Academic literature on the topic 'Carbonate precipitation/dissolution'

Abstract The Amba Dongar carbonatite complex in western India comprises an inner ring of carbonatite breccia surrounded by a sövite ring dike. The various carbonatite units in the body include calcite carbonatite, alvikite, dolomite carbonatite, and ankerite carbonatite. The carbonate phases (calcite and ankerite) occur as phenocrysts, groundmass phases, fresh primary grains, and partially altered grains and/or pseudomorphs when hydrothermally overprinted. Rare earth element (REE) enrichment in the groundmass/altered calcite grains compared to the magmatic ones is ascribed to the presence of micron-sized REE phases. Fluorapatite and pyrochlore constitute important accessory phases that are altered to variable extents. Higher concentrations of Sr, Si, and REEs in fluorapatite are suggestive of a magmatic origin. Fresh pyrochlore preserves its magmatic composition, characterized by low A-site vacancy and high F in the Y-site, which on alteration becomes poorer in Na, Ca, and F and displays an increase in vacancy. The C-O isotope compositions of the carbonates also corroborate the extensive low-temperature hydrothermal alteration of the carbonatites. The REE mineralization is the result of interaction of the carbonatite with a sulfur-bearing, F-rich hydrothermal fluid that exsolved from late-stage carbonatitic magmas. The hydrothermal fluids caused dissolution of the primary carbonates and simultaneous precipitation of REEs and other high field strength element (HFSE)-bearing minerals. Complex spatial associations of the magmatic minerals with the REE fluorocarbonates, [synchysite-(Ce), parisite-(Ce), bastnäsite-(Ce)] and florencite-(Ce) point to the formation of these REE phases as a consequence of postmagmatic hydrothermal dissolution of the REEs from fluorapatite, pyrochlore, and carbonates. Ubiquitous association of fluorite and barite with REE minerals indicates transport of REEs as sulfate complexes in F-rich fluids. Precipitation of REE fluorocarbonates/florencite resulted from fluid-carbonate interaction, concomitant increase in pH, and decrease in temperature. Additionally, REE precipitation was aided and abetted by the removal of sulfur from the fluid by the precipitation of barite, which destabilized the REE sulfate complexes.

As the most frontiers in petroleum geology, the study of dissolution-based rock formation in deep carbonate reservoirs provides insight into pore development mechanism of petroleum reservoir space, while predicting reservoir distribution in deep-ultradeep layers. In this study, we conducted dissolution-precipitation experiments simulating surface to deep burial environments (open and semiopen systems). The effects of temperature, pressure, and dissolved ions on carbonate dissolution-precipitation were investigated under high temperature and pressure (~200°C; ~70 Mpa) with a series of petrographic and geochemical analytical methods. The results showed that the window-shape dissolution curve appeared in 75~150°C in the open system and 120~175°C in the semiopen system. Furthermore, the dissolution weight loss of carbonate rocks in the open system was higher than that of semiopen system, making it more favorable for gaining porosity. The type of fluid and rock largely determines the reservoir quality. In the open system, the dissolution weight loss of calcite was higher than that of dolomite with 0.3% CO2as the reaction fluid. In the semiopen system, the weight loss from dolomitic limestone prevailed with 0.3% CO2as the reaction fluid. Our study could provide theoretical basis for the prediction of high quality carbonate reservoirs in deep and ultradeep layers.

One of the most promising strategies for the safe and permanent disposal of anthropogenic CO2 is its conversion into carbonate minerals via the carbonation of calcium and magnesium silicates. However, the mechanism of such a reaction is not well constrained, and its slow kinetics is a handicap for the implementation of silicate mineral carbonation as an effective method for CO2 capture and storage (CCS). Here, we studied the different steps of wollastonite (CaSiO3) carbonation (silicate dissolution → carbonate precipitation) as a model CCS system for the screening of natural and biomimetic catalysts for this reaction. Tested catalysts included carbonic anhydrase (CA), a natural enzyme that catalyzes the reversible hydration of CO2(aq), and biomimetic metal-organic frameworks (MOFs). Our results show that dissolution is the rate-limiting step for wollastonite carbonation. The overall reaction progresses anisotropically along different [hkl] directions via a pseudomorphic interface-coupled dissolution–precipitation mechanism, leading to partial passivation via secondary surface precipitation of amorphous silica and calcite, which in both cases is anisotropic (i.e., (hkl)-specific). CA accelerates the final carbonate precipitation step but hinders the overall carbonation of wollastonite. Remarkably, one of the tested Zr-based MOFs accelerates the dissolution of the silicate. The use of MOFs for enhanced silicate dissolution alone or in combination with other natural or biomimetic catalysts for accelerated carbonation could represent a potentially effective strategy for enhanced mineral CCS.

Carbon capture and subsequent storage (CCS) is identified as a necessity to achieve climate commitments. Permanent storage of carbon dioxide (CO2) in subsurface saline aquifers or depleted oil and gas reservoirs is feasible, but large-scale implementation of such storage has so far been slow. Although sandstone formations are currently most viable for CO2 sequestration, carbonates play an important role in widespread implementation of CCS; both due to the world-wide abundancy of saline aquifers in carbonate formations, and as candidates for CO2-EOR with combined storage. Acidification of formation brine during CO2 injection cause carbonate dissolution and development of reactive flow patterns. Using calcite-functionalization of micromodels we experimentally investigate fundamental pore-scale reactive transport dynamics relevant for carbonate CO2 storage security. Calcite-functionalized, two-dimensional and siliconbased, pore scale micromodels were used. Calcite precipitation was microbially induced from the bacteria Sporosarcina pasteurii and calcite grains were formed in-situ. This paper details an improved procedure for achieving controlled calcite precipitation in the pore space and characterizes the precipitation/mineralization process. The experimental setup featured a temperature-controlled micromodel holder attached to an automatic scanning stage. A high-resolution microscope enabled full-model (22x27 mm) image capture at resolution of 1.1 µm/pixel within 82 seconds. An in-house developed image-analysis python script was used to quantify porosity alterations due to calcite precipitation. The calcite-functionalized micromodels were found to replicate natural carbonate pore geometry and chemistry, and thus may be used to quantify calcite dissolution and reactive flow at the pore-scale.

The aim of this study is to fabricate CO3Ap scaffolds using a dissolution-precipitation reaction during hydrothermal treatment. Beta-tricalcium phosphate (?-TCP) was used as a precursor instead of the commonly used alpha-tricalcium phosphate (?-TCP). Here, the CO3Ap scaffold fabrication was accomplished in two steps: i) fabrication of ?-TCP scaffold using a combination of direct foaming and a sacrificial template and ii) hydrothermal conversion of the ?-TCP scaffold at 200?C in 2mol/l NaHCO3 and Na2CO3 aqueous solutions for 2-10 days. The effect of two different solutions was identified in the dissolution-precipitation reaction. CO3Ap scaffold with 8.95wt.% carbonate content was successfully fabricated using a NaHCO3 solution. The average pore size of the scaffold was approximately 180 ?m with 72% porosity. The average compressive strength of the CO3Ap scaffold was 0.7MPa. Based on the compressive strength and carbonate content results, NaHCO3 aqueous solutions were chosen as carbonate sources for phase transformation to fabricate a CO3Ap scaffold over 6 days.

