Controlled Directional Drilling

a method of drilling wells that deviate from the vertical according to a predetermined curve. Controlled directional drilling was first used in the USSR in the Groznyi oil fields in 1934. In 1972, approximately 25 percent of the wells drilled for petroleum in the USSR (in terms of length in meters) were drilled by the controlled directional method.

Controlled directional drilling is advantageous in cases of complex terrain (for example, if a deposit is located beneath a large body of water or structures with foundations and basements), under geological conditions of bedding of minerals that make them inaccessible by means of vertical shafts, during multiple or multiple-face drilling, and to extinguish burning oil and gas wells. In geological prospecting, controlled directional drilling is done with drilling rigs (jacks and supports), in which case the well is drilled directly into the earth at an angle; during the opening of oil and gas beds, it is done with turbodrills or by the rotary method (the well is drilled vertically from the surface, with subsequent deviation in the desired direction at a specified depth).

The deviation of the well from the vertical (the change of the zenith angle and the drilling azimuth) is produced by means of deflecting devices, such as turbine whipstocks. Straight inclined portions are drilled with the aid of drilling devices consisting of centering and gauging elements. The greatest deviation from the vertical in controlled directional drilling (3, 836 m) was achieved at Cook Inlet (USA); a deviation of 2, 453 m was made on Sakhalin Island (USSR) in 1972.