Deep drilling

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A deep borehole generally refers to a geological borehole that not only penetrates the nearby subsurface, the ground , but also penetrates deep into the rock below (mining: mountains ).

For geological boreholes, however, experts make a more precise classification in terms of their final depth (depth reached after the drilling work has stopped ) or their diameter. So there except deep drilling and shallow drilling , through deep holes and large borehole drilling. However, this classification cannot be considered absolute. The deep boreholes generally include the boreholes for the development of oil and gas deposits . They are usually at least 500 m deep. At more than 5000 m one speaks of excessively deep boreholes or (abbreviated) excessively deep. Large boreholes are shaft boreholes with a diameter greater than one meter.

History and technology

Confucius reports of wells that were sunk during the Zhou dynasty (1050-256 BC) in China for the extraction of brine . Depths of several hundred meters are said to have been reached. However, there is no indication of the drilling technique used.

In other parts of the world, for a long time, underground raw materials were extracted exclusively from manually dug shafts and wells . Herodotus reports on the extraction of asphalt in what is now northern Iraq (approx. 450 BC). Early oil production in Europe, for example in Pechelbronn in Alsace or on the northern slope of the Forest Carpathians in what is now north-western Ukraine , took place from shafts that were often incorrectly referred to as boreholes until the end of the 18th century.

Hand turning

Twist drill for ice

To drill through the earth, rigid drill rods were initially used to rotate by hand. Depending on the strata of earth encountered, appropriate tools were used: Schappen (cylindrical scrapers) for loam and clay, twist drills for loamy rubble, clay cutters to widen the borehole and chisels to crush rock.

Rotary drilling by hand has been known in Europe since around 1420. Around 1500 Leonardo da Vinci sketched an earth drilling apparatus using a twist drill, but the first documented hole - for water - was not carried out until 1795 near St. Nicholas d'Abremont in France , with a final depth of 330 m being reached. It is uncertain which procedure was used because twist drills fail when they hit rock or very hard soil. Soft earth and sand, on the other hand, can easily cause a borehole to collapse, although this was countered early on by introducing a protective pipe tour.

Because of the great difficulties caused by deep drilling, shaft construction was preferred for a long time. Initially, drilling was mainly for artesian water (in which water flows to the surface of the earth due to its own pressure) and brine.

Impact drilling method

The percussion drilling method developed from the crushing of rock using a manually operated chisel attached to a rod . In China this procedure was already in use around 600 BC. Known. Workers jumped from a platform onto a seesaw that lifted rope and chisel. The bit fell back to the bottom of the borehole when the seesaw was released. A winch driven by a göpel was used to lift the loose rock and to install and remove the pipe fittings made of bamboo pipes. With a drilling progress of around 1 m per day, the Chinese reached drilling depths of more than 500 m.

In Europe and North America, the hammer drilling method did not develop independently of one another until the first half of the 19th century, although steam engines were used to operate the seesaw . The main driving force behind the further development of deep drilling technology was the rapidly increasing use of crude oil from the middle of the 19th century, which soon meant that ever deeper deposits had to be developed. The shaft construction often failed not only because of the required depth, but above all because of the groundwater, which kept the shafts full. This was also the reason for that legendary well in Titusville (Pennsylvania) by "Colonel" Edwin L. Drake , which came across oil on August 27, 1859 at a depth of only 21.2 m and is therefore regarded as the beginning of the oil age. As a result, western Pennsylvania became the first oil region and the drilling technique used by Drake became known as the "Pennsylvanian percussion drill".

The drilling performance was quickly increased through many improvements. Above the chisel z. B. a so-called drill collar attached, which provided a higher impact force of the bit and led him in the borehole.

