Evaluating Porosity and Density Measurement of Organic-Rich Tight Rocks

Abstract Objective/Scope Porosity and density of organic-rich source rocks are fundamental reservoir parameters and have been measured using multiple methods. This study seeks to verify the accuracy and advantages of these methods and to determine optimal technology for characterization of source rock reservoirs. Methods, Procedures, Process In recent years, combination of nuclear magnetic resonance and gas-porosimetry (CNG), which is a noninvasive and much faster method than existing alternatives, has been established as a standard method to evaluate organic-rich tight rocks. 20 plugs from multiple wells of a source rock reservoir were used to test the accuracy of CNG as a comparison to the industry standard GRI method. The plugs were first measured using CNG, then saturated using light oil at 4000 psig for a week to measure porosity and density. GRI measurements were also performed on crushed samples acquired around the plug locations using the core carcass. Results, Observations, Conclusions Porosity and density from three methods are analyzed for convergent validity. The porosities and densities of the 20 samples are very consistent whether using CNG or plug saturation methods. In contrast, significant scattering was observed between these two methods and GRI. By analyzing the sample, experimental procedure, and results, we conclude all the methods are accurate. The observed differences were due to the variations in the samples used for different methods. However, CNG is noninvasive and can be done in hours, in contrast to GRI which is destructive to the sample and takes several weeks to provide needed results. Novel/Additive Information CNG is noninvasive and rapid, holding a significant advantage over industry standard GRI method. This study further establishes CNG as a reliable and optimal method to determine petrophysical parameters of organic-rich source rock reservoirs.