Deep in the hot ores

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

The 20th century was marked by the triumph of man in the air and the conquest of the deepest depressions of the World Ocean. Only the dream of penetrating the heart of our planet and knowing the hitherto hidden life of its bowels remains unattainable. "Journey to the Center of the Earth" promises to be extremely difficult and exciting, fraught with a lot of surprises and incredible discoveries. The first steps on this path have already been taken - several dozen superdeep wells have been drilled in the world. The information obtained with the help of ultra-deep drilling turned out to be so overwhelming that it shattered the established ideas of geologists about the structure of our planet and provided richest materials for researchers in various fields of knowledge.

Touch the mantle

The industrious Chinese in the 13th century dug wells 1,200 meters deep. Europeans broke the Chinese record in 1930 by learning how to pierce the earth with drilling rigs for 3 kilometers. In the late 1950s, the wells extended up to 7 kilometers. The era of ultra-deep drilling began.

Like most global projects, the idea of drilling the Earth's upper shell originated in the 1960s, at the height of space flights and the belief in the limitless possibilities of science and technology. The Americans conceived no less than go through the entire earth's crust with a well and get samples of the rocks of the upper mantle. The concepts of the mantle then (as, by the way, and now) were based only on indirect data - the velocity of propagation of seismic waves in the depths, the change in which was interpreted as the boundary of layers of rocks of different ages and compositions. Scientists believed that the earth's crust is like a sandwich: young rocks on top, ancient ones below. However, only superdeep drilling could give an accurate picture of the structure and composition of the Earth's outer shell and upper mantle.

Mokhol project

In 1958, the Mohol superdeep drilling program appeared in the United States. This is one of the most daring and mysterious projects in post-war America. Like many other programs, Mohol was intended to overtake the USSR in scientific rivalry, setting a world record in ultradeep drilling. The name of the project comes from the words "Mohorovicic" - this is the name of the Croatian scientist who distinguished the interface between the earth's crust and the mantle - the border of Moho, and "hole", which means "well" in English. The creators of the program decided to drill in the ocean, where, according to geophysicists, the earth's crust is much thinner than on the continents. It was necessary to lower the pipes several kilometers into the water, traverse 5 kilometers of the ocean floor and reach the upper mantle.

In April 1961, off the island of Guadeloupe in the Caribbean Sea, where the water column reaches 3.5 km, geologists drilled five wells, the deepest of them entered the bottom at 183 meters. According to preliminary calculations, in this place, under the sedimentary rocks, they expected to meet the upper layer of the earth's crust - granite. But the core raised from under the sediments contained pure basalts - a kind of antipode of granites. The result of drilling discouraged and at the same time inspired scientists, they began to prepare a new phase of drilling. But when the cost of the project exceeded $ 100 million, the US Congress stopped funding. Mohol did not answer any of the questions posed, but it showed the main thing - superdeep drilling in the ocean is possible.

The funeral is postponed

Ultra-deep drilling allowed to look into the depths and understand how rocks behave at high pressures and temperatures. The idea that rocks with depth become denser and their porosity decreases, turned out to be wrong, as well as the point of view about dry subsoil. This was first discovered during the drilling of the Kola superdeep, other wells in ancient crystalline strata confirmed the fact that at a depth of many kilometers, rocks are broken by cracks and penetrated by numerous pores, and aqueous solutions freely move under pressure of several hundred atmospheres. This discovery is one of the most important achievements of ultra-deep drilling. It forced us to turn again to the problem of burying radioactive waste, which was supposed to be placed in deep wells, which seemed completely safe. Considering the information on the state of the subsoil obtained in the course of superdeep drilling, projects for the creation of such repositories now look very risky.

In search of the cooled hell

Since then, the world has fallen ill with ultra-deep drilling. In the United States, a new program for studying the ocean floor (Deep Sea Drilling Project) was being prepared. The Glomar Challenger, built specifically for this project, spent several years in the waters of various oceans and seas, drilling almost 800 wells in their bottom, reaching a maximum depth of 760 m. By the mid-1980s, offshore drilling results confirmed the theory of plate tectonics. Geology as a science was reborn. Meanwhile, Russia went its own way. The interest in the problem, aroused by the success of the United States, resulted in the program "Exploration of the Earth's interior and superdeep drilling", but not in the ocean, but on the continent. Despite its centuries-old history, continental drilling seemed to be a completely new business. After all, we were talking about previously unattainable depths - more than 7 kilometers. In 1962, Nikita Khrushchev approved this program, although he was guided by political rather than scientific motives. He did not want to lag behind the United States.

