A Flash Black Oil Model

Abstract

This paper describes a new Fully-Implicit Black Oil Model, which is different from the conventional Black Oil Model in using a phase equilibrium concept. In this model four basic unknowns, pressure and three component masses per unit formation volume, are solved instead of pressure, water saturation and the third alternative variable (oil saturation or bubble point pressure) in the conventional Black Oil Model. Thus, we can avoid the complicated treatment of the third alternative variable and discontinuity at crossing bubble point in the solution of equations. Although the phase equilibrium calculation is included, the model still uses common PVT data of Black Oil Model. Solving equations is followed by a 'Flash Calculation' for each time. The model includes both sequential and simultaneous schemes, so it can be used in various cases of reservoir simulation. The model has been tested with a three-phase coning study, which is from the Second Comparative Solution Project of Black Oil Model presented at the Sixth SPE Symposium on Reservoir Simulation, 1982.