Experimental study of the influence of geochemical features on the viscoelasticity of organic matter in shale

Abstract

Understanding time-dependent mechanical properties is critical to perform geomechanical risk quantification and reduce the environmental impact of fracking operations. In this study, vitrinite reflectance test, scanning electron microscope (SEM)/helium ion microscope (HIM) observation, atomic force microscopy (AFM)-based nanoscale dynamic mechanical analysis (AFM-nDMA), and micro-Raman analysis were combined as a chemo-mechanical method to investigate the role of thermal maturation in affecting nanoscale viscoelasticity of organic matter with maceral classification. The results of 208 tested areas demonstrated that viscosity is negatively correlated with thermal maturity, while storage modulus is positively correlated with maturity, suggesting that such polymer-like to mineral-like process might be prone to fracture initiation. Moreover, chemical structure changes during the thermal evolution exhibited by micro-Raman analysis were found to contribute to the abovementioned mechanical variations. Characterization of viscoelasticity of organic matter considering geochemical features is a highly promising aspect for inclusion in petrophysical workflows, leading to improved design of hydraulic fracturing and homogenization modeling.