Research On The Formation Of Residual Water In CO₂Geological Storage

Implementation of CO₂geological storage is now recognized as an effective wayto reduce greenhouse gas emissions. CO₂sequestration options include coal seams, oiland gas reservoirs, deep saline aquifers and other locations （Basalt, oil shale, holes）.Saline aquifers have the largest storage potential and it is also the most complexamong the options above. The mechanisms of CO₂storage in deep saline aquifers canbe divided into five types: structural and stratigraphic, hydrodynamic, residual-gas,solubility and mineral traps.Geological storage of CO₂in deep saline aquifers is achieved by injecting CO₂into the aquifers and displacing the brine. Although most of the groundwater isdisplaced, some residual water remains in the rock pore because of the capillary force.The percentage of the rock pore volume occupied by residual water and the wholevolume of rock pore is called as residual water saturation. The formation andsaturation of residual water will affect not only the storage potential, but also thesafety of CO₂geological storage. The amount of residual water will not only affect thetrapping capacity of structural and stratigraphic traps, but also have a strong influenceon the residual-gas traps. The experiments were carried out at aquifer temperature andpressure. We studied the formation of residual water through injecting super criticalCO₂into the rock core saturated with water and also studied the effects of brineconcentration on the formation and saturation of residual water. We used a CO₂migration physical simulation platform in these experiments and selected ahomogeneous isotropic hydrophilic artificial rock sample with a permeability of2.2mD, porosity of14.6%, and dimensions of Φ50×80mm.The results show that the drainage took longer with the higher brine concentrationthan with the lower concentration and the amount of residual water （and theirreducible water saturation） of high concentration was larger than that of the lowerconcentration in all the stages. We divided the drainage process into three stagesaccording to the curve of water flow rate: the Piston Drainage Stage, the Portable Drainage Stage and the Dissolved Drainage Stage. The paper presents a capillarymodel to analyze and interpret the mechanism of the drainage by CO₂in these threestages.