Method and device for dismantling geothermal probes

Abstract

Method for dismantling geothermal probes (3), in which a probe body (30) consisting of probe line (31) and solidified screed filling (32) is overdrilled by means of a drilling device (1) with the supply of flushing fluid, which comprises a drill string (13) driven forward by rotation via a drill head (10) with a tubular cylindrical drill rod (11) and with a drill bit (12) attached to its end region lying in the direction of drilling, characterized in that that the end section (112) of the drill string (13) equipped with the drill bit (12) is advanced rotatingly without or at a small distance of up to a few centimeters, in particular 0 - 20 mm from the probe body (30) or in contact with the probe body (30) - at least partially overlapping it circumferentially in the direction of the current drilling axis, that the drill bit (12), which widens in a funnel shape towards its end face, is set into vibration during drilling while rotating over the drill string (11) in the direction of the drilling axis and that the drill bit (12) is guided along the probe body (30) via a flexible pipe section (111) which is integrated at least in the lower part of the drill string (11).

Description

[0001] The invention relates to a method for dismantling geothermal probes, in which a probe body consisting of probe pipe and solidified screed is overdrilled by means of a drilling device with the supply of flushing fluid, which comprises a drill string driven by a rotating drill head with a tubular cylindrical drill rod and with a drill bit attached to its end region lying in the direction of drilling, as well as to a drilling device for overdrilling geothermal probes with a drill head which has a drive device with a rotary drive to which a drill rod of a drill string is connected, which is provided with a drill bit at its end section lying in the direction of the drilling axis, and with a flushing device for removing drill cuttings and supporting the drilling process.

[0002] The dismantling of geothermal probes using such a method is mentioned in DE 10 2016 103 166 A1 in connection with a sensor system for spatially measuring the trajectory of a borehole with an installed geothermal probe. The patent proposes using directional drilling techniques to determine the probe's trajectory for dismantling the geothermal probes. This approach requires a correspondingly high level of effort.

[0003] Methods for dismantling geothermal probes are also known (though without existing written documentation) in which the probe body, including backfill and probe pipe, is rebored with a large-diameter borehole. These methods are related to larger-diameter well decommissioning. However, since the smaller-diameter borehole for the geothermal probe can have considerable deviations from the vertical of up to several meters over its length of, for example, 80 or 100 meters—significantly more than with wells—it is almost impossible to reliably guarantee that the probe body is rebored along its entire length, even with the traditional method of large-diameter reboring. This is partly due to the fact that, because of the relatively large diameter, the reboring rod is too rigid for the curvature of the probe borehole.

[0004] Various problems with the installation of geothermal probes are mentioned in DE 10 2014 206 042 B4, WO 2011 / 015342 A1, WO 2011 / 015341 A1 and DE 10 2007 033 436 A1, including inadequate execution of borehole backfilling and a hydraulic connection to the groundwater.

[0005] VDI guideline 4640 Part 2, "Thermal Use of the Subsurface - Ground-Coupled Heat Pump System," from 2001, specifies that the geothermal probe should remain in the ground and be filled with a cement grout during decommissioning. If the probe material does not meet the requirements, the probe must be removed. The draft version of the guideline, dated May 1, 2015, requires the geothermal probe to be dismantled in cases of damage. Currently, there is no standardized technique for dismantling geothermal probes.

[0006] In the presentation “Dismantling of an improperly sealed geothermal probe by overdrilling with a newly developed drilling method”, published on September 16, 2015, which also refers to the aforementioned guideline VDI 4640 sheet 2, it is proposed to cement steel cables into the geothermal probe pipes.

[0007] In DE 10 2016 103 166 A1 a sensor system and a method for spatial measurement of the course of a borehole, in particular a geothermal probe, is disclosed.

[0008] As recent incidents of damage demonstrate, sealing problems usually occur in the annular space of the geothermal probe, necessitating its permanent and airtight refilling. To date, no technically reliable methods for overdrilling and removing geothermal probes have been developed.

[0009] The present invention is based on the objective of providing a method and a drilling device for the dismantling of geothermal probes, with which a dismantling that is as reliable as possible can be achieved.

