Carbon capture, utilization, and storage (CCUS/CCS) is a strategic choice for ensuring energy security and reducing carbon dioxide emissions across the globe. The injection of CO₂ into the basaltic reservoir is one strategy for the permanent disposal of carbon emissions. Basaltic rocks, which are widely distributed in Hainan Island, are capable of CO₂ geological sequestration. In this study, the reaction of CO₂-NaOH/Ca(OH)₂-basaltic rocks under conditions of 6.0 M Pa and 30 °C was performed using basaltic samples collected from the Fushan area of the Hainan Province to evaluate the sequestration of CO₂ in basalt by mineralization. Then, the effect of CO₂ mineralization on the permeability and mechanical properties of basaltic rocks was evaluated using X-ray computer tomography and triaxial compression testing at 21.0 MPa. In addition, microwave technology was used to irradiate the basaltic rocks before mineralization. Changes in the permeability of basalt before and after mineralization and microwave irradiation were simulated numerically, and their effects on the mechanical strength deterioration of basalt were analyzed according to the rock mechanics using triaxial testing. Based on these results, a new method for the induction of basalt deterioration, mineralization, CO₂ injectivity, and storage capacity using microwave irradiation is proposed for use in CCUS/CCS engineering.

Nonlinear catastrophes caused by geological fluids are a fundamental issue in rock mechanics and the geoengineering hazard field. For the consideration of hydrodynamic force on red-bed mudstone softening damage, X-ray visualization tests on the fissure flow in mudstone block failure under hydrodynamic force was performed in this study based on block scale, and the physical phenomena of fissure seepage and nonlinear diffusion were further explored. A new method for evaluating the hydro-damage degrees of rocks using an X-ray image analysis was proposed, and the quantitative relation of diffusion coefficients of hydro-damage and seepage was established. The research results revealed that the hydrodynamic force promoted the fluid-filled fissure behavior in mudstone specimen failure. Furthermore, the seepage and diffusion phenomena of fluid in rocks during failures were indicated using X-ray imaging. A dual mechanical behavior was presented in the nonlinear seepage and abnormal diffusion of a red mudstone geological body under hydrodynamic conditions. The damaged degree of mudstone was aggravated by the effect of hydrodynamic force, and the initial seepage–diffusion coefficient with respect to lower hydro-damage was larger than the final seepage–diffusion coefficient with respect to higher hydro-damage of rocks with a decreasing nonlinear trend.

Geo-sequestration storage of CO2 in saline aquifers is an important technological option to reduce carbon emissions in China in the future. The theory of geo-sequestration storage of CO2 in saline aquifers involves complex physical operations and chemical phenomena among reservoir stress, seepage, and temperature fields, and the numerical simulation models coupling thermal-hydro-mechanical (THM) fields are widely applied to analyze the evolution of multiphysical processes in CO2 reservoirs. Based on the geo-sequestration storage project of saline aquifer CO2 in Fushan Sag, Hainan Province, under the premise of considering the change of permeability and porosity after the mineralization of CO2 in the rock reservoirs, this study simulates the evolution of temperature, stress, and seepage fields during the sequestration process of saline aquifer Continuous CO2 injection wells clarifies the range of influence of the temperature field, seepage field, and the boundary of its stress field of saline aquifer Continuous CO2 injection wells in different sequestration periods. It reveals the influence mechanism of the fault structure on the reservoir CO2 sequestration pressure and capacity, and evaluates and estimates the CO2 injection storage capacity of Fu 1# well in Fushan Sag and on this basis. The THM numerical simulation model proposed in this study plays a crucial role in guiding theoretical evaluations of the CO2 geo-sequestration potential in saline aquifers and determining its technical parameters, thereby offering significant value for engineering applications.

Micrometer-scale pore and fracture structures of coal seams are the crucial parameters in the case of enhanced coalbed methane (CBM) recovery as they determine permeability and productivity. A significant study has been made in fracture characteristics; however, the detailed structural and fractal characteristics of micro-fractures and micro-pores of tectonically deformed coals are poorly understood. To get deep insight into the variability and heterogeneity of micro-pores and micro-fractures in different tectonically deformed coals collected from the Guojiahe coal mine, the multifractal analysis using the Menger sponge and box-counting model was employed to study deformed coals based on mercury injection porosimetry and scanning electron microscopy. The results show that tectonic deformation changed the structure of the micro-pores by increasing their diameter and that of the micro-fractures by expanding, intersecting, and creating additional microfracture networks at any scale. For the coals investigated in this study, permeability was nonlinearly correlated with their structural fractal. For undeformed coals, with the increase in the fractal dimension of micro-pores, the distribution of coal permeability exhibits a U-shape. However, it exhibited an inverted U-shape as the fractal dimension of micro-fractures increased. The distribution of the permeability of deformed coal samples is characterized by a U-shape as the fractal dimension of micro-fractures increased, while the fractal dimension of micro-pores decreased. Thus, the structural proportional odds of micro-pores and micro-fractures are vital in defining the maximum value of permeability. As a whole, deformed coals have a relatively high permeability as local micro-pores and micro-fractures are well connected. We suggest that coal seams with brittle deformation at syncline, anticline, and folded areas are favorable for CBM exploitation.

Fluid flow and evolution mechanisms in fractured rocks are fundamental tasks in engineering fields such as geohazards prediction, geothermal resource exploitation, oil and gas exploitation, and geological sequestration of carbon dioxide. This study employed an enhanced X-ray imaging digital radiography to investigate nonlinear flow model of fluid through different roughness fractures. The X-ray images of fluid flow during rock failure were analyzed using a multi-threshold segmentation method applied to the X-ray absorption dose. The result show that a proposed nonlinear flow equation considers the joint roughness coefficient and the uniaxial compressive strength of the jointed rock, enabling a better understanding of the nonlinear flow behavior in fractured rock masses. This modeling approach has important theoretical and practical implications. By accounting for key factors influencing fluid flow behavior, it can help guide monitoring efforts to support early warning of fractured rock mass instability. Additionally, a more mechanistic understanding of flow processes may inform strategies to prevent engineering geological hazards.