Proximity detection system for deep wells

摘要

A method and apparatus for magnetic field measurements to determine the proximity of a nearby target incorporating electrically conductive material includes a drill string (54) having multiple drill pipe sections (56, 57, 58, 59) connected end-to-end, with at least one of the drill pipe sections (57) being electrically conductive and isolated to provide an electrode section. A nonmagnetic drill pipe section (84) is connected in the drill string below the electrode section (57), and a hydraulic motor (62) having a rotatable drill bit sub (70) carrying a magnetic field sensing instrument package (102) is connected to a lowermost end of the drill string. A power supply provides a time-varying current to the drill pipe electrode section (57) to produce a corresponding target current magnetic field to be detected at the drill bit instrument (10)2, and a communication instrument package (94) is locatable within the nonmagnetic drill pipe section (84) to receive magnetic field data from the magnetic field sensing instrument package (102) on the drill bit (70).

主权项

1. Apparatus for target proximity detection from a borehole being drilled, comprising:
a drill string having multiple drill pipe sections connected end-to-end and carrying a drill bit; at least one of said drill pipe sections being electrically conductive to provide a drill pipe electrode section; at least one electrically insulating drill pipe sub electrically isolating said electrode section from adjacent drill pipe sections; a power supply in electrical communication with said at least one drill pipe electrode section and energizable to inject a time-varying current into Earth formations surrounding said borehole; a drill bit instrument at said drill bit comprising sensors for detecting magnetic fields produced by said injected current, said drill bit instrument including an other power supply and a down-hole control computer for processing magnetic field data received from the sensor; communicating the processed magnetic field data to surface instrumentation; and controlling power output by the other power supply based, at least in part, on the presence of output signals from the sensors; and control circuitry coupled to the power supply that energizes the power supply in response to a control signal from surface instrumentation.