Numerical modeling of gas transport in shales to estimate rock and fluid properties based on multiscale digital rocks

Characterization of rock properties in shale gas reservoirs is vitally important for production forecasting and reserve estimation of natural gas in an efficiently and economically viable fashion. Because of nano-scale pore spaces in organic-rich shale formations, the mechanisms of gas transport in shales are far more complex than those in conventional reservoirs such as sandstone formations. Numerical characterization of shale permeability on multiscale digital rocks has become a powerful tool that greatly complements to lab measurements by combing advanced imaging techniques with numerical simulations. One of the key challenges in unconventional reservoir simulation is how to preserve fine-scale information in coarse-scale reservoir simulation for reliable production forecasting and reserve estimation. Accurate prediction of shale permeability using numerical tools requires well understanding of transport mechanisms at the nano-scale, as well as the upscaling from nano-scale to larger scale simulations. In this work, we present the coupling of MD with LBM on multiple-scale digital rocks, and we develop an upscaling workflow that integrates simulations at nanometer-scale, micrometer-scale, and centimeter-scale. The present approach allows calculating macro scale transport properties with minimum amount of loss of critical nano/micro-scale information. (C) 2019 The Authors. Published by Elsevier Ltd.