A New Asymmetrical Array Induction Logging Tool

摘要

While array induction tools are fast approaching the 20 yearrnmark for commercial service, a few nagging questions persist inrnthe minds of induction tool designers. These questions relate tornsome of the compromises in hardware design and datarnprocessing that were necessary in the previous generation ofrntools. These compromises can give rise to various uncertaintiesrnin the data that ultimately degrade log responses. A new arrayrninduction tool has been designed that addresses these issues.rnAll array induction tools promise radial resistivity curvesrnwith focal depths ranging from 10 inches up to 120 inches.rnHowever, few users are familiar with the potential uncertaintyrnthat stems from the design of the fundamental sub-arrays. Inrnthe new tool, dedicated sub-arrays are closely associated withrneach computed radial curve. By doing so, the new toolrnproduces radial curves with a minimum of extrapolation. Thernpayoff for the user is more accurate radial resistivity curves andrna higher fidelity description of the formation and the nearrnwellbore environment.rnThis paper also describes the progress made in calibrationrnmethods and correction for thermal effects. While thesernsubjects typically receive little attention in the literature, theyrnare critical to the accuracy and repeatability of array inductionrnmeasurements. The rigorous calibration method described inrnthis paper assures accuracy across a large population of toolsrnand also insures insensitivity to the calibration environment.rnThe complexity and magnitude of thermal effects on arrayrninduction tools is examined alongside a robust, thermodynamicrnmethod for correcting them.rnFinally, several other methodologies are highlighted. A skinrneffect correction method uses only the in-phase signalrnmeasurements and corrects for the skin effect in the aspect ofrnthe apparent conductivity value and in the aspect of geometricrnfactors as well. A real time borehole correction methodrncomputes the borehole effect with adaptively inverted boreholernsize, tool eccentricity, and mud resistivity. A new inversionmethodology improves the efficiency and stability of the realtimernradial inversion.