Geothermal repurposing of depleted oil and gas wells in Italy

The decarbonisation of the energy sector is probably one of the main worldwide challenges of the future. Global changes urge a radical transformation and improvement of the energy-producing systems to meet the decarbonisation targets and a reduction of greenhouse gas emissions. The hydrocarbon industry also contributes to this transition path. In a mature stage of oil and gas fields, the production of hydrocarbons is associated with formation waters. The volume of produced water increases with the maturity of the assets and the geothermal repurposing of depleted oil and gas wells could be an alternative to the mining closure. In the described transition scenario, the geothermal energy seems very promising because of its wide range of applications depending on the temperature of extracted fluids. This flexibility enables us to propose projects inspired by a circular economic vision considering the integration in the territory and social acceptance issues. In Italy, since 1985, 7246 wells have been drilled for hydrocarbon, of which 898 are located onshore with a productive or potentially productive operational status. This paper presents a preliminary investigation of oil and gas fields located onshore in Italian territory based on the available information on temperature distribution at different depths. Then, taking into account the local energy demand, existing infrastructure, and land use of the territory, a conversion strategy for the producing wells is proposed for three case studies

Data integration and conceptual modelling of the Larderello geothermal area, Italy

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Thermal Modeling of Southern Italy with Heat flow, Gravity and Magnetic Constraints

The estimation of subsurface temperature distributions is an important parameter for geothermal exploration. The thermal structure can be approximated by assuming either the steady-state or transient state solution of the heat conduction equation. The solution requires boundary values to calculate the temperature distribution within the crust and the lithospheric mantle. Such calculations are constrained primarily by surface heat flow and/or temperature measurements and the associated distribution of thermal parameters (thermal conductivity and heat production) within the crust and the lithospheric mantle. Data on near-surface heat flow and temperature are based on measurements in boreholes. Although heat flow and temperature data are considered the most reliable for estimating temperature distributions, their limited depth and scarcity may not be enough in inferring deep thermal gradients. In this study, instead, the results of the Curie isotherm model estimated from magnetic data used as a constraint to map the subsurface temperature distributions. In particular, the temperature at the Curie depth points (580oC) and surface temperature were imposed as Dirichlet boundary conditions for the bottom and top of the model, whereas the sides of the model were marked by a zero-heat flux (Neumann) boundary condition. Other essential information comes from the crustal structure model (crystalline basement and Moho depth), surface heat flow, controlled-source seismic profiles, magnetotellurics, and measurements of crustal radiogenic heat production and thermal conductivity within the subsurface layers. The integrated modeling approach and interpretation of the thermal model and estimated Curie temperature isotherm model, together with gravity, heat flow, geological model, and well log data may allow identifying areas of higher temperature and heat flow, identify potential interest for geothermal exploration, locate aquifers, and outline a production field

Deep geothermal exploration by means of electromagnetic methods: New insights from the Larderello geothermal field (Italy)

The main target of this research is the improvement of the knowledge on the deep structures of the Larderello-Travale geothermal field (Tuscany, Italy), with a focus on the Lago Boracifero sector, particularly on the heat source of the system, the tectonics and its relation with the hydrothermal circulation. In the frame of the PhD program and of the IMAGE project (Integrated Methods for Advanced Geothermal Exploration; EU FP7), we acquired new magnetotelluric (MT) and Time Domain EM (TDEM) data in a key sector of the field (Lago Boracifero). These data integrate the MT datasets previously acquired in the frame of exploration and scientific projects. This study is based also on a integrated modelling, which included and organized in Petrel (Schlumberger) environment, a large quantity of geological and geophysical data. We also propose an integrated approach to improve the reliability of the 2D MT inversion models, by using external information from the integrated model of the field as well as an innovative probabilistic analysis of the MT data. We present our attempt to treat the 1D magnetotelluric inverse problem with a probabilistic approach, by adopting the Particle Swarm Optimization (PSO), a heuristic method based on the concept of the adaptive behaviour to solve complex problems. The user-friendly software “GlobalEM” was implemented for the analysis and probabilistic optimization of MT data. The results from theoretical and measured MT data are promising, also for the possibility to implement different schemes of constrained optimization as well as joint optimization (e.g. MT and TDEM). The analysis of the a-posteriori distribution of the results can be of help to understand the reliability of the model. The 2D MT inversion models and the integrated study of the Larderello-Travale geothermal field improved the knowledge about the deep structures of the system, with a relevant impact on the conceptual geothermal model. In Micaschist and Gneiss complexes we observed a generally high electrical resistivity response locally interrupted by low resistivity anomalies that are well correlated with the most productive sectors of the field. A still partial melted igneous intrusion beneath the Lago Boracifero sector was detected based on the interpretation of the low resistivity anomalies located at a mid-crustal level (> 6 km). New insights on the tectonics are proposed in this research. The fundamental role of a large tectonic structure, i.e. the Cornia Fault, located along the homonymous river, was highlighted. In our opinion, this fault played an important role in the geothermal evolution of the Lago Boracifero sector, favouring both the hydrothermal circulation and the emplacement of magma bodies. In our opinion, the system can be ascribed to a “young convective and intrusive” field feed by a complex composite batholite