Identification of cement in subterranean borehole regions using a ratio of capture to inelastic gamma rays

A method for detecting cement placed in a subterranean borehole region comprising:

• obtaining a pre-procedure data set by:
• emitting neutron pulses from a first neutron source into a borehole and a subterranean formation, and
• detecting in the borehole inelastic gamma rays and capture gamma rays;
• obtaining a first capture gamma ray count rate and a first inelastic gamma ray count rate ratio from the pre-procedure data set;
• mixing cement material with a thermal neutron absorbing material to provide a cement slurry.
• placing the cement slurry in the subterranean borehole region to generate a cemented wellbore;
• obtaining a post-procedure data set by:
• emitting pulses of neutrons from the first neutron source or a second neutron source into the cemented borehole;
• detecting in the cemented borehole inelastic gamma rays and capture gamma rays;
• obtaining a second capture gamma ray count rate and a second inelastic gamma ray count rate ratio from the post-procedure data set;
• and
• detecting cement by combining the first capture gamma ray count rate, the first inelastic gamma ray count rate, the second capture gamma ray count rate, and the second inelastic gamma ray count rate;
• wherein a change observed between the first and second inelastic gamma ray count rates is used to make a correction to the detection of the cement caused by changes in the neutron output of the first and/or second neutron sources by calculating a difference between the first capture gamma ray to inelastic gamma ray count ratio and the second capture gamma ray to inelastic gamma ray count ratio.