Drilling (geology)
Geological drilling is used to reach regions below the earth's surface that cannot be accessed by other methods. On the one hand, they offer the possibility of directly investigating the geological conditions in the subsurface; on the other hand, they can also be used as a transport route to bring substances to the surface of the earth (e.g. crude oil ) or to sink them (e.g. extracted elsewhere Natural gas or oil in underground storage near the point of consumption). Depending on the final depth , a distinction in geological drilling between shallow drilling (<500 m), deep drilling (500-5000 m) and over deep holes (> 5000 m).
Areas of application
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Exploratory drillings or test drillings primarily serve to obtain information from the subsurface:
- to investigate the geological conditions in general: rock types , fissure conditions, conditions of the subsoil, etc.
- to explore potential deposits ( crude oil , coal , ores , salt , groundwater , mineral raw materials).
As a rule, the knowledge gained is implemented in economically viable projects ( extraction of raw materials , tunnel construction, etc.) and is only rarely used for purely scientific information acquisition (drilling is expensive).
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Production wells are used to transport mostly liquid substances. If the requirements are met, primary exploratory wells can be expanded for this purpose:
- Extraction from the depths to the surface of the earth (examples):
- Crude oil and natural gas (so-called fossil hydrocarbons ),
- Groundwater .
- Pumping from the surface of the earth into the interior of the earth (examples):
- underground intermediate storage of natural gas,
- Improving the performance of hydrocarbon production wells by injecting water or other substances into the corresponding rock layers (special case: hydraulic fracturing ).
- Sinking of problematic waste materials
- Extraction from the depths to the surface of the earth (examples):
For most applications, shallow bores with a depth of a few meters ( subsoil investigations ) to a few hundred meters (groundwater, reservoir exploration ) are sufficient . Mobile drilling rigs are often enough to carry them out.
Excessive wells up to approx. 12,000 meters are technically extremely demanding, very expensive and therefore very rare (examples: the Soviet-Russian Kola well and the continental deep well in Windisch-Eschenbach ). Extra-deep wells require stable, permanent drilling rigs and take several years to complete.
Although most of the drilling is on the mainland, oil exploration is also increasingly taking place in the sea in the oil-rich shelf areas . The drilling platforms used for this are among the largest technical systems in the world. For scientific purposes, the IODP , the successor to the ODP , is drilling the seabed .
Technique and Methods
The drilling technique used depends on the bedrock and the drilling depth to be achieved, for which drilling technology has developed a large number of devices.
Basically, two procedures are used:
- Percussive drilling : the rock material is smashed by wedge effect
- rotating drilling : the rock is chipped by rotating drill bits [document?] , e.g. B. with the rotary drilling method .
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High-frequency drilling technology (SONIC) : The drilling tool is made to vibrate via an oscillator in the drill head. At the same time, the drilling tool can be rotated (ROTOSONIC). The advantage is that the generated vibration reduces the skin friction on the drill rod to a minimum. In this process, the rock is both chipped and smashed.
- Tools used in geological drilling are e.g. B.
- Roller chisel
- PDC chisel
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Drill bits , partly set with industrial diamonds for hardening
- In order to avoid rapid wear and overheating of the drill bit, a flushing fluid is usually pumped around the drill hole during the drilling process , the pressure of which also serves to stabilize the drill hole.
Vertical holes are the "normal" shape of the hole - more or less vertically downwards. But there are also applications in which horizontal drilling is necessary, e.g. B. in tunneling. Modern techniques allow deep boreholes in large bends from the vertical to the horizontal.
Scientific boreholes require undestroyed rock material, of which the depth of origin must also be known. For this purpose, techniques have been developed (so-called core drilling ) that allow drilling cores to be extracted from the borehole. The drilling profiles obtained with their help reflect the geological conditions of the subsurface to the nearest meter. The cuttings extracted in the mud also allow an estimate of the depth of origin of the sample taken (calculated from the rate of ascent and the time required for this).
- Rescue drilling
With increasing diameters to find people buried in a mine, to supply them with air, a means of communication (telephony), water and food and finally to rescue them with a Dahlbusch bomb .
literature
- Friedrich Bender (Ed.): Applied Geosciences . Stuttgart 1984.
- Frank Jahn et al .: Hydrocarbon Exploration and Production . Amsterdam 1998.
- Friedrich P. Springer: On the history of deep drilling technology from the perspective of textbooks and specialist books . In: Petroleum-Natural Gas-Coal . Issue 7/8, 125th year 2009.
- German Institute for Standardization eV (Hrsg.): Bohrtechnik: Norms . 1st edition, Beuth, Berlin / Zurich 1998, ISBN 3-410-14386-6 .
- Ron Baker: A Primer of Oilwell Drilling: A basic Text of Oil and Gas Drilling . 6th edition, University of Texas, Austin 2001, ISBN 0-88698-194-8 .
- Australian Drilling Industry Training Committee Ltd. (Ed.): Drilling: The Manual of Methods, Applications and Management . 4th Edition, 1996, ISBN 1-56670-242-9 .
