CO2 flooding properties of Liujiagou sandstone: influence of sub-core scale structure heterogeneity

The Liujiagou formation is an important CO2 aquifer storage unit in the Ordos Basin in central China. Thus far, it has stored over 90% of the total injected CO2 from the Shenhua carbon capture and storage (CCS) project, which is the first full‐chain CCS project in China. Understanding the basic properties of CO2 flooding is critical for site characterization and evaluation. A core‐scale characterization and CO2 flooding study of Liujiagou sandstone is the first step to understanding the flooding properties in a CO2 aquifer storage project. The pore geometry of a sample was characterized using medical, industrial, and micro X‐ray computed tomography (X‐CT) scanners, as well as mercury intrusion porosity and thin section petrography. To study the flooding process, a CO2 core flooding experiment using medical X‐CT scanning was conducted with a Liujiagou sandstone sample. Based on the CT data, experimental data, simplified models and COMSOL software, a three‐dimensional sub‐core scale numerical model that considered porosity, permeability, and capillary pressure heterogeneity was constructed for numerical simulation of CO2 flooding under different scenarios. Laboratory experiments and numerical simulations on a Liujiagou sample revealed the following. The Liujiagou sandstone is a low‐porosity and low‐permeability sandstone with very high heterogeneity. The sub‐core porosity heterogeneity significantly affects CO2 migration. The relative permeability and saturation distribution are significantly affected by the injection velocity of CO2 and are different from those of other sandstones, such as Berea. The analyzed Liujiagou sandstone sample has a very low storage efficiency factor at the core scale.