Physical and numerical simulations of the presence of a forsterite transitional zone at high temperature and pressure: insight for scCO2 geological storage |
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| Authors: | Z Li Y Xu L Yang J Guo |
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| Institution: | 1. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 100083, Beijing, PR China;2. School of Earth Sciences and Resources, China University of Geosciences, 100083, Beijing, PR China;3. Key Laboratory of Groundwater Resources and Environment, Ministry of Education, Jilin University, 130021, Changchun, PR China |
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| Abstract: | Geological sequestration is one of the most effective ways to reduce greenhouse gases, such as carbon dioxide (CO2). The deep oceanic crust dominated by ultrabasic rock could store CO2 permanently. However, the storage mechanism has not been thoroughly understood because of the limited amount of research and experiments conducted. This study explored the reactive mechanisms of water–rock–gas in an ultrabasic system under different conditions. Forsterite, the most dominant mineral found in ultrabasic reservoirs, was used to conduct laboratory physical simulation experiments. Two experimental systems were designed including an scCO2–forsterite–water system and an N2–forsterite–water system. All experiments were performed for 1000 h at an experimental temperature of 150°C and a pressure of 150 bar, respectively, to mimic the geological conditions. The liquid products from the experiments were analysed by inductively coupled plasma-optical emission spectrometry, whereas the solid samples were analysed by scanning electron microscopy with energy disperse spectroscopy. Results showed that: (1) in the early stage during scCO2/N2–forsterite–water interaction, forsterite was dissolved with a reactive transitional zone forming on the surface, which caused H+ to enter into the silicate framework and accelerated the reaction; (2) in the N2 system, the dissolution of forsterite was inhibited by the Mg2+ concentration after reaching its saturation in the late stage; and (3) in the scCO2 system, magnesite was precipitated as a secondary mineral during the late stage, which promoted the dissolution of forsterite. As a result, the degree of dissolution of forsterite in the scCO2 system was far higher than in the N2 system. The experimental results are consistent with the numerical simulation using TOUGHREACT, a geochemical simulation procedure, which showed that CO2 promotes the dissolution of forsterite greatly at high temperature and pressure. |
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| Keywords: | CO2 geological storage forsterite magnesite transitional zone temperature and pressure physical and numerical simulations |
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