In 1968, the Italian company Ente Nazionale per la Energia Elettrica (ENEL), in collaboration with the CHEC, performed the first geothermal study of the Nevado del Ruiz volcanic complex. In this research, lithological–stratigraphic characteristics, volcanology, structural events, and the hydrogeological system were described to determine the existence of favorable conditions for the circulation of fluids that may be used in the generation of electric power [8].

In 1983, the CHEC performed a pre-feasibility study for the development of a geothermal project in the Nevado del Ruiz volcanic complex, where detailed conclusions of the origins and evolution of the hydrothermal system associated with the volcano were drawn. In addition, properties such as pH, conductivity, temperature, and other parameters of the hydrothermal system, were determined [9].

The only geothermal exploration well in Colombia (Nereidas 1) was drilled in 1997 by GEOANDINA S.A. (GESA) on the western flank of the NRV. The well reached a maximum depth of 1469 meters and crossed seven lithological units with hydrothermal alteration. The temperature measured at the bottom of the well was approximately 200°C; however, the study suggested a geothermal reservoir with higher temperatures as the presence of an epidote in the basement indicates temperatures above 250°C [10].

In 2000, INGEOMINAS published the first geothermal map of Colombia wherein the interpolated temperature at a depth of 3 km is shown, which is considered a feasible depth from the point of view of drilling costs for the development of deep geothermal projects [11].

Recent research (2010–2014) related to the geothermal resources of the Nevado del Ruiz volcanic complex has been carried out mainly by ISAGEN, the SGC, CHEC, the National University of Colombia and the Administrative Department of Science, Technology and Innovation (COLCIENCIAS). Forero [12] characterized the hydrothermal alterations in the northwestern flank of the NRV via petrographic analysis, X-ray diffraction, and the stable isotope ratio in thermal waters. Mejía et al. [13] conducted a study of the structural geology around the NRV from aerial photographs, tectonic morphological features, fault striae data, and stress field calculations. In this study, hydrothermal activity to the west of the NRV was assumed to be caused by the structural controls of the area. Rayo [14] developed a model of the geochemical and thermal evolution of the volcano from petrographic, microstructural, and chemical analyses of minerals and rock geochemistry. That same year, Rojas [15] presented a study of the relationship between the magnetic susceptibility and the electrical and thermal conductivity of the Nevado del Ruiz volcanic system based on geophysical information, such as geoelectric, magnetometric, and magnetotelluric data and well records. Almaguer [16] conducted a magnetotelluric study in the northern sector of the NRV, determining the areas of high electrical conductivity associated with anomalous temperatures, which are of great interest for geothermal energy.

Mejía et al. [7] performed updated research on the Ruiz volcanic complex, which included the drilling of three exploratory wells with depths ranging from 174–300 m in 2011. These authors also constructed a geothermal conceptual model and suggested locations for five new exploratory wells with depths ranging from 1.7–2.7 km. These authors mentioned that the next stage would be the drilling of wells, the evaluation of the reservoir, the planning of the field, and the design of a geothermal plant. In this study, the construction and operation of a 50 MW plant was projected for 2018 [7].

González-García and Jessell [17] presented a 3D geological model of the Ruiz–Tolima volcanic massif to assess the uncertainty of the area. Consequently, a more rigorous representation of the geology of the volcanic complex was obtained, reinforcing the information available about this area.

A study of the geothermal potential in the NRV was performed by Vélez et al. [18] via evaluation of the thermal properties of rocks and the construction of a 2D numerical model of heat transfer and groundwater flow in a geological profile located in the northwestern area of the NRV.

Ceballos [19] and Ossa [20], with the support of the CHEC, performed a cartographic, geological, and structural analysis of an area within a geothermal project in the Nereidas Valley, where 6 zones were suggested as possible locations for exploratory wells, with several of these locations defined by zones of dilatational tectonic syntax formed between two faults with opposing movements, which will produce sunken and fractured topographic zones and promote the groundwater flow.

In 2018, Moreno et al. [21] performed 2D modeling of groundwater flow and heat transfer in a fractured geothermal reservoir in the northwestern area of the NRV. This work concludes and validates that secondary permeability, represented mainly by local and regional geological faults, behaves as a natural conduit that connects the surface with deep geological environments, and it is responsible for the hydrothermal activity observed on the surface.

Currently, the University of Medellín is working to characterize and model a fractured geothermal reservoir to the northwest of the NRV and to characterize hot springs in the Nereidas–Botero Londoño area via geochemical analyses [18], [21].

