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Modelling CO2-brine-rock interactions in the Upper Paleozoic formations of Ordos Basin used for CO2 sequestration

Liu, Hejuan, Hou, Zhengmeng, Were, Patrick, Gou, Yang, Xiong, Lun, Sun, Xiaoling
Environmental earth sciences 2015 v.73 no.5 pp. 2205-2222
acidity, alkalinity, aquifers, carbon dioxide, laboratory experimentation, models, pH, salinity, sandstone, silicate minerals, solubility, trapping, China
Subsurface immobilization and conversion of CO₂into solid mineral phases in deep siliciclastic saline formations containing silicate minerals, commonly known as “mineral trapping”, is gaining research attention as a significant option to reduce CO₂emissions in the atmosphere. Although mineral trapping of CO₂is a long-term process, a combination of short-term results from both laboratory experiments and numerical simulations can lead to some general understanding of the required long-term CO₂sequestration mechanisms. This is a 100 year preliminary batch simulation study of four sandstone samples, under CO₂saturated water at 75 °C from the Upper Permian formations in the Ordos Basin, using the TOUGHREACT/ECO2N module to simulate the CO₂-brine-rock interaction processes in deep siliciclastic multilayered saline aquifers. The samples approximately correspond to the four target saline formations selected by the Shenhua Group for a CO₂sequestration field demonstration project in the Ordos Basin, PR China. Preliminary simulation results show that the initial salinity of formation brine plays a significant role in determining the amount of CO₂that will be sequestered by solubility or mineral trapping in a deep saline aquifer. Minimal differences between experimental results and numerical calculation occur in low salinity waters, and significantly larger differences in high salinity waters, which is still under the maximum acceptable difference between experimental and computed data (10 %). The upper Liujiagou formation, with the highest level of salinity (ca. 88.7 g/L TDS) and lowest level of CO₂solubility, offers the highest mineral trapping capacity, with a maximum carbonate mineral storage of ca. 0.7 kg/m³of bulk rock over a 100 year period. Regardless of the initial acidity or alkalinity of the aquifer brine, injection of CO₂will inflict a sudden drop in pH of the brine to acidity levels in a range of 3.0–4.6. The subsequent amount of dissolved and precipitated minerals, arising from the CO₂-brine-rock interaction, is site specific and mainly dependent on initial aquifer mineralogy and brine composition.