Pulsed neutron logging method using cumulative count curves
US4712007A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Apr 1, 1985 |
| Grant date | Dec 8, 1987 |
| Priority date | — |
| Expiry date | Apr 1, 2005 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V5/105
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A method of measuring earth formation characteristics using a pulsed neutron source computes the characteristics by using a cumulative count curve. A pulsed neutron source and detector are pulled upwardly through a borehole. The pulsed neutron source repetitively irradiates the earth formations with pulses of fast neutrons from the neutron source, creating thermal neutrons due to collisions in the formations. Detectors in the downhole instrument detect gamma rays emanating from the irradiated formations as a result of the capture of thermal neutrons. The gamma rays are cumulatively counted in a plurality of separate time bins between each of neutron pulses. The cumulative counts define points on a cumulative count versus time curve which has a mathematical expression. Count data is transmitted to a surface panel, which uses iterative least squares fit techniques to calculate the formation lifetime decay constant. The processor changes the pulse firing rate every two inch depth increment based on the new formation lifetime constant calculated.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.