a) is injected into the dynamic pressure chamber (7) and is converted there into a high-pressure plasma with the aid of the electric plasma generators (8), which heats the rock at the bottom of the borehole (2a) to at least above its liquidus temperature and carries the loosened rock out of the dynamic pressure chamber (7) into the annular space between the propulsion device (4) and the borehole wall (2b) via the peripheral annular gap between the heat shield (5) and the borehole wall (2b), - the second partial flow (19b) is injected into the annular space between the propulsion device and the borehole wall and there cools the part of the propulsion device (4) located above the heat shield (5), the first partial flow loaded with loosened rock and the borehole wall (2b) to below the solidus temperature of the rock, - and a heat-affected zone (21) is formed in the borehole wall (2b) around the borehole (3), at the inner boundary of which the rock is heated to at least the liquidus temperature during the drilling process and at the outer boundary of which the rock does not reach the solidus temperature during the drilling process, characterized bythat the material composition of the respective molten rock is continuously determined and that the feed rate of the propulsion device (4), the energy supply to the plasma generator (8) as well as the pressure and temperature of the two partial flows (19a, 19b) of the gaseous medium are controlled as a function of the respectively determined material composition of the rock in such a way that the heat-affected zone (21) forming in the region of the borehole wall (2b) has a thickness of at least one borehole diameter. [2] Method according to claim 1, characterized by that a heat-affected zone (21) with a thickness of one and a half to two and a half borehole diameters is created in the region of the borehole wall (2b). [3] Method according to claim 1 or 2, characterized bythat the determination of the material composition of the rock molten at the bottom of the borehole (2a) is carried out using UV sensors (22) which detect its UV radiation. [4] Method according to one of claims 1 to 3, characterized by that all pressures and / or temperatures generated during the drilling process are continuously detected. [5] Method according to claim 1, characterized by that the thickness of the resulting heat-affected zone (21) is continuously determined and monitored.

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