Geothermal Networks Can Aid Decarbonization Through Repurposed Hydrocarbon Wells

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 220014, “Decarbonizing the Residential Sector With Geothermal District-Heating Networks: The Contribution of Hydrocarbon Wells,” by Claudio Alimonti, SPE, Sapienza University of Rome and Istituto di Geologia Ambientale e Geoingegneria, and Davide Scrocca, Istituto di Geologia Ambientale e Geoingegneria. The paper has not been peer reviewed. _ This study highlights how the recovery and reuse of existing hydrocarbon infrastructure can contribute to the diffusion of district-heating (DH) projects that implement principles of circular economy. The complete paper presents two examples of reusing hydrocarbon wells to satisfy the energy demand for heating residential buildings through locally available geothermal renewable energy sources. Background The mature phase of oil and gas reservoirs usually is characterized by the production of formation waters together with hydrocarbons. The volume of the produced water generally increases as fields mature until hydrocarbon production becomes uneconomical and wells are cemented and closed. Reservoir fluids could have temperatures high enough to support geothermal exploitation depending on the geothermal gradient. Therefore, when hydrocarbon wells are approaching the end of their productive life, and where geothermal potential exists, conversion to geothermal wells could be a reasonable alternative to closure. The authors’ results show how the repurposing of hydrocarbon wells into geothermal wells constitutes an excellent opportunity to access geothermal resources, reducing investment and mining risks and improving project economics. Considering that the temperature of reservoir fluids accessible through existing active wells generally is lower than 100–110°C, one of the more suitable applications for the harvested heat is to power new-generation DH systems that can operate with delivery temperatures even lower than 60°C. Data and Results Geothermal Potential of Using Hydrocarbon Wells in Italy. Data regarding hydrocarbon production concessions and active hydrocarbon wells are made available by the Italian Ministry of Environment and Energy Security. Further data are provided by the Visibility of Petroleum Exploration Data in Italy project. In Italy, 1,561 active wells are distributed in 183 hydrocarbon concessions. In 111 onshore hydrocarbon production concessions, 847 active wells have different operational statuses, including 436 productive wells and 399 potentially productive wells. A first selection of onshore fields hosting the most-promising productive or potentially productive wells was performed through comparison of the well location and total depth with the known subsurface temperature field. In that study, the reference thermal data were temperature maps at depths of 1000, 2000, and 3000 m below ground level. In one approach proposed in the literature, given that the focus was on space-heating applications, the minimum production temperature was set to 70°C. On this basis, 42 fields have been identified with depths greater than 2000–3000 m and with temperatures greater than 60–70 °C. However, heat recoverable from even-lower-temperature reservoir fluids could have potential uses with the most-recent generations of DH systems and with direct heat.