Computed X-ray Tomography Study of Carbonate Precipitation in Large Portland Cement Pores

Cement degradation caused by CO2 exposure is an increasingly important environmental challenge that must be understood, for example, if former oil reservoirs are to be used for CO2 storage. When exposed to CO2-saturated brine, cement undergoes a chemically complex carbonation process that influences all the physicochemical properties of the cement. It is known that under favorable conditions, fractures and voids in cement can be occluded, or self-sealed, by precipitation of calcium carbonate. Here, we report a detailed X-ray microcomputed tomography (μ-CT) study on the carbonation of gas pores (macropores) of diameter ∼1 mm in cement. Specifically, cured class G Portland cement with sub-millimeter spherical disconnected macropores was exposed to CO2-saturated brine at high pressure (280 bar) and high temperature (90 °C) for 1 week. High-resolution synchrotron-based μ-CT enabled visualizing the morphology of the precipitates inside the macropores within both unreacted and carbonated regions. Quantitative analysis of the type and amount of material deposited in the macropores during carbonation suggests that the filling of the disconnected macropores involves transport of calcium ions from the cement bulk to the macropore interior. A detailed model describing the chemical processes involved is provided. The present study gives a deeper understanding of cement carbonation by literally shedding light on the complex precipitate structures within the macropores.ISSN:1528-7483ISSN:1528-750

Nonionic Fluorinated Surfactant Removal from Mesoporous Film Using sc-CO₂

Surfactant templated silica thin films were self-assembled on solid substrates by dip-coating using a partially fluorinated surfactant R₈^F(EO)₉ as the liquid crystal template. The aim was 2-fold: first we checked which composition in the phase diagram was corresponding to a 2D rectangular highly ordered crystalline phase and second we exposed the films to sc-CO₂ to foster the removal of the surfactant. The films were characterized by in situ X-ray reflectivity (XRR) and grazing incidence small angle X-ray scattering (GISAXS) under CO₂ pressure from 0 to 100 bar at 34 °C. GISAXS patterns reveal the formation of a 2-D rectangular structure at a molar ratio R₈^F(EO)₉/Si equal to 0.1. R₈^F(EO)₉ micelles have a cylindrical shape, which have a core/shell structure ordered in a hexagonal system. The core contains the R₈^F part and the shell is a mixture of (EO)₉ embedded in the silica matrix. We further evidence that the extraction of the template using supercritical carbon dioxide can be successfully achieved. This can be attributed to both the low solubility parameter of the surfactants and the fluorine and ethylene oxide CO₂-philic groups. The initial 2D rectangular structure was well preserved after depressurization of the cell and removal of the surfactant. We attribute the very high stability of the rinsed film to the large value of the wall thickness relatively to the small pore size

Real Time 3D Observations of Portland Cement Carbonation at CO2 Storage Conditions

International audienceDepleted oil reservoirs are considered a viable solution to the global challenge of CO2 storage. A key concern is whether the wells can be suitably sealed with cement to hinder the escape of CO2. Under reservoir conditions, CO2 is in its supercritical state, and the high pressures and temperatures involved make real-time microscopic observations of cement degradation experimentally challenging. Here, we present an in situ 3D dynamic X-ray micro computed tomography (mu-CT) study of well cement carbonation at realistic reservoir stress, pore-pressure, and temperature conditions. The high-resolution time-lapse 3D images allow monitoring the progress of reaction fronts in Portland cement, including density changes, sample deformation, and mineral precipitation and dissolution. By switching between flow and nonflow conditions of CO2-saturated water through cement, we were able to delineate regimes dominated by calcium carbonate precipitation and dissolution. For the first time, we demonstrate experimentally the impact of the flow history on CO2 leakage risk for cement plugging. In-situ mu-CT experiments combined with geochemical modeling provide unique insight into the interactions between CO2 and cement, potentially helping in assessing the risks of CO(2 )storage in geological reservoirs

Real Time 3D Observations of Portland Cement Carbonation at CO2 Storage Conditions

Depleted oil reservoirs are considered a viable solution to the global challenge of CO2 storage. A key concern is whether the wells can be suitably sealed with cement to hinder the escape of CO2. Under reservoir conditions, CO2 is in its supercritical state, and the high pressures and temperatures involved make real-time microscopic observations of cement degradation experimentally challenging. Here, we present an in situ 3D dynamic X-ray micro computed tomography (μ-CT) study of well cement carbonation at realistic reservoir stress, pore-pressure, and temperature conditions. The high-resolution time-lapse 3D images allow monitoring the progress of reaction fronts in Portland cement, including density changes, sample deformation, and mineral precipitation and dissolution. By switching between flow and nonflow conditions of CO2-saturated water through cement, we were able to delineate regimes dominated by calcium carbonate precipitation and dissolution. For the first time, we demonstrate experimentally the impact of the flow history on CO2 leakage risk for cement plugging. In-situ μ-CT experiments combined with geochemical modeling provide unique insight into the interactions between CO2 and cement, potentially helping in assessing the risks of CO2 storage in geological reservoirs.publishedVersio