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The emissions of greenhouse gases, especially CO2, have been identified as the main contributor for global warming and climate change. Carbon capture and storage (CCS) is considered to be the most promising strategy to mitigate the anthropogenic CO2 emissions. This review aims to provide the latest developments of CO2 storage from the perspective of improving safety and economics. The mechanisms and strategies of CO2 storage, focusing on their characteristics and current status, are discussed firstly. In the second section, the strategies for assessing and ensuring the security of CO2 storage operations, including the risks assessment approach and monitoring technology associated with CO2 storage, are outlined. In addition, the engineering methods to accelerate CO2 dissolution and mineral carbonation for fixing the mobile CO2 are also compared within the second section. The third part focuses on the strategies for improving economics of CO2 storage operations, namely enhanced industrial production with CO2 storage to generate additional profit, and co-injection of CO2 with impurities to reduce the cost. Moreover, the role of multiple CCS technologies and their distribution on the mitigation of CO2 emissions in the future are summarized. This review demonstrates that CO2 storage in depleted oil and gas reservoirs could play an important role in reducing CO2 emission in the near future and CO2 storage in saline aquifers may make the biggest contribution due to its huge storage capacity. Comparing the various available strategies, CO2-enhanced oil recovery (CO2-EOR) operations are supposed to play the most important role for CO2 mitigation in the next few years, followed by CO2-enhanced gas recovery (CO2-EGR). The direct mineralization of flue gas by coal fly ash and the pH swing mineralization would be the most promising technology for the mineral sequestration of CO2. Furthermore, by accelerating the deployment of CCS projects on large scale, the government can also play its role in reducing the CO2 emissions. [ABSTRACT FROM AUTHOR]

Abstract Mineral dissolution and secondary mineral precipitation can cause porosity and permeability changes of CO 2 storage reservoirs and caprocks after injection of CO 2. In this paper, a 3-step approach (core-scale experiment →core-scale modeling →reservoir-scale modeling) is developed to simulate reservoir-scale porosity and permeability evolution of CO 2 storage formation and caprock at a model CO 2 storage site. The model site is based on characteristics of a real site in Mississippi, USA. Important chemical and permeability modeling parameters in the reservoir-scale model are validated by core-scale experimental and reactive transport modeling results. The reservoir-scale model predicts a maximum 3.2% permeability increase of the CO 2 storage formation and a maximum 1.1% permeability increase of the caprock after 1000 years of exposure to CO 2 -rich brine, while the core-scale model predicts 7% permeability decrease for a small CO 2 storage formation core and 296% permeability increase for a small caprock core after 180-day exposure to CO 2 -rich brine. The discrepancy between permeability results of reservoir-scale model and core-scale model is attributed to strong pH buffering effect of CO 2 storage formation with large mass of H+-consuming minerals. Therefore, using core-scale experiments/models only is not sufficient to elucidate reservoir-scale permeability evolution. Variations of key model parameters have a small effect on permeability evolution of both CO 2 storage formation and caprock, except for variations of K eq (SiO 2 (am)) and the exponent n in permeability-porosity correlation. SiO 2 (am) is a key mineral that governs permeability evolution of CO 2 storage formation and caprock, given the characteristics of the model CO 2 storage site. Highlights • A 3-step approach to model permeability change induced by CO 2 reaction is developed. • pH buffering causes discrepancy between core- and reservoir-scale modeling results. • SiO 2 (am) is a key mineral that governs permeability change of CO 2 storage formation. [ABSTRACT FROM AUTHOR]

In this study, reaction experiments between CO 2 -saturated brine and wellbore cement samples cured under different pressures were conducted to study microstructural and mineral composition changes using micro-computed tomography (micro-CT), scanning electron microscopy (SEM) and Raman spectroscopy. The CT images of post-CO 2 exposure cement samples showed a dissolution-precipitation-dissolution pattern at the exterior of the samples. The dissolution in the inner hole of the samples, however, was not significant. Instead, only CaCO 3 precipitation was observed in the inner hole. CaCO 3 precipitation in the inner hole contributes to self-sealing of the cement, which reduces the risk of CO 2 leakage through wellbore cement. According to CT and SEM observations, a higher curing pressure caused more precipitation of CaCO 3 , which favored cement self-sealing when exposed to CO 2. The appearance of a C O peak and the disappearance of a –OH peak after reaction with CO 2 were observed by Raman spectroscopy, which was attributed to cement carbonation that converted Ca(OH) 2 into CaCO 3. This study provides solid evidence of cement self-sealing due to cement carbonation under geologic CO 2 storage circumstances. [Display omitted] • Reaction experiments between CO 2 -saturated brine and wellbore cement samples with an open hole at the center were conducted. • CT scanning results showed precipitation of high-density CaCO 3 and formation of low-density amorphous silica. • CaCO 3 precipitation contributed to self-sealing of the cement, reducing the risk of CO 2 leakage through wellbore cement. • Raman observation identified the CaCO 3 produced as calcite. [ABSTRACT FROM AUTHOR]