CO 2 flooding properties of Liujiagou sandstone: influence of sub‐core scale structure heterogeneity

The Liujiagou formation is an important CO 2 aquifer storage unit in the Ordos Basin in central China. Thus far, it has stored over 90% of the total injected CO 2 from the Shenhua carbon capture and storage (CCS) project, which is the first full‐chain CCS project in China. Understanding the basic properties of CO 2 flooding is critical for site characterization and evaluation. A core‐scale characterization and CO 2 flooding study of Liujiagou sandstone is the first step to understanding the flooding properties in a CO 2 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 CO 2 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 CO 2 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 CO 2 migration. The relative permeability and saturation distribution are significantly affected by the injection velocity of CO 2 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.