In-situ atomic force microscopy (AFM) experiments were performed to study the overall process of dissolution of common carbonate minerals (calcite and dolomite) and precipitation of gypsum in Na2SO4 and CaSO4 solutions with pH values ranging from 2 to 6 at room temperature (23 ± 1 °C). The dissolution of the carbonate minerals took place at the (104) cleavage surfaces in sulfate-rich solutions undersaturated with respect to gypsum, by the formation of characteristic rhombohedral-shaped etch pits. Rounding of the etch pit corners was observed as solutions approached close-to-equilibrium conditions with respect to calcite. The calculated dissolution rates of calcite at pH 4.8 and 5.6 agreed with the values reported in the literature. When using solutions previously equilibrated with respect to gypsum, gypsum precipitation coupled with calcite dissolution showed short gypsum nucleation induction times. The gypsum precipitate quickly coated the calcite surface, forming arrow-like forms parallel to the crystallographic orientations of the calcite etch pits. Gypsum precipitation coupled with dolomite dissolution was slower than that of calcite, indicating the dissolution rate to be the rate-controlling step. The resulting gypsum coating partially covered the surface during the experimental duration of a few hours.

Inorganic component of bone is not hydroxyapatite but carbonate apatite. Although pure carbonate apatite (CO3Ap) has not been prepared due to the limited thermal stability of CO3Ap, dissolution - precipitation method using precursor block allows fabrication of pure CO3Ap. Fabrication of CO3Ap, cell response, tissue response and improvement of CO3Ap will be discussed.

Carbonates are important diagenetic cements in siliciclastic rocks thus important to determine these rocks as hydrocarbon reservoirs. The cement is the material had chemically precipitated partial or totally pore filling, affecting rock values of porosity and permeability. The acknowledgment of diagenetic patterns those are associated to the carbonatic cement precipitation and their impacts in the reservoirs quality can decrease the risks of exploration and exploitation of new reservoirs. Therefore is necessary the knowledge of origin and processes of carbonate cement’s precipitation. These cements have distribution patterns, mineralogy, textures and isotopic compositions which vary spatial and temporally, depending of perform conditions in each diagenetic environment. One of the most important diagenetic cement is dolomite and the dolomite’s group is compound by dolomite and ankerite. These minerals can be differentiated by analytical techniques such as optical petrography, staining techniques, cathodoluminescence, scanning electron microscopy and isotopes. Besides that, dolomite cement shape in a reservoir can display different forms: rhombs, poikilotopic and saddle in a variety of dimensions, pore filling, replacing detrital carbonate grains, concretions, nodules or stratified layers. Primaries calcite and aragonite replaced can promote precipitation of dolomite through increase of temperature and by presence of Mg-being fluids. The main entrance conditions to form dolomitic cement are: (i) alkaline solutions from pre-existence rocks weathering or evaporitc environments; (ii) marine waters; (iii) clay alteration; (iv) CaCO3 polymorphs dissolution; (v) dissolution of bioclasts. An interesting example of dolomitic cementation is the Carmópolis Member of the Muribeca Formation, hydrocarbon reservoir of the Camorim Field (Sergipe-Alagoas Basin, northeastern Brazil).

Hydrocalumite is a calcium/aluminium-based layered double hydroxide. This material has a wide range of applications, such as polymer additives, basic catalysts and water treatment agents. There are a variety of synthesis methods available of which co-precipitation is most widely used. The negative aspects of using most of the developed methods are use of high cost metal salts as reagents. These materials are not only high in cost but are highly corrosive and result in damage of production equipment. A salt containing effluent is produced in these processes that can be harmful to the environment, thus requires treatment before disposal. As the interest in the use of hydrocalumite has increased, there is a need for environmentally friendly and more cost effective synthesis procedures. The aim of this study was to explore different reagents, time and temperature reaction conditions for the dissolution-precipitation synthesis of carbonate-containing hydrocalumite. In this method metal oxides/hydroxides reagents are used which are less corrosive and do not lead to harsh effluent production. This method has two distinct steps namely precursor formation followed by intercalation. In the precursor formation step, it was found that for the reaction between calcium oxide and aluminium hydroxide the conversion of both the calcium and aluminium sources increase as reaction time and temperature increase. It was confirmed that the dissolution of aluminium hydroxide is the limiting step. An aluminium conversion of ~90 % is reached at 80 oC at 6 h reaction time. A further increase in temperature reduces the reaction time immensely, with ~90 % aluminium conversion reached within 30 min at 100 oC and 120 oC. Extending the reaction times beyond these points does not have a significant influence on the conversion of aluminium as it remains constant at ~90 %. Of the various carbonate sources tested for intercalation, sodium carbonate showed the most crystalline hydrocalumite samples. Using sodium bicarbonate as a carbonate source renders similar conversion results to sodium carbonate. When reacting these carbonate sources with the precursor, the conversion to hydrocalumite increased with increasing reaction time and temperature. There is a significant spike in the intensity of the primary hydrocalumite diffraction peak of the sodium carbonate samples at 60 oC and 70 oC for 10 h reaction time; resulting in the highest yield of hydrocalumite. Use of air, CO2 (g), calcite and dry ice CO2 (s) as carbonate sources resulted in poor formation of hydrocalumite. Considering the results of the precursor formation and intercalation, the most promising synthesis conditions is to react calcium oxide and aluminium hydroxide at a temperature of 100 oC for 30 min, where after sodium carbonate should be added to the mixture and reacted for a further 10 h between 60 oC and 70 oC.
Dissertation (MEng)--University of Pretoria, 2015.
tm2016
Chemical Engineering
MEng
Unrestricted

