During subsurface energy-transition operations, such as carbon dioxide sequestration, underground hydrogen storage, and geothermal energy extraction, fluid flow into the well and reservoir can induce strong hydraulic and thermal interactions between the well and the near-wellbore region. These interactions are particularly critical during high-pressure CO2 injection into depleted reservoirs, where significant temperature reductions may occur along and around the well, leading to complex phase behavior and potentially reducing injectivity. Conventional standalone well or reservoir models, however, fail to resolve these well–reservoir interactions. A fully coupled well–reservoir model is therefore essential to ensure accurate, safe, and efficient subsurface energy-transition operations. To address this need, we develop an open-source, computationally efficient numerical model for transient, thermal, multiphase flow in a fully coupled well–reservoir system. A multiphase, transient wellbore model is developed using the Drift-Flux Model and fully coupled with the high-performance, open-source Delft Advanced Research Terra Simulator (open-DARTS). Open-DARTS uses Operator-Based Linearization (OBL), where state-dependent properties are grouped as operators and interpolated from multidimensional tables generated on the fly, reducing the cost of evaluating residuals and derivatives in Newton–Raphson iterations. The wellbore model is verified against an analytical solution and benchmarked against industry-standard well simulators for single- and two-phase, isothermal and thermal flow in vertical and inclined wells, and the coupling approach is also benchmarked against a commercial coupled simulator. We then simulate liquid CO2 injection into a North Sea–representative depleted gas reservoir using grid and OBL resolutions selected by convergence analyses. ... Read more

Subsurface CO2 sequestration plays a crucial role in advancing carbon neutrality and supporting the transition to sustainable energy. However, the unique behavior of CO2, particularly during cold CO2 injection into depleted hydrocarbon reservoirs, poses challenges to wellbore injectivity. Addressing these challenges requires a numerical model that captures the complex interplay between wellbore dynamics and reservoir processes. In this work, we present DARTS-well, an open-source, fully coupled wellbore-reservoir model developed using the Operator-Based Linearization (OBL) technique. To this end, a transient, multi-segment, two-phase, non-isothermal wellbore model based on the Drift-Flux Model (DFM) is first developed and then coupled with the Delft Advanced Research Terra Simulator (DARTS) as the reservoir simulator. The model is demonstrated through test cases involving CO2 injection into a depleted reservoir, illustrating its potential to enhance the design and optimization of subsurface CO2 disposal systems. ... Read more

Subsurface CO₂ sequestration is a promising method to advance carbon neutrality and support the shift toward sustainable energy. However, the unique behavior of CO₂ in these operations, particularly for cold CO₂ injection in depleted hydrocarbon reservoirs, poses challenges to wellbore injectivity, reservoir containment, and reservoir capacity. These challenges necessitate the development of a numerical model to better understand and optimize the interplay between wellbore dynamics and reservoir processes. In this work, we present the development of an open-source coupled wellbore-reservoir numerical model, named DARTS-well, which is tailored to CO₂ disposal in subsurface reservoirs. To this end, a multi-segment, multi-phase, non-isothermal wellbore model is first developed using the Drift-Flux Model (DFM), and its results for selected CO2 injection scenarios are validated against the commercial transient wellbore simulator OLGA. The multi-segment wellbore model is then coupled with the Delft Advanced Research Terra Simulator (DARTS) which is used in this study as the reservoir simulator. DARTS is widely used and validated for energy transition applications. The coupled model utilizes the Operator-Based Linearization (OBL) technique, employing state-dependent operators for thermodynamic properties interpolated from predefined tables or generated on the fly. This OBL parametrization approach addresses challenges associated with complex physics and reduces computational time, making it well-suited for modeling subsurface CO₂ sequestration. ... Read more