Geothermics最新文献

The Philippines is the third largest geothermal power-producing country in the world. However, additional opportunities exist to expand the geothermal portfolio of the country with the exploitation of low- and moderate- temperature resources, as well as assessment and development of hidden geothermal systems (i.e., those with no active surface manifestations). As part of the Geothermal Development Initiative (GEODE) funded through the U.S. Department of State award to the University of Nevada, Reno, a collaboration between the Philippines Renewable Energy Management Bureau (REMB) of the Department of Energy and the University of Nevada in Reno, Great Basin Center for Geothermal Energy occurred from September 2022 to March 2024. As part of this collaboration, an expert-driven geothermal Play Fairway Analysis (PFA) was conducted in the northwestern portion of Luzon Island of the Philippines utilizing existing data sets available to the REMB. The goal of this PFA is to identify areas with greater relative geothermal favorability, determine where the data gaps are, and assist in the discovery of hidden geothermal systems. A geothermal PFA requires the compilation and transformation of datasets into appropriate formats (e.g., tables, shapefiles, and raster files) and evaluation of each dataset to determine how it can be used as a proxy for the key attributes of a geothermal system (e.g., heat and permeability). Once the data are organized, they are weighted for integration into the GIS software to develop a favorability model for heat and permeability. The attribute models are then combined to produce two PFA models: the conventional hydrothermal low- to moderate- temperature geothermal favorability and the hidden systems favorability. The data difference between the conventional geothermal favorability and hidden systems models is that hot springs are not used for the hidden systems model. The conventional favorability model of northwestern Luzon Island indicates areas of higher geothermal favorability in the central and southern sections of the study area. Many of the favorable areas identified in the conventional model already have active leases for geothermal exploration, lending more confidence to the methodology and model, and suggesting that the areas with no current leases and high geothermal favorability could represent future exploration targets. The hidden systems model shows favorable zones in the north, central and southern sectors, and can serve as a tool to decide the areas for exploration of potential hidden geothermal systems, particularly, in the Ilocos Norte, Apayao, and Nueva Viscaya regions.

For effective fracture stimulation in Enhanced Geothermal Systems (EGS), characterization of subsurface rock elastic properties is essential. Because seismic anisotropy significantly influences hydraulic fracturing, locating and characterizing microseismic events, and forecasting stress trajectories, our research undertakes laboratory experiments to study seismic anisotropy parameters of core samples from the Utah FORGE EGS site. We evaluated two rock samples from well 58–32, at two depths of 2074.16 m (6,805 feet) and 2268.01 m (7,441 feet), respectively. We analyze the mineralogy and classify the shallower rock as syenogranite, and the deeper rock as orthogneiss and monzonite. We cut cylindrical plugs from these two core samples, imaged them by computed tomography (CT) X-ray imaging, and measured their seismic anisotropy using ultrasonic waves at 1 MHz and under varying confining pressures (5–50 MPa) in ambient temperature conditions. With the assumption of the transversely isotropic (TI) medium, we measured three P-wave velocities and two S-wave velocities along different propagation directions to compute the Thomsen anisotropy parameters. Our results showed that the measured seismic velocities of each rock sample increase with increasing effective pressures, a behavior likely caused by closure of microcracks identified in our CT images. We also find that the measured anisotropies are higher at lower effective pressures. The maximum measured anisotropies for P-waves and S-waves are ∼23% and ∼20%, respectively. Therefore, we expect in the field operation that anisotropy should increase with increasing pore pressure caused by injection, which could be valuable in future EGS reservoir management and monitoring.

Reactive transport modelling plays a crucial role in unravelling the dynamics of geothermal reservoirs as they evolve. By utilising these models, we gain a deeper understanding of the temporal progression of mineral alteration and its influence on the reservoir's characteristics.

This study was designed to understand the mineralogical and geochemical evolutionary process of conventional geothermal reservoirs. An idealised 3D large-scale numerical model was set up to comply with the prevailing conditions in a two-phase liquid-dominated geothermal reservoir with near-neutral pH and a temperature of up to 350 °C. The models were established to assess the long-term fluid-rock interaction in tholeiitic basalt-hosted geothermal systems, including the effects induced by the natural influx of CO₂, H₂S and H₂ from the magmatic body heat source of the theoretical reservoir. As part of the study, gold, which is associated with hydrothermal systems, was included in the geochemical system to investigate ore deposition processes.

