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Two hydrogeological numerical models (2D and 3D) for the geothermal area located to the West of the Nevado del Ruiz volcanic complex (Colombia) are presented here. They are built with the software HydroGeoSphere using data collected in the field, as well as hydraulic and thermal properties measured on rock samples in previous laboratory studies. The purpose of this modeling work is to analyze the influence of faults aperture and depth on groundwater flow circulation and heat transfer in the geothermal reservoir. The 2D model illustrates the relation between fault aperture and temperature distribution. The 3D model shows the behavior of a potential production well located in the Botero-Londoño area that withdraws hot water from a depth of 2600 m. The results highlight the usefulness and limitations of this approach, providing guidelines for future numerical models of this site and for the initial modeling work for any fractured geothermal reservoir. Se presentan aquí dos modelos numéricos hidrogeológicos (2D y 3D) para el área geotérmica situada al oeste del complejo volcánico Nevado del Ruiz (Colombia). Están construidos con el software HydroGeoSphere utilizando datos recolectados en campo, así como propiedades hidráulicas y térmicas medidas en muestras de roca en laboratorio, en estudios previos. El propósito de este trabajo de modelación es analizar la influencia de la apertura y profundidad de las fallas sobre la circulación del flujo de agua subterránea y la transferencia de calor en el reservorio geotérmico. El modelo 2D ilustra la relación entre la apertura de la falla y la distribución de la temperatura. El modelo 3D muestra el comportamiento de un pozo de producción potencial situado en la zona de Botero-Londoño que extrae agua caliente desde una profundidad de 2600 m. Los resultados demuestran la utilidad y las limitaciones de este estudio, proporcionando pautas para futuros modelos numéricos de este sitio y para las etapas iniciales de modelación de cualquier reservorio geotérmico fracturado.

From a literature review, various concepts and methodologies useful for the development of the preliminary stages of planning and design of a ground source heat pump were documented. A prototype of a cooling system for a room in the Universidad EIA was proposed. The heat pump selected to supply the demand has a power of 1-9 kW, and the proposed heat exchanger system corresponds to a closed-loop horizontal slinky-type with an approximate pipe length of 1,301 m, which was calculated through Excel spreadsheets and configured in three or six trenches with a total area required for the installation of 911 and 952 m2, respectively. These results provide the initial conditions for the implementation of an air conditioning project at the site, using shallow geothermal energy. Other alternatives for the heat exchanger systems and considerations for future projects are also presented.

Thermal response tests are used to assess the subsurface thermal conductivity to design ground-coupled heat pump systems. Conventional tests are cumbersome and require a source of high power to heat water circulating in a pilot ground heat exchanger. An alternative test method using heating cable was verified in the field as an option to conduct this heat injection experiment with a low power source and a compact equipment. Two thermal response tests using heating cable sections and a continuous heating cable were performed in two experimental heat exchangers on different sites in Canada and France. The temperature evolution during the tests was monitored using submersible sensors and fiber optic distributed temperature sensing. Free convection that can occur in the pipe of the heat exchanger was evaluated using the Rayleigh number stability criterion. The finite and infinite line source equations were used to reproduce temperature variations along the heating cable sections and continuous heating cable, respectively. The thermal conductivity profile of each site was inferred and the uncertainly of the test was evaluated. A mean thermal conductivity 15% higher than that revealed with the conventional test was estimated with heating cable sections. The thermal conductivity evaluated using the continuous heating cable corresponds to the value estimated during the conventional test. The average uncertainly associated with the heating cable section test was 15.18%, while an uncertainty of 2.14% was estimated for the test with the continuous heating cable. According to the Rayleigh number stability criterion, significant free convection can occur during the heat injection period when heating cable sections are used. The continuous heating cable with a low power source is a promising method to perform thermal response tests and further tests could be carried out in deep boreholes to verify its applicability.

Compared to conventional ground heat exchangers that require a separate pump or other mechanical devices to circulate the heat transfer fluid, ground coupled thermosiphons or naturally circulating ground heat exchangers do not require additional equipment for fluid circulation in the loop. This might lead to a better overall efficiency and much simpler operation. This paper provides a review of the current published literature on the different types of existing ground coupled thermosiphons for use in applications requiring moderate and low temperatures. Effort has been focused on their classification according to type, configurations, major designs, and chronological year of apparition. Important technological findings and characteristics are provided in summary tables. Advances are identified in terms of the latest device developments and innovative concepts of thermosiphon technology used for the heat transfer to and from the soil. Applications are presented in a novel, well-defined classification in which major ground coupled thermosiphon applications are categorized in terms of medium and low temperature technologies. Finally, performance evaluation is meticulously discussed in terms of modeling, simulations, parametric, and experimental studies.

Unconventional geothermal resource development can contribute to increase power generation from renewable energy sources in countries without conventional hydrothermal reservoirs, which are usually associated with magmatic activity and extensional faulting, as well as to expand the generation in those regions where conventional resources are already used. Three recent drilling experiences focused on the characterization of unconventional resources are described and compared: the Campi Flegrei Deep Drilling Project (CFDDP) in Italy, the United Downs Deep Geothermal Power (UDDGP) project in the United Kingdom, and the DEEP Earth Energy Production in Canada. The main aspects of each project are described (geology, drilling, data collection, communication strategies) and compared to discuss challenges encountered at the tree sites considered, including a scientific drilling project (CFDDP) and two industrial ones (UDDGP and DEEP). The first project, at the first stage of pilot hole, although not reaching deep supercritical targets, showed extremely high, very rare thermal gradients even at shallow depths. Although each project has its own history, as well as social and economic context, the lessons learned at each drilling site can be used to further facilitate geothermal energy development.