La concentration croissante de CO2 dans l'atmosphère et les dangers potentiels qu'elle représente pour la terre au travers des changements climatiques, l'acidification des océans et l'élévation du niveau de la mer a conduit à un certain nombre de projets qui tentent de trouver un moyen sûr et inoffensifs pour capturer et stocker le CO2 dans des formations géologiques. Une de ces tentatives se déroule actuellement en Islande à la centrale géothermique Hellisheiði, située à proximité de la capitale, Reykjavik (le projet CarbFix). Le dioxyde de carbone et d'autres gaz comme H2S, N2, H2, CH4, et Ar sont des sous-produits de l'exploitation de l'énergie géothermique et l'objectif est de stocker tout ce CO2 dans les formations basaltiques qui se situent sous Hellisheiði. Le CO2 est dissous dans un courant d'eau injecté par pompage dans puits jusqu'à à 350 mètres de profondeur et qui s'écoule ensuite au sein d'horizons mixtes de verre basaltique et de basalte cristallin. Les roches basaltiques sont caractérisées par des teneurs élevées en cations divalents comme Mg2+, Fe2+ et Ca2+ et des vitesses de dissolution relativement rapides. L'eau acide chargée en CO2 dissout le basalte, libérant ainsi des cations qui peuvent réagir avec les ions carbonates pour former des minéraux carbonatés (magnésite, sidérite, calcite, ankérite ainsi que des solutions solides (Ca-Mg-Fe)CO3)). Si on admet que c'est la dissolution des roches basaltiques qui contrôle ce processus de séquestration du carbone, on peut en déduire que tout ce qui pourra limiter cette dissolution sera préjudiciable à l'ensemble du processus de confinement du CO2. Mon rôle dans le projet CarbFix a été d'examiner les effets de la formation de revêtements de carbonate de calcium sur la dissolution des phases primaires de basalte. Je me suis concentrée sur le verre basaltique et le clinopyroxène, diopside, afin de comparer des phases cristallines et non cristallines. En outre, une série d'expériences ont été menées pour étudier l'effet de la structure du minéral primaire sur la nucléation de calcite. Ces expériences ont été faites pour vérifier si les différentes structures de silicate conduiraient à une différente étendue de la nucléation et croissance de la calcite à la surface des silicates. Enfin, de nombreuses expériences de dissolution de verre basaltique ont été menées en présence de bactéries hétérotrophes mortes et vivantes, Pseudomonas reactans, afin de déterminer l'effet des bactéries sur la dissolution des roches dans le système des eaux souterraines du site Hellisheiði. Les expériences de dissolution de verre basaltique et de diopside ont été réalisés à 25 et 70 °C pour un pH de 7-8 dans des réacteurs à circulation alimentés en solutions de forces ioniques > 0,03 mol / kg contenant CaCl2 ± NaHCO3. Deux séries d'essais ont été menés simultanément, une série appelée essais de 'précipitations' au cours de laquelle la solution dans le réacteur était sursaturée par rapport à la calcite, et l'autre série appelée essais de 'contrôle', pour laquelle la modélisation PHREEQC ne prévoyait pas formation de minéraux secondaires. Ainsi, il a été possible de comparer les vitesses de dissolution du verre basaltique et du diopside à 25 °C avec et sans la formation de carbonate de calcium et d'autres minéraux secondaires afin d'en déduire leur effet sur les vitesses de dissolution. Les images de microscopie électronique à balayage ont montré que des quantités importantes de carbonate de calcium ont précipité au cours des expériences de 'précipitations' mais, dans le cas du verre basaltique la croissance primaire se présente sous forme gros amas discrets de calcite et d'aragonite qui ne se forment pas sur le verre lui-même. Par contre, plusieurs des cristaux de diopside ont été largement envahis par des revêtements de calcite sans aragonite décelable. Dans les deux cas, la présence de calcite / aragonite n'a pas eu d'incidence sur les vitesses de dissolution du verre basaltique et de diopside qui sont les mêmes que celles mesurées dans la série 'contrôle'. Il semblerait que la couverture discontinue et poreuse de carbonates permet aux ions des phases primaires de continuer à diffuser sans entrave à travers la couche secondaire. Pour mieux évaluer l'effet de la surface des silicates sur la nucléation de la calcite, les vitesses de dissolution de six minéraux et roches silicatés ont été mesurées à 25 °C dans des réacteurs à circulation en présence de solutions de pH ~ 9,1 sursaturées par rapport à la calcite. Les phases silicatées étaient les suivantes: olivine, enstatite, augite, labradorite, verre basaltique et péridotite. Les résultats montrent que le temps d'induction pour la nucléation de calcite et l'étendue de la couverture de carbonatée avec le temps varient selon la phase silicatée. Dans un même laps de temps l'olivine, l'enstatite et la péridotite (principalement composé d'olivine riche en Mg) étaient les plus couvertes par les précipitations de calcite, suivis par l'augite, la labradorite et enfin le verre basaltique. Toute la croissance de calcite a eu lieu sur la surface du silicate, y compris sur le verre basaltique. La cinétique favorise la croissance de calcite par nucléation sur les minéraux orthorhombiques (enstatite et olivine) par rapport aux minéraux monocliniques et tricliniques. Les plus faibles quantités de calcite ont été trouvées sur le verre qui n'a pas de structure silicatée ordonnée. Des bactéries hétérotrophes, Pseudomonas reactans ont été extraites de l'un des puits de contrôle à Hellisheiði et ont ensuite été séparées, purifiées et cultivées en laboratoire. Avec le bouillon de culture utilisé, les conditions de croissance optimales de cette bactérie sont 5-37 °C et un pH de 7,0 à 8. Cette bactérie, très commune dans l'eau et le sol, est une bonne candidate pour tester l'impact des bactéries hétérotrophes en général lors de la séquestration du CO2 dans un aquifère naturel comme en Islande. Les vitesses de dissolution du verre basaltique ont été mesurés à 25 °C dans des nouveaux réacteurs à circulation permettant d'opérer en présence de bactéries (BMFR) dans des solutions tamponnées transportant 0,1 à 0,4 g/L de bactéries mortes et 0,9 à 19 g/L de bactéries vivantes à 4 = pH = 10. Les résultats ont montré que la présence de ces bactéries n'avait quasiment pas d'effet effet sur la vitesse de dissolution. La conclusion générale de cette étude est que ni les revêtements de carbonate, ni les bactéries n'ont d'impact majeur sur les vitesses de dissolution des phases primaires silicatées. Ainsi, leur effet devrait être négligeable sur le processus de séquestration du CO2 sur le site Hellisheiði en Islande. Le basalte cristallin pourrait être recouvert plus rapidement en carbonate de calcium, mais le verre basaltique pourrait aussi servir de support pour la nucléation de calcite
The increasing levels of CO2 in the atmosphere and the potential dangers this pose to the Earth through climate change, ocean acidification and sea-level rise has lead to a substantial number of projects attempting to find a safe and benign way to capture and store CO2 in geological formations, also referred to as the CCS (Carbon Capture Storage) technology. One of these CCS attempts is currently taking place in Iceland at the geothermal power plant Hellisheiði, located close to the capital Reykjavik (the CarbFix project). CO2 and other gasses (H2S, N2, H2, CH4) are waste products of the geothermal energy exploitation and the aim is with time to store all of this anthropogenic-made CO2 in the basaltic formations underlying Hellisheiði. The CO2 is dissolved in groundwater as it is pumped down to 350 meters depth and then injected into mixed horizons of basaltic glass and crystalline basalt. The basaltic rocks are characterized by high contents of divalent cations like Mg2+, Fe2+ and Ca2+ and relatively fast dissolution rates. The acidic CO2-loaded water will dissolve the basalt thereby releasing cations, which can react with the aqueous carbonate ions to form carbonate minerals (magnesite, siderite, calcite, ankerite and Ca-Mg-Fe solid solutions). The rate-limiting step of this carbon sequestration process is thought to be the dissolution of basaltic rocks, thus any effect that could potentially limit basalt dissolution would be detrimental to the overall CO2 sequestration process. My part of the CarbFix project has been to look at the effects the formation of calcium carbonate coatings would have on the dissolution of the primary phase, in this case basaltic glass and the clinopyroxene diopside, so there would be a glass phase to compare with the results of a mineral phase. Furthermore, a series of experiments were conducted where we tested the primary mineral structure's affect on calcite nucleation. This was done in order to test if different silicate structures would lead to different extent of calcite nucleation and growth. Finally, extensive series were conducted on the dissolution of basaltic glass in the presence of dead and live heterotrophic bacteria, Pseudomonas reactans in order to determine the potential effect of bacteria on the carbon storage effort at the Hellisheiði site. The basaltic glass and diopside dissolution experiments were run at 25 and 70 ºC and pH 7-8 in mixed-flow reactors connected to solutions containing CaCl2±NaHCO3 with ionic strengths > 0. 03 mol/kg. Two sets of experimental series were run simultaneously, one series called the "precipitation" experiments in which the solution inside the reactor was supersaturated with respect to calcite, and the other series called the "control" experiments, where PHREEQC modeling foretold no major secondary mineral formation. By this, it was possible to compare dissolution rates of basaltic glass and diopside at 25 ºC with and without calcium carbonate and other secondary mineral formation in order to deduce the effect on their dissolution rates. Scanning electron microscope images showed substantial amounts of calcium carbonate had precipitated in the "precipitation" experiments, but in the case of basaltic glass the primary growth appeared as big, discrete cluster of calcite and aragonite with no growth on the glass itself. Opposed to this, several of the diopside crystals were extensively overgrown by calcite coatings and no aragonite was found. In neither cases did the presence of calcite/aragonite have an effect on the dissolution rates of basaltic glass and diopside when compared to the "control' dissolution rates. It appears the discontinuous cover of the carbonate allows the ions of the primary phases to continue to diffuse through the secondary layer unhindered. To further assess the effect of silicate surface on the nucleation of calcite, the dissolution rates of six selected silicate minerals and rocks were measured in mixed-flow reactors in solutions supersaturated with respect to calcite at 25 ºC and pH ~9. 1. The silicate phases were: Mg-rich olivine, enstatite, augite, labradorite, basaltic glass and peridotite. The results show different onset time of calcite nucleation and thus different extent of carbonate coverage with elapsed time depending on silicate phase. Within the same timeframe olivine, enstatite and peridotite (mainly composed of Mg-rich olivine) were the most covered by calcite precipitations, followed by augite, labradorite and finally basaltic glass. All calcite growth took place on the silicate surface including on the basaltic glass. Kinetics favor calcite nucleation growth on the orthorhombic minerals (enstatite and olivine) over the monoclinic and triclinic minerals. Least calcite was found on the glass, which has no ordered silicate structure. Heterotrophic bacteria, Pseudomonas reactans was extracted from one of the monitoring wells at Hellisheiði, and then separated, purified and cultured in the laboratory. Its optimal growth conditions were found to be 5-37 ºC and pH 7. 0-8. 2 on Brain Heart Broth nutrient. Being a common water- and soil bacteria it offered a good candidacy to test what could be expected of heterotrophic bacteria in general when storing CO2 in a natural aquifers like the one at the Hellisheiði site, in Iceland. Basaltic glass dissolution rates were measured at 25 ºC in newly developed Bacterial Mixed-Flow reactors (BMFR) in buffer solutions carrying 0. 1-0. 4 g/L of dead bacteria and 0. 9-19 g/L of live bacteria at 4 = pH =10. The results show that the presence had either no or a slightly rate-limiting effect. The overall conclusion is that neither the carbonate coatings nor the bacteria had major impact on the measured dissolution rates of the primary silicate phases, thus their effect are expected to be negligible on the CO2 sequestration process in basalt. Crystalline basalt might be faster covered by calcium carbonate, but also basaltic glass can act as a nucleation platform for calcite nucleation