The newly created laboratory at the Institute of Drilling Technology was headed by the famous oil worker, Doctor of Technical Sciences Nikolai Timofeev. He was instructed to substantiate the possibility of superdeep drilling in crystalline rocks - granites and gneisses. The research took 4 years, and in 1966 the experts made a verdict - you can drill, and not necessarily with the equipment of tomorrow, the equipment that is already there is enough. The main problem is the heat at depth. According to calculations, as it penetrates into the rocks that make up the earth's crust, the temperature should increase every 33 meters by 1 degree. This means that at a depth of 10 km one should expect about 300 ° С, and at 15 km - almost 500 ° С. Drilling tools and devices will not withstand such heating. It was necessary to look for a place where the bowels were not so hot …

Such a place was found - an ancient crystalline shield of the Kola Peninsula. A report prepared at the Institute of Physics of the Earth read: over the billions of years of its existence, the Kola shield has cooled down, the temperature at a depth of 15 km does not exceed 150 ° C. And geophysicists prepared an approximate section of the Kola Peninsula. According to them, the first 7 kilometers are granite strata of the upper part of the earth's crust, then the basalt layer begins. Then the idea of a two-layer structure of the earth's crust was generally accepted. But as it turned out later, both physicists and geophysicists were wrong. The drilling site was chosen at the northern end of the Kola Peninsula near Lake Vilgiskoddeoayvinjärvi. In Finnish it means "Under the Wolf's Mountain", although there are no mountains or wolves in that place. The drilling of the well, the design depth of which was 15 kilometers, began in May 1970.

Tool for the underworld

The drilling of the Kola well SG-3 did not require the creation of fundamentally new devices and giant machines. We started to work with what we already had: the Uralmash 4E unit with a lifting capacity of 200 tons and light-alloy pipes. What was really needed at that time was non-standard technological solutions. Indeed, in hard crystalline rocks to such a great depth, no one drilled, and what would happen there, they imagined only in general terms. Experienced drillers, however, realized that no matter how detailed the project was, a real well would be much more complex. Five years later, when the depth of the SG-3 well exceeded 7 kilometers, a new Uralmash 15,000 drilling rig was installed, one of the most modern at that time. Powerful, reliable, with an automatic trigger mechanism, it could withstand a string of pipes up to 15 km long. The drilling rig has turned into a fully sheathed derrick 68 m high, defiant to strong winds raging in the Arctic. A mini-plant, scientific laboratories and a core storage have grown nearby.

When drilling to shallow depths, a motor that rotates the pipe string with a drill at the end is installed on the surface. The drill is an iron cylinder with diamond or hard alloy teeth - a bit. This crown bites into rocks and cuts out a thin column from them - a core. To cool the tool and remove small debris from the well, drilling fluid is pumped into it - liquid clay, which circulates all the time along the wellbore, like blood in vessels. After some time, the pipes are raised to the surface, freed from the core, the crown is changed and the column is again lowered into the bottomhole. This is how conventional drilling works.

And if the barrel length is 10-12 kilometers with a diameter of 215 millimeters? The string of pipes becomes the thinnest thread that is lowered into the well. How to manage it? How to see what's going on in the face? Therefore, on the Kola well, at the bottom of the drill string, miniature turbines were installed, they were started by drilling mud pumped through pipes under pressure. Turbines rotated a carbide bit and core cut. The whole technology was well developed, the operator on the control panel saw the rotation of the bit, knew its speed and could control the process.

Every 8-10 meters, a multi-kilometer pipe string had to be lifted up. The descent and ascent took a total of 18 hours.

The insidiousness of the number "7"

7 kilometers - the mark for the Kola superdeep fatal. Behind it began uncertainty, many accidents and a continuous struggle with rocks. The barrel could not be kept upright. When we traveled 12 km for the first time, the well deviated from the vertical by 21 °. Although the drillers had already learned to work with the incredible curvature of the wellbore, it was impossible to go further. The well was to be drilled from the 7 km mark. To get a vertical hole in hard rocks, you need a very hard bottom of the drill string, so that it enters the bowels like oil. But another problem arises - the well is gradually expanding, the drill dangles in it, as in a glass, the walls of the wellbore begin to collapse and can press down on the tool. The solution to this problem turned out to be original - the pendulum technology was applied. The drill was artificially rocked in the well and suppressed strong vibrations. Due to this, the trunk turned out to be vertical.

The most common accident on any rig is a pipe string break. Usually, they try to capture the pipes again, but if this happens at great depths, then the problem becomes unrecoverable. It is useless to look for a tool in a 10-kilometer borehole; such a borehole was thrown and a new one was started, a little higher. Pipe breakage and loss at SG-3 happened many times. As a result, in its lower part, the well looks like the root system of a giant plant. The branching of the well upset the drillers, but turned out to be happiness for the geologists, who unexpectedly got a three-dimensional picture of an impressive segment of ancient Archean rocks that formed more than 2.5 billion years ago.

