Multi-coil electromagnetic focusing methods and apparatus to reduce borehole eccentricity effects
US6541979B2 · kind B2 · utility
Assignee
Inventor
Key dates
| Filing date | Dec 19, 2000 |
| Grant date | Apr 1, 2003 |
| Priority date | — |
| Expiry date | Apr 30, 2021 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V3/28
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
Methods and apparatus are disclosed for canceling or eliminating borehole eccentricity effects on a formation resistivity measurement obtained with transmitter and/or receiver antennas which are substantially time varying magnetic dipoles with their dipole moments aligned at an angle to the axis of the borehole. Various apparatus are configured with a plurality of antennas having tilted or transverse magnetic dipole moments, at least one current sensor, means for conducting alternating current through one or more of the antennas, and means for calculating a scaling factor from signal measurements and for scaling the alternating current with the factor. One method includes scaling an alternating current and passing said current through one or more antennas to obtain the resistivity measurement. Another method includes calculating scaling factors based on spacings between antennas and/or current sensors disposed on an instrument and passing alternating currents scaled by said factors through one or more antennas to obtain the resistivity measurement. Another embodiment includes inputting a borehole fluid resistivity value to derive the formation resistivity.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.