Borehole logging provides critical information about the earth’s subsurface that guides the work of drillers, miners, engineers, and geoscientists. This short post focuses on the compensated density probe, how it works, and some of the applications for which it is suited.
How it Works
The compensated density probe measurement is accomplished using a radioactive source and two radiation detectors. The detectors are designed for use with a Cs137 source, which emits 662 keV gamma particles. The detectors are designed to respond to gamma particles having energies of 200 keV or higher, which is referred to as the Compton energy band. Radiation detectors are made up of a CsI(Th) scintillation crystal coupled with a photomultiplier tube. The detectors are shielded so that they only respond to gamma radiation from the same side of the tool that source energy radiates from.
Radiation emanating from the source travels into the formation on the side of the borehole opposite the caliper arm and is sensed by the two detectors. Compton scattering results from gamma radiation interacting with the electrons in the formation, so total electron density is measured rather than bulk density. The detector response is a function of density and the detector offset from the source.
Coal Seam where Density is an Important Measurement
Typical Applications
- Quantitative In-situ Density
- Petrophysical Properties
- Coal Quality and Delineation
- Density Porosity
- Caliper Borehole Volume
For more information, please go to the QL40-DEN Compensated Dual Density – Caliper product page.