Two projects with pre-feasibility status for the development of geothermal energy in the NRV are currently being executed by the ISAGEN and CHEC companies.

Since 1994, GESA, a subsidiary of CHEC, has had an environmental license for the geothermal project, which has allowed GESA to advance a deep-drilling design and determine the potential in the Nereidas Valley area [22]. ISAGEN requested an environmental license in February 2014 for a 50-MW geothermal generation project in the Ruiz volcanic massif (areas A and B) [23]. However, this license has not yet been granted by CORPOCALDAS, the Environmental Authority that oversees this project.

According to a lecture by Ramírez [24] at the National Geothermal Meeting (RENAG) 2017, some issues that CORPOCALDAS has faced in the study of the environmental license granted to CHEC and in the process of granting the environmental license to ISAGEN are technical and scientific ignorance within CORPOCALDAS on the subject of geothermal energy and the spatial superposition of the projects presented by ISAGEN and CHEC (Figure 2). These issues were presented as barriers that slow the establishment of the geothermal projects led by these companies.

Figure 2. Figure 2. Areas with the potential for geothermal development in Colombia Source: Ramírez Baena [24].

In 2015, CHEC formed an alliance with LAGEO, a Salvadoran company with extensive experience in the development and operation of geothermal projects, to improve knowledge in the Nereidas Valley and to design and build 3 deep wells from 2016 to 2018 [25]. On the other hand, ISAGEN intended to assess the deposit through exploratory drilling between 2013 and 2017 and to design the geothermal plant. In addition, ISAGEN aims to build and operate the geothermal plant between 2017 and 2021 [26]. However, due to the abovementioned problems, the company does not yet have an environmental license for the proper development of the project.

According to the contributions of the SGC at RENAG 2017 [27], the fields of study in which work has already been performed for the Nevado del Ruiz are geology and water geochemistry. Moreover, there have been advances in gravimetry, magnetometry, 2D magnetotelluric modeling, 2D geothermal modeling, conceptual modeling, and the mapping of the geothermal area. Finally, the SGC mentions that more specific studies regarding structural geology, temperature soundings, 3D magnetotelluric models, diffuse gases and gas geochemistry (Radon) are still pending. In 2018, the SGC planned to perform or complete magnetotelluric studies, water and gas geochemistry, and the mapping of the geothermal area [27].

The quantity and diversity of studies that have been performed since 1968 to study the potential and utilization of the geothermal resources at NRV makes this area the most researched geothermal zone in Colombia.

Currently, the largest and most ambitious hydroelectric construction project in Colombia, Hidroituango, has been under a state of emergency since April 28, 2018, when a landslide occurred in the bypass tunnel, generating a high risk of flooding for the communities downstream from the dam [28]. This project is led and developed by the EPM, which, similar to the CHEC, is part of the EPM business group. Due to the large sums of money that the EPM group has had to pay as penalties and compensation to the community, the group has resorted to selling assets to guarantee its liquidity, cutting costs within the company organization, and stopping all new investments in electricity generation projects [29]. On the other hand, due to the recent sale of ISAGEN stock held by the Colombian government, investment plans and the development of new generation projects may be affected. The current situation regarding the two companies most heavily invested in the development of the geothermal project in the Nevado del Ruiz volcano may slow the development of this project.

In 1978, the first geothermal reconnaissance activities were developed by the Ecuadorian Electrification Institute (INECEL), which performed a regional geological survey and created an inventory of thermal manifestations in the area. The following year, in 1979, OLADE developed a geothermal recognition study in Ecuador, where the geovolcanic and hydrogeochemical conditions of the Tufiño–Chiles–Cerro Negro area were found favorable for the existence of geothermal systems [30].

In 1982, OLADE, in collaboration with INECEL and Geotérmica Italiana, developed a study on the use of the geothermal resources of the Tufiño area corresponding to the first phase of a pre-feasibility study for this area, where possible regional thermal anomalies were specified and geothermal models were proposed for the Tufiño–Chiles–Cerro Negro volcanic complex [31].

In 1983, ICEL (Colombian Institute of Electric Energy) presented a preliminary pre-feasibility report, Phase I, describing the geovulcanology of the Chiles–Cerro Negro, Cumbal and Nasate volcanic systems, analyzing their thermal sources, hydrothermal alteration, structures, hydrology, geochemistry, and water classification and presenting a scheme of possible geothermal systems [32]. This same year, OLADE, in collaboration with INECEL, ICEL and Geotérmica Italiana, presented a report describing volcanism in the Quaternary and, in particular, the stratigraphic succession of the Chiles–Cerro Negro volcanic complex [33].

