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Ankerite

About: Ankerite is a research topic. Over the lifetime, 859 publications have been published within this topic receiving 23960 citations.


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TL;DR: In this article, the authors explore alternative sources of increasing calcium and iron, based on the data from the detailed petrographic characterization of the Upper Frio Formation “C”, and evaluate whether dissolution of calcite and oligoclase (anorthite component) can account for the observed geochemical changes.
Abstract: During the Frio-I Brine Pilot CO2 injection experiment in 2004, distinct geochemical changes in response to the injection of 1600 tons of CO2 were recorded in brine samples collected from the monitoring well. Previous geochemical modeling studies have considered dissolution of calcite and iron oxyhydroxides, or release of adsorbed iron, as the most likely sources of the increased ion concentrations. In this modeling study we explore possible alternative sources of the increasing calcium and iron, based on the data from the detailed petrographic characterization of the Upper Frio Formation “C”. Particularly, we evaluate whether dissolution of pyrite and oligoclase (anorthite component) can account for the observed geochemical changes. Due to kinetic limitations, dissolution of pyrite and anorthite cannot account for the increased iron and calcium concentrations on the time scale of the field test (10 days). However, dissolution of these minerals is contributing to carbonate and clay mineral precipitation on the longer time scales (1000 years). We estimated that during the field test dissolution of calcite and iron oxide resulted in ∼0.02 wt.% loss of the reservoir rock mass. The reactive transport models were constructed for 25 and 59 °C temperature and using Pitzer and B-dot activity correction methods. These models predict carbonate minerals, dolomite and ankerite, as well as clay minerals kaolinite, nontronite and montmorillonite, will precipitate in the Frio Formation “C” sandstone as the system progresses toward chemical equilibrium during a 1000-year period. Cumulative uncertainties associated with using different thermodynamic databases, activity correction models (Pitzer vs. B-dot), and extrapolating to reservoir temperature, are manifested in the difference in the predicted mineral phases. However, these models are consistent with regards to the total volume of mineral precipitation and porosity values which are predicted to within 0.002%.

12 citations

Journal ArticleDOI
TL;DR: In this paper, fluid inclusion micro-thermometry and stable isotope and electron microprobe analyses were used to indicate the nature and timing of fracture-filling cements.
Abstract: In the Cambro-Ordovician Warburton Basin, South Australia, reservoir rock porosity and permeability are enhanced by open fractures and by partially-open or incompletely mineral-filled fractures. However in many cases, the fractures are completely filled by cements of several types. A knowledge of the nature and origin of the fracture-filling cements can help to identify areas where cement precipitation is relatively less intense, and where oil and gas production may be improved. In the present study, fluid inclusion microthermometry, and stable isotope and electron microprobe analyses were used to indicate the nature and timing of fracture-filling cements. The study shows that fracture-filling cements in the studied Warburton Basin wells include quartz, siderite, ankerite, kaolin and pyrite. Based upon precipitation temperatures, stable isotope compositions, elemental compositions and quartz cement textures, a hydrothermal source for the silica and carbonate cements is envisaged. The hydrothermal activity may be related to granite intrusions during the Carboniferous. Fluid inclusion microthermometry suggest that Warburton Basin rocks in some areas have experienced temperatures of more than 260°C and cannot therefore be a source of hydrocarbons. The observed low permeabilities occur because most fractures were completely or partially filled by cements precipitated during hydrothermal activity soon after granite intrusion. There is a greater likelihood of finding reservoir rocks with open fractures in areas far from the granite intrusions.

