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Abstract
Public concern about anthropogenic seismicity in Italy first arose in the aftermath of the deadly M ≈ 6 earthquakes that hit the Emilia-Romagna region (northern Italy) in May 2012. As these events occurred in a (tectonically active) region of oil and gas production and storage, the question was raised, whether stress perturbations due to underground industrial activities could have induced or triggered the shocks. Following expert recommendations, in 2014, the Italian Oil & Gas Safety Authority (DGS-UNMIG, Ministry of Economic Development) published guidelines (ILG - Indirizzi e linee guida per il monitoraggio della sismicità, delle deformazioni del suolo e delle pressioni di poro nell’ambito delle attività antropiche), describing regulations regarding hydrocarbon extraction, waste-water injection and gas storage that could also be adapted to other technologies, such as dams, geothermal systems, CO2 storage, and mining. The ILG describe the framework for the different actors involved in monitoring activities, their relationship and responsibilities, the procedure to be followed in case of variations of monitored parameters, the need for in-depth scientific analyses, the definition of different alert levels, their meaning and the parameters to be used to activate such alerts. Four alert levels are defined, the transition among which follows a decision to be taken jointly by relevant authorities and industrial operator on the basis of evaluation of several monitored parameters (micro-seismicity, ground deformation, pore pressure) carried on by a scientific-technical agency. Only in the case of liquid reinjection, the alert levels are automatically activated on the basis of exceedance of thresholds for earthquake magnitude and ground shaking – in what is generally known as a Traffic Light System (TLS). Istituto Nazionale di Geofisica e Vulcanologia has been charged by the Italian oil and gas safety authority (DGS-UNMIG) to apply the ILG in three test cases (two oil extraction and one gas storage plants). The ILG indeed represent a very important and positive innovation, as they constitute official guidelines to coherently regulate monitoring activity on a national scale. While pilot studies are still mostly under way, we may point out merits of the whole framework, and a few possible critical issues, requiring special care in the implementation. Attention areas of adjacent reservoirs, possibly licenced to different operators, may overlap, hence making the point for joint monitoring, also in view of the possible interaction between stress changes related to the different reservoirs. The prescribed initial blank-level monitoring stage, aimed at assessing background seismicity, may lose significance in case of nearby active production. Magnitude – a critical parameter used to define a possible step-up in activation levels – has inherent uncertainty and can be evaluated using different scales. A final comment considers the fact that relevance of TLS, most frequently used in hydraulic fracturing operations, may not be high in case of triggered tectonic events.
Highlights
Since the inception of the use of hydraulic fracturing for shale gas production, human-induced seismicity has become a subject of increasing interest, especially in the USA and Canada (e.g. Davis and Frohlich 1993; McGarr et al 2002; Ellsworth 2013)
A review of human-induced earthquakes on a global scale was given by Foulger et al (2017); Grigoli et al (2017) published a European perspective about challenges in monitoring, discrimination, and management of induced seismicity related to underground industrial activities, while Braun et al (2018b) gave an overview about the state of the art of anthropogenic seismicity in Italy
Italian geology is not suitable for shale gas exploitation; concerns about anthropogenic seismicity in Italy came up after the deadly MW = 6.2 Emilia-Romagna earthquake in May 2012 (Scognamiglio et al 2012; Cesca et al 2013a). Since this seismic sequence occurred in the vicinity of gas and oil production sites, the question surfaced, whether variations in crustal stress accompanying hydrocarbon extraction might have influenced the generation of these earthquakes
Summary
Since the inception of the use of hydraulic fracturing for shale gas production, human-induced seismicity has become a subject of increasing interest, especially in the USA and Canada (e.g. Davis and Frohlich 1993; McGarr et al 2002; Ellsworth 2013). The Italian Oil & Gas Safety Authority (DGS-UNMIG, a Directorate General of the Ministry of Economic Development) charged a group of experts to define guidelines following recommendations from the ICHESE (2014) report, for monitoring seismicity, ground deformation and pore pressure The result of this effort (Indirizzi e linee guida per il monitoraggio della sismicità, delle deformazioni del suolo e delle pressioni di poro nell’ambito delle attività antropiche, ILG, Dialuce et al 2014) represent the first effort towards systematic, well structured, public regulations regarding independent geophysical monitoring of underground anthropic activities in oil/gas operations (extraction, waste-water re-injection, storage) that could be adapted to other technologies, such as dams, geothermal systems, CO2 storage, and mining.
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