An oxygen isotope study of silicates in the larderello geothermal field, Italy

Stable-isotope analyses were carried out on hydrothermal minerals sampled from the deep metamorphic units at Larderello, Italy. The ∂¹⁸O values obtained for the most retentive minerals, quartz and tourmaline, are from + 12.0‰ to + 14.7‰ and 9.9‰, respectively, and indicate deposition from an ¹⁸O-rich fluid. Calculated ∂¹⁸O values for these fluids range from + 5.3‰ to + 13.4‰. These values, combined with available fluid inclusion and petrographic data, are consistent with the proposed existence of an early thermal fluid of probable magmatic origin and a late meteoric water. Mixing between these two fluids occurred locally.     

The oxygen isotope exchange between carbon dioxide and water in the Larderello geothermal field (Italy) during fluid reinjection

The oxygen isotope compositions of CO₂ and water vapor samples collected from Larderello geothermal wells after the start of the fluid reinjection program suggest that if the oxygen isotope exchange in the vapor phase does, in fact, exist, it is a very slow process when compared with the residence time of the fluids in the geothermal reservoir. This is because carbon dioxide and water vapor phases could not have equilibrated significantly in the vapor-dominated reservoir. This conclusion implies that the oxygen isotope composition of carbon dioxide may possibly be used as a tool in geothermal exploration for revealing the presence of liquid water in deep geothermal systems. Based on the interpretation of the oxygen isotope data of the CO₂, I propose that the origin of the low oxygen isotope ratios of carbon dioxide at Larderello is the high-temperature exchange with liquid water in the lower reservoir. In Larderello, the liquid water–rock interaction in the lower reservoir may have increased the ¹⁸O/¹⁶O ratio of the recharge meteoric component. By contrast, lack of high-temperature liquid water in the upper reservoir suggests that the large “δ¹⁸O shift” described for the upper-reservoir steam during the last decades reflects varying degrees of dilution of the lower-reservoir fluid by the low-¹⁸O vaporized liquid water of meteoric origin that recharges the field at shallow depth, with local contribution from still deeper high-¹⁸O water vapor of magmatic origin. The low oxygen isotope composition of the Mesozoic carbonaceous rocks that form the upper reservoir, consequently, likely represents a “fossil” record of the past hot-water geothermal stage.     

An updated numerical model of the Larderello–Travale geothermal system, Italy

Larderello–Travale is one of the few geothermal systems in the world that is characterized by a reservoir pressure much lower than hydrostatic. This is a consequence of its natural evolution from an initial liquid-dominated to the current steam-dominated system. Beneath a nearly impermeable cover, the geothermal reservoir consists of carbonate-anhydrite formations and, at greater depth, by metamorphic rocks. The shallow reservoir has temperatures in the range of 220–250 °C, and pressures of about 20 bar at a depth of 1000 m, while the deep metamorphic reservoir has temperatures of 300–350 °C, and pressures of about 70 bar at a depth of 3000 m. The 3D numerical code “TOUGH2” has been used to conduct a regional modeling study to investigate the production mechanism of superheated steam, the interactions between the geothermal field and the surrounding deep aquifers, and the field sustainability. All the available geoscientific data collected in about one century of exploration and exploitation have been used to provide the necessary input parameters for the model, which covers an area (4900 km²) about 10 times wider than the Larderello–Travale geothermal field (400 km²). The numerical model explains the origin of the steam extracted in about one century of exploitation and shows that, at the current level, the production is sustainable at least for the next 100 years.     

Thermal and petrologic study of the CH-A well from the Chipilapa-Ahuachapán geothermal area, el salvador

Systematic petrological studies were performed at 10-m intervals along the 2700-m-deep Ch-A well. Results show mineralogical variations that define four zones which, in turn, represent different thermal zones. The shallowest zone (Zone l) is characterized by the presence of chalcedony + zeolites + amorphous silica + saponite + montmorillonite + minor amounts of pyrite and calcite; Zone 2 by chlorite + quartz + smectite + zeolites; Zone 3by chlorite + quartz + calcite + epidote + abundant pyrite and hematite + mixed-layeredillite-smectite + chalcopyrite; andZone4 byepidote + clinozoisite + gypsum + sericite + mixed-layered chlorite-illitesmectite + anyhdrite. Fluid inclusion analyses performed at 100-m intervals indicate that a low-to-moderate salinity fluid with ice-melting temperatures of -0.7 to -2.2°C was involved in the hydrothermal alteration of the rocks. At shallow depths, positive values of + 1.6°C were found, which probably indicate an increase in volatile components. Minimum homogenization temperatures gradually increased with depth. They range from 110°C at very shallow depths (153 m) to 244°C at total depth (2700 m); however, peak or maximum temperatures of 265–286°C are found at various depths between 1400 and 2500 m. Bottom-hole fluid inclusion temperatures agree well with static temperatures derived from the Homer (1951) and the Ascencio et al. (1994) methods. Comparisons at other depths show that, in general, Homer temperatures are the lowest and that fluid inclusion temperatures are the highest, except at about 1200 m depth where the Ascencio et al. (1994) method gives the largest values. It is believed that well Ch-A encountered a mineral paragenesis that does not correspond with present thermodynamic conditions of the reservoir and that the geothermal system has undergone natural cooling.     

