Optimal CO2 storage interval in heterogeneous tight formation: Implications for long-term carbon sequestration

The efficiency of CO 2 geo-sequestration relies heavily on the storage capacity and sealing integrity of the heterogeneous strata. Tight formations offer substantial advantages for long-term CO 2 geological storage, however, the stratigraphic variability and lithological heterogeneity introduce substantial uncertainty in real-world engineering applications. Particularly, for tight formations with pronounced heterogeneous lithologies, traditional methods oversimplify their impact on CO 2 geo-sequestration. To address this challenge and identify the most effective intervals for CO 2 geo-sequestration, we investigated the middle Permian Lucaogou Formation (P 2 l) in the Jimusar Sag, Junggar Basin, Northwest China, a region known for its strong lithological heterogeneity. By integrating multi-scale analytical techniques, including X-ray diffraction, permeability and porosimetry, mercury injection capillary pressure, petrography analysis, and nanoindentation, more than 100 consecutive core samples from Borehole J174, covering the stratigraphic interval of 250 m, were analyzed. Our results reveal significant heterogeneity and identify the most favorable intervals for CO 2 geo-sequestration located in the upper P 2 l 1 2 and lower P 2 l 1 1 units (3238–3334 m depth), spanning 96 m. It primarily consists of tuffaceous siltstone, siltstone, interbedded multi-layered dolomitic siltstone and silty dolostone, which exhibit excellent petrophysical properties with high storage capacity and mechanical stability. Above the storage interval, an effective caprock is found in the lower P 2 l 2 2 and P 2 l 1 1 group (3149–3238 m depth, spanning 89 m), characterized by thick mudstone with extremely low porosity, permeability, and appropriate mechanical properties, ensuring long-term sealing integrity. This study provides precise identification for CO 2 geo-sequestration in engineering practice and also demonstrates a scalable methodology to tackle upscaling challenges in heterogeneous formations, providing valuable implications for future CO 2 geo-sequestration projects in similar engineering settings.