Capping(redirected from capping phenomenon)
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a complex of engineering and technological measures that provide for drilling in subterranean waters, oil, and gas, raising them to the surface, and the possibility of exploitation under optimum conditions (yield, chemical composition, and temperature) that remain stable over a period of time. The term “water intake” is also used as a synonym for the interception of subterranean fresh water, thermal springs, and industrial effluents.
Capping, which has been known since the early days of civilization, was highly developed in ancient Rome (the thermal baths of Emperor Caracalla; water-supply works), Mesopotamia, Portugal (Aquae Flaviae), and the Caucasus (karez, or underground irrigation canals).
Modern capping structures for subterranean waters are characterized by great diversity of types and designs, which take into consideration the special features of the hydrogeologic conditions of an area, composition of the water, and technical and sanitary requirements, which are determined by preset conditions of water consumption and the specific purpose for which the water is to be used. The simplest type of capping structure is the shaft well, which intercepts the subterranean waters of shallow-lying water tables; the walls of the well are reinforced with masonry or cast concrete to prevent cave-ins. For drilling in several water-bearing beds, the table designated for recovery is isolated from the underlying and overlying beds (strata) by plugging them. Drifts, which are extended horizontal or gently sloping mine tunnels built in highly broken areas, are used in addition to wells. The drifts are sometimes accompanied by a system of sloping, horizontal, or rising holes drilled into the side walls and face section of an underground gallery to increase the influx of water. In the USSR drift capping has been performed in Piatigorsk; abroad, it has been done in Bagneres-de-Luchon (France) and Ben-Haroun (Algeria). A nonpressured source can be capped by means of a chamber.
Boreholes (singly or in groups) are the most commonly used type of capping structure. Mechanized drilling permits the opening of water-bearing horizons and zones under rather difficult mining and geologic conditions at depths of 2 km or more. This makes possible reliable separation of the water-bearing horizons in well holes (pipe casing or cementing of the annular space), prevention of cave-ins of the walls and the breakthrough of water into the annular space, and installation of pumping equipment that provides withdrawal at constant yield rates. Steel piping is usually used for casing such wells. For the recovery of aggressive subterranean waters (waters containing carbonic acid and hydrogen sulfide, as well as waters with a low pH), capping wells are cased with pipes made of corrosion-resistant materials, such as alloy steels, vinyl plastic, polyethylene, and asbestos cement. Capping structures of underground mineral water deposits are made in the form of pump rooms, pavilions, and galleries.
Capping of oil and gas deposits consists in sealing and separating the interpipe space of wells and control of their operating conditions and the supply of gas or fluid to the well (or withdrawal from it). This is accomplished by special equipment built over the heads of oil or gas wells. Capping differs according to the recovery methods used (flow wells, air-lift wells, gas-lift wells, and pumping wells).
REFERENCESAbramov, S. K., M. P. Semenov, and A. M. Chalishchev. Vodozabory podzemnykh vod, 2nd ed. Moscow, 1956.
Lavrushko, P. N., and V. M. Murav’ev. Ekspluatatsiia neftianykh i gazovykh skvazhin. Moscow, 1964.
Poiski i razvedka podzemnykh vod dlia krupnogo vodosnabzheniia. Moscow, 1969.
Vartanian, G. S., and L. A. Iarotskii. Metodicheskie ukazaniia po pois-kam, razvedke i otsenke ekspluatatsionnykh zapasov mestorozhdenii mineraVnykh vod. Moscow, 1970.
V. G. AFONIN and G. S. VARTANIAN