METHOD OF DETERMINING THE LOCATION OF A DEEP-WELL CASING BY MAGNETIC FIELD SENSING

摘要

METHOD OF DETERMINING THE LOCATION OF A DEEP-WELL CASING BY MAGNETIC FIELD SENSING A method of locating a deep well casing at substantial distances below the earth's surface, and for directing the drilling of a second relief well to intersect the first well at substantial distances below the earth's surface is disclosed. A low frequency alternating electric current flow is produced in the casing of the well to be detected by means of current injected into the earth surrounding the first well. The current flow in the casing produces a magnetic field which is detectable by a sensitive magnetic field sensor suspended in the relief hole and spaced a substantial distance from the current source. The magnetic field sensor detects the magnitude and apparent direction of the alternating field, and this measurement is combined with a concurrent measurement of the earth's magnetic field to determine the direction and distance of the casing from the relief well. This information is then used to direct the continued drilling of the relief well, with periodic measurements being made to provide directional control of the drilling so that the first well is intersected at the desired depth below the earth's surface.