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Theoretical and numerical studies of coupled hydro-mechanical processes during geothermal and hydrocarbon production, nuclear waste disposal, and CO 2 sequestration in geological media have become a research focus worldwide. However, their application in China, especially CO 2 sequestration, is still in infancy and may need several years to develop. In this paper coupled hydro-mechanical processes in CO 2 migration, formation uplift and the state of caprock integrity as a result of CO 2 sequestration have been investigated by simulation at field scale for an integrated CCS (CO 2 Capture and Sequestration) project launched in the Ordos Basin, China. The paper aims at attaining long-term safety and integrity of caprock to ensure success for subsequent project operations at field scale. The linked TOUGH2MP-FLAC3D simulator has been used to study the coupled hydraulic-mechanical responses to primary stresses, injection rate and reservoir permeability during CO 2 injection and post-injection periods by means of 4 case studies. In the short-term operation of a CO 2 sequestration project launched in the Ordos Basin 0.1 Mt CO 2 has been injected in four saline aquifers within a period of 1 year and 9 years of relaxation time allotted for simulation runs. Contrary to using hydraulic field conditions alone, a combination of hydraulic-mechanical effects accounts for lateral migration of CO 2 in aquifer layers that leads to partial volumetric expansion of the reservoir. Amongst the main factors affecting hydro-mechanical processes, injection rate has the most significant impact. This is followed by reservoir permeability that is responsible for gauging the uplift trend rate in the post-injection period through hindering the dissipation of pore pressure. Results indicate that the scope of pore pressure attained will be larger in the isotropic stress state than in the compressional stress condition, pointing to the significance of primary stress. Calculation of the maximum storage pressure within safety limits using the integrity and shear criteria reveals that failure of caprock integrity increases with the amount of CO 2 injected. During injection however, the risk of caprock failure, especially in thin sandstone-caprock interlayered systems, increases with time. This paper estimates the pressure buildup in the four injection aquifers in the Ordos Basin, as a basis to ensure safety in the long-term operation of the CO 2 sequestration project, hence providing important reference for future commercial operations at field scale. [ABSTRACT FROM AUTHOR]

Subsurface immobilization and conversion of CO into 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 CO emissions in the atmosphere. Although mineral trapping of CO is 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 CO sequestration mechanisms. This is a 100 year preliminary batch simulation study of four sandstone samples, under CO saturated water at 75 °C from the Upper Permian formations in the Ordos Basin, using the TOUGHREACT/ECO2N module to simulate the CO-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 CO sequestration 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 CO that 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 CO solubility, offers the highest mineral trapping capacity, with a maximum carbonate mineral storage of ca. 0.7 kg/m of bulk rock over a 100 year period. Regardless of the initial acidity or alkalinity of the aquifer brine, injection of CO will 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 CO-brine-rock interaction, is site specific and mainly dependent on initial aquifer mineralogy and brine composition. [ABSTRACT FROM AUTHOR]