Evolution of light hydrocarbon gases in subsurface processes: Constraints from chemical equilibrium

Sugisaki, Ryuichi; Nagamine, Koichiro

doi:10.1016/0012-821x(95)00065-k

Cited by 15 publications

(6 citation statements)

References 21 publications

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“…As shown by the log(CH 4 /C 2 H 6 ) versus log(C 2 H 6 /C 3 H 8 ) diagram (Figure 10), geothermal gases plot within the isotherms 220–260°C (dashed lines) of the CH 4 ‐C 2 H 6 ‐C 3 H 8 equilibrium, in agreement with the temperatures measured at depth ranging from 1500 to 2400 m in the Berlin geothermal field, and slightly higher than those found in the Ahuachapan‐Chipilapa geothermal field at shallower depth (600–1500 m) [ D'Amore and Mejia , 1999] and with those calculated with the Na‐K‐Ca geothermometer [ Fournier and Truesdell , 1973] by Snyder and Fehn [2002]. This represents an important result because it seems to constitute one of the rare examples of thermodynamic equilibrium attained among the C 1 ‐C 2 ‐C 3 alkanes [ Sugizaki and Nagamine , 1995; Capaccioni and Mangani , 2001]. A second fundamental indication is that gases from both fumaroles and geothermal wells are in the same range of equilibrium temperatures (Figure 10), although, as previously observed (Figures 4 and 5), hydrocarbon contents in fumaroles are strongly affected by secondary interactions.…”

Section: Geothermometrymentioning

confidence: 89%

“…Accordingly, laboratory experiments, conducted at 300 to 350°C and 350 bar to examine chemical interactions of light hydrocarbons with water under the redox control of Fe‐bearing mineral buffers, have demonstrated that alkene‐alkane, alkene‐ketone and alkene‐alcohol pairs are able to achieve metastable equilibrium states within the timescale from hundreds to thousands of hours [ Seewald , 1994, 2001]. In relation to the results of these investigations, the possible application of organic gas composition to geothermometry has been extensively debated [e.g., Sugisaki and Nagamine , 1995; Taran and Giggenbach , 2003; Capaccioni et al , 2004]. Several authors [e.g., Giggenbach , 1997; Taran and Giggenbach , 2003] have stressed the fact that hydrolysis reactions regulating the C 1 ‐C 2 ‐C 3 ‐C 4 alkane system in natural environment are not reversible processes, since the reversibility of the stepwise breakage of C‐C bonds is largely limited by a kinetic barrier [ Stocchi , 1991].…”

Section: Geothermometrymentioning

confidence: 99%

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Scrubbing process and chemical equilibria controlling the composition of light hydrocarbons in natural gas discharges: An example from the geothermal fields of El Salvador

Tassi¹,

Vaselli

Capaccioni

et al. 2007

Geochem Geophys Geosyst

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[1] The compositional features of fluids from both fumarolic discharges and productive geothermal wells of Ahuachapan-Chipilapa, Berlin-Chinameca, and San Vicente geothermal systems (El Salvador) are described and discussed in order to investigate the complex geochemical interactions involving geothermal fluids within the shallowest part of the hydrothermal circulation pathways. Our results highlight that secondary processes are able to strongly affect and modify the chemical characteristics of geothermal gases once they discharge to the surface as natural manifestations, mainly in relation to the chemical-physical properties of each gas species. The effects of both gas dissolution in shallow aquifers and gas-water-rock chemical interactions on gas discharge composition make it difficult to get a correct evaluation of the thermodynamic conditions that characterize the geothermal reservoirs by applying the common geoindicators based on the chemical equilibria of the H 2 O-CO 2 -H 2 -CH 4 -CO system. Differently, the composition of the C 1 -C 2 -C 3 alkanes and the C 3 and C 4 alkane-alkene pair, established within the geothermal reservoirs under the control of chemical reactions, remains stable in samples collected from discharging gas vents. These results suggest that the relative abundances of hydrocarbons characterized by similar structure and molecular size seem to be mainly regulated by the diffusion velocity of gases through the liquid-dominated system. Therefore the chemical features of the light organic gas fraction of naturally discharging fluids can be successfully utilized for the evaluation of geothermal reservoir temperatures and redox conditions, providing useful indications in terms of geothermal exploration and exploitation. On this basis, the distribution, speciation, and relative abundances of light hydrocarbons can also be considered highly promising in geochemical monitoring of active volcanic systems.

