Carbon Dioxide-rich Fluid Research Articles

Phase Behavior of Carbon Dioxide Hydrates: A Comparison of Inhibition Between Sodium Chloride and Ethanol

In view of the possibilities for hydrate formation caused by carbon dioxide-rich fluids in the production lines of the Brazilian Pre-Salt fields, this study focus on experimental measurements to obtain fundamental insight into the phase behavior of carbon dioxide hydrate forming systems. This work considers the influence of sodium chloride and ethanol, hydrate inhibitors, on this phase behavior and its implications to practical applications. In addition, the inhibiting effect of ethanol on hydrates was compared with that of sodium chloride at the same mass fractions. The carbon dioxide hydrate phase behavior was measured using a high-pressure equilibrium cell in the temperature range of 272–279 K and pressures up to 3.9 MPa. Experimental measurements using the isothermal method were performed by monitoring the pressure response of the system with volume changes. Enthalpies of dissociation for carbon dioxide hydrates were estimated from the measured three-phase (Lw–H–V) data by applying the Clausius–Clapey...

Tantalite-(Mn) from the Borborema Pegmatite Province, northeastern Brazil: conditions of formation and melt- and fluid-inclusion constraints on experimental studies

Carbon dioxide-rich fluid and carbonate-rich aluminosilicate melt inclusions in tantalite-(Mn) from the Alto do Giz pegmatite in the Borborema Pegmatite Province, northeastern Brazil were investigated to constrain the formation of the host crystals. The results demonstrate that in the Alto do Giz pegmatite, water- and alkaline carbonate-rich fluids and melts are responsible for the transport and deposition of tantalite-(Mn) at temperatures around 600°C and about 4 kbar. Moreover, evidence is presented to show that during crystallization of the tantalite-(Mn), three different components coexisted, which are now trapped as separate inclusions: two immiscible silicate melts (types A and B melt inclusions) and a CO2-rich aqueous fluid. We hypothesize that immiscible fluid separation may have been a critical factor in producing the water- and alkaline carbonate-rich fluids and melts necessary for Ta and Nb transport. Since the tantalite-(Mn) crystallized during pegmatite formation, this mechanism must also have implications for pegmatite genesis in general.

Chemically driven growth and resorption of bubbles in a multivolatile magmatic system

A carbon dioxide-rich fluid from a deep source fluxes in a water-rich shallow-stored magma and causes a volatile exchange with the melt. We carried out hydrothermal experiments on both bubble-free and -bearing rhyolitic melts in an H 2O–CO 2 system to explore the kinetics of chemical re-equilibration between the fluid and the magma. In the bubble-free experiment, a water-saturated rhyolitic melt was first synthesized at 800 °C and 100 MPa, and this interacted with a carbon dioxide-rich fluid under the same PT conditions for a period of 3 h. The melt temporarily became undersaturated upon the volatile exchange, as water quickly diffused out of the melt, while dissolution of the carbon dioxide was much slower. In the bubble-bearing experiments, the rhyolitic melt was saturated with H 2O–CO 2 fluids at 800 °C and 100 MPa, decompressed to 50 MPa, and then kept for up to 5.56 h. Water-rich bubbles were generated by decompression, and initially grew, but then dissolved in the melt during the retention time. This bubble resorption was attributed to water depletion of the melt upon re-equilibration with the carbon dioxide-rich surrounding fluid. Such water depletion and resulting bubble resorption are specific to multivolatile systems, such as H 2O–CO 2, in which the diffusivity and solubility differ among the end components. The bubble resorption occurring in this mechanism may explain the genesis of carbon dioxide-rich, bubble-poor obsidian pyroclasts, which are considered to have undergone carbon dioxide-rich fluid fluxing. We also discuss possible consequences of this effect on the bulk magma density. The dissolution of a small amount of carbon dioxide may cause expulsion of a much larger amount of water from the hydrous melt, which may increase fluid fraction and thus decrease the bulk density by up to 188 and 104 kg/m 3 at 100 and 200 MPa, respectively, for rhyolitic melts. We suggest that such a process has the potential to trigger a volcanic eruption.

