CO₂-water displacement characteristics of saturated sandstones with different pore structures

Authors

LIU Ting, Hydrogeological and Environmental Geological Survey, China Geological Survey, Tianjin 300304, ChinaFollow
LI Jinglin, Key Laboratory of Coast Civil Structure Safety of Ministry of Education, School of Civil Engineering, Tianjin University, Tianjin 300350, China
LI Yi, Key Laboratory of Coast Civil Structure Safety of Ministry of Education, School of Civil Engineering, Tianjin University, Tianjin 300350, ChinaFollow
DAN Wendong, Key Laboratory of Coast Civil Structure Safety of Ministry of Education, School of Civil Engineering, Tianjin University, Tianjin 300350, China
DIAO Yujie, Hydrogeological and Environmental Geological Survey, China Geological Survey, Tianjin 300304, China
MA Xin, Hydrogeological and Environmental Geological Survey, China Geological Survey, Tianjin 300304, China

Abstract

Objective The pore structures of clastics play a crucial role in assessing the potential of saline aquifers for geologic CO₂ sequestration. Current studies on pore structures during CO₂ sequestration focus primarily on artificial cores. However, compared to artificial cores, natural cores feature more complex pore size distributions and stronger heterogeneity. Methods This study examined a natural core from deep reservoirs in the Ordos Basin and two artificial cores with different porosities through CO₂-water displacement experiments under water-saturated conditions. Using a nuclear magnetic resonance (NMR) analysis and imaging system for multiphase fluid displacement, this study analyzed the impacts of pore structures (pore heterogeneity) on CO₂-water displacement in these cores. Results and Conclusions The artificial cores with porosities of 5% and 15% exhibited CO₂-water displacement efficiencies of 67.09% and 46.71%, respectively, whereas the natural core with a porosity of 15% displayed a displacement efficiency of 37.67%. The NMR-derived transverse relaxation time (T₂) spectra of the natural core showed a unimodal pattern, suggesting strong heterogeneity. In contrast, the T₂ spectra of artificial cores manifested bimodal patterns, with uniform pore size distributions and low residual water saturation. Notably, a lower porosity corresponded to high pore connectivity, which allowed for sufficient contact between CO₂ and the core. This characteristic effectively reduced interfacial tension and significantly enhanced CO₂-water displacement efficiency. Compared to the artificial core with the same porosity, the natural counterpart showed significantly reduced CO₂-water displacement efficiency due to its strong heterogeneity, with residual water occurring predominantly in small pores. Therefore, in the assessment of the potential of clastic reservoirs for CO₂ sequestration, it is necessary to thoroughly consider the impact of core heterogeneity and preferentially utilize natural cores or heterogeneous artificial cores in CO₂-water displacement experiments. This will help predict CO₂ sequestration behavior more accurately and avoid overestimated CO₂ sequestration efficiency parameters arising from the application of artificial cores made of homogeneous materials. The results of this study will provide a theoretical basis and experimental support for siting, potential assessment, and injection scheme design for geologic CO₂ sequestration in saline aquifers.

Keywords

geologic CO2 sequestration, nuclear magnetic resonance (NMR), pore structure, CO2-water displacement efficiency

DOI

10.12363/issn.1001-1986.25.05.0327

Recommended Citation

LIU Ting, LI Jinglin, LI Yi, et al. (2025) "CO₂-water displacement characteristics of saturated sandstones with different pore structures," Coal Geology & Exploration: Vol. 53: Iss. 12, Article 3.
DOI: 10.12363/issn.1001-1986.25.05.0327
Available at: https://cge.researchcommons.org/journal/vol53/iss12/3

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