In another further development - the “Canadian hammer drilling process” - the chisel was attached to a rod made of the particularly hard ash wood . In order to reduce the wear and tear of the rods from the constant blows and to prevent breakage, a sliding shear was located above the drill collar with the chisel, which came loose when the chisel hit and made it possible to push the rod together. The construction was also designed in such a way that the bit rotated slightly when it was pulled up, which resulted in a uniform shape of the drill hole. The wooden rod was soon replaced by a fixed, screwable steel rod. The Canadian William Henry MacGarvey introduced the "Canadian oil rigs" from 1883 on the oil fields of Galicia , the most important oil production area in Europe alongside the Ploieşti region in Romania . Corresponding deep drilling rigs were also built by Bergheim & MacCarvey in Vienna .

The biggest disadvantage of the percussion drilling method, however, was that the chisel had to be removed from the borehole at regular intervals in order to be able to remove the cuttings - also known as Schmant - from the borehole. To do this, a bucket was dropped into the hole that had a flap at the bottom. The flap closed on impact and could be pulled upwards when filled. A solution to the easier removal of the cuttings was technically difficult and therefore took a long time.

When drilling for artesian water in 1833, the Frenchman Pierre-Pascal Fauvelle recognized that water rising at high pressure was able to transport the crushed rock out of the borehole practically automatically. Fauvelle therefore set about replacing the rope or rod on which the drill bit was hanging with a pipe through which water could be pressed at high pressure to the bottom of the borehole. In implementing the idea, many technical problems had to be solved, so that it took 11 years before Fauvelle was able to drive the first well with water flushing to a depth of 219 m in just 54 days near Perpignan in southern France.

The technically less demanding percussion drilling method without flushing continued to dominate deep drilling technology. It was not until around 1875 that the hammer drilling process was increasingly combined with the Fauvelles flushing process, which considerably reduced the drilling time, as the drilling process only had to be interrupted to change a blunt chisel. In 1879, for example, this method was used in the development of the Pechelbronn oil field in Alsace. It was only after Mannesmann succeeded in producing seamlessly drawn pipes in 1892 that the drill rod could be improved to such an extent that drilling with continuous flushing was able to prevail.

In addition to rinsing, great attention was paid to improving the whipping process. The drilling technician Anton Raky , who originally came from Hesse and later mainly worked in Romania, patented his "rapid-impact drilling crane No. 7" in 1894. In order to achieve a higher impact frequency, the stroke of the rocker was reduced. Thanks to special spring mechanisms, the rocker stroke continued in an enlarged boom stroke and this again in an even larger chisel stroke. In addition, continuous flushing was achieved through the use of pipes as drill rods. The practical application took place for the first time at the oil field in Pechelbronn in Alsace, where it was possible to drill holes up to 340 m deep.

But it was not until 1898 that the Pomeranian oil pioneer Albert Fauck developed the “ Fauck Rapid Drilling Process” that the hammer drilling process could be significantly improved. The heavy and therefore sluggish rocker was replaced by a winch mechanism with an eccentric disc. The chisel was set in quick, short up and down movements by the rapidly rotating eccentric disc. With a stroke of only 50 to 100 mm and 100 to 250 strokes per minute, daily outputs of up to 60 m were possible. The most important advantage, however, was that the slightly brittle rock lying above the oil-bearing layer could be drilled through without any problems, whereas this caused major problems with the previous impact drilling methods. The "Fauck'sche rapid drilling method" soon allowed drilling depths of over 1300 m.

Rotary process

Medium-sized deep drilling rig for an extension well in an oil deposit about 2000 m deep. The drill is driven by a top drive on the pulley block on the derrick. Around the derrick are systems mainly for the introduction and preparation of the flushing fluid.
Roller chisel during installation
PDC chisel after removal

In 1844, the Briton Robert Beart registered a patent for a drilling method that largely corresponds to modern rotary deep drilling technology. The rock, which has been shredded by a rotating chisel, is continuously removed by a flushing liquid that is pumped down through the drill rod and emerges from the chisel.

