The Statistical Fingerprint of Fluid-Injection Operations on Microseismic Activity at the Val d’Agri Oil Field (Southern Italy)

Abstract

In this paper, we examined the dynamical properties of the fluid-injection microseismicity at the Val d’Agri oil field (southern Italy) by applying different statistical methods to find correlations and common periodicities with injection parameters, such as injected volumes and injection pressure. Two periods of observation were analyzed: (1) from 2006 to 2015 (the first 10 years after the beginning of injection operations), the seismicity was recorded by the seismic network of the ENI company that manages the exploitation of the oilfield; (2) from 2016 to 2018, the seismicity was recorded by a denser seismic network capable of significantly reducing the completeness magnitude. If a significant correlation between seismicity and fluid-injection variables was found in the first period, in the second period, the seismic activity and injection variables were characterized by common periodicities after the reservoir acidification and for injection rates above 1900 m3/day. Finally, we applied and compared two different approaches proposed in the literature to forecast the maximum expected magnitude. The results showed that one of the approaches yielded an estimated maximum magnitude of Mmax = 1.7 ± 0.4, which is consistent with the maximum observed magnitude.

Keywords

• fluid injection
• induced seismicity
• statistical analysis
• microseismicity
• seismicity rate
• expected maximum magnitude