Experimental and modeling study of fluid pressure‐driven fractures in Darley Dale sandstone

We report measurements of acoustic emissions (AE) generated during formation and growth of pressure driven fractures in cylindrical samples of Darley Dale sandstone that were co‐axially pre‐drilled in order to allow an internal pressure to be applied. A set of 3 to 6 fractures initiate at the wall of the internal bore at a fluid pressure around three times that of the confining pressure, but only 3 propagate to the outer wall of the sample. Time and spatial distributions of acoustic emissions show two distinct bursts of activity, associated with initiation and propagation, respectively. A Particle Flow Code (PFC) model has been used to reproduce the mechanics of fracture initiation and the time and spatial distributions of AE. In both the experiments and the model, we observe a distinct phase of accelerating AE activity preceding fracture formation.