Patent ID: 7568532
Filing Date: 2009-08-04
Classification: E21B

Abstract:
1. Apparatus for measuring the distance and direction between two boreholes extending into the Earth, comprising: a solenoid assembly installed at a first selected point in a first borehole, said first borehole having a known inclination and direction at said selected point; down hole circuitry for energizing said solenoid assembly to generate a characteristic known solenoid field for a short interval of time; electronic circuitry in said solenoid assembly which actively waits for an initiating signal and upon receipt of said initiating signal starts a prescribed electric current flow into said solenoid; a magnetic field sensor deployed at a second selected point in a second borehole, said field sensor measuring three vector components of said characteristic solenoid magnetic field at said second point; orientation circuitry for determining a spatial orientation of said magnetic field sensor at said second point in said second borehole; and a processor responsive to said spatial orientation of said sensor and to said measured vector components at said second point in said second borehole and further responsive to said characteristic known solenoid magnetic field to determine the distance and direction between said first and second points.