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Les signatures isotopiques des minéraux carbonatés sont utilisées pour caractériser de nombreux processus géochimiques. Cette thèse a pour but de déterminer les vitesses auxquelles ces signatures isotopiques peuvent être altérées lors des interactions entre les fluides et les minéraux. A cette fin, une série d'études expérimentales a été conduite avec la dolomite (CaMg(CO3)2), la magnésite (MgCO3) et la calcite (CaCO3). On a mesuré l'évolution temporelle des compositions isotopiques de Ca et Mg pendant une série d'expériences de dissolution en réacteur fermé de la dolomite à des températures de 50°C à 126°C. A T < 120°C la composition isotopique du calcium dans la phase fluide est identique à celle de la dolomite initiale, mais au-delà de cette température, la signature isotopique du calcium dans le fluide (delta(44/42)Ca fluid) après 4 semaines était 0.6±0.1‰ plus lourde que l'originale. En revanche, le rapport delta(26/24)Mg du fluide reste égal à celui de la dolomite à toutes les températures étudiées. Ces résultats indiquent un double transfert de calcium vers et depuis la structure de la dolomite à T > 120°C. En outre, ces résultats suggèrent que la difficulté de la dolomite à précipiter à température ambiante doit être la conséquence de l'incapacité de Mg à s'incorporer dans la structure du minéral. Dans une autre étude on a conduit des expériences de dissolution de la magnésite à 25°C en solution aqueuses pour différents pH et pression de CO2. On a trouvé que la composition isotopique du fluide à proximité de l'équilibre chimique était différente de celle du solide, ce qui reflète un double transfert de Mg en direction et hors du minéral à température ambiante. Cependant, un seul mécanisme de fractionnement ne peut expliquer le comportement isotopique de Mg observé. La dernière partie de ce travail, consacrée au fractionnement isotopique du carbone dans le système calcite-eau, montre une évolution du fractionnement isotopique de cet élément vers le fractionnement isotopique à l'équilibre d'une durée d'une année après l'atteinte de l'équilibre chimique entre la calcite et l'eau. Les vitesses de rééquilibrage des isotopes de carbone sont ainsi quatre ordres de grandeurs plus lentes que la vitesse d'équilibrage de la calcite avec la solution. Ceci suggère que l'étape limitante dans le processus de rééquilibrage des isotopes du carbone est le transport de cet élément dans le cristal après l'échange isotopique à la surface de ce dernier. Les résultats de cette thèse indiquent que la signature isotopique de Mg, Ca et C des carbonates n'est pas invariante à l'échelle des temps géologiques et qu'elle peut être altérée durant l'interaction de ces minéraux avec l'eau. Ainsi, la préservation des signatures isotopiques des carbonates requiert d'une faible perméabilité des roches ou bien quelque mécanisme inhibant les échanges des métaux et du carbone à la surface des cristaux
The isotopic signatures of carbonate minerals have been applied to illuminate a plethora of natural geochemical processes. This thesis is aimed to assess the rates and or conditions at which such isotope signatures might be altered by fluid-mineral interaction through a series of systematic experimental studies performed with dolomite (CaMg(CO3)2) magnesite (MgCO3) and calcite (Ca-CO3). Ca and Mg isotopic compositions were measured as a function of time during closed-system stoichiometric dolomite dissolution experiments at 50 to 126°C. Although identical to that of the original dolomite at low temperatures, at temperatures >120 °C, the calcium isotopic signature of fluid phase (delta(44/42)Ca fluid) became 0.6±0.1‰ higher than that of the dissolving dolomite over a 4-week period. In contrast, the delta(26/24)Mg fluid, remained equal to that of the dolo-mite both at low and high temperatures. This set of experiments evidences the two-way transfer of calcium in and out of the dolomite structure at elevated temperatures. The results suggest that the inhability of dolomite to precipitate at these conditions is due to the difficulty of Mg to be reincorporated in the dolomite structure. In a follow-up study, magnesite was dissolved at 25°C in the presence of fluids with distinct pH and CO2 pressures. The isotopic compositions of the fluid differed from that of the solid at near-to chemical equilibrium indicating the two-way transfer of magnesium into this mineral at ambient temperatures. A single fractionation mechanism cannot explain the distinct Mg isotope behaviors observed. Further work on carbon isotope exchanges in the calcite water system shows a slow by steady evolution of the carbon isotopic composition towards the accepted equilibrium fractionation factor over the course of nearly year-long experiments after the system had attained bulk chemical equilibrium. Carbon isotope reequilibration rates were found to be approximately four orders of magnitude slower than that of bulk calcite dissolution, suggesting that the rate limiting step to the carbon isotope reequilibration process is the transport of carbon into and out of the bulk mineral after it has exchanged on the surface. The results of this thesis suggest that the Mg, Ca and C isotopic signatures in carbonate minerals are not invariant over geological time-frames and can be readily altered by water-mineral interaction. Such results indicate that the preservation of carbonate mineral signatures require low permeability rock formations or some inhibitory mechanism limiting metal and carbon exchange