In June 1990, SG-3 reached a depth of 12,262 m. The well began to be prepared for drilling up to 14 km, and then an accident occurred again - at an elevation of 8,550 m, the pipe string broke off. The continuation of the work required a long preparation, renewal of equipment and new costs. In 1994, drilling of the Kola Superdeep was stopped. After 3 years, she entered the Guinness Book of Records and still remains unsurpassed. Now the well is a laboratory for the study of deep bowels.

Secret bowels

The SG-3 has been a classified facility since the beginning. The border zone, the strategic deposits in the district, and the scientific priority are to blame. The first foreigner to visit the drilling site was one of the leaders of the Academy of Sciences of Czechoslovakia. Later, in 1975, an article about the Kola Superdeep was published in Pravda signed by the Minister of Geology Alexander Sidorenko. There were still no scientific publications on the Kola well, but some information leaked abroad. According to rumors, the world began to learn more - the deepest well is being drilled in the USSR.

A veil of secrecy, probably, would have hung over the well until the very "perestroika", if the World Geological Congress had not happened in 1984 in Moscow. They carefully prepared for such a major event in the scientific world; a new building was even built for the Ministry of Geology - many participants were expecting. But foreign colleagues were primarily interested in the Kola superdeep! The Americans did not believe at all that we had it. The depth of the well by that time had reached 12,066 meters. It no longer made sense to hide the object. An exhibition of achievements of Russian geology awaited the congress participants in Moscow, one of the stands was dedicated to the SG-3 well. Experts all over the world looked in bewilderment at a conventional drill head with worn out carbide teeth. And with this they are drilling the deepest well in the world? Incredible! A large delegation of geologists and journalists went to the Zapolyarny settlement. Visitors were shown the rig in action, and 33-meter pipe sections were removed and disconnected. All around were heaps of exactly the same drill heads as the one that was on the stand in Moscow.

A well-known geologist, academician Vladimir Belousov received the delegation from the Academy of Sciences. During a press conference, he was asked a question from the audience:

- What is the most important thing that the Kola well has shown?

- Gentlemen! Most importantly, it showed that we do not know anything about the continental crust, - the scientist answered honestly.

Deep surprise

Of course, they knew something about the earth's crust of the continents. The fact that the continents are composed of very ancient rocks, aged from 1.5 to 3 billion years, was not refuted even by the Kola well. However, the geological section compiled on the basis of the SG-3 core turned out to be exactly the opposite of what the scientists had imagined earlier. The first 7 kilometers were composed of volcanic and sedimentary rocks: tuffs, basalts, breccias, sandstones, dolomites. Deeper lay the so-called Conrad section, after which the speed of seismic waves in the rocks increased sharply, which was interpreted as the boundary between granites and basalts. This section was passed a long time ago, but the basalts of the lower layer of the earth's crust never appeared anywhere. On the contrary, granites and gneisses began.

The section of the Kola well refuted the two-layer model of the earth's crust and showed that the seismic sections in the bowels are not the boundaries of layers of rocks of different compositions. Rather, they indicate a change in the properties of the stone with depth. At high pressure and temperature, the properties of rocks, apparently, can change dramatically, so that granites in their physical characteristics become similar to basalts, and vice versa. But the "basalt" raised to the surface from a 12-kilometer depth immediately became granite, although it experienced a severe attack of "caisson disease" along the way - the core crumbled and disintegrated into flat plaques. The further the well went, the less quality samples fell into the hands of scientists.

The depth contained many surprises. It used to be natural to think that with distance from the surface of the earth, with an increase in pressure, the rocks become more monolithic, with a small number of cracks and pores. SG-3 convinced scientists otherwise. Starting from 9 kilometers, the strata turned out to be very porous and literally crammed with cracks along which aqueous solutions circulated. Later, this fact was confirmed by other superdeep wells on the continents. It turned out to be much hotter at depth than expected: by as much as 80 °! At the 7 km mark, the bottomhole temperature was 120 ° С, at 12 km it had already reached 230 ° С. In the samples of the Kola well, scientists discovered gold mineralization. Inclusions of precious metal were found in ancient rocks at a depth of 9, 5-10, 5 km. However, the concentration of gold was too low to claim a deposit - an average of 37.7 mg per ton of rock, but sufficient to be expected in other similar places.

