From Digital Outcrops to Digital Rocks - Multiscale Characterization of Structural Heterogeniety Within Porous Sandstones

Large scale faults are important structural elements within many conventional clastic reservoirs, acting as potential conduits, baffles or barriers to hydrocarbon or CO2 migration. Though inconspicuous within most seismic tomography datasets, smaller subsidiary faults, commonly within the damage zones of parent structures, may also play an important role. Within high porosity sandstones these smaller faults typically form through cataclasis (grain reorganisation, dilation, isovolumetric strain, grain fracturing and crushing), creating thin, tabular low permeability zones which serve to compartmentalize the reservoir.

Though microfaults within high porosity sandstones are commonly assumed to adversely impact upon hydrocarbon production and CO2 injection, little is known about their volumetric properties at the continuum scale (esp. volumetric intensity), or the pore-scale processes which govern their capacity to trap mobile geofluids. In this paper, we seek to address these uncertainties, using a novel outcrop constrained discrete fracture network modelling code to obtain estimates of fault volumetric intensity, and employing high pressure-temperature synchrotron tomography to resolve pore-scale multiphase flow across a single cataclastic fault. The coupled studies indicate that whilst fault rocks may form a major fraction of a given rock mass, the presence of intra-fault capillary heterogeneity may significantly reduce their capacity to restrict the migration of geofluids.