Ce travail entre dans le cadre de l’étude des interactions eau-roche dans le cas du stockage du CO2 en milieu géologique. Un intérêt particulier est accordé aux hétérogénéités des paramètres associés aux phénomènes géochimiques. Ces hétérogénéités peuvent s’observer à différentes échelles: celle des grains (les minéraux présentent des défauts de cristallinité et des impuretés), et l’échelle centimétrique/pluri-décamétrique. En particulier, les paramètres thermodynamiques (logK) et de cinétique chimique (dans ce travail nous avons considéré le produit de la constante cinétique k par la surface spécifique S soit kS comme "paramètre de cinétique chimique") sont connus à partir des expériences de laboratoire pour des échantillons de quelques centimètres de dimension, alors que l’on s’intéresse aux réactions minéralogiques à l’échelle des réservoirs.Nous avons évalué les caractéristiques géostatistiques de la variabilité spatiale après réaction à travers des simulations de transport réactif dans lesquelles différents paramètres (logK et kS) sont perturbés avec une première variabilité imposée. Une combinaison de deux approches est ainsi abordée : déterministe et géostatistique. Le code du transport-réactif COORES (IFP-EN et Ecole nationale supérieure des mines de Saint-Etienne) a été utilisé pour les simulations déterministes et le système géochimique étudié concerne la dissolution du diopside avec précipitation de minéraux secondaires comme la calcite et la magnésite.Après analyse par la méthode des plans d’expériences, les résultats montrent qu’une corrélation spatiale élevée combinée avec une grande variance de dispersion des minéraux favorise une réactivité importante des minéraux lorsqu’on perturbe le paramètre de cinétique chimique kS. Par ailleurs une vitesse d’injection élevée accélère le processus de dissolution du minéral étudié. La variabilité spatiale du paramètre thermodynamique n’a cependant pas d’effet significatif sur les résultats, le système se comporte comme dans le cas homogène. Du point de vue de l’homogénéisation du paramètre kS, on retrouve l’influence de l’historique de dissolution
The present work is based on the study of water-rock interactions in the case of CO2 storage in geological media. Particular attention is devoted to heterogeneities at different observation scales geochemical phenomena. These heterogeneities can be observed at different scales: the grain (mineral crystallinity present defects and impurities), and the centimeter scale / multi- decametric (rocks are heterogeneous at different scales). In particular, the thermodynamic parameters logK and chemical kinetics kS (in this work we considered the product of the rate constant k by the specific surface area S is kS as "chemical kinetics parameter") are known from laboratory experiments to a few centimeters in size, while we are interested in mineralogical reactions across tanks.We propose to evaluate the geostatistical characteristics of the local variability after reaction through simulations of reactive transport on a small scale in which various parameters (logK and kS) are perturbed with a first spatial variability imposed. A combination of both approaches is discussed: deterministic and geostatistical for the study of geochemical problems at different scales. The reactive transport code - COORES (IFP - EN and Ecole nationale supérieure des mines de Saint -Etienne) was used for deterministic simulations and the geochemical system studied concerns the dissolution of diopside with precipitation of secondary minerals such as calcite and magnesite.After analysis by the method of design of experiments, the results show that high spatial correlation variance combined with high dispersion of minerals promotes a high reactivity when minerals chemically disturbing is the kinetic parameter kS. In addition, a high velocity injection accelerates the dissolution of the mineral studied. However, the effect of spatial variability of the thermodynamic parameter, did not significantly affect the results, the system behaves as in the homogeneous case. From the standpoint of homogenizing the parameter kS, include the influence of the history of dissolution

En vue de contrôler les émissions de gaz à effet de serre, il est envisagé d’injecter du CO2 dans des réservoirs géologiques. Or le CO2 n'est pas un gaz inerte. En modifiant la composition chimique de l'eau in situ, il est à l'origine d'interactions roche/fluide. Ces réactions géochimiques impactent les propriétés d'écoulement. Aussi, pour s'assurer de la viabilité et de la pérennité du stockage, les opérateurs ont besoin de simulations tenant compte de ces écoulements réactifs. Cependant les paramètres de l'équation macroscopique de transport utilisée sont affectés par les réactions surfaciques. Or, ces spécificités dues au transfert de masse ne sont pas prises en compte actuellement. De même, la loi perméabilité-porosité (K-F) n’est estimée que semi-empiriquement. Le but de cette thèse a été de développer une méthode pour obtenir les coefficients macroscopiques précédents et les relations K-F, en résolvant les équations gouvernant les phénomènes à l'échelle du pore. Pour ce faire, nous avons utilisé l'approche réseau de pores. L'avantage du modèle réseau est qu'il prend en compte explicitement la structure tout en conceptualisant cette dernière à un ensemble de pores et de canaux à la morphologie simplifiée (sphères, cylindres). L'étude est basée sur deux changements d'échelles successifs : du local au pore, puis du pore à la carotte. Le problème de transport réactif est résolu pour des éléments basiques, analytiquement ou numériquement. Puis, en faisant appel aux solutions précédemment trouvées, le transport réactif est traité sur l'ensemble du réseau. Notre model fut validé par des observations sur micromodèles, puis à l'aide d'une expérience d'altération acide
The geological storage of CO2 is considered as an attractive option to reduce the greenhouse gas emissions in the atmosphere. CO2 is not an inert gas, however. Its dissolution in brine forms a weak acid that has the potential to react with the host rock formation. The induced pores structure modification impacts the flow properties. Thus, to ensure the viability and sustainability of CO2 storage, operators need simulations that take into account the specificities of reactive transport. However, the macroscopic coefficients of the reactive transport equation are modified from the values of an inert tracer by surface reactions. These specificities due to mass transfer are currently not considered. Similarly, the permeability-porosity (K-F) relationship is only estimated semi-empirically. The aim of this thesis was to develop a method to obtain the macroscopic coefficients and the K-F laws, by solving the equations governing the pore-scale phenomena. To do this, we used the Pore Network Modelling approach (PNM). The advantage of the PNM is that it explicitly takes into account the pore structure, while conceptualizing the latter to a set of pores and throats whose morphology is simplified into spheres or cylinders for instance. The study is based into two successive upscalings: from local-scale to pore-scale, then from pore-scale to core-scale. The reactive transport problem is solved for basic elements, analytically or numerically. Then, using the solutions previously found at the pore scale, the reactive transport phenomena are treated throughout the network. Our model was validated by observations on micromodels and by a comparison with an acid-induced alteration experiment

Ferrous carbonate has been studied in batch reactions under rigorously anoxic conditions to determine thermodynamic and kinetic information about the compound. This information is particularly of interest in corrosion control and in the comparison of FeCO$\sb3$ to CaCO$\sb3$, a compound which has been studied extensively. The enthalpy of the dissolution reaction has been calculated to be $-22.8$ $\pm$ 0.6 kJ/mole, which is close to the NBS (1) reported value. The precipitation kinetics fit an empirical second order rate law with an activation energy of (9.31 $\pm$ 1.47) $\times$ $10\sp4$ J/mole, indicating surface reaction control. The dissolution kinetics fit an empirical second order rate law more closely than a first order rate law; however, more research is needed to decisively determine the reaction order. With either rate law, the activation energy for dissolution is large enough to suggest surface reaction control.

