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The energy potential of geothermal reservoirs mainly depends on thermal regime, geological structure, and petrophysical properties. However, practical issues have a main importance in the planning, such as the kind of energy utilization, the design of the geothermal doublet, or the vicinity of energy end users. The evaluation approach here described tackles and integrates the different aspects. The approach is tested in the medium-enthalpy geothermal reservoir of Guardia Lombardi (Campania, Italy). The surface area of the entire study region is about 42 km by 28 km. It is characterized by specific surface heat flow of up to 90 mW m-2 and geothermal gradients of about 58 K km-1. The geothermal target is the shallow water Apulian Platform, a fractured and possibly locally karstified carbonate layer, dissected by a number of steep faults. The complex geological structure has been interpreted from several seismic profiles and hydrocarbon exploration wells. A numerical model was set up describing the relevant regional advective and conductive heat transport processes in the reservoir. A set of borehole-temperature data was used for its calibration. As simulator we used the code SHEMAT-Suite. First, we investigate the natural flow and temperature conditions in the entire reservoir. Second, we choose several sub-models, based on temperature and flow rates as well as on social decision parameters such as vicinity to villages or natural reserve restrictions. For these sub-models we assess the rates of energy production and sustainability for various utilization scenarios. Relevant aspects, beside infrastructure and natural reserve restrictions, are: (a) borehole locations and distance between injector and producer; (b) drilling depth vs. estimated temperature; (c) influence of preexisting fracture and fault systems; (d) stimulation.

A region in Southern Italy (Guardia dei Lombardi, Province of Avellino) is being explored as a medium-enthalpy geothermal resource. The chosen area (with overall dimensions of 42 km × 28 km) is characterized by a local heat-flux maximum of 90 mW/m2. Based on seismic profiles and hydrocarbon exploration wells, a three-dimensional geological model has been set up. It shows the upper surface of the Cretaceous Apulia shallow-water carbonate platform as a faulted, thrust-related anticline overlain by dense, partly shale-rich sedimentary layers. In previous work, the basal specific heat flow was calibrated to temperature data from six different wells under the assumption of purely conductive heat transport using the simulation code SHEMAT-Suite. The reservoir is characterized by a natural carbon dioxide emanation along natural faults and fractures. Analogously, it is assumed that water flow occurs primarily through fracture and fault networks. The role of advection on the temperature distribution is studied and a reevaluation of the basal specific heat flow at 6 km depth performed. This inversion is carried out using a deterministic Bayesian approach. Thermal conductivity values for the lithological units and their uncertainties are deduced from laboratory measurements on rock samples together with logging interpretation. Maps of geothermal energy potential are set up at various depths within the reservoir with the overall goal of identifying promising geothermal conditions for future exploitation.

The operative agreement between the Italian Ministry of Economic Development (Directorate General for Nuclear Energy, Renewable Energy, and Energy Efficiency) and the Italian National Research Council (Department of Earth and Environment), signed in 2010, promoted a new project (VIGOR project) to evaluate the geothermal potential and the implementation of innovative use of geothermal resources in the so-called Regions of Convergence (i.e., Campania, Puglia, Calabria, and Sicilia). Within this context, a characterization of medium enthalpy geothermal resources have been carried out in the promising "Guardia dei Lombardi" area, located in the Campania region (Southern Italy, Province of Avellino). Intense subsurface hydrocarbon exploration has been carried out in the area over the last decades (particularly during the 1956-1996 period), providing large quantities of seismic and geochemical data. This exploration activity has demonstrated the presence of a fractured carbonate reservoir, that is constituted by the Cretaceous-Eocene sequence of the Apulian shallow water carbonate platform (e.g., SCROCCA, 2010 and reference therein). Following the Apennine orogenesis, the platform was deformed to shape a buried antiformal stack (NICOLAI & GAMBINI, 2007). In the study area the culmination of the uppermost thrust unit reaches a depth of about -250 m below the sea level (i.e. about 1125 m below the ground level). The reservoir fluids are mainly composed of CO2, which rests above an accumulation of brackish water in the central and upper part of the culmination of the deep carbonatic aquifer (e.g., Monte Forcuso 1 and 2 wells), and saline water along the flank of the buried anticline (e.g., Bonito 1 Dir, Ciccone 1 wells). In previous assessment mainly made by ENEL (1987; 1994), a reservoir fluid has been estimated in the area that reaches temperature of 120°C at the depth of 3000 m below ground level, associated to a heat flow of 90 mW/m2. (DELLA VEDOVA et alii, 2001). These parameters suggest the presence of a medium enthalpy geothermal resource. The presence of thermal waters in the area (Terme di San Teodoro) provides further constrain about the geochemical characteristics of the reservoir water.. Reservoir fluid temperature up to about 124°C were calculated using different geothermometers (DUCHI et alii, 1995). In this study, the overall structural-stratigraphic setting of the reservoir/caprock system has been defined on the basis of the integrated interpretation of a composite dataset of surface and subsurface geological, geophysical and geochemical information. In particular, thanks to the cooperation of ENI Company, we have had access to a wide dataset composed by seismic reflection profiles, well data, logs and cores. A careful assessment of temperature field at depth has been carried out analyzing the well logs through Horner plot construction (RIDER, 1996 and reference therein). Where the data were scarce, the approach proposed by DELLA VEDOVA, et alii (2001) has been applied. On the basis of well tests, cores analysis and mud losses/absorptions, it has been possible to re-estimate the reservoir properties, confirming quite good permeabilities for the fractured carbonate reservoir. One of the main results of this research is the development of an integrated 3D geological model which provides the base for a detailed assessment of the possible geothermal exploitation of the carbonate reservoir. The preliminary results of our analysis suggest that the "Guardia dei Lombardi" site could be indicated as an interesting area for the geothermal medium enthalpy exploitation, although the presence of the CO2 gas cap should be carefully