Four-detector formation-density tool for use in cased and open holes

摘要

An improved formation density logging tool is provided that is effective in cased holes. The improved tool utilizes four detectors which generate four signals enabling the operator to calculate the four unknown variables of interest: formation density, cement thickness, cement density and casing thickness. By providing a means for calculating cement thickness, cement density and casing thickness, a more accurate calculation of formation density is provided. Further, by providing a means for calculating cement thickness, cement density and casing thickness, a more accurate neutron-porosity measurement can be made when the density tool is used in combination with a neutron tool. The tool comprises improvement over currently-available two-detector density tools which are normally useful only in open holes. It is anticipated that the tool provided herein will be useful in both open and cased holes; it is also anticipated that the casing thickness and cement thickness calculations of the tool will be used to enhance the porosity calculation of neutron-porosity tools.