Effects of Kerogen Content on Elastic Properties-Based on Artificial Organic-Rich Shale (AORS)

Quantitative rock physical approaches are becoming increasingly important for both geophysical exploration and geological interpretation. One limiting factor is that experimental measurements in natural rock tend to be restricted by the availability of natural materials particularly if they are obtained from core holes. Artificial physical models that allow for control of composition and structure provide opportunities to carry out many more experiments on a range of samples with different characteristics. In this study, a hot-pressing technique that includes temperature and pressure control is developed to construct artificial organic-rich shales (AORS). The compositions of the AORS were developed from known natural samples and include mixtures of relevant minerals and appropriate organic matter considering grain sizes and shapes. The microstructures of the samples as observed in the scanning electron microscope and the petrophysical properties (density, porosity, permeability, and pressure sensitivity) are similar to those observed in the natural shales and support use of these samples as shale analogs. A total of 10 AORS samples with kerogen contents (KC) ranging from 1.71% to 14.8% was constructed to evaluate the effects of KC on elastic properties. A cross-plot of the V-P/V-SH ratio versus the acoustic impedance indicates patterns that may be useful in remotely assessing KC content. Similarly, cross-plots using the Lame parameters of lambda rho versus mu rho at various confining pressure may also be an effective tool in predicting KC. The linear correlations between the sum of weight percentage of KC and porosity and acoustic impedance tend to be strengthened during the pressurized procedure.