The system H2OCO2CH4H2 at travale, Italy: Tentative interpretation

doi:10.1016/0375-6505(80)90007-3

Geothermics

Volume 9, Issues 3–4, 1980, Pages 287-295

https://doi.org/10.1016/0375-6505(80)90007-3 Get rights and content

Abstract

The Travale geothermal field lies south-east of the well-known geothermal field of Larderello in Tuscany, Italy. It was discovered and exploited at a later date than Larderello. In 1978 samples were taken from all the productive wells in the area for chromatographic and mass-spectrometric analyses of gases and chemical analyses of the condensate. At the same time measurements were made of fluid temperatures at the wellheads and the gas : steam ratios. The chemical composition of the major gas species is presented and interpreted, particularly the relationship between the gases, water, carbon dioxide, methane and hydrogen. Using these relationships and the isotopic results some hypotheses are made on the origin of the gas species and the possible chemical and isotopic equilibria between the different fluid components

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Organic compounds in vent fluids from Yellowstone Lake, Wyoming
2021, Organic Geochemistry
Citation Excerpt :
The opposite is true for the three samples that contain microbial methane, showing higher sampling temperatures than predicted (71–87 °C). Similar observations were reported for fluids from a number of continental geothermal fields and mid-ocean ridge hydrothermal systems (Panichi et al., 1977; Nuti et al., 1980; Lyon and Hulston, 1984; Evans et al., 1988; Welhan, 1988; Podera et al., 1992; Giggenbach, 1997; Kelley and Früh-Green, 1999). A majority of the predicted equilibrium temperatures using the carbon isotope geothermometer (Eq. (3)) are higher than the maximum temperature of the vent fluids at subsurface in both fields (Fowler et al., 2019a,b), and the temperature (360 °C) of the perceived common hydrothermal reservoir shared by hydrothermal waters in Yellowstone (Hurwitz and Lowenstern, 2014).
Hydrothermal fluids were collected over a three-year interval (2016–2018) from two sublacustrine vent fields in Yellowstone Lake, Wyoming: Stevenson Island Deep Hole (YL16 and YL17 series in 2016 and 2017, respectively) and West Thumb (YL18 series in 2018). The TOC content in SI Deep Hole vent fluids varies from 2.7 mg/L to 6.3 mg/L in YL16 and 5.0 mg/L to 16.2 mg/L in YL17. Compared to YL16, the average TOC value of YL17 has more than doubled. The range of TOC is from 7.3 mg/L to 13.7 mg/L in the West Thumb samples. A positive correlation between TOC and dissolved CO₂ concentration is observed in most samples, suggesting their close relationship with sublacustrine heat and mass transfer processes. The organic compounds detected at both vent fields are diverse in molecular structure. In the SI Deep Hole, complex cyclic and unsaturated organic compounds are dominant, with cyclic hydrocarbons having the highest abundance, followed by carboxylic acids, PAHs, and alcohols. At West Thumb vents, propanol is most abundant, followed by alcohols, PAHs, alkanes, and carboxylic acids. This difference in structural complexity and relative quantity of organic compounds may be attributed to the involvement of hydrothermal processes. The vapor-dominated hydrothermal system and extensive fluid-rock interactions in SI Deep Hole facilitate alteration/decomposition of organic precursors. While CO_2(aq) is predominant in vent fluids, dissolved CH₄ is much less abundant. In SI Deep Hole, the carbon isotopic composition of CH₄ in most samples ranges from −20.4‰ to −38.0‰, with values of less than −60‰ in three samples, while CO₂ ranges from −4.4‰ to −10.5‰. A temporal variation of δ¹³C values was obtained for CO₂, with the average increasing from −9.2‰ (YL16) to −5.2‰ (YL17). In West Thumb, the δ¹³C value of CO₂ and CH₄ fall in a similar range, with an average of −10.5‰ and −19.0‰, respectively. There are multiple sources for observed carbon species: the interaction of vent fluids with subsurface rocks and lake sediments is the predominant process, followed by thermal decomposition of organic matter. Microbial activity on the lake floor may contribute to methane formation, while magmatic degassing is the major process that produces CO₂. The connection between vapor-dominated hydrothermal alteration, elevated TOC contents and dissolved CO₂ in vent fluids, and enrichment of ¹³C in CO₂ in YL17 in SI Deep Hole suggests an interplay of geological, chemical, and biological processes and their imprints on vent fluids, all of which make significant contribution to the carbon cycle in the Yellowstone Lake ecosystem.
Carbon isotope exchange in the system CO<inf>2</inf>-CH<inf>4</inf> at elevated temperatures
2001, Geochimica et Cosmochimica Acta
Carbon isotope exchange was investigated for the system CO₂-CH₄ at 150 to 600°C in the presence of several potential catalysts by use of isotopically normal or ¹³C-enriched gases. Silica gel, graphite, molecular sieve Linde 4A, magnetite, and hematite oxidized small amounts of CH₄ in starting CO₂-CH₄ mixtures to CO and CO₂ but failed to enhance the net rate of carbon isotope exchange between CO₂ and CH₄, even after 169 to 1833 h at 400 to 500°C. In contrast, several commercial transition-metal catalysts (Ni, Pd, Rh, and Pt) promoted reactions significantly toward chemical and isotopic equilibrium. With the Ni catalyst, the attainment of carbon isotopic equilibrium between CO₂ and CH₄ was demonstrated for the first time at temperatures from 200 to 600°C by complete isotopic reversal from opposite directions. The experimentally determined carbon isotope fractionation factors between CO₂ and CH₄ (10³lnα) were similar to, but slightly greater than (0.7–1.1‰, 0.89‰ on average), those of statistical-mechanical calculations by Richet et al. (1977). The experimental results can be described by the following equation between 200 and 600°C only: 10³lnα(CO₂-CH₄) = 26.70 − 49.137(10³/T) + 40.828(10⁶/T²) − 7.512(10⁹/T³) (T = 473.15–873.15 K, 1σ = ±0.14‰, n = 44). Alternatively, an equation generated by fitting Richet et al. (1977) data in the temperature range from 0 to 1300°C can be modified by adding +0.89‰ to its constant; 10³lnα(CO₂-CH₄) = 0.16 + 11.754(10⁶/T²) − 2.3655(10⁹/T³) + 0.2054(10¹²/T⁴) (T = 273–1573 K, 1σ = ±0.21‰, n = 44). This and other recent experimental studies in the literature demonstrate that transition metals, which are widespread in many natural materials, can catalyze reactions among natural gases at relatively low temperatures (≤200°C). The role of natural catalysts, “geocatalysts,” in the abiogenic formation of methane, hydrocarbons, and simple organic compounds has important implications, ranging from the exploration of hydrocarbon resources to prebiotic organic synthesis.
