Time-variant filter coefficients

• Main Author: MEYER, JR.; WALLACE H
• Format: Patent
• Language: English
• Published: 18.09.1990
• Subjects: DETECTING MASSES OR OBJECTS; GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; MEASURING; PHYSICS; TESTING

There is disclosed herein an improved method for processing the output signals from the receiver coil of an induction logging tool to account for nonlinear attenuation and phase shift of the induced electromagnetic field in the subsurface formation as a function of formation conductivity. The method includes the calculation of a modified vertical geometrical factor at a plurality of sample intervals for each measure point. The vertical geometrical factor is modified at each sample interval according to an attenuation factor that is a function of the distance in skin depths between the sample interval and the measure point. Using the modified vertical geometrical factor at each sample interval, an approximation for the measured signal in the receiver coil at the measure point is calculated and compared to the skin-effect corrected conductivity at that point to obtain an improved approximation of true formation conductivity at the measure point.