Our reactive transport study results indicate that basalt glass, olivine, augite and the primary plagioclase altered to form secondary albite, chlorite, grossular, epidote, quartz, zeolites and carbonates after 100,000 years. Due to mineral alteration, reservoir porosity and permeability are expected to decrease with time. A near-stable state was achieved based on the temperature profile and a comparative analysis of geochemical results over time. Gold in the basalt was shown to dissolve at depth and re-deposit at shallower locations, resulting in high concentration regions.

The Cambrian limestone of the Pingdingshan coalfield in central China possesses substantial geothermal waters. The efficient extraction and utilization of these mine geothermal resources are crucial for the reduction of carbon emissions, thereby enhancing the sustainability of energy management in this coalfield. In this work, we collected data on geothermal waters in the eastern Pingdingshan coalfield, analyzed the chemical characteristics of geothermal water, and identified the control of regional structure on the geothermal system. Geochemical results show that the main type of Cambrian geothermal water in the eastern Pingdingshan coalfield is Na-Ca-HCO₃-SO₄, which is classified as a peripheral water source and is predominantly a product of water-rock interactions. The mean temperature of the Cambrian thermal reservoir is 68.6 °C, with an average geothermal water circulation depth of 1441 m within the Cambrian limestone. Isotopic data (δ¹⁸O and δ_D) indicate that atmospheric precipitation is the principal source of geothermal water, forming hydrothermal geothermal resources through the heating of high-temperature rock during seepage. A slight positive δ¹⁸O shift suggests minimal water-rock interaction with the surrounding rock, categorizing it as a low-temperature geothermal resource. Heat flow measurements in the eastern Pingdingshan coalfield range from 65 to 80 mW/m², with an average geothermal gradient of 36.3 °C/km, characteristic of a high geothermal region. A distinct jump at the base of the PBR1 temperature curve points to the presence of a high-temperature Proterozoic thermal reservoir beneath the Cambrian limestone. The dual tectonic heat accumulation model determines the occurrence environment of the hydrothermal system in the eastern Pingdingshan coalfield. The geothermal system here is governed by the spatial configuration of regional structures and rock thermal conductivity, where extensional faults dictate the spatial morphology of hydrothermal systems, and variations in rock thermal conductivity influence heat conduction pathways.

Ensuring an optimal nocturnal microclimate within greenhouses is essential for successful crop cultivation. In regions like Tunisia, characterized by arid and semi-arid climates, managing temperature and humidity during the night, particularly in cold winter months, is challenging and often requires external heating sources. This study aims to investigate the use of geothermal energy as a sustainable solution for greenhouse heating, focusing on an innovative helicoidal geothermal system to maintain ideal nocturnal conditions.

The primary objective of this research is to evaluate the effectiveness of the helicoidal geothermal system in achieving optimal temperature and humidity levels for plant growth during the night. Conducted at the Research and Technology Centre of Energy in Tunisia, the experimental investigation involved a new ground heat exchanger coupled with a heat pump system.

The experimental setup consisted of two greenhouses: one serving as a control and the other equipped with two Conic Helicoidal Ground Heat Exchangers (CHGHE) and a Ground-Source Heat Pump (GSHP) system, which includes both underground and suspended heat exchangers. The results demonstrated that the geothermal system, operating at an optimal flow rate of 0.6 kg/s, successfully maintained the nocturnal comfort temperature required for plant growth. The coefficients of performance for the geothermal heat pump ($CO{P}_{hp}$) and the overall system ($CO{P}_{sys}$) were calculated to be 3.12 and 2.7, respectively.

These findings underscore the potential of near-surface geothermal energy, utilizing a geothermal heat pump, to efficiently heat greenhouses under the climatic conditions of Tunisia. This approach not only supports sustainable agricultural practices but also offers significant energy efficiency and cost-saving benefits.