Origins of methane in hydrothermal systems
1988, Chemical Geology
Isotopic and compositional evidence indicates that the principal source of methane in most subaerial hydrothermal systems is from thermocatalysis of organic matter (thermogenesis). No firm evidence exists for abiogenic production at hydrothermal temperatures. However, abiogenesis represents the principal methane source in high-temperature rock-dominated mid-ocean-ridge hydrothermal systems, in which methane is derived from the rock itself.
The importance of carbon-isotope equilibrium between CH₄ and CO₂ at hydrothermal temperatures (≤350°C) is in dispute, although in most systems studied, equilibrium at such temperatures appears unlikely. Carbon isotope compositions of methane in high-temperature systems vary from ∼ −50 to -15‰ vs. PDB, with the most negative values occurring in systems with high CH₄ abundances, i.e. where thermocatalysis is important. Carbon isotope compositions of coexisting CO₂ also decrease with increasing CH₄ abundance (or degree of thermogenic input). This coupled carbon isotope variation suggests that high-temperature oxidation and thermocatalytic breakdown of organic carbon compounds are important in many hydrothermal environments.
The enrichment of ¹³C in methane from high-temperature mid-ocean ridge environments is consistent with isotopic equilibrium at very high temperatures (> 500°C) within the host rocks, and supports the concept of methane genesis within the rock prior to hydrothermal extraction. Unusual ¹³C-enriched methanes are also found in some subaerial geothermal systems, although a rock-derived origin remains speculative in these cases.
In light of the existing evidence, it appears that the sources of methane (either thermogenesis from organic carbon or abiogenesis within rocks) are much more important in determining the relative abundance and carbon isotope composition of hydrothermal methane than any subsequent approach to chemical and/or isotopic equilibrium under hydrothermal conditions.
C- and O-isotope and fluid inclusion studies of carbonates from pyrite and polymetallic ore deposits and associated country rocks (Southern Tuscany, Italy)
1985, Chemical Geology: Isotope Geoscience Section
A total of 42 C- and O-isotopic analyses on 35 samples of carbonates from pyrite and polymetallic deposits of southern Tuscany and associated country rocks are presented. Hydrothermal calcites and dolomites in the ore deposits show a wide range of isotopic compositions, which probably accounts for multiple sources of carbon and oxygen. Calculated isotopic compositions for COH species in equilibrium with calcites are similar to those measured in present-day geothermal fluids of the nearby Larderello-Travale field, suggesting a common link for all late- to post-Apenninic hydrothermal manifestations in the area. The isotopic compositions of country rocks range from typical marine values to lower values, the isotopic depletion likely accounting for metamorphic and hydrothermal effects related to the Mio-Pliocene Apenninic event. In contrast, 10 samples of similar rocks from non-mineralized areas of northern Tuscany show no isotopic evidence of metamorphic and hydrothermal alteration. Data from fluid inclusions indicate important relationships between calcite-forming fluids and sphalerite-forming fluids in the ore deposits here studied.
Elementary and isotopic compositions of noble gases in geothermal fluids of Tuscany, Italy
1984, Geothermics
Analyses were made of the major gases, as well as helium and radon, in fluids from more than 90 geothermal wells in Tuscany. The elementary and isotopic abundances of the noble gases were determined by multiple samplings in seven wells. The results show good correlations between constituents of atmospheric origin and those of deep origin, suggesting the existence of a mixing between cold waters and hot fluids, a process which takes place at considerable depth. The helium isotopic ratios indicate the presence of a radiogenic crustal component. Enrichment of radiogenic argon and excess nucleogenic neon-21 were measured in some samples. Calculations were also made of the ⁴He/²²²Rn ages of the gas sources.
Geothermal fields and thermal waters of Greece: An overview
2014, Geothermal Systems and Energy Resources: Turkey and Greece

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The system H2OCO2CH4H2 at travale, Italy: Tentative interpretation

Abstract

Geochim. Cosmochim. Acta

Geothermics

Report to Commission of EEC, EEC-CNR Contract No. 112-76 EGI

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Erdöl u. Kohle

Erdöl u. Kohle

Investigation of the mechanism of methane oxidation by labelled molecules

Recent development of geothermal exploration in the Travale-Radicondoli area

Carbon isotope composition of individual hydrocarbons from Italian natural gases

Nature

Carbon isotope composition of individual hydrocarbons from Italian natural gases

Nature

Carbon isotope study on methane from German coal deposits

The geochemistry of the stable carbon isotopes

Geochim. Cosmochim. Acta

Notes on the chemistry of geothermal gases

Geothermics

Chemical equilibrium in magmatic gases

Am. J. Sci.

The system H₂OCO₂CH₄H₂ at travale, Italy: Tentative interpretation