Risk Assessment and Monitoring Methods for Geologic Sequestration of CO2 in the Saline Aquifer

Geological sequestration of CO2 is considered to be the most effective measure to realize long-term CO2 emission reduction, which is the key to influence the progress of carbon neutralization. In recent years, CO2 storage in the saline aquifer has been widely utilized in many countries as it is one of the most effective ways of carbon sequestration. This paper first summarizes the geological storage mechanism of CO2 in the saline aquifer as tectonic storage, capillary storage, adsorption storage, dissolution storage and mineral storage, and then considers the criteria for selecting the site of CO2 in the saline aquifer in terms of technology, safety and economy. During the sequestration process, CO2 may leak from wellbores, caprock, and fractures, and to cope with these scenarios, risk assessments are often conducted using the Delphi method, brainstorming method, risk checklist method, SWOT technique, and FEP method, among others. When targeting complex projects, the combined use of these methods can effectively improve the comprehensiveness and accuracy of risk identification, laying the foundation for subsequent risk assessment and the development of countermeasures. In order to ensure that CO2 can be safely stored in the ground for a long time, it is necessary to implement different monitoring methods according to different purposes, which can be generally divided into three categories: CO2 environmental monitoring, CO2 safety monitoring and CO2 transportation monitoring. CO2 environmental monitoring can be divided into the atmosphere, the near-surface and the shallow stratum in terms of vertical spatial stratum distribution. The shallow stratum environmental detection technology is more mature, but due to the meteorological and topographical impact on the accuracy of atmospheric and near-surface environmental monitoring technology, generally using a combination of multi-technology for monitoring. CO2 leakage caused by easy to cause harm, this time the use of CO2 safety monitoring, is divided into surface deformation, stratigraphic deformation, ground stress, wellbore integrity and wellbore corrosion. We also use seismic, logging and geochemical methods to monitor CO2 transportation.