Numerical modeling including hysteresis properties for CO2 storage in Tubåen formation, Snøhvit field, Barents Sea

AbstractIn April 2008 the first injection of supercritical CO2 started into the Tubåen Formation from the Snøhvit field, Barents Sea. At full capacity, the plan is to inject approximately 23 Mtons of CO2 via one well during a 30 year period. The aim of this study was to simulation the 30 years of injection of supercritical CO2 and the following long term (5000 years) storage of CO2 in the Tubåen formation. The formation is at approximately 2600 meters depth and is at 98 °C and 265 bars. The simulations suggested that, because of limited lateral permeability, the bottom hole pressure increases rapidly to more than 800 bars if an annual injection rate of 766000 tons is used. This is significantly higher than the fracture pressures for the formation, and it is therefore suggested that the aim to inject 23 Mtons over the planed 30 years may be unrealistic. To prevent fracturing due to increasing pressure, the bottom hole pressure constraint is applied that leads to significant decrease in the amount of CO2 injected. With the hysteresis property applied, reservoir pressure behavior is the same in the base case (no hysteresis); however, the CO2 plume is distributed over a smaller area than in the base case. Similar to the case of hysteresis, the diffusion flow case shows the CO2 plume to be distributed over a smaller area than in the base case, but reservoir pressure decreases more than in the other two cases

Formation of H2 and CH4 by weathering of olivine at temperatures between 30 and 70°C

Hydrocarbons such as CH4 are known to be formed through the Fischer-Tropsch or Sabatier type reactions in hydrothermal systems usually at temperatures above 100°C. Weathering of olivine is sometimes suggested to account for abiotic formation of CH4 through its redox lowering and water splitting properties. Knowledge about the CH4 and H2 formation processes at low temperatures is important for the research about the origin and cause of early Earth and Martian CH4 and for CO2 sequestration. We have conducted a series of low temperature, long-term weathering experiments in which we have tested the CH4 and H2 formation potential of forsteritic olivine

Latitudinal gradient in dairy production with the introduction of farming in Atlantic Europe

International audienceThe introduction of farming had far-reaching impacts on health, social structure and demography. Although the spread of domesticated plants and animals has been extensively tracked, it is unclear how these nascent economies developed within different environmental and cultural settings. Using molecular and isotopic analysis of lipids from pottery, here we investigate the foods prepared by the earliest farming communities of the European Atlantic seaboard. Surprisingly, we find an absence of aquatic foods, including in ceramics from coastal sites, except in the Western Baltic where this tradition continued from indigenous ceramic using hunter-gatherer-fishers. The frequency of dairy products in pottery increased as farming was progressively introduced along a northerly latitudinal gradient. This finding implies that early farming communities needed time to adapt their economic practices before expanding into more northerly areas. Latitudinal differences in the scale of dairy production might also have influenced the evolution of adult lactase persistence across Europe

Why is Dawsonite Absent in CO2 Charged Reservoirs? Pourquoi la dawsonite est-elle absente des réservoirs chargés en CO2 ?

