Chemistry Of Geothermal Fluids Research Articles

Global Occurrence, Geology and Characteristics of Hydrothermal-Origin Kaolin Deposits

Kaolin-group minerals occur in nature as the result of high-sulfidation acid sulfate, sulfur-poor HCl-, HF- and H2CO3-rich acidic fluid-related hydrothermal alterations and in situ geochemical weathering. These minerals possess different crystallographic and chemical properties that determine their application areas, mainly in the ceramic and paper industries, and as nanocomposite materials. The physicochemical properties of hydrothermal kaolin deposits are the result of the type of parent rock, the effect of the regional tectonism-associated magmatism, and the chemical features of hydrothermal fluids that interact with the deep basement rocks. However, understanding these geothermal systems is one of the most challenging issues due to the rich mineralogical assemblages, complex geochemistry and isotopic data of hydrothermal alteration zones. This study evaluates the formation of hydrothermal-origin kaolin-group minerals by considering their characteristics of hydrothermal alteration, isotopic compositions and differences in characteristic properties of low- and high-sulfidation occurrences; this paper also addresses mineralogical and structural differences between hypogene and supergene kaolin formations, and kaolin–alunite–pyrophyllite association, and it provides examples of worldwide occurrences. The study of the mineralogical assemblages, geochemistry and isotopic data of the hydrothermal alteration zones is one of the most challenging subjects in terms of gaining a detailed understanding of the geothermal systems. Silicification processes are subsequent to late-stage alteration after the completion of kaolinization processes, erasing existing hydrothermal mineralogical and geochemical traces and making interpretation difficult. In the early stages involving magmatic–hydrothermal-origin acidic geothermal fluids, the latter comes from the disproportionation of SO2 (+H2O) and H2S oxidation to H2SO4 in hydrothermal environments. In the later stages, due to spatial and temporal changes over time in the chemistry of geothermal fluids, the system comes to have a more alkali–chloride composition, with neutral pH waters frequently saturated with amorphous silica which characteristically precipitate as siliceous sinter deposits containing large amounts of opal-A.

Geothermal fluid chemistry and isotope for interpreting the formation of complex geothermal system in the Gonghe Basin, northeastern Tibetan Plateau

The Gonghe Basin is located in the northeast of the Tibetan Plateau and is rich in geothermal resources. In recent years, Hot Dry Rocks have been discovered in the basin, and related studies have suggested that localized melts in the middle and lower crust provide an additional heat source. However, there needs to be more conclusive evidence. In this paper, geothermal water chemistry and gas isotope samples from the Gonghe Basin and its neighboring areas were systematically collected. Comprehensive fluid geochemical analysis was carried out in conjunction with the distribution and nature of the regional fracture to propose the circulation pattern of the complex geothermal system and the source of the gas components in the Gonghe Basin. The results show that the hot water in the Gonghe Basin and its surroundings is recharged by meteoric water and can be classified into three types according to its hydrochemical and isotopic characteristics: deep-fluid type (deeper circulation depth or deeper burial of the geothermal reservoirs), runoff type (shallower circulation depth), and mixed type (shallow layered geothermal reservoirs at the center of the basin), with a gradual decrease in the temperature of the geothermal reservoirs accordingly. N2 of atmospheric origin dominates the hot water gas. Except for the relatively high CO2 concentration (7.44%) in the deep geothermal reservoir in the center of the basin, most of the samples contain low CO2 concentration, which is mainly derived from decarbonization of carbonate rocks and sediments, and the contribution of mantle carbon release is almost zero; some of the hot water is detected with a slightly higher content of CH4, which is inferred to be of organic origin. The distribution of deep fractures provides a channel for the uplift of deep mantle-sourced volatiles, which makes some hot springs and geothermal wells show some mantle-sourced diagenesis of He, which provides some corroboration for the existence of partial melts in the crust. This understanding is significant for deepening the understanding of geothermal genesis in the northeast Tibetan Plateau and guiding future geothermal exploration in the region.

Analysis of geothermal fluid chemical characteristics and genetic model—A case study from the urban area of Jingmen China

Over the years, scholars both at home and abroad have been committed to the research of geothermal fluid chemistry and genetic model, and geochemical and isotopic methods are usually the first choice for evaluation. In this paper, the characteristics of geothermal fluids and their genesis patterns in the Jingmen urban area are analyzed and studied by comprehensive utilization of techniques such as hydrochemistry, trace elements, and isotope analysis. The results show that the water chemical type of surface water and groundwater is Ca-HCO3 type, while the geothermal fluid belongs to the Ca-SO4 type. The recharge source of the geothermal fluid is the infiltration recharge of meteoric precipitation, and the recharge altitude is 395–435 m, and the geothermal fluid is modern water (less than 5–10 years old). The water-rock reaction has not reached equilibrium, and the dissolution is still in progress. The estimated mixing ratio of cold-water ranges from 30%–40%. The thermal reservoirs are mainly calcareous dolomite and dolomite of the Lower Triassic Jialingjiang Formation (T1j). The red sandstone and mudstone of the Upper Cretaceous Paomagang Formation (K2p) distributed in the area are good caprocks of the geothermal field. The geothermal energy in the urban area of Jingmen is a system of lateral “seepage.” Thermal water surges up along the Jingmen fracture and fracture zone, forming a relatively high-temperature center, and a part of its “seeps” laterally into the shallow pore aquifer or pore-fracture aquifer, which mixed with the cold water in it to form medium and low-temperature hot water around the center of the geothermal area.

