Steering sub for flexible drilling

Abstract

A flexible steering sub is disclosed for flexible drilling of horizontal wells, geothermal drilling for electric power generation; earth sciences study of and monitoring of earth movement with respect to fault movement; environmental science cleaning up of inaccessible polluted areas; coring to test rock strength prior to large scale constructions such as dams; introduction of chemicals for solution mining, and the like. The flexible sub comprises an elongated housing having a plurality of housing sections connectable at one end to an orientation sub for a PDM drill and connectable at the other end to a wire line connector. An electronics assembly including guidance directional sensors and probe is positioned in a plurality of the housing sections, interconnected electrically, and connected at one end to the wire line connector. Selected housing sections spaced along the length of the housing have portions intermediate their respective ends of sufficiently reduced outside diameter to bend in preference to bending of the housing sections containing the electronics assembly. The steering sub is operable during drilling to bend along its length at the reduced outside diameter housing sections on a short radius without bending the electronics assembly.