Subsurface Explosion Damage Imaging: Linking Electrical Conductivity Differences to Fracture Generation - Laboratory Scale Experiments

Underground explosions create complex fracture networks in the surrounding rock, which controls the transport of gases from the detonation point to the surface. Geophysical imaging technologies can be used to study the creation of these fractures in rock samples as a means of improving our ability to detect gases originating from underground explosions. Due to the inherent challenge in characterizing the subsurface, the nature of gas movement in the subsurface has not been studied as extensively as atmospheric transport. The movement of gases through the first few hundred meters of rock around an explosion could be elucidated by detailed understanding of explosively-created fractures - the so called 'damage zone'. We use electrical resistivity tomography (ERT) to study fracture creation and directly assess rock damage and changes in fluid transport responses. In this presentation, we describe a bench scale experiment to observe fractures in zeolitic tuff created using an exploding bridge wire. We show that fractures manifest in ERT images as changes in bulk electrical conductivity; this is confirmed by comparing ERT images with visual observation and x-ray tomography images. In summary, this simple experiment indicates that ERT has potential to image fractures generated in the subsurface; hence ERT could be used to support field observations and further constrain conceptual and numerical models of fracture generation and subsurface fluid transport.