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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Superdeep well drilling. History of invention and production
Directory / The history of technology, technology, objects around us The earth as an object of geology research is available for direct observation only from the surface. Its composition and structure can be judged only by indirect data. That is why geologists strive to penetrate as far as possible deep into the Earth with the help of drilling. Modern technology allows drilling wells on the continents to a depth of 10-15 kilometers. Boreholes are most often made for the exploration of mineral deposits, for the extraction of water, oil and gas from the bowels, as well as for engineering surveys and other applied purposes. In addition, since the 1970s, drilling has been increasingly used as a method of solving the fundamental scientific problems of modern geology. By the way, the very results of scientific drilling turned out to be unexpected in many respects and forced us to reconsider the theoretical concepts that had previously seemed obvious and unshakable. The beginning of systematic scientific drilling dates back to the 1960s. In 1968, a special drilling ship was launched in the United States, and an international deep-sea drilling program began in the oceans. For more than thirty years of history, hundreds of wells have been drilled in the World Ocean, which crossed the loose sediments of the ocean floor and went deep into the underlying basalts. The deepest of the wells was drilled in the Pacific Ocean south of the coast of Costa Rica. Its depth reached 2105 meters below the ocean floor. Ocean drilling opened a new page in geology, since there were practically no accurate data on the structure of the ocean floor before.
Now about drilling on land. Scientific drilling wells on the continents are usually classified as deep (3-7 kilometers) or ultra-deep (more than 7 kilometers). In this regard, they can only be compared with wells that are drilled for the search, exploration and exploitation of deep-seated oil and gas fields in the United States. The deepest well of them - Berta Rogers (9583 meters) was drilled in 1973-1974 in just 502 days. This high rate of penetration is due to two factors. The first is the capabilities of American technology. The second - drilling was carried out without core sampling, that is, without lifting rock samples to the surface. Core sampling requires a lot of additional time, but is absolutely necessary for scientific drilling. For this reason, deep and ultra-deep prospecting and exploration wells are of rather limited value as sources of scientific information. The first program of systematic ultra-deep continental drilling for scientific purposes was developed and implemented in the USSR. The foundations of this program were formulated as early as 1960-1962. In May 1970, in the north of the Murmansk region, ten kilometers from the city of Zapolyarny, drilling of the Kola super-deep well began. Its design depth was determined at fifteen kilometers. But it was not possible to reach it, in 1991 drilling was stopped at a depth of 12261 meters. Nevertheless, the Kola well is still the deepest in the world.
The successes of the Soviet Union could not but spur other countries. We accelerated the development of programs for scientific continental drilling in Germany, France, the USA, Canada, Japan, and the UK. One of the best results was achieved by the Germans who drilled the ultra-deep well KTB-Oberpfalz in Bavaria (1990-1994), which reached a depth of 9101 meters. “There are different drilling methods,” V.S. Popov and A.A. Kremenetsky write in the Soros Educational Journal. “If the depth of the wells is small (hundreds of meters), then the engine located on the surface rotates a steel drill pipe string a drill bit reinforced with hard alloys or diamonds is attached to the lower end of the pipe.Rotating, the bit cuts out a cylindrical column of rock, which gradually fills a special inner (core) pipe.When drilling without coring, drill heads are often used, which are a system of several rotating cones, reinforced If the well walls are unstable, a steel casing pipe is lowered in. During drilling, the pump constantly pumps a special clay solution into the well, which is necessary to stabilize the walls, cool the tool, remove small rock particles (sludge) and for other purposes. time, the drill pipe string is lifted to the surface with the help of a winch installed on the drilling rig, the core is unloaded, if necessary, the worn bit is replaced with a new one and the drill string is again lowered to the bottom. Drilling is accompanied by measurements of the physical properties of rocks along the wellbore. To do this, instruments are lowered into the well on a special cable, which record the temperature, electrical conductivity, magnetic susceptibility, radioactivity and other properties of the rocks. This process is called well logging. Drilling experience in the US and other countries has shown the following. Due to the power of the engines and the pressure of the pumps that inject the drilling fluid, as well as an increase in the carrying capacity of winches and the strength of steel drill pipes, wells up to 9-10 kilometers deep can be drilled in this way. Drilling deeper wells requires other unconventional engineering solutions. And such solutions were proposed and implemented in the course of the implementation of ultra-deep scientific drilling programs. It turned out that in cases where the bottom hole is located at a depth of many