[0010] This problem is solved for the method by the procedure described in claim 1. Here, the end section of the drill string equipped with the drill bit is advanced rotatingly, either without or at a small distance (in the millimeter or centimeter range, particularly 0-20 mm) from the probe body, or in contact with the probe body, at least partially overlapping it circumferentially in the direction of the current drilling axis. A procedure that is functionally important for tracking during overdrilling, in connection with the overburden, consists of vibrating the drill bit in the direction of the drilling axis during rotation via the drill string. For passive tracking during overdrilling, it is further provided that the drill bit is guided along the probe body via a flexible pipe section integrated at least in the lower part of the drill string.The flexible pipe section is more flexible than the pipe section that may connect to the drill head, with both pipe sections being made, for example, of steels specifically designed for drilling requirements. The flexible pipe section is, for example, several meters long, preferably in the range of 2 to 8 meters.

[0011] Regarding the drilling device, the problem is solved by the features specified in claim 6. Here, it is provided that the drill string, at least near the drill bit, is equipped in a section facing the drill bit with a flexible pipe section, to the end of which, in the direction of the drilling axis, the drill bit is connected, and that the drill bit is funnel-shaped and widened in the direction of the drilling axis. The design of the drilling device for overdrilling is such that the drive device is provided with a vibrator component, by means of which the drill string can be set into vibration during its rotation in the direction of the drilling axis.

[0012] The vibration frequency and amplitude are preferably predefined or predefined in the ranges of 50 Hz to 200 Hz and a few mm to a few cm.

[0013] Claim 4 describes an application of a drilling device for the decommissioning of a geothermal probe, which also solves the problem. When using the drilling device for overdrilling the probe body, the drive device additionally includes a vibrator component. This vibrator allows the drill bit to be subjected to vibrations acting in the direction of the drilling axis during its rotation via the drill string. The vibration frequency is in the range of 50 Hz to 200 Hz. The amplitude of the vibration in the axial direction is, for example, a few millimeters to a few centimeters. The vibration reduces the friction between the inner wall of the drill string and the probe pipes or the probe line, including the surrounding grout, thus preventing twisting of the probe body. Twisting would lead to a blockage inside the overdrill string, preventing further drilling.During application, the drill string is also equipped with a flexible pipe section in at least one section facing the drill bit, ensuring tracking even in curved areas of the probe body along its longitudinal direction. For passive tracking, the end section of the drill string, particularly the drill bit, is further designed to widen in the direction of the drilling axis.

[0014] With the aforementioned method, or rather the drilling device, the probe body is reliably tracked during overdrilling, even in curved areas that deviate from a straight line, and can, for example, be extracted section by section, as demonstrated in extensive investigations by the inventors. The probe body, with its backfill injection line and solidified backfill, can, for example, be twisted and extracted piece by piece with a reduced or even stopped supply of flushing fluid, thereby increasing friction.

[0015] An advantageous measure here is that the vibration frequency is in the range of 50 Hz to 200 Hz.

[0016] Further advantageous measures for carrying out the method include matching the rotational speed and the thrust force to the properties of the rock mass, the probe body, in particular the backfill, and also the probe line. In addition, the rotational speed can be matched to the vibration frequency, or the vibration frequency can be selected depending on the rotational speed.

[0017] Further advantages for overdrilling result from the fact that the drill bit is provided with drill teeth projecting in the direction of the drilling axis on its end face and on its inner surface.

[0018] Another advantageous measure for overdrilling is that the inner circumferential surface of the drill bit is provided with drill teeth projecting in the direction of the drilling axis.

[0019] The invention is explained in more detail below with reference to exemplary embodiments and the drawings. The drawings show: Fig. 1 A schematic side sectional view of an overdrilling process of a geothermal probe using a drilling device and Fig. 2 a side sectional view of a drill bit.

[0020] Fig. Figure 1 schematically shows essential components of a drilling device 1 during the dismantling of a geothermal probe 3 by overdrilling the probe body 30, which comprises a U-shaped (or possibly other, such as concentric) probe pipe 31 embedded in a solidified intumescent material 32. The intumescent material 31 fills the space between the borehole wall of an original probe borehole and the probe pipe 31, in order to ensure good heat transfer from the surrounding soil to the heat transfer fluid circulating in the probe pipe 31.

