Measuring Fluid Flow and Tracking Bio-Mediated Precipitation in Propped Shale Fractures

Hydraulic fracturing has enabled the extraction of oil and gas from ultra-low permeability shale formations by creating propped fractures that serve as primary fluid flow conduits. While numerical models have advanced understanding of fluid flow through these fractures, experimental analyses remain limited. In this study, pulsed field gradient nuclear magnetic resonance (PFG NMR) velocimetry was used to characterize fluid transport through propped shale fractures and evaluate flow behavior before and after biologically driven mineral precipitation. Phase-shift velocimetry was used to generate high-resolution 2D velocity maps, which were validated with propagator measurements. Results demonstrated strong velocity heterogeneity, flow channeling, and fracture roughness effects. Following microbially induced calcium carbonate precipitation, velocity maps revealed more tortuous and disrupted flow paths, while bulk propagators failed to resolve the full velocity distribution. This study highlights the potential of PFG NMR as a unique, noninvasive experimental tool for investigating complex, reactive flow in rock fractures. Article Highlights Noninvasive nuclear magnetic resonance velocimetry can measure fluid flow in shale fractures. Proppant and biomineral precipitation increase channeling and flow heterogeneity. This method enables study of complex flow in subsurface energy systems.