Method for investigating the composition of an earth formation traversed by a borehole
US4587424A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Aug 22, 1983 |
| Grant date | May 6, 1986 |
| Priority date | — |
| Expiry date | Aug 22, 2003 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V5/101
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
In the illustrative embodiments of the invention disclosed, a more accurate elemental analysis of an earth formation surrounding a borehole is achieved by comparing a gamma ray energy spectrum measured in the borehole, following irradiation of the borehole and the surrounding earth formation with high-energy neutrons, with a composite spectrum made up of a combination of weighted standard spectra of elements postulated to have contributed significantly to the borehole spectrum, wherein the standard spectra include a tool background spectrum that accounts for the spectral contribution due to neutron interactions with the tool constituents. The tool background spectrum is derived by isolating the tool contribution to one or more of the elemental standard spectra, and by using one or a combination of such isolated tool contribution spectra as the tool background spectrum. In the case of thermal neutron capture gamma ray spectra, the tool background spectrum is also preferably stripped from certain of the raw elemental standard spectra to arrive at the final elemental standard spectra for inclusion in the composite spectrum compared with the borehole spectrum. In addition to an improve…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.