Grand Canonical Monte Carlo simulation model for phase behavior of confined hydrocarbons, A

Abstract

With the increased interest in primary and improved recovery from unconventional reservoirs, unusual characteristics of PVT behavior in nano-pores have attracted more attention. It has been established that the pore size influences thermodynamic properties and PVT behavior of the reservoir fluids due to the change in inter-molecular, capillary, and surface forces. There have been a number of studies on phase behavior in nano-pore confinement which reveal inconsistent and contradicting results about the shift of the critical point and the shift of the pressure-temperature diagram. This thesis focuses on Monte Carlo simulation technique taking the statistical mechanics into account to model the PVT behavior of hydrocarbons. Grand Canonical Monte-Carlo ensemble is studied to observe the effect of confinement on phase behavior of pure methane by taking into consideration the effects of the inter-molecular forces and the interaction between fluid particles and solid surface. Under isothermal conditions, density of methane is calculated from Monte Carlo simulation at different pressures to determine the bubble point. Results are compared with the published studies and the differences are discussed. The size of the simulation box affects the results of Grand Canonical Monte Carlo simulation significantly. Therefore, this thesis questions some of the conclusions drawn in the literature about the bubble point and the critical point shift. Consequently, it is suggested that the results of molecular simulations should not be used as absolute phase-behavior benchmarks in nano-pore systems without confirmation by independent means.