The impact of mineral reactive surface area variation on simulated mineral reactions and reaction rates

Mineral reactive surface area (RSA) is one of the key factors that control mineral reactions, as it describes how much mineral is accessible and can participate in reactions. This work aims to evaluate the impact of mineral RSA on numerical simulations for CO2 storage at depleted oil fields. The Farnsworth Unit (FWU) in northern Texas was chosen as a case study. A simplified model was used to screen representative cases from 87 RSA combinations to reduce the computational cost. Three selected cases with low, mid, and high RSA values were used for the FWU model. Results suggest that the impact of RSA values on CO2 mineral trapping is more complex than it is on individual reactions. While the low RSA case predicted negligible porosity change and an insignificant amount of CO2 mineral trapping for the FWU model, the mid and high RSA cases forecasted up to 1.19% and 5.04% of porosity reduction due to mineral reactions, and 2.46% and 9.44% of total CO2 trapped in minerals by the end of the 600-year simulation, respectively. The presence of hydrocarbons affects geochemical reactions and can lead to net CO2 mineral trapping, whereas mineral dissolution is forecasted when hydrocarbons are removed from the system.

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Reactive transport model of kinetically controlled celestite to barite replacement

10.5194/egusphere-egu21-9832 ◽

2021 ◽

Author(s):

Morgan Tranter ◽

Maria Wetzel ◽

Marco De Lucia ◽

Michael Kühn

Keyword(s):

Surface Area ◽

Reactive Transport ◽

Scale Formation ◽

Partial Replacement ◽

Geothermal Systems ◽

Digital Rock ◽

Reactive Surface Area ◽

Reactive Surface ◽

Loss Models ◽

The Impact

Barite formation is of concern for many sustainable utilisations of the geological subsurface, ranging from oil and gas extraction to geothermal reservoirs, and also acts as a scavenger mineral for the retention of radium for nuclear waste disposal. The surface reaction-controlled nature of its formation in these dynamic systems entails a strong sensitivity of the host rock's permeability towards heterogeneities and boundary conditions. The impact of precipitation on effective flow properties can vary by many orders of magnitude as shown by barite scale formation and injectivity loss models for geothermal systems [1], emphasising the need for robust prediction models.A relevant example case is the replacement of celestite (SrSO4) with barite (BaSO4), which was investigated for various barite supersaturations with flow-through experiments on the core-scale [2]. Three distinct cases were observed for supersaturations from high to low: (1) quick overgrowth and passivation of soluble celestite grains, (2) partial replacement of celestite with barite, (3) slow moving reaction front with complete mineral replacement. The authors presented heuristic approaches that include linking reactive surface area development to molar fractions to model the results. We provide a comprehensive, full-physics geochemical modelling approach using precipitation and dissolution kinetics as well as nucleation and crystal growth [3] for a more flexible representation of the problem. Additionally, the generation of a digital rock representation based on CT-scans of the granular sample is utilised to derive its inner surface area [4]. The experiments were modelled using core-scale reactive transport simulations. The three observed cases at varying supersaturations were reproduced with regard to evolution of sample rock composition and porosity.In a next step, the characteristic values taken from the calibrated reactive transport models can be further integrated into the existing digital rock physics model [4], thus enabling the development of up-scaled relationships such as reactive surface area as a function of mineral fractions and porosity. The resulting models can then be applied to reservoir-scale simulations for various applications related to subsurface utilisation.&#160;---[1] Tranter, M., De Lucia, M., Wolfgramm, M., K&#252;hn, M., 2020. Barite Scale Formation and Injectivity Loss Models for Geothermal Systems. Water 12, 3078. https://doi.org/10/ghntzk [2] Poonoosamy, J., Klinkenberg, M., Deissmann, G., Brandt, F., Bosbach, D., M&#228;der, U., Kosakowski, G., 2020. Effects of solution supersaturation on barite precipitation in porous media and consequences on permeability: Experiments and modelling. Geochimica et Cosmochimica Acta 270, 43&#8211;60. https://doi.org/10/ghntxn [3] Tranter, M., De Lucia, M., K&#252;hn, M., 2021. Numerical investigation of barite scaling kinetics in fractures. Geothermics 91, 102027. https://doi.org/10/ghr89n [4] Wetzel, M., Kempka, T., K&#252;hn, M., 2020. Hydraulic and Mechanical Impacts of Pore Space Alterations within a Sandstone Quantified by a Flow Velocity-Dependent Precipitation Approach. Materials 13, 3100. https://doi.org/10/ghsp42

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Numerical analysis of the chemical kinetic mechanisms of ozone depletion and halogen release in the polar troposphere

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-24171-2013 ◽

2013 ◽

Vol 13 (9) ◽

pp. 24171-24222 ◽

Cited By ~ 1

Author(s):

L. Cao ◽

H. Sihler ◽

U. Platt ◽

E. Gutheil

Keyword(s):

Boundary Layer ◽

Surface Area ◽

Ozone Depletion ◽

Reaction Rates ◽

The Arctic ◽

Strong Impact ◽

Reactive Surface ◽

A Value ◽

Halogen Species

Abstract. In recent years, the role of halogen species (e.g. Br, Cl) in the troposphere of polar regions is investigated after the discovery of their importance for boundary layer ozone destruction in the polar spring. Halogen species take part in an auto-catalytic chemical cycle including key self reactions. In this study, several chemical reaction schemes are investigated, and the importance of specific reactions and their rate constants is identified by a sensitivity analysis. A category of heterogeneous reactions related to HOBr activate halogen ions from sea salt aerosols, fresh sea ice or snow pack, driving the "bromine explosion". In the Arctic, a small amount of NOx may exist, which comes from nitrate contained in the snow, and this NOx may have a strong impact on ozone depletion. The heterogeneous reaction rates are parameterized by considering the aerodynamic resistance, a reactive surface ratio, β, i.e. ratio of reactive surface area to total ground surface area, and the boundary layer height, Lmix. It is found that for β = 1, the ozone depletion process starts after five days and lasts for 40 h for Lmix = 200 m. Ozone depletion duration becomes independent of the height of the boundary layer for about β≥20, and it approaches a value of two days for β=100. The role of nitrogen and chlorine containing species on the ozone depletion rate is studied. The calculation of the time integrated bromine and chlorine atom concentrations suggests a value in the order of 103 for the [Br] / [Cl] ratio, which reveals that atomic chlorine radicals have minor direct influence on the ozone depletion. The NOx concentrations are influenced by different chemical cycles over different time periods. During ozone depletion, the reaction cycle involving the BrONO2 hydrolysis is dominant. A critical value of 0.002 of the uptake coefficient of the BrONO2 hydrolysis reaction at the aerosol and saline surfaces is identified, beyond which the existence of NOx species accelerate the ozone depletion event – for lower values, deceleration occurs.

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