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Three-Phase Darcy Migration in Basin Modeling


The understanding of hydrocarbon fluids generation and migration within sedimentary basins is one of the main purposes of basin modeling. For relevant pressure and temperature conditions of sedimentary basins, the hydrocarbon fluids can exist in two different thermodynamic states: liquid and gas. Until nowadays, the Darcy hydrocarbon migration in TemisFlowTM simulator, is modeled by a two-phase flow thermodynamic scheme: an aqueous phase and a single hydrocarbon phase, whose properties result from the lumping of a mixture of the hydrocarbon components. Once the migration calculation is done, the properties of each phase are determined by thermodynamic calculations in post-processing. However, to take into account complex phenomena occurring along the migration pathway, such as appearance/disappearance of one phase, difference of migration velocity between liquid and gas phases, or the potential dissolution of some components in water/hydrocarbon phases, the three phases (aqueous phase, liquid hydrocarbon, gas hydrocarbon) flow modeling is mandatory. The modeling of such coupled thermodynamic and migration phenomena remains an important challenge at basin scales, often related to thermodynamic flash convergence criteria, which increases drastically the simulation time with the number of components. To face this issue, a new approach is proposed by doing several hypotheses to manage the thermodynamic model with a care of ensuring accuracy on phases exchange and numerical performance of the computations. The determination of phase equilibrium, has been optimized by being performed on a pre-processing step. So, during the migration process, appropriate phase properties such as liquid-gas equilibrium constants or components density/viscosity are interpolated from the tabulated values as a function of pressure, temperature and global composition. The computation of the phases composition is thus eased and the coupling with fluid displacement calculation speeded up. The results obtained on models inspired from real basins show that a three-phase flow migration scheme can be simulated at the basin time and size scales with manageable simulation time. It can improve the precision of the structural traps load history, especially in petroleum system where gas presence plays an important role, such as methane or acid gases dominant reservoirs.