(sverkhglubokoe burenie), the drilling of wells or boreholes to depths of 6,000 m or more in order to study the earth’s crust and upper mantle and to locate deposits of useful minerals. The term “ultradeep drilling” appeared in the Russian literature in the 1950’s; until the early 1960’s it was used to designate the process of drilling wells to depths exceeding 4,500 m. In the 1970’s ultradeep drilling was used in conjunction with the international Geodynamic Project, which sought to obtain direct data on the material composition and physical properties of the lower layers of the lithosphere and to explain the structure, origin, and development of these layers. Ultradeep drilling makes it possible to determine the age of the geochemical and geophysical characteristics of the rocks composing the lithosphere, to study gaseous and liquid emanations from deep within the earth, and to determine the geological nature of physical fields, limits, and layers, as well as the temperature conditions and thermal radiation of the earth’s interior.
Ultradeep drilling is used to evaluate the potential oil- and gas-bearing capacities of deep sedimentary basins and to conduct prospecting and exploration work and the subsequent exploitation of oil and gas deposits. It has also been proposed for use in studying earthquake foci.
By 1974, more than 400 ultradeep wells had been drilled, including the following wells drilled on land: Bertha Rogers No. 1 (9,583 m) and Bayden Unit (9,160 m; both in Oklahoma, USA), Shevchenkovo No. 1 (7,024 m; western Ukraine, USSR), and Aralsor (6,806 m; Caspian Lowland, USSR). Plans are under way to drill ultradeep wells on land to depths of 15,000 m, for example, on the Baltic Shield within the USSR. The Mohole Project (USA) contained proposals for ocean drilling in the seabed to depths of several kilometers.
Ultradeep wells are sunk by rotary drilling (abroad), turbo-drilling, or by a combination of both methods (USSR). The principal difficulties are caused mainly by the high temperatures and pressures at great depths and the increased weight of drill pipes and casings in the well. The drilling process is improved by using heat-resistant rock-crushing tools and drilling fluids, by controlling pressures within the well, and by increasing the strength and reliability of drill pipes.
IU. G. APANOVICH and A. V. OORLOV