Water-rock interaction of weakly cemented mudstone is intense due to its complex pore structure and mineral compositions. As primary channels for water imbibition, pore structures determine water migration. In this paper, pore properties of weakly cemented mudstone are measured by scanning electron microscopy (SEM), nitrogen adsorption/desorption (NAD), and mercury intrusion porosimetry (MIP), respectively. Water imbibition tests under free and lateral restraints are performed on self-developed water absorption instruments. The results show that skeleton aggregates, pore zone, and fissure zone constitute the basic structure of the rock, together with pore scales in nanoscale, submicron-scale, and micron-scale, respectively. The porosities of each zone are inferred with the values of 13.5%, 7.3%, and 2.3% by comparison of different methods. The main pore type is mesopore. Based on water imbibition tests, water rises along the large fissure and pore zones initially. Pores in the skeleton aggregates absorb water from pore and fissure zones subsequently. However, water imbibition is limited under lateral restraints. Owing to lateral restraints, the ascending height and rate of the sample with lateral restraints are lower than those of the sample with free confinements. The results suggest that lateral restraints can restrain water migration and water-rock interaction for weakly cemented mudstones, and measures can be taken to control swelling deformation by strengthening lateral restraints.

The injection of CO 2 into deep unrecoverable coal seams can serve the dual purpose of facilitating the efficient extraction of coal-bed methane (CBM) and geological storage of CO 2 . However, due to the nonhomogeneous and anisotropic nature of coal seams, which are influenced by depositional environment, geological structure, and hydrogeology, the anisotropy of the deep unrecoverable coal seams can affect the CO 2 − water−coal reaction. The mechanical properties and damage of coal after the physical and chemical reactions of supercritical CO 2 (SCO 2 )−water−coal at different seam inclinations have not been extensively studied. In this study, we analyze the mechanical properties and damage of coal before and after the reaction by utilizing noncontact full-field strain, acoustic emission, ultrasonic nondestructive testing, and nuclear magnetic techniques. The results demonstrate that the mechanical properties of the coal underwent significant changes after SCO 2 treatment, with the largest decreases in compressive strength and elastic modulus observed in the 90°coal samples at 62.7 and 67.4%, respectively. Furthermore, the strain distribution of the treated coal samples exhibited distinct characteristics of laminar dip angle. Acoustic emission analysis revealed that the damage variable D 1 of the 45°coal sample had the largest value, while the acoustic emission damage variable D 1 of the 90°coal sample had the largest increase of 99.5%. The longitudinal wave velocity of a coal sample is highest at 0°, followed by 45°, and lowest at 90°. At 90°, the maximum value of the wave velocity damage factor is 0.577. Additionally, as the total porosity of the coal increases, the maximum increase observed after testing a coal sample at 90°is 1%. Moreover, the pore structure undergoes changes during this process. The number of micropores decreases, while the number of mesopores and macropores increases. The findings of this study provide theoretical guidance for CO 2 injection into deep unrecoverable coal-bed methane.

No abstract