Reaching the depth of 12262 meters Kola Peninsula superdeep borehole (CG-3) still remains the deepest artificial point on Earth among hundreds of thousands wells drilled on our planet. UNESCO considers it as one of the outstanding achievements of XX century mankind. In 1997 the record was accepted for the Guinness Book of Records.
At the beginning of 1980-ies the 12-km borehole drilled by superdeep rig could only be comparable with Soviet space exploration missions. This is justifiable if we take into account the complexity of engineering solutions and stupendous expenditures for superdeep drilling. Georgy Alekseevsky, the chief engineer of Uralmash-15000 drilling rig, now deceased, would demonstrate a core sample from 10 thousand meters below the surface and comment:
– This piece of rock is of a considerable age – about two billion and eight hundred million years. As a comparison the age of Earth is four and a half billion years. This simple rock would cost the same price as the moon rock of the same size.
It may sound like exaggeration though a slight one. Superdeep drilling operations with massive expenditures on them have never been affordable for every country.
Nikita Khrushchev must have been a godfather of Soviet superdeep drilling. Since that was him who in spite of skepticism and objections of his fellow-members, approved state superdeep drilling program (i.e. drilling over six thousand meters below the surface) in 1963. Most likely Khrushchev was more concerned with political results rather than scientific ones. By that time the United States have adopted the North American drilling research program which implied well drilling with maximum well depth of 15 km. The Soviet leader by no means would stand USSR lagging in science and technology, whatever the cost. The scope of practical and research work was extraordinary broad therefore: over 150 research and development institutions in the Soviet Union were involved into earth crust research project.
The first attempt to sink a superdeep well was made in North Kazakhstan but eventually the rig drilled 5600 meters only. Kola Peninsula well was the third one and thence received a state code – SG-3 (the 3rd superdeep well). It was the place where Uralmash-15000 drilling rig was used first.
THE WAY IT WAS
A place for unique drilling complex and research center was planned 10 km from Zapolyarny settlement. There the earliest (three billion years) igneous rocks form extrusive rocks on the surface. The rocks are poorly explored since often are covered with sedimentary mantle.
The first drilling operations started in May 1970 and were performed by Uralmash-4E drilling rig. It took the researchers four years to reach the depth of 7263 meters. Then drilling was stopped for about a year to erect Uralmash-15000 – specially designed and manufactured rig for superdeep drilling. (Later another three machines were produced for Saatlinskaya, Urengoyskaya and Uralskaya boreholes).
As specialists from Kola Peninsula geological survey expedition reported the rig proved to be reliable and of high performance. System automation (round-trip operations, bit feeding) and DC drive resulted in drilling rate increase as against standard drilling rigs.
Unique drilling rig was a brainchild of many engineers and designers. We should first and foremost name those who made an outstanding contribution to the development of the rig. First of all this was G.V.Alekseevsky. For him Uralmash-15000 became a swan song. At the time Alekseevsky, the man of advanced years, clearly understood that it was his last engineering development of such scale. High-duty pumps (with production output of 1829 l/s) were designed by Yu. Corniltsev, L.Goronovich and V. Gerasimov; A.Spirukov was in charge of the drill tower design; V. Malofeeva and V.Gramolin (later a head of drilling-equipment engineering department) designed draw works and round-trip automation mechanisms respectively. V.Razuvaev was in charge of pulley blocks; A.Lazarev and V.Kasantsev designed swivel.
Various engineering solutions introduced at Uralmash-15000 were later used in series drilling rigs.
Specialists of All-Union Drilling-equipment research and design institute (VNIIBT) elaborated hole-boring method. For superdeep borehole turbo-drilling method was used: drilling mud was delivered through drill pipe and rotated multistage turbine with 214-mm drill bit. Special annular-shaped core drill was used to obtain cylindrical 60-mm sections of rock or sediment (core samples). A core receiver continued through the full length of the turbine sections and served to collect cylindrical sections - the main expedition objectives.
The deeper well Uralmash-15000 drilled, the more difficult it was to perform drilling and subsequent operations. Earlier the researchers considered that the temperature would not exceed 1500C even at a depth of 15 kilometers. However, at a depth of 8 kilometers the temperature reached 1690 C and 2300C at 12 kilometers deep down. VNIIBT specialists had to develop new technologies, heat-resistant and highly-resistant light-weight pipes and equipment.
Then coring procedure got more and more complicated. The core samples obtained from deep underground got ruined under the pressure of kilometers-long rock mass. The drill core sample was poor: only 30% were extracted from 5km depth and separate 2-3cm wide plates of the hardest rocks were obtained from 9-km depth.