In 1987, a pre-feasibility study was presented by the Aquater Consulting Agency. This study defined two possible horizons for producing geothermal fluids: a deep reservoir with an approximate depth of 2000 m and temperatures >200°C and a shallow reservoir ranging from 500–1000 m deep with temperatures approximately 150°C [30], [34].

For approximately 2 decades (1990–2009), this binational geothermal project was stalled for political reasons. The project was resumed in 2009 when HIGGECO Cia. Ltda. drilled the first vertical gradient, known as PGT-1, which reached a depth of 554.30 m; however, its temperature was not measured [33].

In July 2010, a binational agreement was signed between the governments of Colombia and Ecuador for the generation of electricity by geothermal energy. In the execution of this agreement, in 2012, ISAGEN and Corporación Eléctrica del Ecuador (CELEC) signed a specific technical cooperation agreement with the purpose of continuing the pre-feasibility studies of the Tufiño–Chiles–Cerro Negro binational geothermal project. The area where the project would be developed covers approximately 49000 hectares, with an estimated generation capacity of 138 MW [7].

In 2015, ISAGEN and CELEC presented a report containing geological maps at a 1:10,000 scale, hydrothermal alterations, and structural information for the area. In addition, ISAGEN and CELEC performed 10 radiometric data measurements and re-logged the PGT-1 well. This report mentions that geophysical studies were not performed to define the reservoir because the community in the Colombian territory did not authorize these studies [33], [35].

Bocanegra and Sánchez [36] mapped the faults found in the region of interest for the binational geothermal project based on data mining and in-field validations. In the same year, Chancusig [33] characterized the lithostratigraphic sequence and the mineralogy of the hydrothermal alteration of the PGT-1 well, and the results validated the conceptual geothermal model proposed in 1988.

Currently, the binational project for electric generation through geothermal energy from the Tufiño–Chiles–Cerro Negro volcano is in the pre-feasibility stage and is led by the ISAGEN and CELEC companies. This binational agreement is expected to terminate in 2018. However, taking into account the sale of Colombian participation in ISAGEN and the project’s status as part of a binational agreement, ISAGEN, in its 2016 growth management report [37], requested that the Ministry of Mines and Energy designate another government entity to provide continuity to the binational geothermal project, with which they would liaise in terms of investments made. This request adds to some of the problems that have been presented in terms of the affected communities and hinders the anticipated development of the Tufiño–Chiles–Cerro Negro binational geothermal project.

Interest in the geothermal area of the Azufral volcano began in 1982 with the OLADE report on geothermal resources in Colombia, which classified this area as a high priority for the possible development of a geothermal project [38]. As of this year, the SGC has developed and supported numerous studies with the objective of identifying the geothermal potential of this area. Cepeda et al. [39] conducted a study that involved the chemical and petrographic characterization of the Azufral, Cumbal, and Chiles–Cerro Negro volcanoes. Studies were performed on the activity of the Azufral volcano and its petrological, vulcanological, and geochemical evolution [40], [41], [42], [43], and a first Visit and Recognition Report was presented on the geothermal pre-feasibility of the Azufral volcano by Calvache et al. [44] (as Phase 1). Between 1997 and 2002, numerous studies were carried out on the geology, stratigraphy, pyroclastic products, and volcanic deposits of the Azufral volcano [45],[46], [47], [48], [49] in addition to a geochemical study of the geothermal system of the Azufral volcano [50].

Between 2005 and 2007, a series of field studies were performed to collect gravimetric, magnetometric, geoelectric, and seismic data, which were described in the Underground Water Exploration project of the SGC in collaboration with the National University of Colombia. Some of these works are the Gravimetric Study of the Hydrogeological Basin of the Guachucal–Azufral Valley, Nariño, and the Nariño highlands [51], [52]; the Structural Scheme for the Hydrogeological Exploration in the Nariño highlands [53]; the interpretation of the geochemical information of thermal outcrops in Colombia [54]; and Magnetometry Applied to groundwater Exploration in Nariño [55].

Carvajal et al. [56] presented the first geothermal model of the Azufral volcano created by identifying hydrothermal alteration zones, which illustrated a mature high-temperature geothermal system (>250°C) with a localized magmatic heat source located mainly to the east of the volcano. These results were consistent with a geochemical model based on the distribution and characterization of the thermal and fumarole manifestations of the Azufral volcano [56].

