• Energy Research

The Salcheto winery has undertaken a process of reduction of its primary energy consumption and the implementation of green energy technologies. They adopted solar photovoltaic, wood biomass, and geothermal energy sources. A horizontal ground source heat exchanger (GSHE) plant is used to cool a part of the pressed grapes and control the wine production temperature. The goal of this work was to investigate some technical issues of the plant and to increase the efficiency of the whole system. The first step was the evaluation of the actual operating conditions of the GSHE plant, by performing a thermal response test. The results allowed us to find the thermal diffusivity of 3.5 × 10−7 m2/s, and the calculation with the IGSHPA standard indicated a cooling performance of about 6 kW. A survey during the harvest highlighted a peak power of 6 kW. Therefore, to improve the plant, some modifications were proposed and analyzed. In the new layout, the geothermal plant serves the condenser of the refrigeration unit, allowing cooling of the all production lines, instead of only one. The peak power was evaluated as 32 kW, and the GSHE can fulfil this, up to 18 kW. For higher power, the evaporative tower will supply the remainder, covering a maximum of 45%. Furthermore, the refrigeration unit may cover the cooling requirements of the entire residential and office building, without other plant improvements.

Abstract The available literature on the WellBore Heat eXchangers (WBHX) has been analyzed giving prominence to three aspects. First, the heat transfer through the geothermal reservoir and between the formation and the well has been analyzed. Then, the design of the WBHX and the modelling of the heat exchange has been reviewed. Lastly, the analysis of the performance of the WBHX in the production of thermal and/or electrical energy has been focused. Regarding the modelling of the heat transfer in the reservoir and between the wellbore and the formation, the sensitivity studies in literature highlight as key parameter the residence time of the fluid into the device. At fixed flow rate the residence time of the fluid in the WBHX is function of the well diameter. From analyzed papers, it raises the need of the insulation of the upward pipe in order to avoid heat losses. The range of produced thermal power is 0.15÷2.5 MW and of electrical power is 0.25÷364 MW. The WBHX is a promising technology if and only if is applied in the more convenient geothermal assets. The continuous study of the possible designing solutions and the improvements to enhance heat transfer is fundamental to allow this technology ready to market.

The target of this work is to produce a vision of the geothermal potential stored in the depleted oil & gas fields in Italy, by using the available information provided by the Ministry of Economic Development, the published data on hydrocarbon fields, and the estimated temperature at depth from the Italian National Geothermal Database. Five most promising fields have been selected and the volume method has been applied to assess their geothermal potential. Then a probabilistic approach has been adopted to obtain not a single value but a distribution of values of the technical potential TP. The results indicate that the available heat in hydrocarbons fields is encouraging and it is fundamental to analyze the production capacities of the existing wells to have a clearer idea of the possible uses of this existing and wasted heat.

This study describes the geothermal response of the Phlegraean Fields as well as the impact of changes in its thermal and hydrodynamic properties brought on by a deep borehole heat exchanger (DBHE). For this purpose, we have developed a specialized model based on the Galerkin Method (GM) and the iterative Newton–Raphson algorithm to perform a transient simulation of heat transfer with fluid flow in porous media by solving the related system of coupled non-linear differential equations. A two-dimensional domain characterized with an anisotropic saturated porous media and a non-uniform grid is simulated. Extreme characteristics, such as non-uniformity in the distribution of the thermal source, are implemented as well as the fluid flow boundary conditions. While simulating the undisturbed geothermal reservoir and reaching the steady temperature, stream function, and velocity components, a DBHE is placed into the domain to evaluate its impact on the thermal and fluid flow fields. This research aims to identify and investigate the variables involved in the Phlegraean Fields and provide a numerical approach to accurately simulate the thermodynamic and hydrodynamic effects induced in a reservoir by a DBHE. The results show a maximum temperature change of 107.3°C in 200 years of service in the study area and a 65-year time limit is set for sustainable geothermal energy production.

