Component-wise and Unconditionally Energy-Stable VT Flash Calculation.

Flash calculations of the hydrocarbon mixture are essential for determining how the mixture phase behaves, which will ultimately affect subsurface flow and transport. In this paper, a novel numerical scheme is proposed for calculating the two-phase equilibrium of Peng-Robinson (PR) fluid at constant volume, temperature, and moles, namely the volume-temperature (VT) flash framework based on the dynamic model. Since the dynamic model is based on the energy dissipation law and the Onsager’s reciprocal principle, we proposed a linear energy-stable scheme with the help of the convex-concave splitting technique, the energy factorization approach, and the component-wise iteration framework. The scheme eventually results in a fully explicit algorithm, and it avoids the challenges of solving non-linear systems and other difficulties in the traditional flash calculation methods. This scheme inherits the original energy stability and significantly reduces the implementation burden. It also achieves convergence unconditionally, even with a huge time step. Numerical experiments are carried out to illustrate its accuracy.