12 citations

Journal ArticleDOI
TL;DR: In this paper, a basalt-CO2 water saturated interaction modelling under hydrothermal-like conditions was carried out on the Deccan basalt of the Mandla area to understand apposite pCO2 and time parameters.
Abstract: Deccan basalt contains primary silicates rich in Ca, Mg, and Fe ions, suitable for CO2 sequestration. Previous, basalt-water-CO2 interaction studies were focused on other than Deccan basalt types. However, such studies on the Deccan basalt are rare. Thus, present basalt-CO2 water saturated interaction modelling under hydrothermal-like conditions was carried out on the Deccan basalt of the Mandla area to understand apposite pCO2 and time parameters. Modelling results were further validated by experiments run in a laboratory time framework. Present results show negative entropy (ΔS) and enthalpy (ΔfH) that suggest feasibility of plagioclase, pyroxene and magnetite dissolution. Obtained negative Gibb’s free energy (ΔfG), ΔfH and ΔS values for calcite, dolomite and magnesite indicate spontaneous reaction, whereas, positive ΔfG and negative ΔfH and ΔS values of the siderite suggest non-spontaneous and opposing reactions. Calcite is the first carbonate mineral to form, but, at a faster rate. Magnetite dissolution begins after a time lag (not initiated along with the plagioclase and pyroxene). X-ray Powder Diffraction results of post-experiment residues revealed formation of calcite, aragonite, ankerite, huntite, siderite, smectite, chlorite, smectite/chlorite mixed layers and chabazite. Scanning electron microscopic images show tiny calcite crystal growth over the larger calcite crystal and incipient-disordered calcite with imperfections on crystal faces. Thus, basalt carbonation is mainly controlled by time, but temperature, pCO2 and pH played sub-ordinate role. Largely, thermodynamic models do not agree well with the experimental results as numerical models indicate larger carbonate growth. Additionally, transition state theory based models work well to predict dissolution rates for most of the minerals, but, they overpredict growth of the secondary minerals.

12 citations

Journal ArticleDOI
TL;DR: In this article, the dolomite-ferroan-dolomites-ankerite series of carbonate minerals has been investigated in flowing carbon dioxide using high-temperature DSC.
Abstract: The dolomite-ferroan-dolomite-ankerite series of carbonate minerals has been investigated in flowing carbon dioxide using high-temperature DSC. Decomposition products were analysed by X-ray diffraction. The minerals studied included dolomite containing no iron, and members substituted by iron in the molar ratio range of 0.082 to 0.49. Complete resolution of the three main endothermic features was observed and enthalpy values AH, determined from each. The individual and total enthalpy values showed a linear dependence upon the Fe and Mg content of the members across the series. A decrease in the enthalpy of decomposition occurs with increasing Fe content. The effect of Fe substitution was readily observed and the estimated limit of detection is less than 1% FeO. Accuracy of the measurements was limited by the purity of the minerals themselves.

12 citations

Journal ArticleDOI
Marco A. S. Moraes1
TL;DR: In this article, three sandstone turbidite sequences of the Campos basin (offshore, state of Rio de Janeiro, Brazil) were petrologically studied: (1) the Albian-Cenomanian Namorado Sandstone on the Macae Formation, (2) the Upper Cretaceous Carapebus Member of Campos Formation, and (3) the Eocene Carape bus Member of the campos Formation.
Abstract: Three sandstone turbidite sequences of the Campos basin (offshore, state of Rio de Janeiro, Brazil) were petrologically studied: (1) the Albian-Cenomanian Namorado Sandstone on the Macae Formation, (2) the Upper Cretaceous Carapebus Member of the Campos Formation, and (3) the Eocene Carapebus Member of the Campos Formation. The sequences represent deep marine deposits consisting mostly of massive sandstones rather than classical turbidites, indicating sand-rich submarine fans were the main depositional system of these sequences. The framework composition of the sandstones averages for quartz, feldspar, and lithics are Q60F40Ltr for the Cretaceous rocks and Q71F29Ltr for the Eocene rocks, plotting granitic r ck fragments at the feldspar pole. The main diagenetic phases that affected the sandstones studied were (1) development of a clay matrix due to compaction of rip-up mud clasts, (2) partial replacement of the matrix by opal, (3) precipitation of small pyrite framboids, (4) widespread direct precipitation or replacement of different materials by calcite, (5) intense generation of secondary porosity, (6) localized kaolinite development, (7) minor precipitation of quartz and feldspar overgrowths, (8) development of dolomite, ferroan dolomite, and ankerite, and (9) replacement of different materials with minor direct precipitation of late pyrite. Geologic and geochemical evidence lets us infer the main processes that controlled diagenetic transformations and mass transfer within the sequence studied. The principal source of carbonate cements was pressure solution of the underlying Macae Formation. Most of the diagenetic evolution of the sandstones was apparently controlled by the relative balance between the activity of CO2 and carboxylic acid species in the formation waters, both related to organic matter transformations within adjacent marine shales. The timing of hydrocarbon (generated in deeper lacustrine shales) migration to the reservoirs was an important factor in preserving diagenetically enhanced porosity.

12 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202332
202270
202140
202027
201946
201842