Life cycle assessment of geothermal power generation technologies: An updated review

The market of energy production coming from geothermal energy is growing around the world. However, in some countries little attention is given to the life cycle environmental impacts of this industrial sector. In addition to the available work presented in previous reviews about this matter, this paper provides an updated review of life cycle environmental studies for the geothermal power generation. For the first time, these results have been compiled by energy conversion technology: dry steam, binary cycle, single flash, and double flash, including the generation pilot projects of enhanced geothermal systems.The analysis of the review shows that the environmental impacts are evaluated by considering from 1 to 18 impact categories commonly used in life cycle assessment (LCA). These impacts are mainly affected by: (i) reservoir characteristics; (ii) geothermal fluid chemistry; (iii) power generation technology; (iv) type of emissions of the life cycle inventory; and (v) data availability. Most of the LCA studies reported global warming, which is mostly caused by the fuel consumption in the construction and operation stages. A deeper analysis of the life cycle environmental impacts to promote an environmental sustainable management of geothermal power generation is proposed, which still represents a challenge for this industrial sector.

Diurnal variations in the chemistry of geothermal fluids after discharge, Champagne Pool, Waiotapu, New Zealand

Champagne Pool, Waiotapu, New Zealand discharges reduced geothermal fluids rich in CO 2, H 2S trace elements, and over-saturated with respect to several sulfide minerals including orpiment, stibnite and carlinite. After discharge from Champagne Pool, the geothermal fluid cools, degasses and flows over a silica-sintered terrace that hosts a diverse microbial community. Geothermal fluid from Champagne Pool was sampled every 2 h for a 24-h period at five sites between the spring and above the first major downstream dilution. Systematic diurnal variations in composition occur at the three most downstream sample sites whereas the composition of the two upstream sites remains comparatively constant. At the three downstream sites, daytime increase in the concentration of dissolved As, Sb and Tl coincides with peak photosynthetic dissolved oxygen (DO) concentrations. Field observations, analyses and modelling with PHREEQC indicate that sulphur, and amorphous equivalents of orpiment, stibnite and carlinite precipitate at night within Champagne Pool and on some of the sinter terrace area. However, on the sinter terrace, daytime increases in DO concentrations from photosynthetic bacteria are sufficient to destabilise the sulfide minerals and sulfur that precipitate at night, enabling oxidation of the amorphous precipitates during the day. Oxidation of As, Sb and Tl sulfides and sulfur is probably biologically catalysed and causes a pronounced daytime decrease, >2 pH, at the two most downstream sites. Diurnal increases in the concentrations of Be, Ba and Sr at the two furthest downstream sites are likely to be related to the pH decrease caused by upstream oxidation. The geochemical mechanism responsible for daytime concentration increases in Be, Ba and Sr is unclear. Two processes that could be disrupted by daytime pH decrease are precipitation of silicate, sulfate or carbonate minerals on the sinter terrace or adsorption of trace elements onto clay minerals, viable/non-viable organic material or amorphous sulfide precipitates. These findings have implications for sampling programmes within geothermal areas and other environments such as estuaries and wetlands, where reduced mineral species could interact with photosynthetic biological processes.

High salinity fluid handling in Milos geothermal field

On Milos island, where a high enthalpy gecthermal field capable:of producing high salinity fluids has been discovered a 2MW Pilot plant was installed. Systematic production tests have been carried out at the production well, with emphasis on geothermal fluid chemistry and behaviour. During successive long term operation trials of the Unit (turbogenerator, steam gathering and brine transmission system), problems arose in both steam and brine cycles due to severe scaling phenomena encountered. The sequence of events in identifying the scaling problems and the technical approaches applied to remedy them, are reported in this paper together with data concerning the plant's operational problems and with the direct hot reinjection used as brine disposal method.

Chemistry of Geothermal Fluids Discharged from Exploration Wells at Mokai/New Zealand

Chemistry of Geothermal Fluids Discharged from Exploration Wells at Mokai/New Zealand

Geothermal fluid chemistry of the Orakeikorako field, New Zealand

Abstract Samples of water and steam from natural discharges in the Orakeikorako geothermal area of the Taupo Volcanic Zone have been analyzed for their chemical and stable isotopic components. The waters are near neutral, with chloride contents less than 400 mg/kg. A model of the subsurface hydrology, based upon well measurements and chemical and isotopic measurements has been developed, in which the dilute waters discharged at the surface are considered to result from the dilution of deeper fluids which may have temperatures as high as 280°C. In the northern parts of the field waters with relatively lower chloride and higher bicarbonate composition have further diluted the rising fluid. There is no evidence that local lake or river waters have changed the field character or water composition significantly since the river water level was raised.

Geothermal fluid chemistry and human health

Several effects on the environment arising from the utilization of geothermal resources may affect human health. (1) Human surroundings: changes in noise level, local climate, and landscape. (2) Water pollution: hot water geothermal fields emit large quantities of saline fluids which contain fluoride, boron, arsenic, and minor amounts of other heavy metals. Heavy metal sulphide precipitates form from some geothermal waters and collect in river sediments. Processing of geothermal waters to remove heavy metals may be necessary. Sulphide, boron, ammonia, and mercury may also enter local waters from geothermal steam condensates. (3) Air pollution: emission of CO 2 and H 2S from geothermal power stations in some extreme cases may approach the outputs from similar-sized coal-fired stations. Sulphide emission can be controlled by chemical processing of condensate and waste gases. Mercury from geothermal steam is unlikely to cause local levels in air to rise by more than 1 ppb. The significant environmental problems from geothermal development are capable of technical solution but add significantly to the cost of geothermal power.