Supercritical CO₂-water-rock interactions significantly impact the mechanical integrity of heterogeneous conglomerate reservoirs, challenging their suitability for CO₂ sequestration and enhanced oil recovery. To evaluate these microscale mechanical and structural changes, this study uses a combination of micro-scratch testing, scanning electron microscopy, and nuclear magnetic resonance. The results reveal that the micro-scratch method enables the acquisition of a continuous mechanical property profile, addressing the limitation of traditional rock mechanics that only allows discrete point measurements. Importantly, the scratch failure modes significantly depend on the lithology of conglomerate reservoirs: Felsic and quartz conglomerates exhibit sharp grooves with interfacial shear failure, whereas debris-rich variants develop wavy, fragmented paths. CO₂-water exposure reduces the deformation resistance and causes fracture toughness to initially increase and then decline, with the most severe reduction observed in quartz conglomerates. The degradation of mechanical properties is mainly through mineral dissolution and increased porosity. The findings of this study offer key insights for optimizing storage and recovery strategies in complex reservoirs.

The deep eastern edge of the Ordos Basin is rich in coalbed methane, presenting great potential for development. Meanwhile, CO₂ imbibition is an important method to increase production. To study the CO₂-water-rock interactions and microstructural damage characteristics before and after supercritical carbon dioxide immersion in deep coal rocks, CO₂ imbibition experiments were conducted on these rocks by using nuclear magnetic resonance and scanning electron microscopy imaging techniques. The results showed that CO₂ imbibition leads to pore dilatation and reveals the key role of coal rock anisotropy on imbibition efficiency under different physicochemical conditions. Specifically, the immersion of CO₂ produces cracks due to the brittle action of the coal rock, as well as calcite dissolution that exacerbates crack production and expansion. Due to adsorption of CO₂, part of the coal rock becomes swollen, which leads to detachment and changed the physical properties and surface characteristics of the coal rock.