Petrophysical Characterization of Unconventional Reservoir Core At Multiple Scales

Tight unconventional reservoirs have become an increasingly common target for hydrocarbon production. Exploitation of these resources requires a comprehensive reservoir description and characterization program to estimate reserves, identify properties which control production and account for fracturability. Multiscale imaging studies from the whole core to the nanometer scale can aid in understanding the multiple contributions of heterogeneity, natural fracture density, pore types, pore throat connectivity, mineral and organic content to the petrophysical response and production characteristics. In this paper we present three examples of the application of multiscale imaging to challenging unconventional reservoirs; a deep clastic tight gas reservoir, a fractured basement reservoir and coal seam gas reservoir. All of these samples exhibit features at multiple scales which present major challenges to petrophysical evaluation. In all cases heterogeneity and geological rock typing is undertaken at the core scale. FIBSEM imaging can then used to reveal the nanoporous microstructure of the key intervals within the phases of the core material. Petrophysical properties (porosity, permeability, elastic moduli) can also be computed for each key phase and the data upscaled using standard techniques. The presented case histories demonstrate that multiscale imaging and modelling provides a quick complimentary method to characterize the distribution and nature of different pore types and matrix components to characterize the elastic and dynamic rock properties even on rock fragments that are not suitable for conventional core analysis. Moreover the results have the potential to enhance our understanding of petrophysical, fracturing and multiphase flow processes in challenging unconventional reservoirs with low porosities and permeabilities.