Fluid-inclusion evidence for past temperature fluctuations in the Kilauea East Rift Zone geothermal area, Hawaii

Heating and freezing data were obtained for fluid inclusions in hydrothermal quartz, calcite, and anhydrite from several depths in three scientific observation holes drilled along the lower East Rift Zone of Kilauea volcano, Hawaii. Compositions of the inclusion fluids range from dilute meteoric water to highly modified sea water concentrated by boiling. Comparison of measured drill-hole temperatures with fluid-inclusion homogenization-temperature (T_h) data indicates that only about 15% of the fluid inclusions could have formed under the present thermal conditions. The majority of fluid inclusions studied must have formed during one or more times in the past when temperatures fluctuated in response to the emplacement of nearby dikes and their subsequent cooling. The fluid-inclusion data indicate that past temperatures in SOH-4 well were as much as 64°C hotter than present temperatures between 1000 and 1500 m depth and they were a maximum of 68°C cooler than present temperatures below 1500 m depth. Similarly, the data show that past temperatures near the bottoms of SOH-1 and SOH-2 wells were up to 45 and 59°C, respectively, cooler than the present thermal conditions; however, the remainder of fluid-inclusion T_h values for these two drill holes suggest that the temperatures of the trapped waters were nearly the same as the present temperatures at these slightly shallower depths. Several hydrothermal minerals (erionite, mordenite, truscottite, smectite, chlorite-smectite, chalcedony, anhydrite, and hematite), occurring in the drill holes at higher temperatures than they are found in geothermal drill holes of Iceland or other geothermal areas, provide additional evidence for a recent heating trend.     

Application of fluid inclusions to the study of Bagnore geothermal field (Tuscany, Italy)

A fluid inclusion study of the hydrothermal minerals in two breccias from two wells in the Bagnore geothermal field (Italy) has provided information on the evolution of the fluids, and has also demonstrated that fluid inclusions can be utilized as geothermometers in this geothermal field. Both breccias come from reservoir zones: one (Bagnore 3bis (Bg 3bis)) was cored at a depth of 3111 m below ground level (b.g.l.), whereas the other (Bagnore 22 (Bg 22)) was ejected during a blow-out, probably from a fractured zone present between 2200 and 2300 m b.g.l. The hydrothermal cement of the breccias is mostly made up of quartz, K-feldspar, Na-rich plagioclase, calcite, chlorite and illite. Fluid inclusion studies were carried out on quartz (Bg 3bis and Bg 22 breccias) and adularia (Bg 22 breccia). Three types of fluid inclusions were recognized in the Bg 3bis breccia. Type I (liquid-rich) inclusions trapped an aqueous fluid with a CO₂ concentration (1.7–2.7 mol/kg) that is significantly higher than present-day fluids (0.5 mol/kg). Type II (liquid-rich) inclusions formed after type I, and trapped a fluid with less CO₂ (0.6–1.0 mol/kg). Type III (vapor-rich) coexist with type I inclusions, and record an early fluid circulation under boiling conditions. The decrease of the CO₂ (and total gas) concentrations from type I inclusions to type II inclusions, and on to present-day conditions can be related to boiling with gas loss and/or mixing. Only one type of fluid inclusion (type II), with moderate CO₂ concentration (0.7–0.3 mol/kg), was found in the Bg 22 breccia. Boiling and/or mixing explain the variation of the CO₂ content in the Bg 22 reservoir fluid from inclusion formation to modern CO₂ concentration (0.3 mol/kg). The absence of any type I inclusions in Bg 22 breccia may be related to non-uniform CO₂ concentrations in different parts of the field. Present-day temperatures (295±10 °C for Bg 3bis and 320±10 °C for Bg 22) are close or equal to fluid inclusion average total homogenization temperatures (around 290 °C for Bg 3bis and 320 °C for Bg 22), suggesting that fluid inclusions can be useful for estimating local temperatures when direct measurements are not available or dubious.     

