Numerical Simulation Study Of CO₂ Local Trapping Mechanism In Porous Media

Global warming due to greenhouse gas emissions has had a great impact on production and life of human society.Carbon dioxide(CO2)is the major component of greenhouse gases and,hence,reducing CO2 emissions into the atmosphere is critical to reduce greenhouse effects.CO2 sequestration in saline aquifers is widely recognized as one of the most promising technologies for reducing CO2 emissions.CO2 sequestration in saline aquifers is subject to the effects of several factors such as petro-physical properties and geochemical reactions and generally involves complex hydrogeology processes.Numerical modeling can improve the understanding of the mechanism of CO2/brine multiphase flow in porous media and provide important basis for reliable assessment of storage capacity and safety in saline aquifers.This thesis models CO2 local trapping in front of regular-and irregular-shaped low-permeability cross-beddings(namely dense layer)inside a Mt.Simon sandstone core from Illinois,USA,based on a fully heterogeneous CO2/brine multiphase flow model.Computational Results reveal: 1)the high capillary pressure of the dense layer(D-layer)dominates CO2 local accumulation and its low permeability plays an important role in influencing spatial distribution of CO2 saturation(SCO2);The irregular-shaped D-layer changes migration path of CO2 plume nearby and leads to homogeneous SCO2 distribution in front of it;2)Compared with the regular-shaped D-layer,the irregular-shaped one causes thicker heterogeneous zone with lower contrast in petro-physical properties with the surroundings and,hence,has more moderated but wider effect on abrupt average CO2 saturation(SCO2,ave)decrease in this zone.A porous-medium model with small-scale high randomness heterogeneity is also established to numerically analyze the influence of such heterogeneity on CO2/brine multiphase migration.Unlike the previous studies,only the measured petro-physical properties of several sandstone cores are used to specify the local petro-physical parameters of the porous-medium model.Results show that heterogeneity in porosity,permeability anisotropy and changing the random method can affect the CO2/brine multiphase flow migration;the higher CO2 injection rate can cause a certain increase of CO2 saturation in the domain.In addition,we study the influence of the equilibrium phase partition in supercritical CO2/brine systems on CO2 plume migration and local trapping in heterogeneous porous media based on a series of numerical simulations.The results show that such chemical reaction between CO2 and brine cause solid NaCl precipitate.NaCl precipitate occupies pore space near the region with high capillary entry pressure,reducing the permeability and increasing capillary pressure.This further strengths the availability of the local capillary trapping.