Method and apparatus for epithermal neutron porosity well logging
US5051581A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 1, 1990 |
| Grant date | Sep 24, 1991 |
| Priority date | — |
| Expiry date | May 1, 2010 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V5/108
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
The porosities of subsurface earth formations surrounding a borehole are investigated using a logging tool run in the wellbore by repeatedly irradiating the formations with discrete bursts of high energy neutrons, measuring the populations of epithermal neutrons at near and far locations from the neutron source, and also measuring the rate of decay of the epithermal neutron population at a third location following each neutron burst and deriving therefrom a measurement of the epithermal neutron slowing down time. Formation porosity values derived from the near-and-far location population measurements are corrected for detector standoff effects by use, in accordance with a predetermined empirical relationship, of the epithermal slow down time measurement. Alternatively, formation porosities may be derived both from the near-and-far location measurements and from the epithermal slowing down time measurement, and the two differently-derived porosity values may be used independently to provide enhanced information of formation porosity or they may be compared to derive a standoff-corrected porosity value.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.