Geomicrobiology, the marriage of geology and microbiology, is about the impact of microbes on Earth materials in terrestrial systems and sediments. Many geomicrobiological processes occur over long timescales. Even the slow growth and low activity of microbes, however, have big effects when added up over millennia. After reviewing the basics of bacteria–surface interactions, the chapter moves on to discussing biomineralization, which is the microbially mediated formation of solid minerals from soluble ions. The role of microbes can vary from merely providing passive surfaces for mineral formation, to active control of the entire precipitation process. The formation of carbonate-containing minerals by coccolithophorids and other marine organisms is especially important because of the role of these minerals in the carbon cycle. Iron minerals can be formed by chemolithoautotrophic bacteria, which gain a small amount of energy from iron oxidation. Similarly, manganese-rich minerals are formed during manganese oxidation, although how this reaction benefits microbes is unclear. These minerals and others give geologists and geomicrobiologists clues about early life on Earth. In addition to forming minerals, microbes help to dissolve them, a process called weathering. Microbes contribute to weathering and mineral dissolution through several mechanisms: production of protons (acidity) or hydroxides that dissolve minerals; production of ligands that chelate metals in minerals thereby breaking up the solid phase; and direct reduction of mineral-bound metals to more soluble forms. The chapter ends with some comments about the role of microbes in degrading oil and other fossil fuels.

Whilst about 12 per cent of the earth’s dry and ice-free land is covered by carbonate rocks (limestone, marble, and dolomite), the proportion is significantly higher in the landscapes that border the Mediterranean Sea. These rock types are especially widespread in the northern part of the region and limestones in particular reach great thicknesses in Spain, southern France, Italy, the Balkan Peninsula, and Turkey and in many of the Mediterranean islands. Abundant precipitation in the uplands of the Mediterranean has encouraged solutional weathering of these carbonate rocks for an extended period. The region contains some of the deepest karst aquifers in the world, with many extending deep below present sea level (e.g. Bakalowicz et al. 2008). The regional fall in base level associated with the Messinian Salinity Crisis allowed the formation of very deep, multiphase karst systems in several parts of the Mediterranean basin (e.g. Mocochain et al. 2006). Thus, karst terrains and karstic processes are very significant components of the physical geography of the Mediterranean basin. Indeed, along with the climate and the vegetation, it can be argued that limestone landscapes (including limestone bedrock coasts) are one of the defining characteristics of the Mediterranean environment. Much of the northern coastline is flanked by mountains with bare limestone hillslopes (Figure 10.2) drained by short and steep river systems whose headwaters commonly lie in well-developed karst terrain. Karst terrains are also well developed in the Levant and in the Atlas Mountains of Morocco and Algeria, while relict karst features can be identified in the low-relief desert regions of Libya and Egypt (Perritaz 2004) (Figure 10.1). Mediterranean karst environments are also associated with distinctive soils, habitats and ecosystems as described in Chapters 5, 6, and 23. The nature and evolution of the karst landscapes across the Mediterranean region displays considerable spatial variability due to contrasts in relief, bedrock composition and structure, climatic history, and other factors. The karst geomorphological system is distinguished from other systems (e.g. glacial, fluvial, coastal, and aeolian) because of the dominant role of dissolution which results in water flowing in a subterranean circulation system rather than in surface channels (Ford 2004).

In Chapter 7 I showed how much computational effort could be avoided in a system consisting of a chain of identical equations each coupled just to its neighboring equations. Such systems arise in linear diffusion and heat conduction problems. It is possible to save computational effort because the sleq array that describes the system of simultaneous linear algebraic equations that must be solved has elements different from zero on and immediately adjacent to the diagonal only. This general approach works also for one-dimensional diffusion problems involving several interacting species. In such a system the concentration of a particular species in a particular reservoir is coupled to the concentrations of other species in the same reservoir by reactions between species and is coupled also to adjacent reservoirs by transport between reservoirs. If the differential equations that describe such a system are arranged in appropriate order, with the equations for each species in a given reservoir followed by the equations for each species in the next reservoir and so on, the sleq array still will have elements different from zero close to the diagonal only. All the nonzero elements lie no farther from the diagonal than the number of species. More distant elements are zero. Again, much computation can be eliminated by taking advantage of this pattern. I will show how to solve such a system in this chapter, introducing two new solution subroutines, GAUSSND and SLOPERND, to replace GAUSSD and SLOPERD. I shall apply the new method of solution to a problem of early diagenesis in carbonate sediments. I calculate the properties of the pore fluid in the sediment as a function of depth and time. The different reservoirs are successive layers of sediment at increasing depth. The fluid's composition is affected by diffusion between sedimentary layers and between the top layer and the overlying seawater, the oxidation of organic carbon, and the dissolution or precipitation of calcium carbonate. Because I assume that the rate of oxidation of organic carbon decreases exponentially with increasing depth, there must be more chemical activity at shallow depths in the sediment than at great depths.

Abstract CO2 geo-sequestration has shown potential to mitigate global warming caused by anthropogenic CO2 emissions. In this context, CO2 can be immobilized in subsurface formations due to chemical dissolution/precipitation via mineral trapping. However, long-term mineralization involves interdependent complexity of dissolution and precipitation kinetics. In this study, a numerical approach is developed and implemented to analyze the effect of rock type, reservoir temperature, brine salinity on CO2 mineral trapping in compositionally distinct subsurface carbonate reservoirs. Here, we simulated field-scale models for three different subsurface reservoirs’ compositions (calcite, dolomite, and siderite) to assess the mineral trapping capacity. The base case of a 3D carbonate formation was created. The petrophysical parameters were then upscaled (Sw, Sg, K, and φ) to capture the subsurface conditions. Subsequently, CO2 mineral trapping capacity was computed for different rock compositions mimicking carbonate/brine/CO2 systems. Moreover, the CO2 geo-storage potential was assessed under reservoir temperature, salinity, storage duration, and cumulative injected CO2. The effect of reservoir mineralogy was analyzed via the amount of CO2 mineralized within 100 years of storage duration following 2 years of injection as a base case. The results revealed significant variation in storage capacity as the mineral type changed. In particular, 100% calcite surface showed the highest CO2 storage capacity compared to both dolomite and siderite. The results could be attributed to the distinction of each mineral in terms of its relative cations dissolve-out rate. Moreover, increasing the reservoir temperature resulted in a monotonic increase in mineralization potential with an insignificant increase in case of siderite. Notably, calcite outperformed both siderite and dolomite as a preferable medium for CO2 mineralization as the injection duration increased over both 100 and 200 years of storage. Additionally, the increase in salinity either significantly decreased the amount of CO2 mineralized in case of calcite and siderite or showed no effect at all in case of dolomite. This work provides a new insight for underpinning the effects of carbonate reservoir composition on CO2 mineral trapping capacity which has not been investigated much. Overall, the results showed that CO2 trapping in subsurface carbonates immobilized CO2 for a long-term stable geo-storage.