The high technical demands (transmission of a large force to a movable drill pipe, continuous supply of the flushing fluid in a constantly rotating pipe, need to regulate the load acting on the drill bit) prevented the implementation of the concept for a long time. Even after solving most of the problems, the rotary method was considered to be too susceptible to failure and thus inferior to the hammer drilling method until after the First World War.

The first famous application of the Rotary method was the drilling on Spindletop Hill near Beaumont (Texas) , which on January 10, 1901, encountered high-pressure crude oil at a depth of 347 m. A huge eruption ensued, as a result of which around 100,000 barrels of crude oil were ejected uncontrollably from the borehole and siphoned off from the oil lake that had formed. Suddenly, US oil production had tripled.

The main feature of the rotary drilling process is the rotating drill bit . This is often designed as a roller chisel and has several toothed tapered rollers that grind the rock to be drilled. Today, however , PDC chisels with hard metal or artificial diamonds without moving parts are also frequently in use. The crushed rock is continuously removed via a flushing liquid - water with clay or barite meal - fed through the drill pipe (a screwable pipe string) and exiting the chisel and reaches the surface of the earth in the annular space between the borehole and the drill pipe. It is cleaned of the rock material brought along by means of vibrating sieves (called shale shakers) and centrifugal separators (called desander and desilter) and can thus be used again and again - after supplementing the admixture losses. The drilling fluid usually consists of water mixed with clay or barite meal, which achieves a density that comes close to the rock drilled through. This not only facilitates the removal of the cuttings, but also prevents the borehole from collapsing in soft or sandy layers. At the same time, the considerable frictional heat generated on the drill bit is dissipated.

In the conventional rotary process, the drill bit is set in rotation by the drill rod. In the past, a so-called turntable on the drilling rig was used for this purpose, which transferred the rotation to the drill rod by means of a square drive rod. Modern drilling rigs mostly have a top drive (Engl. Top Drive ) on the pulley of the derrick , which the kelly is eliminated and so the ever necessary renewal of the drill string is simplified.

In the case of very deep or directional bores , a drilling turbine is usually used, which is located directly above the drill bit. In this case, the drill rod does not rotate, but only serves to feed the chisel and feed the flushing fluid.

Modern drill bits with diamond or hard metal trim last 70 to 100 hours in normal soil conditions. To replace a worn drill bit, the entire pipe string has to be pulled out of the borehole and dismantled so that it can then be lowered back into the borehole with the new drill bit. This is fixed to the drill rod with a conical fine thread; To ensure that the drill bit can rotate clockwise and counter-clockwise, the external and internal threads of the drill bit and the first drill rod are coated with special high-strength two-component adhesive before screwing .

The borehole must be cased to prevent collapse. This takes place in stages, which is illustrated by the example of a 3000 m deep oil well as follows: The starting point of the well is a pipe with an outer diameter of 18-5 / 8 inches (473 mm), which however only extends to a depth of about 5 m. After a depth of 150 m, a casing ( called casing ) 13-3 / 8 inches (340 mm) is inserted. After the casing has been pushed in to the bottom of the borehole, cement slurry is pumped into the space between the borehole wall and the casing. After reaching a depth of approximately 1,500 m, another 9-5 / 8 in. (245 mm) casing is made and the cavity is re-cemented outside. When the final depth is reached, 5-1 / 2 inches (140 mm) of end-casing and cement is carried out.

After the completion of the casing, the so-called perforation takes place in the section of the deposit , in which a series of holes are drilled into the casing of the borehole using a special device in order to enable the inflow of, for example, crude oil or natural gas. The end of the work is the so-called completion, in which a separate production string is pushed into the borehole, which is sealed above the deposit with a so-called packer to the casing pipes in order to prevent their corrosion. At the earth's surface, the borehole is closed with an eruption cross .

