Kerogen Density in the Marcellus Shale

Abstract

Abstract As interest in the Marcellus shale began to increase early regional characteristics of the shale were derived from existing borehole log data supplemented by sparse core and laboratory data. Some of the earliest work on Devonian shales based on gamma and density logs had a goal of predicting the volume of low density high gamma ray organic material (kerogen) as a guide to understanding the deposition of the shales. Subsequently, work focused on not only calculating the density of upper Devonian shales, but applying a correction to the density and neutron logs to correct them for the effect of organic material. Once corrected the logs are suitable for porosity calculation. Analysis of upper Devonian core data for the derivation of kerogen density indicated that there is a relationship between thermal maturity and the density of organic material. Review of key wells from regional work focused on three wells in West Virginia for which a modern log suite is available and geochemical work is present. The three wells have thermal maturity that range fro Ro of 1.5 to 2.68. Log analyses from these wells suggest that the density of the kerogen ranges from 1.53 to 1.79 gr/cc. Current practice in log analysis and core analysis often assumes that kerogen density is fixed near 1.1 gr/cc. Log and core analysis in the Marcellus shale should be completed with the concept that the density of the kerogen is not fixed, but varies as a function of thermal maturity.