Clay and Framework Mineralogy, Cation Exchange Capacity, Matrix Density, and Porosity from Geochemical Well Logging in Kern County, California

Michael M. Herron, James A. Grau

Elemental concentrations of several inorganic elements were determined on a continuous basis with depth using the Schlumberger gamma-ray spectrometry (GST) and natural gamma-ray spectrometry (NGS) logs in a Santa Fe Energy Company well in the Kern Front field in Bakersfield, California. Logs of Al, Si, Ca, K, Fe, Ti, and non-pore H were processed by a matrix multiplication procedure, used previously for a Venezuelan well, into estimated abundances of quartz, feldspar, calcite, ilmenite, and the clay minerals kaolinite, illite, and smectite. A total of 64 core-plug samples were analyzed for elemental content by x-ray fluorescence and neutron activation analysis and for mineralogy by bulk and < 4 µm clay x-ray diffraction analyses. Log-derived elemental concentratio s and mineral abundances show good agreement with the core values. Cation exchange capacity (CEC) is estimated from the abundances of the clay minerals and typical values for these clays. The CEC log agrees well with CEC values determined on the core samples. The mineral abundance logs also permit an estimation of the average matrix density as a function of depth, derived from typical grain densities for each mineral phase. This matrix density log, combined with the bulk density log, yields a porosity log that compares well with over 200 measurements on core.

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