1. n. [Formation Evaluation]

A type of logging while drilling density log in which the density is measured at different azimuths around the drill collar. The density measurement is focused so that when the collar rotates, the measurement sees different azimuths around the borehole. An average density can be calculated by summing all the azimuthal data. Alternatively, the data can be summed over different segments, for example in four quadrants, to give an azimuthal density in four directions. When the hole is overgauge, certain quadrants will be firmly pressed against the borehole wall, while others may have a significant standoff and too high a delta rho. The good quadrants can then be chosen for formation evaluation.

See related terms: azimuthal resolution,  compensated density log,  density measurement,  quadrant density,  spine and ribs plot