Accurate simulation of CO2 sequestration in deep saline aquifers requires consistent treatment of history-dependent processes. Operator-Based Linearization (OBL) provides an efficient and robust framework for compositional flow simulation. However, it was originally designed for reversible physical processes, since the operator evaluation depends solely on the instantaneous thermodynamic state. In this work, we extend the OBL approach by introducing history-dependent variables into the operator parameter space while keeping them outside the Newton unknown vector, thereby augmenting OBL with history dependency while preserving the dimension of the Jacobian matrix. To apply the augmented OBL framework to hysteresis modeling, a new hysteresis algorithm is proposed, in which the maximum gas saturation is used as the history coordinate; the flow equations are solved fully implicitly with respect to the primary variables, while this history variable is held fixed during Newton iterations and updated locally after timestep convergence to capture drainage–imbibition transitions and CO2 dissolution feedback. The augmented OBL approach is validated against the academic DARSim simulator and the commercial CMG simulator, demonstrating close agreement with conventional hysteresis modeling approaches. A sensitivity analysis of the operator parameterization shows that the resolution of the parameter space governs both accuracy and computational cost within the OBL framework. Numerical experiments in one-dimensional homogeneous and two-dimensional heterogeneous models further demonstrate that the proposed approach provides a practical and accurate means of incorporating history-dependent physics into reservoir-scale compositional simulations of CO2 sequestration. ... Read more

In supercritical CO2 pipeline transport, the operation of pumps and valves often causes the pipeline to enter a transient state. Accurately describing the dynamic response in this state is crucial for making safety control decisions. This paper proposes a nonisothermal one-dimensional transient flow model for supercritical CO2 pipelines based on one-dimensional transient flow equations and equipment characteristic equations. By comparison with experimental data, the GERG-2008 equation, known for its high accuracy, is chosen to calculate the physical property parameters of CO2. By comparing with several sets of literature data, the results show that the errors are all within the acceptable range, which verifies the high accuracy of the model. The study investigates the hydraulic and thermal changes in the pipeline under transient operating conditions, including valve closure, slow startup, and sudden shutdown of the centrifugal pump. The results showed that the water-strike intensity of a supercritical CO2 pipeline is one-third that of a water pipeline but 12 times that of a methane pipeline, which requires sufficient attention. The effect of impurity composition on water strike is significant, particularly when the N2 content reaches 5%, at which point the maximum pressure decreases by 15.1%. In addition, the timing and method of valve shutoff significantly impact water strikes. It is recommended to prioritize the calculation of piping cycles, determine the maximum valve closing time in conjunction with industry standards, and use a linear valve closing method to reduce the water strike pressure. Studies have shown that the startup or sudden shutdown of centrifugal pumps at the inlet can cause sharp fluctuations in the pressure and flow rate, but the new equilibrium state will be established quickly. In addition, doping reduces the magnitude and rate of pressure changes in the pipeline. This study provides an essential foundation for the safe and stable operation of supercritical CO2 pipelines. ... Read more

This work presents an extension of the Operator-Based Linearization (OBL) framework to model irreversible thermodynamic behavior in geological carbon storage (CCS). Traditional OBL employs adaptive parameterization over primary state variables (pressure, temperature, and composition) but lacks the ability to represent hysteresis phenomena critical to CO2–brine systems. To address this, we introduce an additional state parameter—the historical maximum gas saturation into the OBL operator space, enabling accurate modeling of hysteresis in relative permeability and capillary pressure.

The extended framework is validated through a series of numerical tests. A single-cell simulation demonstrates how Land–Killough hysteresis formulations capture saturation-path-dependent permeability behavior. A 2D aquifer model further illustrates improved CO2 trapping and sharper plume fronts due to hysteresis effects. Finally, we apply the model to the heterogeneous SPE11 benchmark, showing enhanced capillary trapping and reduced dissolution under realistic subsurface conditions.

This approach allows for the rigorous integration of irreversible physics into adaptive interpolation without altering the solver structure. Future work includes incorporating capillary pressure hysteresis, validating against field-scale simulators, and extending to fully implicit formulations. ... Read more