Climate change and the energy crisis forced industrialized countries to contain CO2 emissions and use indigenous renewable energy sources. Geothermal energy undoubtedly has great potential, particularly thermal energy, given that 48% of the final energy consumption in the EU20 countries in 2021 was related to heating and cooling systems. The present study verifies and compares the feasibility of realizing district heating systems in two different contexts: (i) depleted hydrocarbon fields with the repurposing of existing hydrocarbon wells into geothermal wells and (ii) areas with documented geothermal resources. The two selected case studies are located, respectively, near Romentino (Northern Italy, province of Novara) and Tuscania (Central Italy, province of Viterbo). Following an assessment of the geothermal resources in the two selected case studies, specific methodological tools have been developed to evaluate the energy demand in the municipalities and determine the projects’ economics. Both case studies show positive economic indices assuming heat tariffs aligned with the values recorded in the 2020–2021 period. However, our results show how reusing hydrocarbon wells in geothermal wells constitutes an excellent opportunity to access geothermal resources, significantly reducing the necessary investment and the mining risk and strongly improving the economics of the projects.

Geothermal energy plays a key role in the green energy transition since it represents a low-carbon alternative to traditional fuels, but the high exploration costs and mining risks still hinder its use. Therefore, the reuse of pre-existing subsurface geological data can represent a way to counteract these limiting factors and promote the use of geothermal resources. We reconstructed a 3D geological model of the Guardia Lombardi area (Campania Region, southern Italy) and evaluated its geothermal potential interpreting vintage oil and gas subsurface data (i.e., seismic reflection profiles and well data). The exploitation potential of the geothermal resource and the related costs were also evaluated. The study revealed the presence of a geothermal reservoir with 125 °C at just 2300 m depth and an exploitation potential of about 70 kg/s, employable for residential heating and/or cooling and for electricity production in the nearby Grottaminarda town, with an appreciable economic benefit. These results demonstrate how the reuse of pre-existing subsurface geological data provided by past oil & gas exploration can considerably reduce costs and mining risks associated with geothermal resource exploration, contributing to a faster and considerable reduction in CO2 emissions.

Growing awareness and interest in renewable resources has raised the need to homogenise the reporting requirements for geothermal resources so that they can be applied worldwide. As no globally agreed standards, guidelines or codes exist, there remains too much latitude in geothermal assessment, which leads to increased resource uncertainty, more investment risk and less confidence in development. Reconciling the various reporting of geothermal resources is a major challenge as it is difficult to define what the target actually is: the source, the reservoir, the fluids, the stored heat, the recoverable volume, the recoverable heat, the recoverable power, or the net profit. Formulating an agreed procedure to classify geothermal resources is further complicated by changing environmental, policy and regulatory constraints around the globe. Present day techniques of computing geothermal resources provide only ballpark estimates at best. This paper addresses the existing gaps in standardising geothermal resources assessment and reporting by capturing: current methods used to identify potential geothermal projects; current practices in classifying and reporting geothermal resources and reserves; key decision parameters for operators, investors, governments and insurance companies; and current obstacles to a common and transparent way to secure investment in geothermal energy.

The geothermal industry is fronted by a fundamental decade to grow and become an energy supplier in transitioning to a sustainable energy system. The introduction of Closed-Loop Geothermal energy systems (CLG) can overcome the negative social response and increase the attractiveness of geothermal developments. The present work aims to investigate and compare the performance of CLG systems. For the comparison, the case study of Campi Flegrei was chosen. The maximum depth was fixed at 2000 m, and the two configurations were set up to analyse the performance and evaluate the best operational configuration. Both CLG configurations showed decay in the output temperature of the working fluid during the production time. For a U-shaped design, it is possible to find a working condition that allows constant thermal power over time. The DBHE specific power was always more significant, up to 350 kW/m, compared to the U-shaped, which attained a maximum of 300 W/m (15%). The comparison with Beckers et al. analysis highlights the similarity of our results with their base case. The consideration of the CLG system’s length is related to the heat exchange and investment costs. For longer exchangers, there are higher investments and lower specific power.