This study investigated the photocatalytic activity of an Fe containing TiO 2 film produced in the FePO 4 electrolyte via the plasma electrolytic oxidation (PEO) method. For this purpose, the PEO process was carried out on titanium substrate under ac condition in two different alkaline electrolytes containing K 3 PO 4 and FePO 4 respectively. The structure, chemical composition and constituent phases of the PEO treated samples were analysed via SEM, X-ray photoelectron spectroscopy and X-ray diffraction. The optical properties of the samples were also examined by an ultraviolet-visible spectrophotometer. In terms of the photocatalytic activity judging from the decomposition of methylene blue under visible light illumination, the sample formed in the FePO 4 electrolyte was better than that in the K 3 PO 4 electrolyte due to the incorporation of an Fe compound that has a narrow band gap.
Mechanical failure of cap rock is one of the main reasons of CO2 leakage from the storage formations. Through comprehensive assessment on the petrophysical and geomechanical heterogeneities of cap rock, it is possible to estimate the pressure distribution more accurately and to predict the risk of unexpected caprock failure. To describe the fracture reactivation and fracture permeability, modified Barton-Bandis model and dual permeability system are applied. Porosity-permeability relationship is calculated with power law. In order to generate hydro-geomechanically heterogeneous fields, the negative correlation between porosity and Young's modulus/Poisson's ratio is applied. In comparison to homogeneous model, effects of heterogeneity are examined in terms of vertical deformation and the amount of leaked CO2. To compare the effects of heterogeneity, heterogeneous models for both geomechanical and petrophysical properties in coupled simulation are designed. Simulation results show that CO2 leakage occurs after 4-6 years from injection. After 10 year injection with petrophysically heterogeneous and geomechanically homogeneous caprock, CO2 leakage is larger than that of homogeneous model. In contrast, heterogeneity of geomechanical properties is shown to mitigate additional escape of CO2. Vertical displacement of every heterogeneous model is larger than homogeneous model. According to results from model with petrophysically heterogeneous and geomechanically homogeneous caprock, the higher Dykstra-Parsons coefficients (VDP) the larger vertical displacement is obtained. The vertical displacement with petrophysically homogeneous and geomechanically heterogeneous model is also larger regardless of VDP.
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