Solid wood gives the shape to walls, while panels are the coating and they are nailed or screwed to the wood sections. In the cavities between the wood elements and the panels, a thermal and acoustic insulator must be added. Unfortunately, almost all of the currently used insulators (mineral wool, expanded polystyrene, polyurethane) are not biodegradable and require the use of vapor barriers (polyethylene sheets, aluminum foils, etc.) that deteriorate rapidly and that are relatively environmentally unfriendly. In this article, the use of coconut fiber instead of conventional insulators is suggested. The acoustic absorption and thermal conductivity coefficients of composite sections taken from wood walls with coconut fiber are estimated. In this way, good thermo-acoustic conditions inside the wood building are achieved using an ecological insulating material.

Tunnels commonly go through fracture zones that used to be analyzed as an equivalent porous medium with homogeneous permeability. However, it is a rough simplification that overlooks the connection triggered by underground works in fractured massifs. This study introduces the use of synthetic discrete fracture networks (DFN) to analyze groundwater inflows through tunnel excavation in a fractured zone considering the daily advance of the drilling front. First, a hypothetical case with six different settings varying the fracture density, the fracture length, and the aperture distribution is analyzed. Each setting has about 100 iterations. DFN hydraulic properties were estimated and compared with previous DFN studies, displaying the same behavior even though the magnitude of the estimated parameters differs. As an application example, structural measurements of the Alaska fault zone in the La Linea massif (Colombia) are used to obtain the statistical parameters of the fracture length and aperture distributions to generate the DFN. Five settings varying the fracture density are built, obtaining measured and simulated groundwater inflows of the same order of magnitude. These results highlight the potential of the synthetic DFN to analyze tunnels’ effects on groundwater flow.

This research contributes to the knowledge of the geothermal area of the Nevado del Ruiz Volcano (Colombia) by analyzing the secondary permeability and connectivity of fractures at microstructural and macrostructural level. Although the Nevado del Ruiz Volcano (NRV) area has had geothermal exploration studies for power generation since 1968, there is still no exploitation of its geothermal resources. The NRV geothermal reservoir is characterized by a low primary permeability and the presence of several geological faults crossing a tectonically active and complex region. The analysis was performed comparing a zone affected by intense faulting with another one characterized by the same lithology, but with less influence of faulting and located further from the volcano. Fractures were characterized at outcrops with the window sampling method, and petrographic analysis was performed to confirm the mineralogy of samples collected. At the microstructural scale it was found that faulting does not necessarily influence the interconnectivity of fractures, but it does influence their intensity, quantity, and strike. To analyze the influence of fractures on groundwater flow, it is suggested to consider three main aspects: secondary permeability, connectivity, and fracture intensity. The lithology of major geothermal interest in the NVR area (Pes) presented greater connectivity and fracture intensity, which, combined with the high foliation observed in field, increase its effective permeability. The secondary permeability of different lithologies in the NRV area ranged between 1.15 × 10 –6 and 10.32 × 10 –7 m 2 . Most of the hot springs were in areas of high macrostructural connectivity, supporting the idea that groundwater flow is dominated by the secondary permeability of rocks. Estimation of the secondary permeability and identification of areas of high fracturing and connectivity, contributes to the understanding of the NRV geothermal area, which is a key aspect when drilling for successful well production. The methodology presented is useful in the initial exploration phase in fractured geothermal reservoirs.

This paper presents simulation results of groundwater flow in fractured rocks. A stochastic approach is employed to build the conceptual model, a stochastic Equivalent Porous Medium fractured rock facies model, for the low-permeability bedrock found at Olkiluoto (Finland), which is the site chosen for the case-study. The volume of rock investigated is located around a cluster of boreholes and it covers an area of 160000 square meters. Field measurements during hydraulic interference tests are used to calibrate the groundwater flow model. Multiple stochastic facies realizations are considered to evaluate the impact of distribution and number of facies on simulated hydraulic heads and flow rates. This study quantifies the variability of numerical results, which is important for uncertainty analysis of hydrogeologic systems. Moreover, it shows that the stochastic facies conceptual model is a suitable alternative to discrete fracture network conceptual models.

La madera maciza da la forma al muro, los paneles son el recubrimiento y se clavan o atornillan a las secciones de madera. En las cavidades formadas entre los elementos de madera y el panel se debe adicionar un aislante térmico y también un aislante acústico. Infortunadamente, casi todos los aislantes usados en la actualidad (lanas minerales, poliestireno expandido, poliuretano) no son biodegradables y requieren el uso de barreras de vapor (láminas de polietileno, láminas de aluminio, etc.) que se deterioran rápidamente y son relativamente poco amigables con el medio ambiente. En este artículo, se propone usar la fibra de coco para reemplazar los aislantes convencionales. Se estiman los coeficientes de absorción acústica y de conductividad térmica de secciones compuestas tomadas de un muro de madera con fibra de coco. De esta forma, se busca mantener unas buenas condiciones termo-acústicas en el interior de la edificación de madera usando un material aislante ecológico Solid wood gives the shape to walls, while panels are the coating and they are nailed or screwed to the wood sections. In the cavities between the wood elements and the panels, a thermal and acoustic insulator must be added. Unfortunately, almost all of the currently used insulators (mineral wool, expanded polystyrene, polyurethane) are not biodegradable and require the use of vapor barriers (polyethylene sheets, aluminum foils, etc.) that deteriorate rapidly and that are relatively environmentally unfriendly. In this article, the use of coconut fiber instead of conventional insulators is suggested. The acoustic absorption and thermal conductivity coefficients of composite sections taken from wood walls with coconut fiber are estimated. In this way, good thermo-acoustic conditions inside the wood building are achieved using an ecological insulating material.