Phase behavior simulation of light oil in the process of gas injection by using PVT simulation

Abstract

For studying the phase behavior of light oil in the process of gas injection, a series of phase models was built by PVTsim software for understanding the evolution of phase states and physical properties including the gas-oil ratio (GOR), density and viscosity. In this study, a light oil as an initial composition was mixed with methane gas in different degrees of gas injection from 0 to 400 mol%CH4 for phase modeling, and the temperature-pressure condition at a deep reservoir as well as on the ground was used to calculate their physical properties. Our results show that the process of gas injection can not only impact on the physical properties of pre-oil reservoirs but also change phase states of them overwhelmingly. Especially, a light oil reservoir with a good trap can become either a condensate gas reservoir in a middle degree of gas injection or a saturated reservoir (gas-liquid phases) in a high degree of gas injection. In addition, wet gas and waxy oil can be separated from a light oil reservoir with a poor trap under a high degree of gas injection. This study proved gas injection or gas washing altering the phase state and composition of pre-oil reservoirs is one important mechanism to form the condensate gas, waxy oil, and wet gas in some petroliferous basins, and also provided a new solution to study the gas injection of pre-oil reservoir in some more complex cases.