New drilling methods

In California, work is being carried out on new drill technologies (from Potter) that do not require a chisel. In a flame similar to that of a welding torch, water is injected at high pressure and overheats the rock, which means that it splinters and can be removed more quickly than by mechanical means. There is no mechanical wear of the "drill bit". The process was developed in the USA in the 1960s. Work is currently underway on the practicality for 30 cm holes.

A project funded by the Federal Ministry for Economic Affairs and Energy at TU Dresden and TU Freiberg is testing a method in which the drill head crushes the rock using high-voltage electrical pulses. This EIV method allows drilling up to one meter per hour.

Drilling records

  • The longest well used for oil production is currently (Feb. 2008) 11,680 m long. It was sunk in 2007 as part of the development of the Chayuo oil field off the northeast coast of Sakhalin . This oil field is about 2500 m deep, but several kilometers off the coast. The main development is by directional drilling from the mainland.
  • The longest borehole in Europe for oil production opens up Germany's most productive oil deposit to date, Mittelplate , which is located around 2000 to 3000 m below the Wadden Sea off the west coast of Schleswig-Holstein . The production takes place both from an artificial island in the Wadden Sea and from the Dieksand drilling site on the mainland not far from Friedrichskoog . From Dieksand 7 strongly deviated boreholes have been drilled so far, the longest of which is 9,275 m.
  • The deepest productive hydrocarbon well in Europe was sunk in 1980 near Zistersdorf in Lower Austria . The Zistersdorf Übertief 1a well hit an abundant natural gas deposit at a depth of 7,544 m . The borehole collapsed in its as yet unsecured part, causing the gas flow to dry up. The Zistersdorf Übertief 2a well , which was then set up , penetrated to a depth of 8553 m in 1983, but was unable to reach the gas reserves hoped for.
Information board on the world's deepest earth drilling 1884–1893
  • Several drilling records were set at the end of the 19th and the beginning of the 20th century. Part of the former German territory:
Memorial stone to the world's deepest earth drilling in 1878

In 1878 at Klein Nordende in Schleswig-Holstein 1338 m were reached, in 1884 at Schladebach in Saxony-Anhalt 1748 m and in 1893 in Rybnik district Paruschowitz in Upper Silesia 2003 m. Karl Köbrich supervised all three wells. In 1914, the record in Rybnik was increased to 2240 m.

While most of the deep boreholes are aimed at exploring or extracting raw materials or for geothermal exploitation, some deep boreholes are carried out for research purposes (exploring the structure of the upper crust of the earth ). As a rule, this involves geophysical exploration of the drilled geological layers, e.g. B. by means of borehole geophysics or the temporary extraction of drill cores . The deepest borehole to date into the interior of the earth, between 1970 and 1994 on the Russian Kola peninsula , was also used for research purposes. This so-called Kola well reached a depth of 12,262 meters.


  • G. Prikel: Deep drilling technology. Vienna 1959.
  • AT Bourgoyne et al .: Applied Drilling Engineering. Richardson 1991, ISBN 1-55563-001-4 .
  • FP Springer: Basics of a model to minimize the costs of sinking deep wells. In: Erdoel-Erdgas-Zeitschrift. Issue 2, 1969.
  • FP Springer: On the history of deep drilling technology from the perspective of textbooks and specialist books. In: Erdoel-Erdgas-Kohl. Issue 7/8, 2009, pp. 308-314.
  • M. Reich: On the hunt underground - with high-tech searching for oil, gas and geothermal energy. Verlag add-books, Bad Salzdetfurth 2009, ISBN 978-3-00-028049-8 .
  • Heinrich Rischmüller: Deep drilling technology - a key instrument in the energy industry. In: The Geosciences. 8, 10, 1990, pp. 317-323. doi: 10.2312 / geosciences . 1990.8.317 .

See also

Individual evidence

  1. Potter Drilling
  2. Development and testing of an EIV drill head for deep geothermal energy
  3. Matthias Cassel: A dream of a hole. In: GEO. 7/2010, p. 128 ff.