Patent ID: 6353322
Filing Date: 2002-03-05
Classification: G01V

Abstract:
A method for determining resistivity of earth formations penetrated by an uncased wellbore having irregularities in a wall thereof, the method comprising:(a) imparting a first electrical current to said wellbore and earth formations from a first electrode disposed in said wellbore; (b) returning said first electrical current at a second electrode in said wellbore at an axially spaced apart location from said first electrode; (c) adjusting circuits used to measure voltage differences until a measured voltage difference between a first pair of electrodes located axially between said first and second electrodes is substantially the same as a measured voltage difference between a second pair of electrodes located axially between said first and second electrode wherein at least one of said voltage difference is in part dependent on said irregularities in the wellbore wall; and (d) after steps (a)-(c), imparting a second electrical current into the formation at the first electrode and returning said second electrical current to an electrode distal from said first electrode, repeating said steps of measuring said voltage differences and determining a difference of said voltage differences, whereby said difference of voltage difference represents a current leakage into said earth formation substantially unaffected by said irregularities, said current leakage related to said resistivity of said earth formations.