Spine and Ribs Plot
The spine and ribs plot is, for a two detector density tool, the plot of long-spacing versus short-spacing count rates for different formation densities, mud cake densities and mud cake thicknesses. The plot takes its name from the spine, which is the locus of points with no mud cake, and the ribs, which show the effect of mud cake at certain fixed formation densities. The plot illustrates graphically that for a given formation density there is only one rib for all normal mud cake densities and thicknesses. Thus, although there are three unknowns, it is possible to make a correction using two measurements.