Growth of the sodiumaluminium-hydroxy carbonate dawsonite (NaAl(OH)2CO3) after charging saline aquifers with CO2 has been assumed in a plethora of numerical simulations at different mineralogies, aqueous solutions, pressures and temperatures. It appears however that dawsonite is less abundant than expected in natural CO2 storage analogues if we take into account the thermodynamic stability alone. We have mapped the thermodynamic stability of dawsonite relative to mineral phases like albite, kaolinite and analcime from 37° to 200°C and performed closed-system batch kinetic simulations using a new kinetic expression including a nucleation term based on classical nucleation theory, and a growth term that was based on BCF growth theory. Using this rate equation, we have performed a sensitivity study on dawsonite growth on mineralogy, temperature, CO2 pressure, nucleation rate and its dependencies on temperature and affinity, and on the dawsonite precipitation rate coefficient. Simulations with dawsonite growth disabled showed that the maximum oversaturation reached for dawsonite for seawater-like solutions never exceeded 3-4 times oversaturation. The positive effect on dawsonite growth of increasing the CO2 pressure was mostly neutralized by higher acidity. Decreasing the precipitation rate coefficient by 5 orders of magnitude had a limited effect on the onset of significant growth, but the amount of dawsonite formed at the end of the 1 000 years simulated time was only 37% below the high-rate case. Reducing the nucleation rates had similar effects leading to postponed dawsonite growth. Finally, based on thermodynamic considerations and numerical simulations, we suggest that the potential of dawsonite growth is limited to a medium-temperature window framed by a high thermodynamic stability relative to competing mineral phases at low temperatures, but with rapidly diminishing nucleation and growth rates at lower temperatures constrained by energy barriers. La possibilité pour la dawsonite – un hydroxy-carbonate de sodium et d’aluminium (NaAl(OH)2CO3) – de précipiter dans les aquifères salins dès lors que l’on y injecte du CO2 a été suggérée dans maintes simulations menées sur différentes compositions (minéraux et solution aqueuse) et dans des conditions de pression et de température variées. Pourtant, sur le strict plan de la stabilité thermodynamique, la dawsonite paraît moins communément répandue que l’on pourrait s’y attendre dans les analogues naturels de stockages de CO2. On a cartographié la stabilité thermodynamique de la dawsonite par rapport à des phases minérales comme l’albite, la kaolinite et l’analcime, entre 37 et 200 °C, puis on a simulé numériquement des évolutions minérales en système fermé à l’aide d’un nouveau formalisme cinétique pour la précipitation, formalisme qui inclut (1) un terme de nucléation, basé sur la théorie classique de la nucléation, et (2) un terme de croissance, dérivant de la théorie BCF de la croissance. Utilisant cette équation de vitesse, on a réalisé une étude de sensibilité pour examiner comment la croissance de la dawsonite varie avec la composition minérale, la température, la pression partielle de CO2, la vitesse de nucléation – et les variations de cette dernière avec la température et l’affinité chimique –, et enfin la constante de vitesse adoptée pour la loi de précipitation de la dawsonite. Lorsqu’on empêche la dawsonite de précipiter, le rapport de sur-saturation ne dépasse jamais 3 ou 4 pour des solutions de type eau de mer. La propension accrue à précipiter si la pression partielle de CO2 augmente est contrebalancée par l’effet d’acidification de la solution. Diminuer jusqu’à 5 ordres de grandeur la vitesse de précipitation n’a qu’un effet limité sur le démarrage d’une croissance significative, et au bout de 1 000 ans de simulation la quantité de dawsonite formée est de 37 % ce qu’elle est dans le régime de précipitation maximale. Réduire le taux de nucléation a le même effet de retarder la croissance du minéral. Au bout du compte, sur la base de considérations thermodynamiques et au vu des simulations présentées, on suggère que le potentiel de croissance de la dawsonite est restreint à une fenêtre de températures médianes. À basse température, la stabilité relativement grande de la dawsonite vis-à-vis des minéraux en compétition est contrecarrée par la forte diminution des vitesses de nucléation et de croissance, ce qui reflète une puissante barrière énergétique

Why is Dawsonite Absent in CO

Growth of the sodiumaluminium-hydroxy carbonate dawsonite (NaAl(OH)2CO3) after charging saline aquifers with CO2 has been assumed in a plethora of numerical simulations at different mineralogies, aqueous solutions, pressures and temperatures. It appears however that dawsonite is less abundant than expected in natural CO2 storage analogues if we take into account the thermodynamic stability alone. We have mapped the thermodynamic stability of dawsonite relative to mineral phases like albite, kaolinite and analcime from 37° to 200°C and performed closed-system batch kinetic simulations using a new kinetic expression including a nucleation term based on classical nucleation theory, and a growth term that was based on BCF growth theory. Using this rate equation, we have performed a sensitivity study on dawsonite growth on mineralogy, temperature, CO2 pressure, nucleation rate and its dependencies on temperature and affinity, and on the dawsonite precipitation rate coefficient. Simulations with dawsonite growth disabled showed that the maximum oversaturation reached for dawsonite for seawater-like solutions never exceeded 3-4 times oversaturation. The positive effect on dawsonite growth of increasing the CO2 pressure was mostly neutralized by higher acidity. Decreasing the precipitation rate coefficient by 5 orders of magnitude had a limited effect on the onset of significant growth, but the amount of dawsonite formed at the end of the 1 000 years simulated time was only 37% below the high-rate case. Reducing the nucleation rates had similar effects leading to postponed dawsonite growth. Finally, based on thermodynamic considerations and numerical simulations, we suggest that the potential of dawsonite growth is limited to a medium-temperature window framed by a high thermodynamic stability relative to competing mineral phases at low temperatures, but with rapidly diminishing nucleation and growth rates at lower temperatures constrained by energy barriers

Experimental determination of natural carbonate rock dissolution rates with a focus on temperature dependency

