Patent ID: 8305083
Filing Date: 2012-11-06
Classification: G01V

Abstract:
1. A method for making calibrated microresistivity logging measurements, the method comprising: (a) deploying a microresistivity logging tool in a nonconductive medium, the tool including (i) a current injection electrode configured to inject electrical current into a formation, (ii) a return electrode spaced apart from the current injection electrode, the return electrode providing a return path for the electrical current, and (iii) at least first and second spaced potential electrodes; (b) applying a first alternating current between the current injection electrode and the return electrode; (c) measuring a first AC potential difference between the first and second potential electrodes; (d) redeploying the logging tool in a subterranean borehole including a nonconductive drilling fluid; (e) applying a second alternating current between the current injection electrode and the return electrode; (f) measuring a second AC potential difference between the first and second potential electrodes; (g) causing a processor to subtract a first parameter derived from the first AC potential difference measured in (c) from a second parameter derived from the second AC potential difference measured in (f) to obtain a calibrated impedance; and (h) causing a processor to compute a formation resistivity from the calibrated impedance obtained in (g).