Simultaneous thermal neutron lifetime and boron content well log
US4002904A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 20, 1974 |
| Grant date | Jan 11, 1977 |
| Priority date | — |
| Expiry date | Dec 20, 1994 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V5/108
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A system for logging earth formations traversed by a borehole wherein a high energy pulsed neutron source (14 MeV) repetitively irradiates earth formations. Two time gates operated after each neutron pulse are provided for detecting count rates from which the decay time and the macroscopic capture cross-section .SIGMA. can be determined. Background gate means are also provided to eliminate the effects of background and detector radiation. In the detection system, output pulses whose voltage level is proportional to the energy detected are produced. A cut-off voltage level is set at approximately 0.8 MeV, which is above the energy of gamma rays produced following neutron capture by the element Boron and below the energy of most gamma rays produced following capture by all other significant formation elements. By comparison of the count rates (obtained by summing these voltage pulses) in a Boron containing formation with macroscopic capture cross-section .SIGMA. to the count rate in an unborated formation having the same .SIGMA. value, the concentration of boron can be determined and plotted as a function of depth.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.