Fracture capture of organic pores in shales

Shales are heterogeneous media with porosity at many scales and in many microtextural positions, including within organic matter and clay aggregates. Because these materials have contrasting mechanical properties, it remains unclear how induced fractures manage to connect with this porosity whether during hydrocarbon production, wastewater injection, or carbon-capture-and-storage efforts. To explore porosity changes related to fracturing, we experimentally failed shale samples in a triaxial load apparatus and observed changes in microstructure through scanning electron microscopy, low-pressure nitrogen sorption, and nuclear magnetic resonance. We observed a system of microcracks, many of which were likely experimentally induced and localized on grain boundaries. In some cases these fractures propagated into regions of natural porosity in organic matter. In the subsurface this fracture capture likely enhances pore connectivity, but only selectively depending upon mechanical conditions. Fracture capture is one possible mechanism by which multiscale compositional heterogeneity in shales may affect rheological heterogeneity.