Abstract
Abstract. One of the concerns of underground CO2 onshore storage is the triggering of induced seismicity and fault reactivation by the pore pressure increasing. Hence, a comprehensive analysis of the tectonic parameters involved in the storage rock formation is mandatory for safety management operations. Unquestionably, active faults and seal faults depicting the storage bulk are relevant parameters to be considered. However, there is a lack of analysis of the active tectonic strain field affecting these faults during the CO2 storage monitoring. The advantage of reconstructing the tectonic field is the possibility to determine the strain trajectories and describing the fault patterns affecting the reservoir rock. In this work, we adapt a methodology of systematic geostructural analysis to underground CO2 storage, based on the calculation of the strain field from kinematics indicators on the fault planes (ey and ex for the maximum and minimum horizontal shortening, respectively). This methodology is based on a statistical analysis of individual strain tensor solutions obtained from fresh outcrops from the Triassic to the Miocene. Consequently, we have collected 447 fault data in 32 field stations located within a 20 km radius. The understanding of the fault sets' role for underground fluid circulation can also be established, helping further analysis of CO2 leakage and seepage. We have applied this methodology to Hontomín onshore CO2 storage facilities (central Spain). The geology of the area and the number of high-quality outcrops made this site a good candidate for studying the strain field from kinematics fault analysis. The results indicate a strike-slip tectonic regime with maximum horizontal shortening with a 160 and 50∘ E trend for the local regime, which activates NE–SW strike-slip faults. A regional extensional tectonic field was also recognized with a N–S trend, which activates N–S extensional faults, and NNE–SSW and NNW–SSE strike-slip faults, measured in the Cretaceous limestone on top of the Hontomín facilities. Monitoring these faults within the reservoir is suggested in addition to the possibility of obtaining a focal mechanism solutions for micro-earthquakes (M<3).
Highlights
Industrial human activities generate CO2 that could change the chemical balance of the atmosphere and their relationship with the geosphere
We propose that the description, the analysis and establishment of the tectonic strain field have to be mandatory for long-term GSC monitoring and management, implementing the fault behavior in the geomechanical models
The age of the outcrops ranges from Early Triassic to post-Miocene, and they are mainly located in Cretaceous limestone and dolostone (Fig. 5, Table 2)
Summary
Industrial human activities generate CO2 that could change the chemical balance of the atmosphere and their relationship with the geosphere. Caprock, permeability and porosity, plus injection pressure and volume injected, are the main considerations to choose one geological subsurface formation as the CO2 host rock In this context, the tectonically active field is considered in two principal ways: (1) to prevent the fault activation. The prediction of site performance over long timescales requires an understanding of CO2 behavior within the reservoir, the mechanisms of migration out of the reservoir, and the potential impacts of a leak on the near-surface environment The assessments of such risks will rely on a combination of predictive models of CO2 behavior, including the fluid migration and the long-term CO2–porewater–mineralogical interactions (Pearce, 2006). The role of the faults inside these models is crucial for the tectonic longterm behavior and the reactivation of faults that could trigger earthquakes
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