Abundant buried mafic rocks located at coastal region may offer a promising near-source storage option for CO2 mineralization in eastern China, while their storage potential remains poorly constrained. Here, we examined the storage potential of the buried mafic reservoir at Bailonggang, Shanghai, a representative site near the high-emission Yangtze River Delta. Adopting regional hydrogeological data and experimental measurements on borehole cores, we characterized the reservoir architecture, mineral composition, and petrophysical properties, and established a storage assessment framework for CO2-rich water injection that incorporated effective storage space, mineral reaction capacity, and injectivity constraints. The Bailonggang mafic rocks extend over an area of 86 km2 and can be subdivided into shallow (350-490 m), middle (490-650 m) and deep (650-960 m) intervals, which exhibit distinct lithofacies assemblages and strong vertical heterogeneity. Porosity and permeability range from 1.894% to 25.464% and from 0.671 to 33.437 mD, respectively. Under a borehole-constrained screening scenario using the mapped mafic-rock distribution as the areal constraint, the CO2 storage capacities of the shallow, middle and deep intervals are estimated at 11.70, 9.73 and 15.57 Mt, yielding an idealized baseline storage estimate of 37.01 Mt. We show that the effective storage potential of the Bailonggang reservoir is governed primarily by effective pore volume, aqueous-phase transport capacity and injectivity accessibility, rather than by mineral reaction availability alone. Considering storage efficiency, injectivity accessibility, lithofacies continuity and storage-risk constraints, the middle interval is identified as the most balanced target horizon, while the shallow interval remains a promising but safety-sensitive supplementary target. Our results highlight the potential of buried mafic rocks for near-source CO2 mineralization storage in Shanghai, thereby providing a screening-scale framework for evaluating analogous coastal reservoirs in eastern China.
From a spectroscopic perspective, this paper systematically elucidates the mechanism of rock strength softening. By integrating uniaxial compressive strength tests, near-infrared spectroscopy, as well as one-dimensional and two-dimensional correlation spectroscopy analyses, it thoroughly reveals the intrinsic mechanism and spectral response characteristics of sandstone strength softening during water absorption. The results indicate that: (1) during the water-induced softening process of sandstone, four characteristic absorption peaks are observed in its one-dimensional near-infrared spectrum. Specifically, the peak intensities at approximately 1400 nm and 1900 nm increase significantly, while those at around 2200 nm and 2320 nm show only minor changes; (2) during the rapid softening phase (AB stage), the sensitivity of characteristic spectral bands to moisture content follows the order 1935 nm > 1440 nm; in the slow softening phase (BC stage), the sensitivity order remains 1935 nm > 1440 nm.(3) During the water absorption and strength softening process of sandstone, changes in the population of water molecules near 1440 nm and 1935 nm are the primary factors influencing water-induced strength softening. Notably, the variation in adsorbed water around 1935 nm exhibits the highest sensitivity and is the dominant mechanism responsible for the strength softening of sandstone. (4) The strength-saturation relationship follows an exponential decay, while the spectral absorbance increases monotonically with saturation. When both are examined as functions of saturation, the spectral characteristics and strength softening exhibit consistent parallel trends. The spectral characteristics provide an effective means to qualitatively interpreting and monitoring rock strength softening in water.
