The Influence of CEC, Salinity, and Silt Content on the Stress Dependent Petrophysical Properties of Resedimented Mudrocks

摘要

Mudrocks are fine grained low permeability sedimentary rocks. Due to this low permeability, they are difficult to characterize in terms of physical properties. The use of the reconsolidation technique allows us to determine mudrock properties while controlling mineralogy, brine salinity, and stress. Cation exchange capacity (CEC) makes these rocks water sensitive to double layer effects. Three properties were varied for this study: the cation exchange capacity, salinity, and silt content. To characterize the CEC we have performed conductometric titration and methylene blue colorimetry measurements. Our results are consistent with an external laboratory measured CEC using the cobalt hexamine technique. The methylene blue technique CEC measurements were -25% higher for two of the three samples. The titratated CEC also correlates well with permeability and grain size. Salinity was observed to have a minimal effect on mudrock porosity. Double layer effects play a dominant role in determining permeability, based on the measured salinity effects as a function of CEC. Grain size however also has an influence. .The effect of increasing silt content was to increase both porosity and permeability.