Shrinkage of liquid CO2 droplets in water

The shrinkage rate of liquid CO₂ droplets in water at 3°C was measured by the use of high-pressure vessel placed in a constant-temperature room. The change of the diameter of the droplet was observed at pressures of 28 MPa and 35 MPa using a time-lapse video camera. Bromocresol green was employed as a pH indicator, and was effective in monitoring the profile of carbonic acid distribution. When a droplet of liquid CO₂ was injected, CO₂ hydrate immediately formed and covered the surface of the droplet. The diameter of the liquid CO₂ droplet reduced gradually at a rate of 5.0 × 10^?7 m/s. It is predicted, from the viewpoint of ocean CO₂ sequestration, that a thin film of hydrate will form at the interface of sea water and liquid CO₂, and that the hydrate film will greatly control the dissolution of CO₂ into sea water.     

超临界二氧化碳扇贝阻尼密封动力稳定性研究

为研究超临界二氧化碳(Supercritical Carbon Dioxide, SCO₂)扇贝阻尼密封在不同工况下动力稳定性,建立SCO₂扇贝阻尼密封数值计算模型,分析进口压力、温度及转速对SCO₂扇贝阻尼密封动力特性及泄漏特性的影响。结果表明：直接复合刚度随涡动频率增加由正变负;交叉复合刚度随进口温度、压力增加而减小,随转速增加而增大;SCO₂扇贝阻尼密封的有效阻尼随进口温度、转速增加而减小,随进口压力增加而增大,进口压力为8.1 MPa时有效阻尼约为7.7 MPa时的1.7～2.9倍;扇贝阻尼密封直接复合刚度、有效阻尼整体上大于迷宫密封,稳定性高于迷宫密封,但泄漏量略高于迷宫密封。     

Stability of liquid CO2 in seawater at high pressures

The stability of liquid CO₂, in seawater at 3°C under high pressures were investigated by observing the pH and temperature changes around liquid CO₂ as well as its state. There was no distinct change of the state of liquid CO₂ at 37 MPa, while the liquid CO₂ at 32 MPa was unstable. Our experimental investigations suggest that a huge amount of liquid CO₂ can be sequestered for a very long time with reducing CO₂ dissolution and its impacts on ecosystems, if we dispose liquid CO₂ at the depth greater than 3700 m in an ocean.     

Effects of the “pays de bray” fault on fluid paleocirculations in the Paris basin dogger reservoir, France

Clay fractions and fluid inclusions were studied in the Aulnay sous Bois and Cerneux (CER-1 and CER-P6) wells located 10 km, 1.3 and 0.6 km, respectively, from the “Pays de Bray” fault (Paris Basin, France). It was shown that a connection was probably established between the Dogger and Triassic reservoirs during the active period of the fault. Chemical and heat transfers have locally modified the diagenesis conditions in the Dogger formation, inducing an overmaturation of clay minerals. These effects, although attenuated, are still identifiable in the Aulnay and CER-1 wells. A maximum temperature of about 90°C was maintained in CER-P6 site even during the uplift stage of the basin.     

Hydrothermal alteration in the Aluto-Langano geothermal field, Ethiopia

The hydrothermal mineral assemblages found in eight wells (with a depth range of 1320–2500 m) of the active geothermal field of Aluto-Langano (Ethiopia) indicate a complex evolution of water-rock interaction processes. The zone of upflow is characterized by high temperatures (up to 335°C) and the presence of a propylitic alteration (epidote, calcite, quartz and chlorite, as major phases) coexisting with calcite and clay minerals. The zone of lateral outflow is characterized by mixing of deep and shallow waters and the occurrence of a calcite-clay alteration that overprints a previous propylitic assemblage. Clay minerals have a mushroom-shaped zonal distribution consistent with the present thermal structure of the field. Microprobe analyses have been carried out on chlorite and illite in order to apply several geothermometers. Most of the chlorite is iron-rich chlorite. It is found that the temperatures calculated from the chlorite geothermometer (159–292°C) after Cathelineau and Nieva [Contrib. Mineral. Petrol. 91, 235–244 (1985)] are in good agreement with in-hole measured temperatures (155–300°C). In the upflow zone, temperatures calculated from this geothermometer (217–292°C), together with fluid inclusion data of Valori et al. [Eur. J. Mineral. 4, 907–919 (1992)], and computed saturation indices of alteration minerals, indicate thermal stability or slight heating. On the other hand, evidence of a significant cooling process (up to 171°C) in the outflow zone is provided by the comparison between fluid inclusion homogenization temperature (240–326°C) and in-hole temperature (155–250°C). The apparent salinities (0.8–2.3 wt% NaCl eq.) of the fluid inclusions are generally higher than the salinity of the present reservoir fluid (0.29–0.36 wt% NaCl eq.). Clay minerals (illite, smectite, Ill/S mixed layers, vermiculite and chloritic intergrades) generally occur at temperatures consistent with their stability fields.     

