Porosity from Neutron Logs II: Interpretation

摘要

This second tutorial on neutron porosity logging is part of an ongoing series on the general topic of porosity being published in Petrophysics. Part 1 dealt with the physics of the measurement and introduced a generic thermal neutron tool whose response was studied in detail with a Monte Carlo model. Its empirical response to porosity was shown to be related to a macroscopic parameter of the formation - the slowing-down length. In this section the three major tool perturbations lithology, shale, and gas-are examined and explained. Some typical log formats are shown, and the use of the neutron/density crossplot is illustrated. The paper concludes with a short discussion of the LWD tool and its depth of investigation.