Method and apparatus for measuring formation density and the formation photo-electric factor with a multi-detector gamma-gamma tool
US5841135A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 19, 1997 |
| Grant date | Nov 24, 1998 |
| Priority date | — |
| Expiry date | Feb 19, 2017 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V5/125
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
The present invention is an improved method and tool for determining formation density by using an array of gamma-ray detectors. This invention can correct for large standoffs encountered in abnormally shaped boreholes and in particular for the increased standoffs typically encountered by mandrel tools. In this invention, the collimated detectors have varying depths of investigation into the formation. At small standoffs a short spaced (SS) detector investigates mainly the mud and mudcake and a shallow layer of the formation. Unlike the SS, a mid spaced (MS) detector has a deeper depth of investigation and is sensitive to borehole and formation even at increased standoffs. A long spaced (LS) detector is mainly sensitive to the formation density and its density reading is corrected by using the standoff information from the MS and SS detectors. In addition to measuring density, this invention can measure the photo-electric factor (PEF) of the formation. Because photo-electric absorption preferentially removes low energy gamma-rays, the tool housing needs to allow passage of low energy gamma-rays. This can be accomplished through the use of a window of a material with a low atomic nu…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.