Application Of Multi-field Coupling Model To Prediction And Analysis Of CO₂ Sequestration In Saline Aquifers

According to the highly anticipated Special Report by the Intergovernmental Panel on Climate Change（IPCC）in 2018,195 nations had reached an agreement to take steps to limit the temperature rise to 1.5 ^oC by the end of the century.In order to achieve this target,global net human-caused emissions of CO₂ would need to fall by about 45 percent from 2010 levels by2030,reaching‘net zero’around 2050,which reinforces the significance of continued CO₂emission reduction in the next several decades.CO₂ storage in deep saline aquifers is such technology that can truly meet the international climate change targets due to the advantages of wide distribution location and huge potential storage capacity.After CO₂ is injected into the deep saline aquifers,CO₂ migration and storage are controlled by a complex coupling process of thermo-hydro-mechanical process.In this paper,a multi-field coupling model of thermo-hydro-mechanical is established to predict and analyze the In Salah CO₂ storage project in In Algeria and Shenhua CO₂ storage project in China.1)The coupled thermo-hydro-mechanical multi-field model can effectively predict the CO₂ migration and formation deformation of the In Salah CO₂ sequestration project.The stress change caused by thermal effect is significant and can potentially lead to the fracture of caprock.The heat transfer caused by the temperature difference between the injected CO₂and the formation can affect the reservoir and caprock stress field.The permeability of the reservoir has a limited effect on the increase of CO₂ storage capacity.By contrast,the influence of permeability anisotropy on CO₂ storage capacity is significantly greater.The stronger the anisotropy is,the farther the CO₂ plume migrates and the more obvious the concentrated distribution of CO₂ is.,However,the size and propagation distance of the surface uplift change little with the anisotropy of permeability.The evolution trend of the surface uplift near the well point with CO₂ injection is almost the same under different anisotropy conditions.Young’s modulus of formation has a significant effect on surface deformation,so it is necessary to carefully select the value of Young’s modulus in the model when paying attention to the security of reservoir.2)The application of thermo-hydro-mechanical multi-field coupling numerical model can improve the understanding of the storage capacity and safety of Shenhua CO2 sequestration project.The CO₂plume uniformly displaces the brine and the gas saturation is relatively uniform.This homogeneity effect which plays an important role in improving the safety and ability of CO₂ storage can be seen from all five injection layers.The lateral migration distance of CO₂ plume depends not only on the permeability and porosity but also on the difference in reservoir thickness.The final CO₂ saturation of injection layer 1 and 2,injection layer 3 and 4 is basically the same at the same distance from the well,while the injection layer 5 with the lowest reservoir permeability and porosity have the highest final CO₂ saturation at this position,which proves that the influence of reservoir thickness on CO₂ saturation is greater than that of permeability and porosity to some extent.The influence range of temperature is much smaller than that of CO₂ plume migration and pressure propagation distance.The maximum surface uplift is about 0.146 m,which occurs about 600 m away from the well,indicating that the surface subsidence caused by temperature decrease near the well is relatively large.Moreover,the farther away from this position,the smaller the surface uplift.The surface deformation becomes smaller with the injection time,and the maximum deformation displacement is less than 0.16 m.It can be predicted that if the injection continues,the surface uplift will not rise much and is still within the range of formation safety influence.