INITIATING A FIELD DEMONSTRATION OF THE DEVELOPMENT OF A BIOLOGICAL BARRIER IN A FRACTURED SHALE

摘要

To demonstrate the concept of the biological barrier at field scale, a fracture plane was isolated in shale (25 m × 25 m, average fracture aperture 165 μm) and 29 boreholes were equipped to monitor the fracture bioclogging. As a biostimulation approach, molasses and a source of nitrate are supplied under a forced-gradient flow on a 4-week cycle. This includes one week of starvation, which is used for tracer experiments. Background data revealed a relatively high groundwater salinity and a planktonic bacterial density of 5 log . mL-1, which decreased to 4 log . mL-1 during the spring. Tracer experiments were conducted in pre-clogging conditions to confirm the absence of a hydraulic connection between the control/source borehole and the monitoring boreholes, via point dilution tests under natural gradient. After establishing the flow regime for the biobarrier development, tracer tests were conducted to determine initial groundwater velocities, which averaged 58.4 m . D-1 between the injection borehole and the withdrawal borehole. Winterization of the equipment was required before starting the biostimulation; an ongoing nutrients supply for the biobarrier development, which is monitored both in situ and via monthly groundwater sampling.