Delayed Induced Seismicity in Geological Gas Storage (spain)

Induced seismicity is widely related to injection/withdrawal of underground fluids. The mechanics of these earthquakes are related to changes in the pore pressure, changes of the stress tensor configuration and lubrication of fault planes. Here we have related the injection of natural gas in Yela (Centre of Spain) with the occurrence of earthquakes in a seasonal behaviour since 2012, and showing a delayed triggering between 2 and 3 months. Lateral fluid migration could be related although from the last three years the frequency and magnitude of earthquakes have decreased. The maximum induced earthquake was M = 2.3. A preliminary analysis of cross-correlation between the volume of the injected gas and the seismic energy 20 km around Yela shows a lag of 3 months between the injection and the earthquake occurrence. This time lag could be related to the lateral fluid migration during the injection and the permeability constraints of the reservoir rock host. However, it is worthy to say that the induced seismicity shows lesser maximum magnitude (Mimax) in comparison with the recorded natural seismicity Mnat(max); Mind(max) = 2.3 (1.8 * 108 J) and Mnat(max) = 4.1 (8.9 * 1010 J), respectively. Moreover, the seasonal seismic peaks after the injection manoeuvres decreased from 2019 to present, which suggests that the accommodation of the porous rock pressure is close to an aseismic mode.