On the Russian trail

The demonstration of the Kola well in 1984 made a deep impression on the world community. Many countries have started preparing scientific drilling projects on the continents. Such a program was also approved in Germany in the late 1980s. The ultra-deep well KTB Hauptborung was drilled from 1990 to 1994, according to the plan, it was supposed to reach a depth of 12 km, but due to unpredictably high temperatures, it was only possible to get to the 9.1 km mark. Due to the openness of data on drilling and scientific work, good technology and documentation, the KTV ultra-deep well remains one of the most famous in the world.

The location for drilling this well was chosen in the southeast of Bavaria, on the remains of an ancient mountain range, whose age is estimated at 300 million years. Geologists believed that somewhere here there is a zone of joining of two plates, which were once the shores of the ocean. According to scientists, over time, the upper part of the mountains has worn away, exposing the remnants of the ancient oceanic crust. Even deeper, ten kilometers from the surface, geophysicists discovered a large body with abnormally high electrical conductivity. They also hoped to clarify its nature with the help of a well. But the main challenge was to reach a depth of 10 km in order to gain experience in ultra-deep drilling. Having studied the materials of the Kola SG-3, the German drillers decided to first drill a test well 4 km deep in order to get a more accurate idea of the working conditions in the subsoil, test the technique and take a core. At the end of the pilot work, much of the drilling and scientific equipment had to be altered, and something had to be re-created.

The main - superdeep - well KTV Hauptborung was laid just two hundred meters from the first. For the work, an 83-meter tower was erected and a drilling rig with a lifting capacity of 800 tons, the most powerful at that time, was created. Many drilling operations have been automated, primarily the mechanism for lowering and recovering the pipe string. The self-guided vertical drilling system made it possible to make an almost vertical hole. Theoretically, with such equipment, it was possible to drill to a depth of 12 kilometers. But the reality, as always, turned out to be more complicated, and the scientists' plans did not come true.

The problems at the KTV well began after a depth of 7 km, repeating much of the fate of the Kola Superdeep. At first, it is believed that due to the high temperature, the vertical drilling system broke down and the hole went obliquely. At the end of the work, the bottom deviated from the vertical by 300 m. Then, more complicated accidents began - a break in the drill string. Just like on Kola, new shafts had to be drilled. Certain difficulties were caused by the narrowing of the well - at the top its diameter was 71 cm, at the bottom - 16.5 cm. Endless accidents and high bottomhole temperature –270 ° C forced the drillers to stop working not far from the cherished goal.

It cannot be said that the scientific results of KTV Hauptborung struck the imagination of scientists. At the depth, amphibolites and gneisses, ancient metamorphic rocks, were mainly deposited. The zone of convergence of the ocean and the remains of the oceanic crust have not been found anywhere. Perhaps they are in another place, here is a small crystalline massif, upturned to a height of 10 km. A deposit of graphite was discovered a kilometer from the surface.

In 1996, the KTV well, which cost the German budget 338 million dollars, came under the patronage of the Scientific Center for Geology in Potsdam, it was turned into a laboratory for observing deep subsoil and a tourist destination.

The deepest wells in the world

1. Aralsor SG-1, Caspian lowland, 1962-1971, depth - 6, 8 km. Search for oil and gas.

2. Biikzhal SG-2, Caspian lowland, 1962-1971, depth - 6, 2 km. Search for oil and gas.

3. Kola SG-3, 1970-1994, depth - 12,262 m. Design depth - 15 km.

4. Saatlinskaya, Azerbaijan, 1977-1990, depth - 8 324 m. Design depth - 11 km.

5. Kolvinskaya, Arkhangelsk region, 1961, depth - 7,057 m.

6. Muruntau SG-10, Uzbekistan, 1984, depth -

3 km. The design depth is 7 km. Search for gold.

7. Timan-Pechora SG-5, North-East of Russia, 1984-1993, depth - 6,904 m, design depth - 7 km.

8. Tyumen SG-6, Western Siberia, 1987-1996, depth - 7,502 m. Design depth - 8 km. Search for oil and gas.

9. Novo-Elkhovskaya, Tatarstan, 1988, depth - 5,881 m.

10. Vorotilovskaya well, Volga region, 1989-1992, depth - 5,374 m. Search for diamonds, study of Puchezh-Katunskaya astrobleme.

11. Krivoy Rog SG-8, Ukraine, 1984-1993, depth - 5 382 m. Design depth - 12 km. Search for ferruginous quartzites.

Ural SG-4, Middle Urals. Laid down in 1985. Design depth - 15,000 m. Current depth - 6,100 m. Search for copper ores, study of the structure of the Urals. En-Yakhtinskaya SG-7, Western Siberia. Design depth - 7,500 m. Current depth - 6,900 m. Search for oil and gas.