A dual-spacing formation density log. The compensated formation density logging device employs two detectors spaced at different distances from the source. The detector at the shorter spacing is particularly sensitive to the density of material immediately adjacent to the face of the pad. The contribution of this material, which includes mud cake and drilling mud filling minor borehole wall irregularities, affects the response of each detector to a different degree. The measurements from both detectors provide a means for making a correction for the influence of drilling mud and mud cake on the measurements. This correction is automatically added to the uncompensated density measurement from the detector at the longer spacing. Through the use of appropriate instrumentation, the parameters recorded are: a corrected or compensated value of bulk density, a measure of the correction, Δr, used in making the compensation, and a caliper curve. With the unwanted borehole effects removed, the measurement is recorded directly in terms of bulk density on a linear scale. See also density log, spine-and-ribs plot, and Z/A effect.
