This paper proposes a new compositional simulation approach which has an implicit equation for the oil-phase pressure and water saturation, an explicit equation for the hydrocarbon saturation, and explicit equation for the overall composition of each hydrocarbon component that satisfies thermodynamic equilibrium. The proposed formulation uses an Equation of State for phase equilibrium and property calculations. Interfacial tension effects are included in this research to characterize the thermodynamically dynamic nature of the relative permeability. A two-dimensional relative permeability algorithm is included which handles lumped hydrocarbon phase hydrocarbon phase as well as individual phase flows.

For each grid block two equations are required, namely total hydrocarbon and water-phase flow equations. These equations are highly non-linear and they are linearized by using Newton-Raphson method. The resulting set of equations are solved by an efficient Conjugate Gradient based iterative technique to obtain pressures and saturations simultaneously, and hydrocarbon-phase saturations are deduced from their respective equations.

The new compositional simulation approach is validated through analytical and other numerical methods. lt is demonstrated in this present paper that the results are compared favourably with analytical techniques and published numerical results. They also confirm that the proposed codified formulation is unconditionally stable and it is as stable as the fully compositional model yet the computational cost reduction was substantial.

Impact of sequence-based on correlation style on volatile oil recovery is modelled with this approach. Specifically, the effect of clino-formal permeability barriers on predicted displacement efficiency of oil by injected water and injected gas into volatile oil reservoirs is assessed. The results show that oil recovery factors are strongly affected by the combination of the structure of permeability and the transmissibility barriers between the layers.

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