Numerical Study Of Carbon Dioxide Storage In Saline Aquifers

The significant increase of emissions of carbon dioxide (CO2) intensifies greenhouse effect, which leads to environmental problems like global warming, glaciers melting and the arise of sea level. Carbon dioxide capture and storage is currently one of the most promising measures for mitigating CO2emissions. Saline aquifers’wide distribution and enormous capacity make saline aquifers become the most attractive-storage sites for long-term storage of CO2.The pressure and temperature in the targeted injection formations keep CO2in supercritical state. The characteristics of high density, low viscosity and good mobility of supercritical CO2are beneficial for CO2storage in the saline aquifers. The CO2injected into the aquifers firstly enters into the pores of the rock. Then, buoyant force drives CO2upward within the formation until it reaches the cap rock. At the following time, the injected CO2have a series of physical and chemical reaction with the saline and the rock. Main storage mechanisms, including static trapping, residual trapping, solubility trapping and mineral trapping, operate to trap CO2.Based on the theory of seepage mechanics, multiphase hydrodynamics and computational fluid dynamics, this paper focuses on studying the storage of CO2in the saline aquifers. By using numerical simulations, the present work studies the influence of water injection on the distribution and dissolution of CO2during geological storage and the distribution of CO2after its leakage into groundwater aquifers and the leakage remediation measures.On the study of the influence of water injection, relative parameters related to the water injection, including the injection mode, rate, and position of injection point, as well as the hydrogeological parameters, rock porosity and salinity, are taken into account. Then this paper discusses the methods for accelerating solubility trapping and improving the security of geological storage. Results show that most of the supercritical CO2gathers quickly after injection around the injection well at the top of the saline aquifers, and appears in a shape of an inverted cone. During the CO2injection and subsequent standing, the CO2inverted cone tends to expand with time in the radial direction, along with increasing degree of CO2dissolution. Injection of water during or after CO2injection does not change severely the CO2distribution, but can significantly enhance the CO2dissolution. Increasing the injection rate of water, as well as reducing the distance between the injection point of water and the CO2inverted cone, results in higher CO2dissolution rate. Simultaneous injection of water and CO2leads to much more pronounced CO2dissolution than the case of water injection following the CO2injection, which may be attributed to better contact of CO2with water. It is also found that, lower salinity of the saline aquifers is more beneficial for achieving higher CO2dissolution rate. In contrast, the CO2dissolution is almost unaffected by the change of the rock porosity. The present study provides simulation data for the dissolution of CO2in saline aquifers, which can be used to guide development of more secure CO2storage technology.On the study of the distribution of CO2after its leakage into groundwater aquifers and the leakage remediation measures, this paper discusses the distribution of CO2under five leakage scenarios and the distribution of pressure build-up. Then, the extraction rate of the extraction well, dissolution rate of injection wells, and relative parameters are analyzed to evaluate remediation measures. Results show that most CO2gathers around the leakage well and gas saturation lessens along the radial and axial direction. The contours of pressure build-up oblique around the leakage areas, while they distribute like a vertical line far away from the leakage areas. Water injection can enhance the CO2dissolution and reduce the concentration of CO2in aqueous phase. A larger injection rate of water leads to a higher CO2dissolution rate. Extraction well can remove CO2from the aquifer in both gas and aqueous phase. When the remediation measure is using vertical extraction well, increasing the depth of the well, as well as reducing the vertical distance between the well and the leakage point and augmenting the radial distance between the well and the leakage point, results in higher CO2extraction rate. While using horizontal extraction well, a larger distance between the well and the leakage point leads to a higher CO2extraction rate. Hydrogeological parameters are also taken into account. Lower permeability of the rock is more beneficial for achieving higher CO2extraction rate. In contrast, lower porosity of the rock results in a lower CO2extraction rate. The present study provides simulation data for the remediation measures of CO2leakage into groundwater aquifers, which can be used to guide development of more reliable remediation technology of CO2leakage.