THE RIDS: A DENSITY LOGGER FOR ROUGH HOLES

Abstract

The RIDS (acronym for rugosity‐insensitive density system) is a gamma‐gamma system that can operate in very rough boreholes by virtue of special sensors that make contact with the walls of the hole. It has been tested over a density range of 0.6 to [Formula: see text] in the laboratory, and from 1.3 to [Formula: see text] in the field. Error is believed to be less than ±2.5 percent over much of the range. Tight collimation and energy discrimination limit detection to singly Compton‐scattered gamma energy, with the data obeying [Formula: see text], where I is detected intensity, ρ is density, and [Formula: see text] and [Formula: see text] are constants. Output spectra of counts versus energy over the density range appear to confirm this equation. It is shown that substantial errors in density measurements can occur in other logging systems, in particular where the hole is rough enough to cause gaps between the sonde and the wall. For example, such errors can range from 4 to 25 percent in other systems for only a 1‐cm gap between sonde and wall, whereas the RIDS does not permit such a gap. RIDS results agree within a few percent with those of other logging systems where the latter are not perturbed by gaps between sonde and wall, and with core data when available.