Thermal modelling of the Larderello geothermal field (Tuscany, Italy)

Abstract

We present a 3-D thermal model of the Larderello geothermal field (Tuscany) to evaluate (i) the extent and contribution of the heat transfer mechanisms (conduction vs. convection) at the intermediate-upper crust levels, (ii) the variability of the heat and mass fluxes entering from below and (iii) the crucial role of the formation permeability. The model is composed by three main layers and considers the upper ten km of the crust to better constrain the simulations with the experimental data, from borehole, fluid inclusion studies and hypocentral distributions. Several sets of simulations were carried out, with different bottom boundary temperatures and different formation permeability values for the two deeper layers. The results indicate that the present temperature and pressure distribution with depth in the Larderello field requires deep reservoir rocks with higher permeabilityies than the overlying capping units and the underlying intermediate crust. Permeability values of one mDarcy for the reservoir rocks are enough to allow fluid convection, if the temperature at 10 km depth is as high as 500 ± 50 °C. The presence of localized zones with formation permeability 50-100 times higher than the surrounding rocks strongly favours the migration of over-pressurized fluids, which episodically break through the overburden, feeding the exploited geothermal fields

On the morphology and amplitude of 2D and 3D thermal anomalies induced by buoyancy-driven flow within and around fault zones

“…Finally, the pulsating behavior observed in Fig. 7 has been used by Deveaud et al (2015) to suggest one possible dynamical mechanism at the origin of rare-element pegmatite emplacement. Indeed, these magmatic liquids have an extremely low viscosity (e.g., Bartels et al, 2013).…”

Influence of depth, temperature, and structure of a crustal heat source on the geothermal reservoirs of Tuscany: numerical modelling and sensitivity study

“…The Ligurian unit is the most important cover of the Burano unit in our study area. The thin Pliocene sediments and the carbonates and pelagic sediments of the Tuscan unit above the Burano are also known to have permeabilities that are at least 50-100 times less than those of the reservoir rocks (Della Vedova et al 2008). Therefore, a permeability of 10 −18 m 2 has been assigned to all three cover units, which is about 100 times less than the lowest permeability value of the Burano unit.…”

Geothermal resource assessment of remote sedimentary basins with sparse data: lessons learned from Anticosti Island, Canada

“…Such complex sensitivity analysis can only be made at a late stage of geothermal exploration and could not be realized at Anticosti Island. The rock properties or boundary conditions were varied one by one in other studies to evaluate their sensitivity (Della Vedova et al 2008;Ebigbo et al 2016;Frick et al 2015;Noack et al 2012). While this approach can be more similar to what was done in the present study, it differs by the absence of calibration process in the work flow.…”

“…The temperature data at depth were used for comparison with modeled temperature only, while in the present study, temperature data are used to calibrate the Basement thermal unit heat generation rate for each scenario. Only one to three parameters were varied in these studies, except for the work of Della Vedova et al (2008), which can be due to the important time needed to complete a full-sensitivity analysis in 3D. As a consequence, a new approach had to be defined for Anticosti Island to rigorously consider parameter sensitivity while facing the challenges caused by data sparsity common to remote regions.…”