Electrical resistivity measurement of a flowing drilling fluid using eddy currents generated therein
US4536713A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Mar 3, 1983 |
| Grant date | Aug 20, 1985 |
| Priority date | — |
| Expiry date | Mar 3, 2003 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V3/102
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A high permeability ferrite core, which includes a gap between adjacent ends thereof, is combined with a magnetic coil encircling the core, and is located in a sub positioned in the drill string just above the drill bit of a borehole drilling rig. The core is positioned so that the gap thereof lies across a recess region formed in the outer wall of the sub. Drilling fluids flow along the outer surface of the sub on the return path from the drill bit to the mud pits located at the surface of the borehole. A constant current, or voltage, at a frequency within the range of 20 KHz-20 MHz is applied to the terminals of the coil encircling the core and the eddy currents developed in the gap region produce a measurable back emf at the coil terminals. The current produced by this emf voltage is indicative of the resistivity of the drilling fluid within the recess region in the wall of the sub and the fluctuations of the voltage accurately follow the variations in drilling fluid resistivity.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.