[0021] The drilling device 1 has a drill head 10 located above the earth's surface, which includes a rotary drive with axial vibration 100. A drill string 13 is rotatably connected to the drive. The drill string 13 comprises a drill rod 11 connected to the rotary drive 100, with a hollow, cylindrical drill pipe 110. In its lower section, which is remote from the drill head 10, the lower section transitions into a similarly hollow, cylindrical pipe section 111 that is flexible relative to the section of the drill pipe 110 above it. Both the flexible pipe section 111 and the section of the drill pipe 110 above it, coupled to the rotary drive 100, are made, for example, of a steel suitable for such drilling applications. The flexible pipe section 111 has correspondingly elastic or more flexible properties and is approximately a few meters long, e.g., between two and eight meters.A drill bit 12 is attached to the lower end of the flexible pipe section 111, which points in the direction of drilling. This drill bit is used to remove material during overdrilling when creating the borehole 2. For this purpose, the drill bit 12 is equipped with suitable drill teeth 120 that project in the direction of drilling. The drill bit 12, either alone or together with an adjoining section of the drill pipe 110 or the flexible pipe section 111, forms an end section 112 of the drill string 13. The drill bit 12 is attached to the drill pipe 110, in particular the flexible pipe section 111, via a coupling section 122 with connecting elements 123, such as interlocking threads.

[0022] To remove the drill cuttings produced during drilling, reduce friction during drilling, and improve the drilling process, a flushing system 4 is provided for supplying and removing drilling fluid. The drilling fluid is circulated downwards through the drill string 11 to the drill bit 12 and discharged laterally through the drill bit, particularly through openings located at its end. It then flows back up between the outer surface of the drill pipe and the borehole wall into a flushing trough 41 located on the ground surface for clarification. From the flushing trough 41, the drilling fluid is pumped and piped back into the drill pipe 110 and downwards to complete a flushing circuit.

[0023] To contain the overgrowth of the uppermost area of ​​borehole 2, a standpipe 5, open at the top and protruding above the earth's surface, is inserted into the earth around borehole 2, spaced all around from the drill string 11, and sealed on its circumference to the outside towards the soil by means of a clay seal 6.

[0024] Detailed investigations by the inventors have shown that for reliable overdrilling of the probe body 30 over its entire length, it is essential to adapt the diameter or circumference of the drill string 13 to the diameter or circumference of the probe body 30, so that the drill bit 12 with the subsequent drill string 11 is reliably guided by the probe body 30, in particular by the solidified dam filling 32 and the probe line 31, which may not always run centrally therein and may be located at the edge, during overdrilling, especially considering the fact that the original probe bore and therefore the probe body 30 may deviate considerably (by several meters) from a vertical or straight extent.The drill string 11, which is largely adapted to the diameter of the probe body 30 and is therefore slim, is able, unlike a large-diameter overdrill string, to follow the probe body 30 passively guided along its entire length. As further investigations by the inventors have shown, the flexible pipe section 111, which extends for several meters in the end region of the drill string 11 or drill pipe 110 in the direction of drilling, is of considerable advantage in this regard. The flexible pipe section 111, which is more flexible than conventionally used drill pipes, can alternatively also extend over the entire length of the drill pipe 110.

[0025] Furthermore, it has been found according to the invention that equipping the drill head 10 with a vibrator 101 for passive guidance by the probe body 30 during overdrilling is of significant importance. The vibrator 101 of the drill head 10 causes vibrations in the direction of the current drilling axis (drilling axis direction) during the rotation of the drill string 13. This significantly reduces the friction between the rotating overdrill string and the stationary geothermal probe, which is fixed in the rock. Advantageously, the vibrator frequency is in the range of 50 Hz to 200 Hz and can be individually adjusted to the material properties of the rock, the probe body 30 with the sealing material 32, and the probe line 31, as well as depending on the rotational speed, in order to obtain an optimal overdrilling result. The amplitude of the vibrations is, for example, in the range of one or a few centimeters, as is the case, for example,0.5 cm and 5 cm, especially from 1 cm to 3 cm.

[0026] As a further advantageous measure for the method and the drilling device 1 for overdrilling geothermal probes, it has been found that an extension of the drill bit 12 towards its end face offers significant advantages for passive guidance along the probe body 30. The extension, particularly of the inner circumference of the drill bit 12, can be stepped in the axial direction or at least partially conical with a conical section 121, or curved or funnel-shaped, and has a centering effect with respect to the probe body 30, especially in conjunction with vibration. The inner circumferential surface of the drill bit 12 can be provided with axially projecting drill teeth. The outer shape of the drill teeth is advantageously adapted to the material to be removed; for example,The teeth on the outer side of the bore axis are sharp-edged and therefore more abrasive to the clayey backfill. In contrast, the teeth on the inner side of the bore axis are rounded to protect the PE pipes required to guide the drill string. Thus, the outer shape of the drill teeth in the drill bit 12 leads to advantageous effects during overdrilling. The drill bit is also equipped with pins that maintain the outer diameter and has teeth on its crown shoulder (tapering towards the hanging wall) to hone the borehole during the rotating withdrawal of the drill string, enabling small bending radii and the removal of swelling rock and subsidence.

