a method of prospecting and exploring for mineral deposits by means of boreholes. Exploratory drilling is also used in geological-engineering and hydro-geological surveying.
Shallow drilling without flushing is used to explore deposits lying close to the surface and in geological-engineering surveys in soft and loose rocks. Shallow drilling includes auger drilling, percussion drilling, and vibration drilling with vibrating borers and vibrating coring tools. Several methods of combined drilling are used in complex geological sections. Most deep-lying deposits of hard minerals (coal, ferrous and nonferrous metals) are surveyed by core drilling.
Placer deposits and isometric stockwork-structured ore bodies are often explored by cable-tool drilling. Heavy-duty turbine or rotary drilling rigs are employed in prospecting and surveying gas and oil deposits.
Hydrogeological drilling to explore for and survey subterranean waters is done with the aid of cable-tool and self-propelled rotary rigs.
Geological sections are studied by means of geological documentation and sampling of cores and cuttings and by electric, magnetic, and radiometric logging methods. Inclinometric, core-analysis, caliper-logging, and thermometric measurements are taken in the borehole to evaluate its condition.
Exploratory boreholes may be several kilometers deep.
REFERENCESKulichikhin, N. I., and B. I. Vozdvizhenskii. Razvedochnoe burenie, 2nd ed. Moscow, 1973.
Tekhnologiia i lekhnika razvedochnogo bureniia. Moscow, 1973.
B. I. VOZDVIZHENSKII