A plot used in the computation of the compensation to be added to the measured value of [[bulk density]] from the dual-spacing formation density log; i.e. [[compensated formation density log]]. The spine-and-ribs plot is a crossplot of the long-spacing [[detector]] counting rate versus the short-spacing detector counting rate. For small thicknesses of [[mud cake]] and other borehole irregularities of small dimension, the slope of the line, passing through the value for correct bulk density and the measured values of density (from each detector), is virtually the same for the usual [[density|densities]] and thicknesses of intervening materials separating the detectors and the [[formation]] wall. The importance of this finding with dual-spacing density measuring systems is that it provides a means for estimating the amount of correction to be added to or subtracted from the measured response from the long-spacing detector. Both the [[compensated density log|compensated density]] measurement and the amount of compensation, Δr, are then recorded on the [[log]]. See [[compensated formation density log]].

{{ :terms:glsp90f2.gif }}