Numerical Simulation Of The Influence Of CO₂ Large-scale Injection And Its Leakage Along Abandoned Wells On Reservoirs

Since the industrial revolution,massive emissions of carbon dioxide?CO₂?have led to a range of environmental problems.Although countries are actively exploring green energy,the energy structure based on fossil fuels will not change in a short period of time.As one of the ways to effectively reduce carbon emissions,CO₂ geological storage is widely recognized by the international community.The deep saline layer is regarded as the most potential storage site by its unique advantages.During CO₂ storage,changes in reservoir pressure fields and the diffusion of CO₂ in the reservoir may affect the safety of shallow groundwater.Moreover,a large number of abandoned wells around the storage site will become a leak path for CO₂,causing serious environmental and safety problems such as CO₂ leakage.Therefore,study of the impact of large-scale CO₂ injection on reservoirs and the impact of CO₂ along the leakage characteristics of abandoned wells is of great significance for CO₂ storage safety and environmental impact.This paper relies on the CO₂ enhanced saltwater mining technology demonstration site in the Junggar Basin,and takes the target reservoir of the Cretaceous Donggou Formation as the research object.Under the guidance of the theory of geology,hydrogeology and multiphase seepage,the TOUGH2/ECO₂ N numerical simulation software was used to explore the basis of the boundary condition setting of the numerical model through the combination of field investigation and numerical simulation.The reservoir pressure field evolution and CO₂ migration distribution characteristics under large-scale CO₂ injection conditions are analyzed systematically,and the impact on the shallow groundwater safety of surrounding water sources is analyzed.The effects of the distance between the CO₂ leakage well and the injection well on the pressure field evolution,CO₂ spatial distribution and leakage characteristics of the reservoir system are analyzed.The main results achieved are as follows:?1?Through the numerical simulation of the radial 2D model,the reservoir pressure field evolution and CO₂ migration distribution characteristics under single well CO₂ injection conditions are investigated.During the 10-year constant pressure injection process,the further away from the injection well,the smaller the reservoir pressure increment.The farthest impact distance is 50 km.In the 100-year simulation period,the maximum CO₂ migration distance is only about 1300 m.Combined with the geological conditions of the test site,the distance between the injection well and the model boundary in the 3D model is determined to be 30 km,and the injection well spacing is set to 2 km.The results not only provide a scientific basis for the multi-well CO₂ injection and the numerical model boundary range setting of CO₂ leakage along the abandoned well,but also provide a method reference for the boundary condition setting of similar numerical simulation.?2?The three-dimensional numerical model of large-scale injection of CO₂ in the site is established.The effects of CO₂ injection on the evolution of reservoir pressure field and the distribution characteristics of CO₂ migration in the reservoir are analyzed under different injection well conditions.During the 10-year CO₂ constant pressure injection process,the greater the number of injection wells,the greater the reservoir pressure increment.After the CO₂ injection is stopped,the reservoir pressure is basically restored to the initial reservoir pressure level in about 10 years,and the pressure recovery time is weakly correlated with the number of injection wells.In the 100-year simulation time,the number of injection wells has no significant effect on the maximum migration distance of CO₂,which is about 1600 m.However,under multi-well conditions,the interwell high pressure zone causes a decrease in the well pressure difference,resulting in a significant reduction of CO₂ well migration distance by 20%-40% compared to the outside.?3?The impact of large-scale CO₂ injection on the water safety of the groundwater system around the study area and the existing groundwater source is determined.Based on the influence of CO₂ large-scale injection on reservoir pressure field evolution and CO₂ migration distribution in reservoirs,taking into account the distance between each water source and the injection well,and the stratigraphic separation between the CO₂ reservoir and the groundwater exploitation horizon of the water source.According to the analysis,in the case of the injection of 7.98 million tons of CO₂ in the current 10-year period,large-scale CO₂ injection will not affect the water safety of groundwater sources around the study area.?4?The three-dimensional numerical model of the leaking well and the injection well at different distances is established.The influence of the distance between the injection well and the leaking well on the evolution of the pressure field of the reservoir,CO₂ spatial migration and CO₂ leakage characteristics is analyzed.The closer the leaking well is to the injection well,the larger the CO₂ leakage.The highest CO₂ leakage in this study can reach 12%,but the leakage ratio between the two is only 0.1%.The reduction of the distance between the leaking well and the injection well can significantly increase the CO₂ injection rate and injection volume,and the injection volume can be increased by up to 6%.The research results can provide a basis for the investigation of abandoned wells and engineering safety evaluation within the project site.