Methods and apparatus for environmental correction of thermal neutron logs
US4445033A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 14, 1981 |
| Grant date | Apr 24, 1984 |
| Priority date | — |
| Expiry date | Sep 14, 2001 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V5/108
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
An on-line environmentally-corrected measurement of the thermal neutron decay time (.tau.) of an earth formation traversed by a borehole is provided in a two-detector, pulsed neutron logging tool, by measuring .tau. at each detector and combining the two .tau. measurements in accordance with a previously established empirical relationship of the general form: EQU .tau.=.tau..sub.F +A(.tau..sub.F +.tau..sub.N B)+C, where .tau..sub.F and .tau..sub.N are the .tau. measurements at the far-spaced and near-spaced detectors, respectively, A is a correction coefficient for borehole capture cross section effects, B is a correction coefficient for neutron diffusion effects, and C is a constant related to parameters of the logging tool. Preferred numerical value of A, B and C are disclosed, and a relationship for more accurately approximating the A term to specific borehole conditions.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.