Multi-Scale Environmental Risk Assessment Methodology for CO2 Geological Storage in Deep Saline Aquifers: A Case Study of the Ordos Basin

Carbon dioxide capture and storage (CCS) is an essential technological strategy for climate change mitigation, though its large-scale deployment remains constrained by prevailing environmental risk uncertainties. This study developed a feasible environmental risk assessment framework for saline aquifer CCS projects, based on the Yulin CO2 storage demonstration project in the Ordos Basin. PETREL-based reservoir simulations determined the assessment scope, obtaining CO2 plume migration radii of 300 m, 500 m, and 600 m under 0.1 Mt injection, 1.0 Mt injection, and 50 years shut-in scenarios. A 1000 m circular area around the injection well was conservatively set as the assessment scope. We further screened 15 technical indicators across four categories with two to five alternative parameters for each, and applied questionnaires from 15 experienced experts alongside a two-tiered risk matrix to assess risk probability, and the overall leakage risk was rated as unlikely. Combined numerical simulation and literature review verified that CO2 migration and pressure fluctuations remained within safe ranges during operation and shut-in, with CO2 leakage posing negligible impacts on the atmosphere, soil, microorganisms, crops, animals, and human populations. In accordance with China’s official Guidelines, the environmental risk level of CO2 leakage in this project is classified as low. The proposed multi-scale method provides a reliable reference for environmental risk evaluation of saline aquifer CO2 storage projects.