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The problem of having enough drinking water has been getting more and more acute for the residents of the northern city of Mirny in Yakutia, located near a diamonds deposit bearing the same name*. The Irelyakhskoye artificial lake was built for the needs of that industrial center four decades ago, and the builders put into the embankment some frozen ground (the region is located in the permafrost zone).
With time, however, there began serious problems caused by the thermal impact of large masses of water so that ice inclusions in the dam began to thaw. And the leakage continued to grow so that a lake appeared at the under water location. A pumping station had to be built there and it pumps back into the lake several thousands of cubic meters of water per day. And even the vast losses of energy involved fail to remedy the crisis.
Specialists in dam construction came up with a proposal to pump cement mortar into the cavities produced through specially built boreholes or wells. But in this concrete situation this traditional method proved to be ineffective and even damaging because streams of water washed out the mortar before it could solidify and carried it into the lower reach of a canal, polluting the lake located there.
* See: O. Bazanova, "Riches of the North", Science in Russia, No. 4, 2004. - Ed.
In that situation scientists of the Institute of Oil Chemistry of the RAS Siberian Branch (Tomsk) decided to help. One of the authors of the project Prof. V. Kuvshinov, Cand. Sc. (Chem.), recalled: "At that time we were busy with criogelspolymers which turn into jelly at low temperatures. And if this jelly is exposed to seasonal cycles of freezing and thawing it becomes more resilient and strong, with the best antifiltration properties. It demonstrated very good performance in oil wells. And we decided to try it as waterproofing in that reservoir."
That was the right approach, but it called for a non-trivial solution. What they were dealing with was a source of drinking water and that ruled out the use of reagents detrimental to human health (no such limitations for hydrocarbon raws). And the experts had to select an ecologically safe polymer, resistant to microbes.
The scientists from Tomsk were joined by their Moscow colleagues in the experiments on the dam. They tested silicate-cement mixtures which turned out to be very "capricious": it is very difficult to regulate the time of their hardening which often started already in the well.
The tests of polymer muds were just as difficult because no one really knew which equipment is best to be used, how the operations must be conducted and what would be the final effect (the principle of action of these muds consists in their adhesion to the walls of the pores to which they are glued, gradually filling the cavity). After a number of trials the experts chose the optimal regime. The gel screen blocked the stream of water.
After check measurements, the clients (management of the ALROSA Company) decided that the suggested technique was effective enough and could be used to save the water reservoir. It was decided to drill 300 wells, each 45 m deep, and pump into them, from the depth of 20 m, some 20 tons of dry polymer - 10 times less as compared with the required volume of cement mortar.
According to international experience, gel screens retain their strength for 5 - 7 years. That would be enough for building a new dam downstream, and especially since the old one was at the end of its service life.
But that was not all. Diamond mines are complex systems of structures-canals and ditches-which should be fortified so that in one cases water would not escape and, in others, would not accumulate.
A complicated situation emerges in diamond mines. In some places cracks appear with mineralized water pouring through them. These can be blocked by cryogels and in the building of drifts polymer screens should be set up in advance.
That unexpected application was found for the physico-chemical methods of boosting the output of oil-bearing beds. In addition to theoretical studies it has been necessary-at clients' request-to take care of the introduction of new technologies together with the ultimate industrial tests; cooperation with oilmen of Samara proved to be fruitful in that respect. In order to "heal" the dam they designed and built a unit for the preparation of the mortar and pumping it into boreholes. The unit consists of two vans on wheels. In one the polymer is heated (from a Finnish steam generator) and mixed up after which special pumps transport it into the second van where it cools down. This has to be done because hot mortar cannot be pumped into frozen ground: that will cause active thawing and produce new caverns.
The new equipment makes it possible to work non-stop in Yakutia in bitter frosts and in hot summers.
Nauka v Sibiri (Science in Siberia), 2004
Prepared by Rudolf BALANDIN
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