Method and apparatus for obtaining formation density

A method for evaluating a formation density of a subterranean formation, comprising:

• S1:
• deploying a nuclear logging tool into the subterranean formation, wherein the nuclear logging tool comprises one or more neutron generators and two or more dual-function detectors configured to simultaneously detect neutrons and gamma rays;
• S2:
• causing the one or more neutron generators to emit neutrons into the subterranean formation;
• S3:
• detecting neutrons and gamma rays from the subterranean formation at the two or more dual-function detectors to form electric signals, wherein the two or more dual-function detectors comprise a near detector and a far detector;
• S4:
• separating electric signals from neutrons and gamma rays for each of the two or more dual-function detectors;
• S5:
• obtaining detector count rates of total neutrons, fast neutrons and thermal neutrons;
• obtaining neutron fluence rates of fast neutrons and of thermal neutrons;
• S6:
• obtaining detector count rates of inelastic gamma rays and the energy spectrum of inelastic gamma rays;
• and
• S7:
• obtaining a first formation density value based on a ratio of the gamma ray count rate at the far detector and the gamma ray count rate at the near detector.