Ponce [57] published a study on the exploration of the geothermal resources of the Azufral volcano from the interpretation of potential field anomalies. Ponce found an area where geothermal gradients vary between 120°C km-1 and 250°C km-1, in addition to low-density lithologies that would probably allow for the presence of hot fluids. This observation demonstrated the possible existence of a geothermal field of medium-to-high temperature in the Azufral volcano’s influence area.

In 2015, Alfaro et al. [58] presented a preliminary conceptual model of the Azufral geothermal system based on an integration of existing studies that included seismic information from the volcanic activity monitoring program. This study concluded that a high-temperature geothermal system, with a temperature close to 225°C, dominates the current activity of the Azufral volcano. The thermal manifestations and hydrothermal surface alterations are mainly governed by faults and their intersections. The geothermal reservoir is possibly 2–2.5 km deep. The discharge zones are favored by faults with NW–SE orientations, which transport fluid from the center of the volcanic building 6–8 km to the east, where they accumulate. Finally, the authors mentioned that the geothermal fluid obtains an important contribution of surface water throughout its ascent.

According to the SGC at RENAG 2017 [27], a project in the geothermal area of the Azufral volcano is in pre-feasibility status. The fields of study in which work has already been performed are geology, gravimetry, magnetometry, structural geology, temperature sounding, 2D and 3D magnetotelluric modeling, and water geochemistry. It was mentioned that 3D geological and conceptual models are currently under way, in addition to gas geochemistry and diffuse gas (Radon) studies and the mapping of the geothermal area. By 2018, the SGC is expected to complete the gas geochemistry studies, the 3D geological model, and the mapping of the geothermal area.

The first study in the Paipa geothermal area was conducted by Boussingault and Roulín [59], who performed a chemical analysis of the thermal waters and described the area’s high salinity. Navia and Barriga [60] gave a geological description of the area, in which they revealed the existence of salt banks, included the physicochemical and radioactive characterizations of some of the thermal outcrops, and performed a beneficial study of the waters. In these studies, the geothermal energy production potential of the Paipa area was not mentioned.

In the study published by OLADE in 1982 on the recognition of Colombia's geothermal resources, the Paipa area was mentioned as an area with geothermal potential of medium to high priority, mainly due to geological criteria, such as the existence of volcanic rings of pyroclastic deposits, the phenomena of hydrothermal alteration, the existence of rocks of rhyolitic composition, the alkaline character, and the its age of 2.5 million years. This study also classified the hot springs according to their chemical composition [38].

In 1983, ICEL asked the Japan Consulting Institute to conduct a preliminary feasibility study for the construction of a geothermal plant in Boyacá. This study concluded that although some geothermal reservoirs may be suitable for exploitation, more advanced exploration activities were required [61].

Ferreira and Hernández [62] defined geothermal systems based on their geology and geochemistry and on the stable isotope analysis of water and gases, identifying these systems as heat sources due to magmatic intrusion within a sedimentary sequence; a reservoir of primary porosity in sedimentary formation (Une); a shallow reservoir with secondary permeability in fractured rocks; a clay seal layer (Churuvita Group); a primary permeability recharge zone; and a discharge zone fed by deep fluids flowing through a normal fault with NE–SW orientation. In addition, a reservoir temperature exceeding 200°C was estimated using alkaline geothermometers.

Bertrami et al. [63] mentioned the existence of a high-temperature geothermal system in the Paipa area based on the chemical and isotopic composition of the aqueous and gaseous phases of the thermal outcrops in the area.

Several studies have been performed since 2002 by SGC (formerly INGEOMINAS), with the purpose of better understanding the geothermal system in the Paipa area. Alfaro [64] and [65] developed studies on the aqueous-phase geochemistry of thermal outcrops, and Velandia [66] developed a technical report on the geological and structural cartography of the area at a scale of 1:25000.

Alfaro et al. [67] formulated a preliminary conceptual geothermal model based on the integration of existing geological, geophysical, and geochemical studies, wherein they concluded that the heat source in the Paipa area is magmatic with an age under 2.5–2.1 million years and that it is related to the Paipa volcano. The study noted that the reservoir is probably located in a caldera, approximately 3 km in diameter, formed by the Paipa volcano, which is probably associated with normal faults such as the Paipa–Iza and the Cerro Plateado and surrounded by areas fractured by the ascent of magma and/or water. Finally, the authors noted that the discharge area is structurally controlled, mainly in the ITP–Laceros sector.

In recent years, resistivity and geophysical, gravimetry and magnetometry studies have been performed [68], [69], [70], [71], which could be integrated and could contribute to the revision of the existing geothermal model.

