A General Purpose Model for Multiphase Compositional Flow Simulation

Abstract Reservoir simulation has come a long way since its birth in the 1950s and now is an important tool for reservoir engineers to predict oil and gas production and optimize reservoir management. In the past, many existing models were developed to simulate fluids with a specific fluid characterization such as black oil, compositional and thermal models. Today, the need for optimizing reservoir life with different recovery techniques and different fluid characterizations is urgent to fully evaluate oil and gas fields assets. In this paper, a flexible general purpose model has been developed for multiphase isothermal or thermal compositional flow simulation in porous media, including formulations, phase behavior calculation, various numerical techniques. Based on general mass balance equations and energy balance equations, a mass variable set has been chosen for the generality for all types of fluids (black-oil, compositional and thermal) to ensure that each grid block has the same amount of primary unknowns and it is convenient for Jacobian matrix construction. The model decouples fluid and formulation from the rest of simulator and makes is possible to model different reservoir physics in one single simulator. The model have tested and validated on various standard comparative benchmark problems like black-oil model, compositional model as well as large complex field cases with over one million grid blocks and an actual reservoir simulation. The test results show that the simulator is comparable with current commercial simulators in accuracy and speed. When different recovery techniques are used in a reservoir life cycle, the model is more efficient and accurate without the need of switching simulators. The generic and modular design architecture provides convenience for extensions of modeling additional flow processes and implementing new numerical solution methods. Developing a general purpose reservoir simulator is the main focus in state-of-the-art reservoir simulation research. The proposed general purpose model for multiphase compositional flow simulation in this paper is one step closer to the goal.