Abstract The impact of carbonated brine-rock geochemical reactions on porosity, permeability, and multiphase flow responses is relevant to the determination of CO2 storage capacity of deep saline aquifers. In this research, carbonated brine flooding experiments were performed on core samples consisting of poorly sorted, quartz-rich sand with laminated bedding from a target CO2 storage formation in Wyoming. Complementary pre- and post-injection lab measurements were performed. Results showed that both core porosity and permeability increased after a seven-day carbonated brine injection, from 6.2% to 8.4% and 1.6mD to 3.7mD, respectively. These changes were attributed to carbonate mineral dissolution, which was evidenced by the effluent brine geochemistry, pore-throat size distribution and surface area. To be more specific, within the more permeable section of core samples, containing larger pore size, the permeability increment is apparent due to dolomite mineral grains and cements dissolution. However, for the lower permeability section, corresponding to the smaller pore size, mineral precipitation possibly lessened dissolution effects, leading to insignificant petrophysical properties changes. Consequently, the observed heterogeneous carbonated brine-rock interactions resulted in changes of CO2/brine relative permeability. This research provides a fundamental understanding regarding impacts of fluid-rock reactions on changes in multiphase flow properties of eolian sandstones, which lays the foundation for more accurate prediction/simulation of CO2 injection into deep saline aquifers.

Abstract Conventional acidizing of high temperature reservoirs is currently facing different challenges including high corrosion rate, face dissolution, rapid and uncontrolled reaction and formation damage. In this study, a new in-situ generated acid system is introduced to address the shortcomings of the conventional acid systems. This paper presents an acidizing fluid with delayed acidification properties that can be tailored to different reservoir conditions. A new acidizing system based on sodium salt of monochloroacetic acid (SMCA) is developed and introduced to resolve the technical challenges that conventional acid systems usually fail to tackle appropriately. The hydrolysis rate (i.e., acidification rate) of SMCA, which brings the delayed properties to the acid system, was further optimized by addition of halogen salts. Furthermore, the dissolution capacities of the acid system were measured for different minerals using the main formulation as well as boosted acid by addition of an organic/inorganic acid. Also, the precipitation potentials of the by-products were also investigated after the acid was fully spent and cooled down. Several additives were tested to improve the solubility of the calcium salt. Finally, the performance of the acid system was investigated by performing several coreflooding experiments using Indiana limestone cores. The coreflood experiments were conducted at different injection rates and at various degrees of hydrolysis. From the hydrolyzation experiments, it is found that addition of 1 wt% sodium iodide increases the SMCA hydrolyzation rate with a factor 1.7. It proved that fast hydrolysis can even be obtained at lower temperatures. It was shown that the reaction products from the calcite dissolution are fully soluble and chelation is the main responsible mechanism. In addition, it was found that scale inhibitors made from polymaleic acids, polyacrylic acids and copolymers thereof can also efficiently prevent solid precipitation. It was shown that the addition of hydrochloric acid in the range between 0.5 and 5 wt% can increase the dissolution capacity by at least 30%. From the coreflooding results, it was found that the new acid system can efficiently stimulate the limestone formations with no face dissolution under varying conditions in terms of temperature and injection rate. The CT-scan images confirmed the favourable wormhole propagation characteristics of the new acid system. The new acid system introduced in this paper is an in-situ acid generator which releases an organic acid over time and as function of temperature allowing deeper penetration. The main ingredients in the acid system are solid which allow safe handling and onsite preparation for offshore applications.

Abstract This work presents a matrix acidizing formulation which comprises a salt of monochloroacetic acid giving a delayed acidification and a chelating agent to prevent precipitation of a calcium salt. Results of dissolution capacity, core flood test and corrosion inhibition are presented and are compared to performance of 15 wt% emulsified HCl. Dissolution capacity tests were performed in a stirred reactor at atmospheric pressure using equimolar amounts of the crushed limestone and dolomites. Four different chelating agents were added to test the calcium ion sequestering power. Corrosion tests were executed using an autoclave reactor under nitrogen atmosphere at 10 barg. Core flood tests were performed to simulate carbonate matrix stimulation using limestone cores. It was found that the half-life time of the hydrolysis reaction is 77 min at a temperature of 100 °C. Sodium gluconate and the sodium salt of D-glucoheptonic acid were identified to successfully prevent the precipitation of the reaction product calcium glycolate at a temperature of 40 °C. Computed Tomography (CT) scans of the treated cores at optimum injection rate showed a single wormhole formed. At 150 °C an optimum injection rate of 1 ml/min was found which corresponds to a minimum PVBT of 6. In addition, no face dissolution was observed after coreflooding. Furthermore, the corrosion rates of different metallurgies (L80 and J55) were measured which are significantly less than data reported in literature for 15wt% emulsified HCl. The novelty of this formulation is that it slowly releases an organic acid in the well allowing deeper penetration in the formation and sodium gluconate prevents precipitation of the reaction product. The corrosivity of this formulation is relatively low saving maintenance costs to installations and pipe work. The active ingredient in the formulation is a solid, allowing onsite preparation of the acidizing fluid.

Abstract Scale-dissolver technology has been developed and applied with varying degrees of success over the past few years to remove carbonate and the more challenging sulphate/sulphide scales from production tubing and process equipment. It can often seem a much safer, more cost-effective remediation approach than physical removal, in particular, in the new generation of HP/HT fields, where any physical well intervention carries high risk, while the high temperatures would normally be beneficial in enhancing scale solubility and dissolution rate. The current paper reports dissolution characterstics of three solvents for calcite, barite, celestite and anhydrite in the temperature range 85°C to 176° to verify their performance up to the very high temperatures of a specific HP/HT development. These solvents included a typical alkaline-pH chelant for sulphate scale, an organic-acid mixture for carbonate scales, and a novel neutral-pH chelant as a less corrosive solvent for carbonate scale removal. In some tests the liquid-to-solid ratiowasvaried to evaluate the impact of excess scale on solvent performance. The performance against BaSO4 of the alkaline-pH chelant unexpectedly declines very significantly at 176°C relative to that observed at 85°C. Thermal instability was ruled out as the cause becausethe solvent showed very limited decline in performance when tested at 85°C after it had been thermally aged at 176°C. Performance at 176°C showed an initial rise followed by a decreasein aqueous barium ions, strongly indicating secondary re-precipitation of a barium-containing species at this temperature. In contrast, dissolution rates of carbonate scale by organic acid were greaterat the higher temperature, as would be expected. The novel neutral chelant showed a decline in calcite dissolution performance during the 176°C test but unlike the alkaline-pH chelant used for sulphate scale, this chelant showed degradation after thermal ageing and re-testing at 85°C. The findings from this paper suggest that there is temperature limit above which effective removal of sulphate scales may not be feasible with the selected solvents due to re-precipitation of a secondary reaction product, while for carbonate removal the current neutral chelants tested have a thermal stability issue at 176°C. These findings need to be considered when evaluating the potential role of chemical remediation in the overall scale-control strategy for HP/HT fields.

Abstract Oil and gas industry deals with fluid streams with different ions and concentrations that might cause scale precipitation. The scale precipitation, will thereafter, affect the fluid flow characteristics. Many problems will be raised by the scale deposition that affects the overall petroleum production. This paper aims to develop a non-corrosive acid system with high dissolution efficiency for field complex scales. The paper provided a series of lab analysis that covers the compositional analysis for the collected scale sample, and evaluating the developed acid system for compatible and stable properties, dissolution efficiency, and the corrosive impact. A field scale sample that has a composite chemical composition of calcium carbonate, calcium sulfate, kaolinite, barium sulfate, magnetite, and halite with different weight percentages by employing the diffraction of X-ray technology. Developing the new scale dissolver was achieved by specific compositional study for the organic acids to achieve high dissolution efficiency and low corrosive impact for the field treatment operations. The study results showed the successful scale removal for the developed dissolver at 160 and 210 °F by dissolution efficiency 100 % for 5 hours. The fluid showed a stable and compatible performance with low rate of solids precipitation after the scale treatment (2.3 %). The developed dissolver has a pH of 9. The corrosion test was conducted without any scale inhibitors and the results showed the low corrosion effect by 0.0129 lbm/ft2. The obtained successful results will help to dissolve such complex field scales, maintain the well equipment, and maintain the petroleum production from scale issues.

