The LDT reveals important formation characteristics. The LDT provides measurements of the bulk density and photoelectric effect (Pe) of the formation.
The Pe measurement is related to formation lithology, while the bulk density is related to formation density. The LDT measures porosity and lithology and in combination with other tools will also detect gas. A caliper log is also recorded. The tool is fully adjusted for mudcake build-up, the LDT displays the entire energy spectrum at the surface.
The LDT tool has a pad section that contains a radioactive 2 Ci (74 Gbq) Cesium 137 gamma source and two scintillation detectors. The pad is pressed against the formation wall by the caliper while focused high-energy gamma rays are emitted from the source. Some of the gamma rays are absorbed by the formation. The LDT tool monitors the energy levels of the gamma rays that return to the detectors and records this energy spectrum. By examining the position of the gamma ray energy in the spectrum, both the bulk density and the formation lithology can be determined. The two-detector arrangement of the LDT compensates for mud cake effects.