The denudation of carbonate rocks at landscape scale is controlled by factors like mineral composition, temperature, precipitation, runoff, fracture spacing and vegetation cover. Knowledge on carbonate denudation is important in order to understand landscape development and long-term terrestrial/marine carbon transport, but there are few laboratory studies done on weathering rates of natural carbonate rocks under the low temperatures relevant for glacial-interglacial periods. To enhance the understanding of carbonate dissolution kinetics we studied low-temperature dissolution reactions of various natural Triassic carbonate rocks belonging to the Lower Muschelkalk in Germany. We conducted batch and flow-through experiments investigating the direct correlation of dissolution rates with temperature, and to establish whether the fine-grained carbonate rocks (micrite) are more reactive than the coarser-grained sparitic limestones. By increasing the temperature from 5 to 26 °C far-from-equilibrium dissolution rates of micritic and sparitic limestone samples increased from 2.42 × 10− 07 to 10.88 × 10− 07 and 4.19 × 10− 07 to 7.74 × 10− 07 mol m− 2 s− 1, respectively (Specific Surface Areas (SSA) of about 0.006–0.01 m2/g). The dissolution rates of dolomite rock samples varied only slightly from 1.06 × 10− 07 to 2.02 × 10− 07 mol m− 2 s− 1 (SSA approximately 0.002 m2/g) in the temperature range 5–25 °C at circum-neutral pH. The obtained apparent activation energies are in the range of earlier experiments done at higher temperatures, but there is a distinct difference between the calcite in the micrite (~ 51 kJ/mol) and sparitic (~ 20–22 kJ/mol) lithologies, indicating that the dissolution mechanisms are not the same. Using these activation energies in modelling of natural carbonate denudation we see that there is a clear effect of changing temperature, but this is mostly through the increased solubility at lower temperatures and not through the increasing far-from-equilibrium dissolution rates at higher temperatures. Formation of fluid pathways by preferential dissolution of framework calcite crystals is suggested to form infiltration pathways and affect denudation rates. The difference in crystal size between the micritic and sparitic limestones will affect the formation of such pathways (larger crystals may create fewer and larger conduits) and this is expected to be more important for the long-term denudation than the differences in activation energies

Experimental hydrothermal alteration of basaltic glass with relevance to Mars

International audienceAbstract Phyllosilicates, carbonates, zeolites, and sulfates on Mars give clues about the planet's past environmental conditions, but little is known about the specific conditions in which these minerals formed within the crust and at the surface. The aim of the present study was to gain increased understanding on the formation of secondary phases by hydrothermal alteration of basaltic glass. The reaction processes were studied under varying conditions (temperature, pCO 2 , water:rock ratio, and fluid composition) with relevance to aqueous hydrothermal alteration in fully and partly saturated Martian basalt deposits. Analyses made on reaction products using X‐ray diffraction ( XRD ) and scanning electron microscope ( SEM ) were compared with near infrared spectroscopy ( NIR ) to establish relative detectability and spectral signatures. This study demonstrates that comparable alteration minerals (phyllosilicates, carbonates, zeolites) form from vapor condensing on mineral surfaces in unsaturated sediments and not only in fully water‐saturated sediments. In certain environments where water vapor might be present, it can alter the basaltic bedrock to a suite of authigenic phases similar to those observed on the Martian surface. For the detection of the secondary phases, XRD and SEM ‐ EDS were found to be superior to NIR for detecting and characterizing zeolites. The discrepancy in detectability of zeolites between NIR and XRD / SEM ‐ EDS might indicate that zeolites on Mars are more abundant than previously thought

Injection of CO2-saturated brine in geological reservoir: A way to enhanced storage safety

Injection of free-phase supercritical CO2 into deep geological reservoirs is associated with risk of considerable return flows towards the land surface due to the buoyancy of CO2, which is lighter than the resident brine in the reservoir. Such upward movements can be avoided if CO2 is injected in the dissolved phase (CO2aq). In this work, injection of CO2-saturated brine in a subsurface carbonate reservoir was modelled. Physical and geochemical interactions of injected low-pH CO2-saturated brine with the carbonate minerals (calcite, dolomite and siderite) were investigated in the reactive transport modelling. CO2-saturated brine, being low in pH, showed high reactivity with the reservoir minerals, resulting in a significant mineral dissolution and CO2 conversion in reactions. Over the injection period of 10 yr, up to 16% of the injected CO2 was found consumed in geochemical reactions. Sorption included in the transport analysis resulted in additional quantities of CO2 mass stored. However, for the considered carbonate minerals, the consumption of injected CO2aq was found mainly in the form of ionic trapping