The core samples from SG-3 were presented at International Geological Congress in Moscow in 1983 when the well reached 12 kilometers. Also a drill bit with worn hard-alloy teeth was demonstrated at the congress. No one would expect a common drill bit to make such a stir! As it turned out, many scientists would expect to find a technological wonder and thus some doubt arouse as whether these achievements did take place. It was quite understandable and the request was accommodated: working Uralmash-15000 was demonstrated to the scientists. The drill string was pulled out and 33-meter pipe sections were disconnected; scientists numbered them and acknowledged: the 12000-meter depth was reached indeed. And the drill bit that had been presented to the scientists earlier was that particular instrument to drill the well: a stock of similar worn drill bits was left close to the drill rig. Later, a bombshell effect was made by Soviet statement that the SG-3 core samples extracted from the Earth crust were almost identical to those obtained on the Moon.
Someone of those present made a joke, saying that apparently the Moon was a part of the Earth that had broken off and the mankind just needed to find a specific place wherefrom it had been torn off.
SG-3 photos and articles circulated over the world press, books published, stamps and occasional envelopes issued, prizes and awards conferred and received. However, the shower of awards and medals just passed by all those engineers and designers who had elaborated Uralmash-15000 project, except for one engineer who worked at district Communist Party Committee at the time of award receipt.
LOST AND FORSAKEN
In the latter half of 1980s the interest towards Kola Peninsula geological survey expedition gradually waned and then it was almost forgotten.
So, what happened then? It was rumored, jokingly of course, that Soviet engineers drilled a borehole so deep that it broke through into hell and they even heard the tormented screams of the damned. Others with a serious look on their face would say that demons and imps came roaring out of the deepest well on Earth…
But if we scrutinize the situation and the way it actually developed we’ll see how it all happened…
While the turbo-drill penetrated seven kilometers of granites it met hard homogeneous rock and the wellbore remained straight. Then, starting from 7-km depth the machine drilled fractured formations with slight interlays of hard rocks. The drill started to swerve to softer rocks and the borehole took a twisting course. To reduce borehole deviation specially-designed deflectors along with drilling tools were lowered into the well. The cases when the drill string got stuck (as if its sections adhered to the wellbore walls) repeated with increasing frequency.
The catastrophe happened on September 27th 1984. After drilling to 12066 meters, a drill string got stuck. Usually a load exceeding a drill-string weight (about 200 tons) needed to unseat the drill string. The procedure was followed as usual but the drill string did not even move. Then the load was slightly increased and indications became less than expected. It seemed that the drill-string weight was lessened which should not happen in the course of operation. Later it turned out that a 5000-meter section of the drill string twisted off and was left in the hole. Along with drill-string section and turbo-drill the researchers lost five years of hard work.
A few months later when breakdown elimination was found impossible an alternative borehole drilling restarted from 7000 meters. Six years later the hole reached 12000 meters again. However breakdowns kept happening. That resulted in other 12 boreholes drilled after 7000 meters, four of them varied from 2200 to 5000 meters. The bore well began to look like gigantic root system. It was that circumstance that caused longer drilling operations of a last section.
In 1992 drilling operations at SG-3 were stopped. It is believed that current technology has exhausted its potential. Perhaps, it’s true but SG-3 still remains the deepest borehole in the world though the attempts have been made to beat the record. Thus, a borehole in Germany reached its depth of 9600 meters and then drilling was stopped due to constant breakdowns. The foreign superdeep drilling projects could not even come closer to Soviet success as yet!
SG-3: PRESENT DAY
Newsmen rarely visit SG-3 today, and that’s how they describe its present condition:
– Traces of desolation and decay are everywhere. Ground-floor window openings are boarded-up. Cold dampness and odor of a long-abandoned place dominate in the rooms and premises where the pioneers once debated over new drilling methods, explored Earth crust and examined core samples. Rusty structures, defunct machines and indicators stand there in the dusk of superdeep borehole, forsaken. Daylight travels through wide windows of 70-meter tower and falls on the wellhead. The nominee of Guinness Book of World Records looks plain, like any other ordinary pipe.
Today the unique borehole may serve as geological observatory to predict earthquakes, explore Earth structure and microcosm.
“Surely, it seemed possible to drill another one and a half kilometers” - comments David Guberman, the unchallenged head of Kola Peninsula geological survey expedition and director of research and development center “Kolskaya sverkhglubokaya”.
According to D.Guberman, SG-3 will remain the deepest borehole on the Earth for the foreseeable future. It takes too much spending, as well as knowledge and experience gained by SG-3 old-timers.
(Abstract from “United Heavy Machinery Gazette”, 2004, No.28)