Source Localization of Microseismic Emissions During Pneumatic Fracturing.

Localization of signals is a widely applied technique used in different areas of science telecommunication, medicine, or seismology. In this work, we study microseismic emissions due to stick‐slip events during pneumatic fracture in a transparent setup at laboratory scale and apply a localization method "Estimated Source Energy Homogeneity." The seismic location results are compared with the image correlation results for displacement maps corresponding to the event times. We have observed (using optics and acoustics) that the movement starts inside the porous medium and progresses toward the channel tips, eventually causing channels to grow further. This finding could be of interest in understanding fluid‐induced earthquake nucleation processes. Similar to in‐site applications of pneumatic or fluid‐related fracturing, it shows that the area influenced extends beyond the fracture tips. This also shows why even after the end of pumping, we may get earthquakes, such as in the Basel case (Haring et al., 2008, https://doi.org/10.1016/j.geothermics.2008.06.002). Plain Language Summary: An uncompacted granular medium having a fixed grain size is placed between two glass plates as a very thin layer. Using air injection, this porous medium is compacted and fractured. This system is monitored using a camera capable of recording more than 100 images per second and accelerometers which can record vibrations in high frequencies. During this injection, earthquake‐like vibrations are generated by the system. Sources of these vibrations are located using acoustic recordings and image processing. We have observed that the channeling starts with a compaction inside the medium; this compaction propagates toward the channel tips and cause them to advance further inside the medium. Key Points: Pneumatic fracturing experiments in a Hele‐Shaw cell are monitored using accelerometers and a high‐speed cameraAcoustic emissions are localized using an energy‐based signal location method, and displacement maps are obtained from image correlationBy comparing the acoustic and the optical results, we observe that motion starts within porous medium and propagates toward the channel tips [ABSTRACT FROM AUTHOR]