[0027] When over-drilling the geothermal probe 3 or the probe body 30, it can be extracted, for example, in sections. For this purpose, the probe body 30, with the sealing material 32 and the embedded probe pipe 31, can be twisted at the relevant points by temporarily reducing or stopping the supply of drilling fluid and the vibration. This increases the friction of the core sample against the inner circumferential surface of the drill pipe 110 and the drill bit 12, causing the core sample to rotate temporarily with the drill string. The twisted-off section, which may be several meters long, can then be extracted.

[0028] During the overdrilling of the probe body 30 with the drill bit 12 and the subsequent drill pipe 110, the relevant section of the drill string 13 overlaps the drill core containing the remaining probe body in contact with it or at a short distance from it, so that the drill string 11 with the drill pipe 110 can be kept of a correspondingly small diameter, thereby increasing the flexibility and thus improving the tracking of the drill string 13.

[0029] To dismantle the geothermal probe 3, the borehole can then be filled with suitable filling material in accordance with the respective soil layers, whereby hydraulic short circuits can also be sealed, for example.

Claims

[1] Method for the dismantling of geothermal probes (3) in which a probe body (30) consisting of probe line (31) and solidified screed filling (32) is overdrilled by means of a drilling device (1) with the supply of flushing fluid, which comprises a drill string (13) driven by rotation over a drill head (10) with a tubular cylindrical drill rod (11) and with a drill bit (12) attached to its end region lying in the direction of drilling, characterized by , that the end section (112) of the drill string (13) equipped with the drill bit (12) is advanced rotatingly without or at a small distance of up to a few centimeters, in particular 0 - 20 mm from the probe body (30) or in contact with the probe body (30) - at least partially overlapping it circumferentially in the direction of the current drilling axis, that the drill bit (12), which widens in a funnel shape towards its end face, is set into vibration during drilling while rotating over the drill string (11) in the direction of the drilling axis and that the drill bit (12) is guided along the probe body (30) via a flexible pipe section (111) which is integrated at least in the lower part of the drill string (11). [2] Method according to claim 1, characterized by that the vibration frequency is in the range of 50 Hz to 200 Hz. [3] Method according to any one of the preceding claims, characterized by that the rotational speed and the thrust force are adapted to the properties of the probe body (30), in particular the dam filling (32) and the rock mass. [4] Use of a drilling device (1) in the dismantling of a geothermal probe (3), wherein the drilling device (1) is provided with a flushing device (4) and has a drill head (10) with a drive device including rotary drive (100) and a drill string (13) connected thereto, which comprises a tubular cylindrical drill string (11) and a drill bit (12) connected to its end region located in the direction of drilling, characterized by , that the end section (112) of the drill string (13) equipped with the drill bit (12) is dimensioned in its inner circumference such that the outer circumference of the probe body (30) is at least partially overlapped in the direction of the drilling axis, that the drive device additionally has a vibrator part (101) by means of which the drill bit (12) is subjected to vibrations acting in the direction of the drilling axis during its rotation via the drill string (11), that the drill string (11) is provided with a flexible pipe section (111) at least in one section facing the drill bit (12) and that the end section of the drill string (13) has a funnel-shaped widening of the drill bit (12) towards its end face in the direction of the drill axis. [5] Application of the drilling device according to claim 4, characterized by , that the drill bit (12) is provided with drill teeth projecting in the direction of the drilling axis on its end face and on its inner surface. [6] Drilling device (1) for overdrilling geothermal probes with a drill head (10) which has a drive device with a rotary drive (100) to which a drill string (12) of a drill string (13) is connected, which is provided with a drill bit (12) at its end section lying in the direction of the drilling axis, and with a flushing device (4) for removing drill cuttings and supporting the drilling process, characterized by , that the drill string (11) is provided with a flexible pipe section (111) at least in one section facing the drill bit (12), to the end of which the drill bit (12) is connected in the direction of the drilling axis, that the drill bit (2) is widened in a funnel shape in the direction of the drilling axis and that the drive device is provided with a vibrator part (101) by which the drill string (13) can be set into vibration during its rotation in the direction of the drilling axis. [7] Drilling device (1) according to claim 6, characterized by , that the inner circumferential surface of the drill bit (12) is provided with drill teeth projecting in the direction of the drilling axis.

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