CCS Development Optimisation via a Cost-Effective Reservoir Simulation Technology: Full-Field Simulation of CO2 Sequestration with Conductive Faults by Embedded Discrete Fracture Model

Abstract For the robust planning and implementation of Carbon Dioxide Capture and Storage (CCS) projects, capacity and injectivity of target reservoirs and containment capability of cap rock formation need to be evaluated thoroughly through high-fidelity flow simulations with various hypothetical subsurface scenarios. Impact of conductive faults, which may act as high permeability conduits for the injected CO2, should be carefully assessed as the fault conductivity is typically highly uncertain. However, it is challenging to incorporate numerous faults with high conductivity and complex multi-phase displacement process in a practical framework of flow simulations. In this study, we present an efficient workflow using an Embedded Discrete Fracture Model (EDFM) to simulate CO2 flow via conductive faults and its application to the full-field scale assessment. The EDFM approach has been proposed to efficiently incorporate discrete fractures in flow simulations. Based on the pre-defined permeability, geometry and location of discrete fractures, transmissibility is computed (1) between each fracture and reservoir matrix and (2) at intersections of two fractures. In our application, conductive faults were assumed as discrete fractures. Extra grid blocks are added to the original reservoir grid system to represent discrete fractures by assigning the computed transmissibility via non-neighbor connections (NNCs). This approach involves no upscaling, no unstructured gridding and no local grid refinement and can be coupled with any commercial reservoir simulators. Multi-phase displacement process through individual faults can also be modeled. We demonstrate the efficiency and robustness of our proposed approach for synthetic and field scale examples. We first validated the CCS simulation with the EDFM approach for a producing gas reservoir using an illustrative 3-D example. Next, we present the application to a full-field simulation model where more than one hundred faults were interpreted based on the seismic data, to evaluate the CO2 breakthrough risk to up-dip gas producers. The simulation results show that the injected CO2 preferably migrates along conductive faults. leading to the earlier breakthrough as compared to the case without conductive faults. However, it was also confirmed that the CO2 production rate was not significantly increased even after the breakthrough. This study showed the effectiveness of the EDFM approach to simulate CO2 flow via numerous conductive faults in both edge aquifer and gas zones. This approach is also simple and easy to implement, which allows efficient application to full-field simulation models.