Continuous Copolymerization of Vinylidene Fluoride with Hexafluoropropylene in Supercritical Carbon Dioxide: Low Hexafluoropropylene Content Semicrystalline Copolymers

The copolymerization of vinylidene fluoride with hexafluoropropylene (HFP) was carried out in supercritical carbon dioxide by precipitation polymerization using a continuous stirred tank reactor. Copolymers with ca. 10 mol % HFP were synthesized at 40 °C and pressures in the range of 207−400 bar using perfluorobutyryl peroxide as the free radical initiator. The effects of feed monomer concentration and reaction pressure were both explored at otherwise constant conditions. The rate of polymerization (Rp) and the number-average molecular weight (Mn) increased linearly with the total monomer concentration up to about 6 M, the highest concentration investigated. The Rp and the Mn were strongly influenced by the reaction pressure. An 80% increase in both Rp and Mn was observed when the reaction pressure rose from 207 to 400 bar. The molecular weight distributions of the synthesized copolymer showed a long tail that increased to become a broad shoulder with increasing total monomer concentration. This tail increased with increasing reaction pressure. The data suggest that the carbon dioxide-rich fluid phase is the primary locus of polymerization.

EMPLACEMENT DEPTH AND CARBON DIOXIDE-RICH FLUID INCLUSIONS IN INTRUSION-RELATED GOLD DEPOSITS

Phanerozoic intrusion-related gold deposits have many consistent characteristics such as a spatial, temporal, and geochemical association with moderately reduced (predominantly ilmenite-series) I-type intrusions. The deposits exhibit a range of characteristics that vary over a wide range of emplacement depths ( 7 km). Deposits in shallow crustal settings (~ 5 km) have characteristics of mesothermal environments, and are hosted by plutons containing sheeted veins, greissen, and disseminated gold. Fluid characteristics also vary with depth. Deposits in shallow environments contain high-temperature (>350°C), immiscible brine (>30 wt % NaCl equiv) and low-salinity (<5 wt % NaCl equiv) vapor that commonly contains carbon dioxide. Deposits in deeper environments contain abundant low-salinity, carbon dioxide-rich aqueous fluids (<10 wt % NaCl equiv) that, in some deposits, are postdated by moderate- to high-salinity brines (10–40 wt % NaCl equiv). These contrasting fluid types are interpreted to be magmatic in origin and are the result of the complex interplay between exsolution of different volatiles (carbon dioxide, water, and chlorine) from felsic magmas emplaced at different crustal levels. Experimental studies have shown that carbon dioxide will exsolve from felsic magmas at much higher pressures than water and chlorine, due to its lower solubility in the melt. Thus, deposits formed from felsic magmas in deeper environments will contain abundant, carbon dioxide-rich fluids. Subsequent fluids released from the magma are likely to be water rich and more saline. Felsic magmas in shallow environments will contain lower concentrations of carbon dioxide that will partition into the vapor phase during phase separation between brine and vapor.

Carbonic fluid inclusions in South Indian granulites: evidence for entrapment during charnockite formation

Field evidence and fluid inclusion studies on South Indian incipient charnockites suggest that charnockite formation occurred during a decompressional brittle regime following the ‘peak’ of metamorphism and regional deformation. The most abundant type of inclusions in quartz and garnet grains in these charnockites contain high-density carbonic fluids, although lower-density fluids occur in younger arrays of inclusions. Discrete fluid inclusion generations optically are observed to decrepitate over well-defined temperature intervals, and quantitative measurements of CO2 abundance released from these inclusions by stepped thermal decrepitation show up to a four-fold increase (by volume) in the incipient charnockites relative to the adjacent gneisses from which they are derived. Studies based on optical thermometry, visual decrepitation and stepped-heating inclusion release together indicate that entrapment of carbonic fluids coincided with charnockite formation. We confirm that an influx of carbon dioxide-rich fluids is associated with the amphibolite-granulite transition, as recorded by the incipient charnockites, the remnants of which are commonly preserved as the earliest generation of high-density fluid inclusions.

Geochemistry of Gneiss-Granulite transformation in the ?incipient charnockite? zones of southern India

Upper amphibolite facies gneisses in the southern Indian Shield show local transformation into veins, clots and patches of orthopyroxene-bearing dry granulites (“incipient charnockites”). Depending upon the protolith composition, these desiccated zones are classified into ortho- and para-charnockites and have developed within rocks of distinct mineralogy and chemistry at different time intervals through the structurally-controlled influx of carbon dioxide-rich fluids. Our geochemical investigations at five critical quarry sections indicate that the incipient charnockites have undepleted chemistry and very low K/Rb values. In the paracharnockite localities, where granulite formation is characterized by consumption of garnet, biotite and quartz to produce orthopyroxene, loss of Rb and Ba and enrichment of Ti are observed. In contrast, the orthocharnockite localities show marked LILE enrichment with gain of K, Rb and Ba and loss of CaO, suggesting extensive replacement of plagioclase in the gneisses by K-feldspar in the charnockite through K-Na-Ca exchange reactions with influxing carbonic fluids. The marked depletion in Fe, Mg, Ti and P in these rocks correlates with progressive dissolution of hornblende, biotite, magnetite and accessory apatite. Our study indicates that gneiss to granulite transformation, even if on a local scale, is not an isochemical phenomenon, but attended by distinct element mobilities, although they are contrastingly different from the geochemical trends in some regional high grade terrains.