This present study indicates experimental investigation about the impact of CO2 flooding on oil recovery and rock’s properties alteration in carbonate reservoir under the miscible condition. In order to compare the effect to initial pore characteristic, two type of carbonate rock was used; an Edward white represents homogeneous mainly consisted micropore, whereas an Indiana limestone represented heterogeneous mainly consisted macropore in this study. Under the miscible condition (9.65 MPa and 40°C), five pore volume of CO2 were injected into oil-wet carbonate rock, which was fully saturated with oil and connate water. After CO2 flooding, several analyses for each sample conducted to investigate oil recovery and rock properties change in porosity, permeability, and pore structure by chemical and physical reaction between CO2, water, and carbonate mineral before and after CO2 flooding by using core analysis, MICP, SEM, ICP, and X-ray CT techniques. From the results of oil recovery, it was more effective and larger in Edward white than in Indiana limestone. Because homogeneous characteristic with a large ratio of low permeable micropore in Edward white contributed to occur long reaction time between oil and CO2 for enough miscibility as well as to displace stably oil by CO2. Conversely, heterogeneous pore structure mainly consisted of high permeable conduit (macropore) in Indiana limestone has brought ineffective and low oil production. From the analysis of rock’s properties alteration, we found that, for the homogeneous sample, dissolution dominantly changed pore structure and became better flow path by improving permeability and reducing tortuosity. While plugging by precipitation of mineral particles was not critically affected rock’ properties, despite the sample mainly consisted small pores. In the case of the heterogeneous sample, both dissolution and precipitation critically affected change of rock’s properties and pore structure. In particular, superior precipitation in complex pore network seriously damaged flow path and change of rock’s properties. The largest porosity change markedly appeared in inlet section because of exposing rock surface from fresh CO2 during a long time. In conclusion, it shows that CO2 miscible flooding in carbonate reservoirs significantly affected to alteration of rock’s properties such as porosity, permeability, tortuosity, and pore connectivity, in particular in heterogeneous system compared with in homogeneous system. These experimental results can be useful to characterize carbonate rock as well as to study rock properties alteration on CO2 EOR and CCS processes.

The potential biogeochemical and ecological impacts of ocean alkalinity enhancement were tested in a 5-weeks mesocosm experiment conducted in the subtropical, oligotrophic waters off Gran Canaria in September/October 2021. In the nine mesocosms, each with a volume of about 10 m3 inhabiting a natural plankton community, alkalinity enhancement was achieved through addition of a mix of sodium bicarbonate and sodium carbonate, simulating CO2-equilibrated alkalinization in a gradient from control up to twice the natural alkalinity. The response of the enclosed plankton community to the alkalinity addition was monitored in over 50 parameters which were sampled or measured in situ daily or every second day. In addition to the mesocosm experiment, a series of side experiments were conducted, focusing on individual aspects of mineral dissolution, secondary precipitation and biological responses at the primary producer level. This campaign, in which 47 scientists from 6 nations participated, generated the most comprehensive data set collected so far on the ecological and biogeochemical impacts of ocean alkalinity enhancement.

Juab Valley is a north-south-trending basin in the eastern Basin and Range Province. Juab Valley is bounded on the east by the Wasatch normal fault and the Wasatch Range and San Pitch Mountains, bounded on the west by Long Ridge and the West Hills. Juab Valley is at the southern end of Utah’s Wasatch Front, an area of projected rapid population growth and increased groundwater use. East-west-trending surface-water, groundwater, and water-rights boundaries approximately coincide along the valley’s geographic midline at Levan Ridge, an east-west trending watershed divide that separates the north and south parts of Juab Valley. The basin includes, from north to south, the towns of Mona, Nephi, and Levan, which support local agricultural and light-industrial businesses. Groundwater use is essential to Juab Valley’s economy. The Juab Valley study area consists of surficial unconsolidated basin-fill deposits at lower elevations and various bedrock units surrounding and underlying the basin-fill deposits. Quaternary-Tertiary basin-fill deposits form Juab Valley’s primary aquifer. Tertiary volcanic rocks underlie some of the basinfill deposits and form the central part of Long Ridge on the northwest side of the valley. Paleozoic carbonate rocks that crop out in the Mount Nebo area of the Wasatch Range, which receives the greatest average annual precipitation in the study area, likely accommodate infiltration of snowmelt and subsurface groundwater flow to the basin-fill aquifer. The Jurassic Arapien Formation also crops out in the Wasatch Range and San Pitch Mountains, and dissolution of gypsum and halite in the formation and sediments derived from it increases the sulfate, sodium, and total-dissolved-solids concentrations of surface water and groundwater. We grouped the stratigraphy of the Juab Valley study area into 19 hydrostratigraphic units based on known and interpreted hydraulic properties.

Environmental impacts associated with the mining of carbonatite deposits are an emerging concern due to the demand for critical metals. This study investigates the chemistry of tailings seepage at the former Saint Lawrence Columbium mine near Oka, Québec, Canada, which produced pyrochlore concentrate and ferroniobium from a carbonatite-hosted Nb-REE deposit. Its objectives are to characterize the mineralogy of the tailings and their pore water and effluent chemistries. Geochemical mass balance modeling, constrained by aqueous speciation modeling and mineralogy, is then used to identify reactions controlling the chemical evolution of pore water along its flow path through the tailings impoundment. The tailings are composed mainly of REE-enriched calcite (82 wt. %), biotite (12 wt. %) and fluorapatite (4 wt. %). Minor minerals include chlorite, pyrite, sphalerite, molybdenite and unrecovered pyrochlore. Secondary minerals include gypsum, barite and strontianite. Within the unsaturated zone, pore water chemistry is controlled by sulfide oxidation and calcite dissolution with acid neutralization. With increasing depth below the water table, pore water composition reflects gypsum dissolution followed by sulfate reduction and FeS precipitation driven by the oxidation of organic carbon in the tailings. Concomitantly, incongruent dissolution of biotite and chlorite releases K, Mg, Fe, Mn, Ba and F, forming kaolinite and Ca-smectite. Cation exchange reactions further remove Ca from solution, increasing concentrations of Na and K. Fluoride concentrations reach 23 mg/L and 8 mg/L in tailings pore water and effluent, respectively. At a pH of 8.3, Mo is highly mobile and reaches an average concentration of 83 µg/L in tailings effluent. Although U also forms mobile complexes, concentrations do not exceed 16 µg/L due to the low solubility of its pyrochlore host. Adsorption and the low solubility of pyrochlore limit concentrations of Nb to less than 49 µg/L. Cerium, from calcite dissolution, is strongly adsorbed although it reaches concentrations (unfiltered) in excess of 1 mg/L and 100 µg/L in pore water and effluent, respectively. Mine tailings from carbonatite deposits are enriched in a variety of incompatible elements with mineral hosts of varying reactivity. Some of these elements, such as F and Mo, may represent contaminants of concern because of their mobility in alkaline tailings waters.