Regional Seismotectonic Zonation of Hydrocarbon Fields in Active Thrust Belts: A Case Study from Italy

Abstract

AbstractThe study of seismic activity triggered by transient stress changes associated with hydrocarbon reservoir exploitation and deep fluid injection is especially important, in a seismic risk perspective, in regions, where relevant natural seismicity is coupled with widespread and regionally distributed petroleum fields. Hydrocarbon occurrences in Italy derive from a variety of petroleum systems characterized by source/reservoirs distributed in age from Mesozoic to Quaternary. Several of them are located along and in the proximity of the Apennine Outer Thrust System which started to develop in Late Pliocene times and is still active, as well as seismogenic, along most of its extent (especially northern-central Italy and Sicily). Other occurrences are sited along the front of the more internal Pede-Apennine compressional belt, which was mainly active in Early Pliocene times. Still, a large percentage of hydrocarbon fields are observable within the Adriatic-Pelagian foreland, whereas a small number of fields, highly relevant in terms of oil and/or gas extraction, are sited within the intermountain Apennine active extensional domain. In this paper, after grouping the Italian oil and gas fields in stratigraphically and kinematically homogenous Hydrocarbon Field Assemblages (HFAs), we build a regional seismotectonic zonation of the HFAs, taking into account their surface and depth location with respect to the 3D boundary of regional seismogenic provinces. The provinces differ in kinematics (extensional, compressional, strike-slip) and in characterizing seismogenic thickness and depth, which may coincide or not with the depth range of the hydrocarbon recovery, as well as with the depth of fluid withdrawal and injection activities. The HFAs zonation is a new conceptual product intended as a regional-scale tool that contains base 3D geometric-kinematic information on the active and potentially seismogenic deformation in correspondence of all large Italian hydrocarbon fields. In case of a seismic sequence ongoing near an HFA (epicentral distance <~10 km), it could provide information on the Quaternary fault pattern and structural style characterizing the area, as well as on the associated crustal state of stress, as input constraints to the discussion on the likelihood of a direct or indirect link, controlled by tectonics, between the hypocentral area and the hydrocarbon field.KeywordsHydrocarbon fieldsEarthquakesQuaternary faultsSeismotectonic provincesTriggered seismicityItaly