Venting of Carbon Dioxide-Rich Fluid and Hydrate Formation in Mid-Okinawa Trough Backarc Basin

Carbon dioxide-rich fluid bubbles, containing approximately 86 percent CO(2), 3 percent H(2)S, and 11 percent residual gas (CH(4) + H(2)), were observed to emerge from the sea floor at 1335- to 1550-m depth in the JADE hydrothermal field, mid-Okinawa Trough. Upon contact with seawater at 3.8 degrees C, gas hydrate immediately formed on the surface of the bubbles and these hydrates coalesced to form pipes standing on the sediments. Chemical composition and carbon, sulfur, and helium isotopic ratios indicate that the CO(2)-rich fluid was derived from the same magmatic source as dissolved gases in 320 degrees C hydrothermal solution emitted from a nearby black smoker chimney. The CO(2)-rich fluid phase may be separated by subsurface boiling of hydrothermal solutions or by leaching of CO(2)-rich fluid inclusion during posteruption interaction between pore water and volcanogenic sediments.

Solubility of triethylene glycol in supercritical CO 2

The volatility of triethylene glycol in carbon dioxide at sub- and supercritical carbon dioxide pressures was determined as the second of a series of such studies conducted on liquid desiccant/inhibitors for carbon dioxide-rich fluids. Three isotherms at 40, 50 and 60°C were studied at pressures ranging from 2.76 to 11.03 MPa. A steady-state elution technique developed earlier in our laboratory was employed to carry out the calibrations and the measurements to TEG concentrations as low as 0.7 × 10 −6 ±0.05 × 10 −6 mole fraction using a flame ionization detector. During the measurements, the carbon dioxide densities varied from 0.05092 to 0.5978 g cm −3. The increase in CO 2 density largely accounted for the increase in the enhancement of triethylene glycol by carbon dioxide to a value as high as 1190 at the highest density reached so far (40°C and 9.653 MPa). The vapor phase concentrations are correlated in terms of the CO 2-rich fluid density in accordance with the formulations of Dewan (1985). The liquid phase concentrations were interpolated/extrapolated by applying the Krichevsky-Kasarnovsky correlation to Takahashi's solubility data (1984).

Venting of carbon dioxide-rich fluid and hydrate formation in mid-Okinawa Trough backarc basin: Sakai, H. et al., 1990. Science, 248(4959):1093–1096

Venting of carbon dioxide-rich fluid and hydrate formation in mid-Okinawa Trough backarc basin: Sakai, H. et al., 1990. Science, 248(4959):1093–1096

Diagenetic Relationships Between Inorganic Matrix and Kerogen in Wilcox Group, Southwest Texas: ABSTRACT

Eighteen core samples of shale from the Eocene Wilcox formation in the Gulf Coast of Texas were extracted in organic solvents and digested in hydrofluoric acid in order to examine the bitumen and kerogen fractions. The kerogen was found to be largely terrigenous in origin with stable carbon isotope values ranging between -26 and -29 ppt (PDB). Smectite dehydration in the area begins at less than 1 km depth (60°C). At the depths of initial petroleum generation (1.5 km and 85°C), expandable layers comprise only 30% of the illite-smectite clays. It therefore does not seem likely that water expelled during smectite dehydration can mobilize significant amounts of hydrocarbons. Geopressuring of pore fluids occurs toward the end of the main stage of petroleum generation, below 3 km. In the gas zone, hydrocarbon concentrations increase between 3.6 and 4.6 km from a low of 7 mg/gC to 15 mg/gC. Two samples in this region showed anomalously high concentrations of hydrocarbons (100 mg/gC). These observations may indicate subsurface migration of hydrocarbons, perhaps in a methane and carbon dioxide-rich fluid phase. In addition to facilitating hydrocarbon migration, carbon dioxide generated from kerogen may also be involved in the precipitation of ankerite cement in sandstones below 2.5 km. End_of_Article - Last_Page 1691------------