Enhancing the CO2 trapping capacity of Saudi Arabian basalt via nanofluid treatment: Implications for CO2 geo-storage.

Mineralization reactions in basaltic formations have gained recent interest as an effective method for CO2 geo-storage in order to mitigate anthropogenic greenhouse gas emissions. The CO2/rock interactions, including interfacial tension and wettability, are crucial factors in determining the CO2 trapping capacity and the feasibility of CO2 geological storage in these formations. The Red Sea geological coast in Saudi Arabia has many basaltic formations, and their wetting characteristics are rarely reported in the literature. Moreover, organic acid contamination is inherent in geo-storage formations and significantly impacts their CO2 geo-storage capacities. Hence, to reverse the organic effect, the influence of various SiO2 nanofluid concentrations (0.05-0.75 wt%) on the CO2-wettability of organic-acid aged Saudi Arabian (SA) basalt is evaluated herein at 323 K and various pressures (0.1-20 MPa) via contact angle measurements. The SA basalt substrates are characterized via various techniques, including atomic force microscopy, energy dispersive spectroscopy, scanning electron microscopy, and others. In addition, the CO2 column heights that correspond to the capillary entry pressure before and after nanofluid treatment are calculated. The results show that the organic acid-aged SA basalt substrates become intermediate-wet to CO2-wet under reservoir pressure and temperature conditions. When treated with SiO2 nanofluids, however, the SA basalt substrates become weakly water-wet, and the optimum performance is observed at an SiO2 nanofluid concentration of 0.1 wt%. At 323 K and 20 MPa, the CO2 column height corresponding to the capillary entry pressure increases from -957 m for the organic-aged SA basalt to 6253 m for the 0.1 wt% nano-treated SA basalt. The results suggest that the CO2 containment security of organic-acid-contaminated SA basalt can be enhanced by SiO2 nanofluid treatment. Thus, the results of this study may play a significant role in assessing the trapping of CO2 in SA basaltic formations.

Hydrogen wettability of carbonate formations: Implications for hydrogen geo-storage.

HYPOTHESIS: The mitigation of anthropogenic greenhouse gas emissions and increasing global energy demand are two driving forces toward the hydrogen economy. The large-scale hydrogen storage at the surface is not feasible as hydrogen is very volatile and highly compressible. An effective way for solving this problem is to store it in underground geological formations (i.e. carbonate reservoirs). The wettability of the rock/H2/brine system is a critical parameter in the assessment of residual and structural storage capacities and containment safety. However, the presence of organic matters in geo-storage formations poses a direct threat to the successful hydrogen geo-storage operation and containment safety. EXPERIMENTS: As there is an intensive lack of literature on hydrogen wettability of calcite-rich formations, advancing (θa) and receding (θr) contact angles of water/H2/calcite systems were measured as a function of different parameters, including pressure (0.1-20 MPa), temperature (298-353 K), salinity (0-4.95 mol.kg-1), stearic acid (as a representative of organic acid) concentration (10-9 - 10-2 mol/L), tilting plate angle (0° - 45°) and surface roughness (RMS = 341 nm, 466 nm, and 588 nm). FINDINGS: The results of the study show that at ambient conditions, the system was strongly water-wet, but became intermediate wet at high pressure. The water contact angle strongly increased with stearic acid concentration making the calcite surface H2-wet. Moreover, the contact angle increased with salinity and tilting plate angle but decreased with temperature and surface roughness. We conclude that the optimum conditions for de-risking H2 storage projects in carbonates are low pressures, high temperatures, low salinity, and low organic surface concentration. Therefore, it is essential to measure these effects to avoid overestimation of hydrogen geo-storage capacities and containment security.