(456d) Molecular Modeling of Retrograde Vaporization in Enhanced Oil and Gas Recovery

Liquid dropout due to retrograde condensation during production of rich natural gas leaves valuable condensate fluids in the reservoirs, leading to significant loss of well productivity and potentially unfeasible recoveries. Thus, accurate modeling of fluid properties across a wide range of conditions is vital for the design and optimization of enhanced oil and gas recovery processes. In this work, Gibbs-ensemble Monte Carlo simulations using transferable force fields, the Peng-Robinson equation of state, and the perturbed-chain statistical association fluid (PC-SAFT) theory are applied to investigate double retrograde vaporization in vapor-liquid phase equilibria of fluid mixtures near the critical point of the lower-boiling compound. Multicomponent mixtures representative of rich natural gas and enhanced recovery fluids are discussed. The molecular simulations allow one to provide molecular-level understanding of the solution behavior of these mixtures at relevant reservoir operation conditions, whereas the equations of state serve as supporting data and guide for the set-up of Gibbs ensemble simulations (i.e., by providing information on appropriate overall composition and volume/pressure to be used). The agreement obtained between these approaches and with limited experimental data demonstrates the versatility of molecular simulations in advanced PVT modeling.