Geochemical reactions may alter the permeability of leakage pathways in caprocks, which serve a critical role in confining CO₂ in geologic carbon sequestration. A caprock specimen from a carbonate formation in the Michigan sedimentary Basin was fractured and studied in a high-pressure core flow experiment. Inflowing brine was saturated with CO₂ at 40°C and 10 MPa, resulting in an initial pH of 4.6, and had a calcite saturation index of −0.8. Fracture permeability decreased during the experiment, but subsequent analyses did not reveal calcite precipitation. Instead, experimental observations indicate that calcite dissolution along the fracture pathway led to mobilization of less soluble mineral particles that clogged the flow path. Analyses of core sections via electron microscopy, synchrotron-based X-ray diffraction imaging, and the first application of microbeam Ca K-edge X-ray absorption near edge structure, provided evidence that these occlusions were fragments from the host rock rather than secondary precipitates. X-ray computed tomography showed a significant loss of rock mass within preferential flow paths, suggesting that dissolution also removed critical asperities and caused mechanical closure of the fracture. The decrease in fracture permeability despite a net removal of material along the fracture pathway demonstrates a nonintuitive, inverse relationship between dissolution and permeability evolution in a fractured carbonate caprock.

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.

Laser-induced breakdown spectroscopy (LIBS) was used to detect rare earth elements (REEs) in natural geological samples. Low and high intensity emission lines of Ce, La, Nd, Y, Pr, Sm, Eu, Gd, and Dy were identified in the spectra recorded from the samples to claim the presence of these REEs. Multivariate analysis was executed by developing partial least squares regression (PLS-R) models for the quantification of Ce, La, and Nd. Analysis of unknown samples indicated that the prediction results of these samples were found comparable to those obtained by inductively coupled plasma mass spectrometry analysis. Data support that LIBS has potential to quantify REEs in geological minerals/ores.