Digital rock physics for elastic characterization of kerogen

Abstract

High-resolution focused-ion-beam scanning-electron-microscopy (FIB-SEM) is a powerful tool that can be used to image and characterize source rock structure where significant micro- and nanoscale heterogeneity exists. The challenges in multi-physics characterization of unconventionals are quite different from those in conventional rocks. Source rock properties are difficult to measure, understand, and simulate because of their nanoscale heterogeneities, low porosity, and tiny pore-sizes. We focus on elastic characterization of the soft organic component of source rocks, that typically occurs in layers within a stiff, inorganic matrix. Physical measurements on organic matter that occurs within source rocks are extremely difficult to undertake because of the microscopic sample size. Variation in elastic properties of kerogen as a function of intra-kerogen porosity, or pore-fluids, is even more challenging because of the difficulty in measuring those quantities physically at the nanoscale. Digital computations based on 3D microscopic images of kerogen can be used to characterize the elastic properties of porous kerogen, as well as to study their variation with porosity and pore-fluid. We present a digital rock physics workflow to characterize the elastic properties of porous kerogen and follow up by proposing a rock physics model based the digital simulation results and well-known effective medium theories. A digital rock-based workflow was developed, that predicts elastic properties of organic-rich carbonate mud-rocks. We successfully used digital simulations to predict the elastic moduli of porous organic matter (kerogen) from 10 nanometer resolution FIB-SEM images. This is a unique capability, as it is very difficult to measure the porosity and elastic properties of kerogen in the physical lab because of its sub-micron sample size.