kilometers, it is advisable to use downhole motors installed not on the surface, but in the lower part of the drill string, which itself does not rotate. Downhole motors are miniature turbines or screw mechanisms that are driven by drilling fluid injected under pressure into the well. To reduce the weight of the drill pipe string, reaching a length of several kilometers, they are made of special light, but sufficiently strong and heat-resistant alloys. The aluminum alloys used in drilling the Kola well were 2,4 times lighter than steel. When a large depth is reached, there is a significant difference between the hydrostatic pressure of the drilling fluid column and the lithostatic (rock) pressure due to the weight of the rocks. This can lead to the destruction of the walls of the well, and this, in turn, causes serious complications during drilling. To achieve an equilibrium of rock pressure, the density of the drilling fluid is increased by adding special fillers to it. “One of the most difficult technical challenges,” write Popov and Kremenetsky, “is to ensure the reliable operation of drilling equipment at high temperatures that exist in ultra-deep wells. This applies to metal parts, their connections, lubricants, drilling fluid and measuring equipment. Although at the bottom, that is, at the lowest point of the Salton Sea well in the USA at a depth of 3220 meters, a temperature of 355 degrees Celsius was recorded, and in another well drilled to 1440 meters in one of the young volcanic structures in the western United States, the measured temperature reached 465 degrees, modern technical means do not allow drilling ultra-deep wells at such high temperatures for a long time, since the thermal stability of existing drilling equipment does not exceed 200-300 degrees.The biggest problems arise with measuring equipment, especially with electronics, which fail already at 150 degrees. Aqueous drilling fluids retain technological properties up to 230-250 degrees. At a higher temperature, it is necessary to switch to an oil-based solution and use more complex mixtures. The high temperature of the earth's interior remains one of the main factors limiting the depth of scientific drilling. Serious technical difficulties are associated with spontaneous curvature of deep wells during drilling due to uneven destruction of rocks at the bottomhole, geological inhomogeneities of the section and other reasons. For example, the bottomhole of the Kola well at a depth of about 12 kilometers deviated from the vertical by 840 meters. There are techniques to keep the well in a vertical position. So, thanks to the successful design of a special device, the KTB-Oberpfalz well in Germany remained the most vertical well in the world up to a depth of 7500 meters. However, deeper this fixture failed due to high temperature and pressure, and the well went its own way; as a result, at a depth of 9101 meters, it deviated from the vertical by 300 meters. Ultra-deep drilling required the creation of special measuring equipment that controls the conditions along the wellbore and at the bottom. Conventional logging technology with sensors that are lowered into the well on a heat-resistant cable turned out to be of little use. As a result of long-term searches, it was possible to develop telemetry and other electronic equipment mounted on a drilling string, as well as autonomous measuring instruments that go down and are carried up by the drilling fluid flow. Now the sensor signals can be transmitted not by wires, but by hydraulic means by creating pressure pulses in the drilling fluid. It should be noted that deep and ultra-deep wells have a telescopic design. Drilling starts with the largest diameter, and then moves on to smaller ones. So, in the Kola well, the diameter from 92 centimeters in the upper part decreased to 21,5 centimeters. And in the well KTB-Oberpfalz - from 71 centimeters to 16,5 centimeters. The mechanical speed of drilling ultra-deep wells is 1-3 meters per hour. For one trip between round trips, you can go deep by 6-10 meters. The average speed of lifting the drill pipe string is 0,3-0,5 meters per second. In general, drilling a single ultra-deep well takes years and is very expensive. For example, drilling an ultra-deep well in Germany cost DM 583 million. The cost of ultra-deep drilling in our country was no less. When drilling deep wells, of course, it is not without accidents. Most often they are caused by the dead stick of the drill string. Troubleshooting takes a long time. Sometimes they do not allow you to continue working, and you have to start drilling a new shaft. One can understand how expensive both literally and figuratively a multi-kilometer core column with a diameter of 5 to 20 centimeters, which is one of the main, but not the only result of scientific drilling. The core is carefully documented and stored in special rooms. Then it is studied in detail by large teams of specialists. So, the material obtained during the drilling of a German super-deep well was studied by about 400 scientists. They later published 2000 scientific papers based on them! When the actual drilling is completed, work on the ultra-deep well does not stop. The well turns into a permanent laboratory. Specialists continue to monitor the change in the regime of the earth's interior along the wellbore and in the near-wellbore space, and conduct various experiments. Such laboratories were created on the basis of the Kola and Vorotilovskaya wells in Russia and the KTB-Oberpfalz well in Germany. Author: Musskiy S.A.
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