Method and apparatus for measuring strata resistivity adjacent a borehole
US5089779A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Sep 10, 1990 |
| Grant date | Feb 18, 1992 |
| Priority date | — |
| Expiry date | Sep 10, 2010 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V3/28
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
The method and apparatus relies on a modified induction approach and preferably is incorporated into a metal drill collar for MWD measurements. Directional nulls are created in a primary changing magnetic field formed in a formation by a transmitting antenna which is in a groove on the surface of the drilling collar. Detecting antennas are placed at the directional nulls to enable the primary magnetic field to be decoupled from the same and allow it to be distinguished from the secondary field caused by the current induced in the formation by such primary field. The drill collar also carries a plurality of current detectors which detect the value of current induced in the formation to provide a resistivity profile immediately adjacent the borehole. A preferred embodiment uses a hybrid modified induction and electrical approach.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.