Lu Shi

Evaluating Reservoir Risks and Their Influencing Factors during CO2 Injection into Multilayered Reservoirs

Wellbore and site safety must be ensured during CO2 injection into multiple reservoirs during carbon capture and storage projects. This study focuses on multireservoir injection and investigates the characteristics of the flow-rate distribution and reservoir-risk evaluation as well as their unique influences on multireservoir injection. The results show that more CO2 enters the upper layers than the lower layers. With the increase in injection pressure, the risks of the upper reservoirs increase more dramatically than those of the low reservoirs, which can cause the critical reservoir (CR) to shift. The CO2 injection temperature has a similar effect on the injection flow rate but no effect on the CR’s location. Despite having no effect on the flow-rate distribution, the formation-fracturing pressures in the reservoirs determine which layer becomes the CR. As the thickness or permeability of a layer increases, the inflows exhibit upward and downward trends in this layer and the lower layers, respectively, whereas the inflows of the upper layers remain unchanged; meanwhile, the risks of the lower layer and those of the others decrease and remain constant, respectively. Compared to other parameters, the reservoir porosities have a negligible effect on the reservoir risks and flow-rate distributions.

Improvement of the finite-element-based limit equilibrium method to include changes in groundwater: a case study of a deforming bank slope from the Three Gorges Reservoir

Changes in groundwater are an important factor affecting slope stability. In this study, the finite-element-based limit equilibrium method (FELE), which does not require any predetermined assumptions, is improved to include groundwater. The seepage force in the improved FELE is directly regarded as a body force and can be transformed into the equivalent nodal force. Moreover, a practical technique of employing the signed distance function is used to represent the groundwater level, making the improved FELE insensitive to the mesh. An analysis of a benchmark slope is performed to validate the effectiveness of the improve FELE, and the results show that the seepage force has a significant influence on the stability of the slope. Moreover, a case study of a deforming bank slope from the Three Gorges Reservoir is analyzed by the improved FELE to study the relationships between the deformation and changes in the phreatic lines within the sliding body.