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Section: Geothermometrymentioning

confidence: 89%

Section: Geothermometrymentioning

confidence: 99%

Scrubbing process and chemical equilibria controlling the composition of light hydrocarbons in natural gas discharges: An example from the geothermal fields of El Salvador

Tassi¹,

Vaselli

Capaccioni

et al. 2007

Geochem Geophys Geosyst

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“…This may suggest that the C 1 /C 2 ratios are in excess what may be expected from equilibrium as calculated from inorganic species. According to Sugisaki and Nagamine (1995) this is typical of a not thermochemically controlled biogenic production of gas. Instead of this hypothesis we believe that the observed disequilibrium could be related to re-equilibration of methane in the system CH 4 /CO/CO 2 and the quenching of the system CH 4 /C n H 2n /C n H 2n12 during cooling.…”

Section: Degradation Of Hydrocarbon Compoundsmentioning

confidence: 99%

Organic and inorganic geochemistry of low temperature gas discharges at the Baia di Levante beach, Vulcano Island, Italy

Capaccioni

Tassi

Vaselli

2001

Journal of Volcanology and Geothermal Research

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Discharge from subaereal and submarine gas vents of the Baia di Levante beach gases from the Vulcano Island were sampled for major and trace gas components in May and November 1995.Chemical compositions and equilibrium calculations suggest three different groups of CO 2 -rich gas emissions depending on their distance from the La Fossa crater: (1) gas vents close to the Faraglione area are characterised by high H 2 S contents, high calculated equilibrium temperatures based on inorganic species and relatively high proportion of alkene compounds; (2) gas vents close to Vulcanello are characterised by low calculated equilibrium temperatures and low amounts of alkenes; and (3) Pontile sample has the highest equilibrium CO 2 pressure (up to 68 bars) which may account for the observed absence of benzene. The relative large variability of H 2 S in the Baia di Levante beach gas discharge may be attributed to either different interactions between iron sulphides and weakly acid waters or catalytic effect of elemental sulphur on the de-hydrogenation of cyclo-hexane. Thermodynamic calculations suggest that the main inorganic species and CH 4 may have re-equilibrated at relatively shallow depth (10±200 m b.s.l. and 30±600 m b.s.l. for a lithostatic and hydrostatic pressure, respectively). The slow kinetics of reactions in the C n H 2n /C n H 2n12 systems, with respect to that of CH 4 ±CO±CO 2 , may explain the observed propene/propane ratios, which can only be reached at reaction temperatures of 300±3508C. This low speed of reactions can also explain the observed disequilibrium of C1±C4 alkanes. q

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“…But 0 can only occur in an environment of very high temperature, such as the mid-ocean rift, so that the origins of organic gases in crustal fluids usually include 0 and 0 (Wellan, 1988). Sugisaki and Nagamine (1995) studied the chemical equilibrium behaviors among light hydrocarbons and found that an equilibrium among three lightest alkanes CH4, C2& and C3H8 is attainable at temperatures higher than 200°C: C€&+C3H8=2C&…”

Section: 2mentioning

confidence: 99%

“…(1) For organic gases generated by microorganism activity, lgK,-lgKT <O in reaction (l), where lgK, is the calculated equilibrium constant of reaction (1). and lgKT is the equilibrium constant of reaction (1) at homogenization temperature (Shock and Helgeson, 1990); while for those originating from thermal cracking of kerogens, lgK,-lgK+O in reaction (1) (Sugisaki and Nagamine, 1995). In Fig.…”

Section: 2mentioning

confidence: 99%

Light Hydrocarbons in Fluid Inclusions and Their Constraints on Ore Genesis: A Case Study of the Songxi Ag (Sb) Deposit, Eastern Guangdong, China

Sun

Norman

Sun

et al. 2003

Acta Geologica Sinica (Eng)

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The Songxi deposit is a newly discovered large Ag (Sb) deposit. By using a suite of high‐vacuum quadrupole gas mass spectrometer systems, the authors have recognized many kinds of light hydrocarbons in fluid inclusions of minerals. These hydrocarbons are mainly composed of C1‐C4 saturated alkanes, while the contents of C2‐C4 unsaturated alkenes and aromatic hydrocarbons are quite low, suggesting that the metallogenic processes have not been affected by magmatic activities. Chemical equilibrium studies show that these hydrocarbons may be a mixture of organic gases generated by microorganism activity and those by thermal cracking of type‐II kerogens (kukersite) in sedimentary host rocks, and the former may constitute more than two‐thirds, implying that microorganism might have played an important role in the metallogenesis. The equilibrium temperature of the latter is about 300°C, which is much higher than the geothermal temperature at the estimated depth of metallogenesis. Thus, the light hydrocarbons generated by thermal cracking of kerogens probably originated in the deep part of the sedimentary basins and then migrated through a long distance to shallower horizons of the basin. Based on the composition of light hydrocarbons in fluid inclusions, the authors infer that the Songxi deposit was formed in a continental rift. The analytical data presented in this paper support from one aspect the genetic model that the Songxi deposit may be a sedimentary hot brine transformed deposit instead of a submarine basic volcanic exhalation and low‐medium temperature volcanic hydrothermal fluid filling deposit proposed by most previous researchers.

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Evolution of light hydrocarbon gases in subsurface processes: Constraints from chemical equilibrium

Cited by 15 publications

References 21 publications

Scrubbing process and chemical equilibria controlling the composition of light hydrocarbons in natural gas discharges: An example from the geothermal fields of El Salvador

Scrubbing process and chemical equilibria controlling the composition of light hydrocarbons in natural gas discharges: An example from the geothermal fields of El Salvador

Organic and inorganic geochemistry of low temperature gas discharges at the Baia di Levante beach, Vulcano Island, Italy

Light Hydrocarbons in Fluid Inclusions and Their Constraints on Ore Genesis: A Case Study of the Songxi Ag (Sb) Deposit, Eastern Guangdong, China

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