Anthropogenic emissions of CO2 and CH4 in an urban environment

Regular observations of atmospheric mixing-ratios of carbon dioxide and methane in the urban atmosphere, combined with analyses of their carbon-isotope composition (δ¹³C, δ¹⁴C), provide a powerful tool for assessing both the source strength and source partitioning of those gases, as well as their changes with respect to time. Intense surface fluxes of CO₂ and CH₄, associated with anthropogenic activities result in elevated levels of these gases in the local atmosphere as well as in modifications of their carbon-isotope compositions. Regular measurements of concentration and carbon-isotope composition of atmospheric CO₂, carried out in Krakow over the past two decades, were extended to the period 1995–2000 and also to atmospheric mixing-ratios of CH₄ and its carbon-isotope composition. Radiocarbon concentrations (δ¹⁴C) in atmospheric CO₂ recorded at Krakow are systematically lower than the regional background levels. This effect stems from the addition of ¹⁴C-free CO₂ into the local atmosphere, originating from the burning of fossil fuels. The fossil-fuel component in the local budget of atmospheric carbon calculated using a three-component mixing model decreased from ca. 27.5 ppm in 1989 to ca. 10 ppm in 1994. The seasonal fluctuations of this component (winter–summer) are of similar magnitude. A gradually decreasing difference between the ¹⁴CO₂ content in the local atmosphere and the regional background observed after 1991 is attributed to the reduced consumption of ¹⁴C-free fuels, mostly coal, in southern Poland and the Krakow municipal area. The linear regression of δ¹³C values of methane plotted versus reciprocal concentration, performed for the data available for Krakow sampling site, yields the average δ¹³C signature of the local source of methane as being equal to −54.2‰. This value agrees very well with the measured isotope signature of natural gas being used in Krakow (−54.4±0.6‰) and points to leakages in the distribution network of this gas as the main anthropogenic source of CH₄ in the local atmosphere.     

Effect of calcite/activated carbon-based post-combustion CO2 capture system in a biodiesel-fueled CI engine—An experimental study

The present study aims to reduce carbon dioxide (CO₂) emission from a CI engine using calcite/activated carbon-based post-combustion CO₂ capture system fueled with Calophyllum inophyllum biodiesel (B100). The tests were conducted in a two-cylinder CI engine used in tractors at different load conditions. The performance and emission parameters of diesel and B100 with and without calcite and activated carbon-based CO₂ capture system were studied. The results show that compared to diesel, CO₂ emission increased by 19% for B100 due to high fuel-bound oxygen and carbon. Higher NO emission with a slightly reduced smoke opacity is observed with B100 combustion. CO₂ emission is reduced with the CO₂ capture system for both diesel and B100. CO₂ emission is reduced by 11.5% and 7.3% for diesel with calcite and activated carbon, respectively, and reduced by 15.8% and 10.5% for B100 with calcite and activated carbon. Due to the adsorption capacity of both calcite and activated carbon, NO and smoke opacity are reduced considerably. The results display that calcite is better in reducing CO₂ compared to activated carbon-based CO₂ capture system. It is perceived that the combination of biofuel and calcite-based CO₂ capture system can both reduce engine-out emissions and cause a net negative CO₂ emission as it is renewable aiding in mitigation of global warming effects.     

北方秸秆燃料高效应用分析及固化成型技术

全面分析了二氧化碳减排的国际、国内的各大措施,包括：国际气候变化协议体系、国际区域间碳排放交易体系等国际措施,征收碳税、企业间碳排放交易体系、政府补助等市场化手段,森林减排、地质减排、发展循环经济、开发新能源等非市场化手段。通过对这些措施的特点研究、可行性分析和利弊比较,为二氧化碳的减排提供了优化选择的前瞻性思路,并指出国际间的合作与国内政策落实应当有机结合,市场化与非市场化手段需要相互渗透,各大减排措施的合理有效利用,逐步实现国家乃至世界向低碳经济发展模式的转换。     

Photocatalytic reduction of carbon dioxide over ferrocyanide-coated titanium dioxide powder

Photocatalytic reduction of carbon dioxide in aqueous media has been carried out over potassium-ferrocyanide-coated titanium dioxide powder. Formic acid and formaldehyde were identified as photoproducts, and were measured spectrophotometrically using Nash reagent. The effect of the variation of different parameters such as potassium ferrocyanide concentration, amount of photocatalyst (potassium-ferrocyanide-coated titanium dioxide powder), light intensity and particle size on the yield of photoproducts was also investigated. A tentative mechanism for this reduction has been proposed. © 1997 John Wiley & Sons, Ltd.