Correlative XRM and FIB-SEM for (Non)Organic Pore Network Modeling in Woodford Shale Rock Matrix

Abstract

Typical shales are characterized by their small pores and their very low porosity and permeability, hence making these rocks challenging in obtaining economically viable gas and/or oil. A considerable amount of effort has gone into measuring and characterizing the pore volume both within organic matter and mineral shale rock matrix, and investigating which pores really contribute to these petroleum systems. Therefore, quantifying the amount, size distribution and connectivity of pores within shale reservoirs is at the heart of both production and storage issues. A new holistic approach for characterization of nanoscopic scale structural heterogeneity in shale, presented here, couples micro and nano X-ray microscopy (micro- and nano-XRM) with focused ion beam scanning electron microscopy (FIB-SEM). This integrated approach provides a unique opportunity to characterize in great detail the complex three-dimensional (3D) microstructure of shale over multiple length scales, from the centimeter length scale to the single nanometers. To explore the practical significance and reach of this newly developed analytical framework, a shale specimen from the Woodford formation was imaged several times with non-destructive XRM at successively higher resolutions, and then finally imaged with the ultra-high-resolution by destructive FIB-SEM serial sectioning. Further to the imaging, the organic- and nonorganic-matter-related pore networks within Woodford Shale matrix were extracted using the FIB-SEM images, in order to quantify the evolution of porosity associated with both organic and nonorganic matter. The findings indicated that the organic-matter-related pore network strongly dominates over the nonorganic-matter-related pore network within the investigated specimen, suggesting a strong relationship between porosity and organic content.