For investigating the wellbore flow process in CO₂ injection scenarios, coupled wellbore-reservoir (WR) and conventional equivalent porous media (EPM) models were compared with each other. In WR model, during the injection, conditions for the wellbore including pressure and temperature were dynamically changed from the initial pressure (7.45–8.33 MPa) and temperature (52.0–55.9°C) of the storage formation. After 3.35 days, the wellbore flow reached the steady state with adiabatic condition; temperature linearly increased from the well-head (35°C) to the well-bottom (52°C). In contrast, the EPM model neglecting the wellbore process revealed that CO₂ temperature was consistently 35°C at the screen interval. Differences in temperature from WR and EPM models resulted in density contrast of CO₂ that entered the storage formation (~200 and ~600 kg/m³, resp.). Subsequently, the WR model causing greater density difference between CO₂ and brine revealed more vertical CO₂ migration and counterflow of brine and also developed the localized salt-precipitation. Finally, a series of sensitivity analyses for the WR model was conducted to assess how the injection conditions influenced interplay between flow system and the localized salt-precipitation in the storage formation.

Multiscale forecasting of groundwater levels (GWLs) is essential for ensuring the sustainable management of groundwater resources, particularly considering the potential impacts of climate change. Such forecasting requires a model that is not only accurate in predicting GWLs but also computationally efficient, ensuring its suitability for practical applications. In this study, a temporal convolutional network (TCN) is implemented to forecast GWLs for 17 monitoring wells possessing diverse hydrogeological characteristics, located across South Korea. Using deep learning, the influence of meteorological variables (i.e., temperature, precipitation) on the forecasted GWLs was investigated by dividing the input features into three categories. Additionally, the models were developed for three forecast intervals (at 1-, 3-, and 6-month lead times) using each category input. When compared with state-of-the-art models, that is, long short-term memory (LSTM) and artificial neural network (ANN), the TCN model showed superior performance and required much less computational complexity. On average, the TCN model outperformed the LSTM model by 24%, 21%, and 25%, and the ANN model by 24%, 37%, and 47%, respectively, for 1-, 3-, and 6-month lead times. Based on these results, the proposed TCN model can be used for real-time GWL forecasting in hydrological applications.

In geologic media, fluids exist in gas, liquid, and supercritical phases, generating multiphase and multicomponent systems. As fluids migrating through geologic fractures reach the speed of sound, choked flow can be developed in microfractures. To elucidate such choked flow, thermodynamic analysis and numerical simulations were conducted with CO₂, H₂O, and CO₂‐H₂O mixtures at various phases ranging from supercritical to gaseous CO₂ and liquid H₂O. Compressible CO₂, with a relatively low speed of sound (~225 m/s at 31.1 °C and 7.38 MPa), demonstrated significant changes in thermodynamic properties with small pressure and temperature variations. In contrast, H₂O, having a relatively high speed of sound (1,524 m/s), showed little thermodynamic variation. For CO₂‐H₂O mixtures, a small addition of CO₂ (or H₂O) dramatically reduced the speed of sound relative to those for pure H₂O or CO₂. For an idealized converging‐diverging microfracture with CO₂ flow, choked flow and a shock wave were generated as outlet pressure was decreased to less than 6.8 MPa. The H₂O flow did not generate choked flow at any outlet pressures. For CO₂‐H₂O mixtures, choked flow was generated when the CO₂ void fraction was greater than 0.7 with an outlet pressure of 6.5 MPa, indicating that presence of H₂O inhibited occurrence of choked flow. Choked flow and shock waves can occur in various geologic environments including geologic CO₂ sequestration, geothermal energy development, geysers, and volcano eruptions.