Absolute Elemental Concentrations Estimated from Geochemical Well Logging Using Neutron-Induced Gamma-Ray Spectrometry and a Geological Model

James A. Grau, Michael M. Herron

Elemental concentrations of several inorganic elements were determined on a continuous basis with depth using the Schlumberger gamma-ray spectrometry (GST) log in a Santa Fe Energy Co. well in the Kern Front field, Bakersfield, California. Relative gamma-ray yields of Si, Ca, Fe, S, Cl, H, Ti, Gd + Sm, and K were determined using a weighted least-squares fitting of standard elemental spectra, determined from laboratory measurements, to the measured spectra. The relative yields were then placed on an absolute basis using measured sensitivity coefficients and the assumption that, excluding Cl and H, the abundances of these elements plus Al, considered as oxides and, for Ca, carbonates, total 100% of the rock. This assumption removes variations in porosity and salinity from mpacting the denormalization procedure. The output is estimated absolute concentrations in weight percent of the rock that are compared with elemental analyses made on over 60 core plug and sidewall samples by x-ray fluorescence and neutron activation analysis.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.