The SGC organized a symposium in 2016 to celebrate 100 years of scientific production, where the geothermal conceptual model of the Paipa geothermal area was updated by the Geothermal Resource Exploration group [72].

Table 1. Table 1. Summary of existing scientific studies for the geothermal areas previously described Source: Adapted from Alfaro [27]. *

There is information available about these scientific studies.

Table 1 shows a summary of existing scientific studies (finalized or ongoing) for the previously described geothermal areas. Most of the existing studies in the Azufral Volcano and Paipa are being conducted or guided by SGC. In the case of NRV, studies are being conducted by SGC, ISAGEN and CHEC. Finally, in the case of the Tufiño–Chiles–Cerro Negro volcanoes, most of the studies are being or were conducted by ISAGEN and CELEC EP.

Articles 172 and 173 define geothermal resources as natural or injected water in an underground endogenous heat source resulting in the spontaneous or induced production of hot springs or steam. Geothermal resources are also those that emerge naturally or by human effort with a temperature higher than 80 degrees Celsius. Geothermal resources that do not reach a minimum temperature of 80 degrees Celsius shall not be considered hot springs.

Article 175 discusses the uses of geothermal resources, such as energy production, cooling and heating, and extraction of minerals.

Articles 176 and 177 describe the permits required for the exploitation of geothermal sources. In addition, these articles mention that those requesting exploration permits shall be responsible for taking the necessary measures to eliminate the polluting effects of water or condensed vapors.

Articles 23 and 31 define Regional Autonomous Corporations as agencies appointed by law to manage, monitor, and control, within the area of their jurisdiction, both the environment and renewable natural resources and to strive for their sustainable development. These functions include the issuance of the proper environmental licenses, permits, concessions, authorizations, and laissez-passer documents.

Article 50 defines environmental licenses as authorization granted by a competent Environmental Authority for the execution of a work or activity, subject to compliance with the established requirements in relation to the prevention, mitigation, correction, compensation, and management of environmental effects from the authorized works or activities.

This law includes geothermal energy as a renewable source of energy.

This law integrates non-conventional renewable energies into the national energy system. This law declares these as energies of national interest, essential to guarantee the supply of energy. This law establishes fiscal incentives to encourage research, development, and investment in the sector of non-conventional sources of energy (nuclear, biomass, small hydroelectric, wind, geothermal, solar, and tidal). These incentives allow for the deduction of 50% of the investments made during 5 years from annual income; value-added tax (VAT, known as IVA in Colombia) exemption on local or imported equipment, items, machinery, and services destined for pre-investment and investment activities; and tariff incentives and the accelerated depreciation of assets [79].

This executive order is the single regulatory decree that defines the guidelines for the application of incentives provisioned in Law 1715 of 2014. This executive order specifically explains the requirements and the scope of the benefits, such as a special deduction on income and supplementary taxes, VAT exclusions, tariff levy exemptions, and the tariff depreciation regime, in addition to describing the procedures required and their intended addressees.

This executive order defines the competence of the Regional Autonomous Corporations as the environmental authority for the exploration, construction, and use of generating plants and virtually polluting sources with an installed capacity equal to or greater than 10 MW and less than 100 MW. Projects with an installed capacity greater than or equal to 100 MW will be overseen by the National Agency for Environmental Licenses (ANLA), an autonomous government authority that provides permissions for the development of projects that significantly impact the environment.

This resolution establishes the procedures and requirements for issuing certifications and endorsing projects from Non-Conventional Sources of Energy, seeking to obtain the benefits of VAT exclusion or exemptions from the tariff charges provisioned in Articles 12 and 13 of Law 1715 of 2014, and determining the expiration date of these certifications and their renewal procedures, among other provisions.

This resolution establishes the procedure and requirements for the issuance of the environmental benefit certification for new investments in Non-Conventional Sources of Renewable Energy and efficient energy management projects to obtain the tax benefits provisioned in articles 11, 12, 13, and 14 of Law 1715 of 2014 and other determinations as adopted.

This resolution details the VAT exclusion procedure at UPME.

This resolution details the VAT exclusion procedure at ANLA.

To summarize, Executive Order 2811 of 1974 defines geothermal resources; Law 99 of 1993 creates the Environmental Authorities and their instruments for the authorization, control, and monitoring of the exploitation of geothermal resources; Executive Order 1076 of 2015 defines the competence of the Environmental Authorities for Resource Generation and Use projects; Law 1715 of 2014, Executive Order 2143, Resolutions 045 and 1283 of 2016, and Resolutions 585 and 2000 of 2017 define geothermal energy incentives and the corresponding procedures to secure them for a given project.