The formation, precipitation, and deposition of the so-called “iron silicate” in geothermal waters have been among the problematic issues in some geothermal installations. Our approach aims to systematically study the influence of phosphonate-based chemical additives on the formation of precipitates in the presence of both silicate and ferric (Fe³⁺) ions. The selection of this type of antiscalants was based on their extraordinary affinity for metal ions in general, and in particular for ferric cations. For this purpose, various phosphonate additives that possess diverse chemical structures and variable numbers of functional groups have been systematically evaluated. These additives are PBTC (2-phosphonobutane-1,2,4-tricarboxylic acid), HEDP (hydroxyethylidene-1,1-diphosphonic acid), AMP (amino-tris(methylenephosphonic acid)), HDTMP (hexamethylenediamine-tetrakis(methylenephosphonic acid)), DTPMP (diethylenetriamine-pentakis(methylene phosphonic acid)) and BHMTPAMP (bis-hexamethylenetriamine-pentakis(methylenephosphonic acid)). Experiments were conducted in solutions containing silicate (150 ppm, expressed as SiO₂) and iron (150 ppm, as Fe) at pH 7.0. The phosphonate additives used were found to act as stabilizing agents, most likely by complexing the Fe³⁺cations, thereby preventing ferric silicate formation. The experimental design included a plethora of physicochemical parameters, such as antiscalant concentration, salinity, and temperature. Based on the generated experimental data, numerous functional insights have been generated, contributing to a more complete and comprehensive understanding of the mechanism of ferric silicate control.

This work presents an evaluation method for thermal response tests (TRT) on geothermally activated building systems (gTABS). In contrast to borehole heat exchangers (BHEs), the infinite plane source model is appropriate for a gTABS. However, the time criteria defining the applicability of the analytical model are more restrictive than those for BHEs. A minimum time criterion serves as the starting point for the evaluation and a maximum time criterion sets an upper limit. With consistent values for the heat penetration coefficient in all three TRTs performed, the method shows good consistency in compliance with these criteria. Together with the investigation of the undisturbed ground temperatures, the TRT method presented here yields valuable data that allows to assess the performance of a gTABS as a heat source for heat pump applications.

The interest in the utilization of geothermal energy has increased exponentially in the past few decades, and researchers internationally are currently focusing on improving harvesting methods and promoting it due to its numerous benefits compared to traditional energy sources. Corrosion and scaling are two of the significant problems in modern geothermal industry that occur during the harvesting of geothermal energy. Scaling occurs due to the variety of anions and cations that the majority of geothermal reservoir waters contain. High levels of dissolved Fe³⁺ and silicate ions cause the formation of the elusive “iron silicate”, the latter term usually referring to ferric silicate. Its identity, as it is formed in geothermal waters, differs from its geological counterparts. Usually, deposits that contain Fe and Si are referred to as “iron silicate”, revealing very little about its true identity. This research is focused on revealing the true nature of the so-called “ferric silicate”, performing a series of synthesis experiments under various conditions that take into account iron and silicate concentrations (at the supersaturation regime), solution pH, temperature and different sources of iron. Although solutions containing 150 ppm silicate (no ferric) are stable and do not undergo any polycondensation at pH = 7.0, the presence of ferric induces variable silicate loss from solution. Its severity is enhanced as the ferric concentration increases. Ferric loss from solution in the presence of silicate ions is also severe, regardless of the silicate concentration. Both silicate and ferric loss from solution are pH-dependent processes, with a maximum observed around pH = 7.0. This loss is accompanied by precipitate formation, which is corroborated by turbidity measurements. The solubility of ferric silicate (under the conditions studied) increases with temperature. There is a roughly 4-fold solubility increase when the temperature is increased from 25 °C up to 220 °C. However, enhanced ferric incorporation into the final precipitate was observed at higher temperatures. The ferric silicate precipitates were characterized by several techniques, such as powder XRD, ATR-IR, SEM, and EDS, and showed that ferric silicate is an amorphous precipitate with variable Fe:Si atom ratios and a random Fe distribution throughout the solid. These results can serve as a roadmap for ferric silicate precipitation, taking into account the water chemistry of a specific scale-forming brine.