An Integrated Technique for Natural Gas Numerical PVT Modelling: Case Study of Retrograde Condensate Gas with Python Programming

Abstract

After the discovery of a gas field, PVT analyses are performed in laboratory to understand the behavior of the reservoir f luid when pressure, temperature, or volume changes. Thereafter, physical or numerical representations of the fluid, called PVT fluid models, are designed to simulate the real fluid behavior when pressure, volume or temperature conditions change. This study aims to propose an integrated technique for natural gas numerical PVT modelling that will help petroleum engineers in determining the mol fractions and compositions of the vapor and liquid phases of hydrocarbon systems as function of pressure and temperature, as well as their trends in some pressure and temperature conditions. A case study has been performed on a historical retrograde condensate gas. The results show that over the production, when the reservoir pressure declines, the gas becomes much dryer and will therefore free less condensate into the reservoir. During its motion from the reservoir to the well head, the liquid phase mol fraction becomes lower so that the condensate-to-gas ratio (CGR) will be low. At pressures under 1000 psia, the decline rate of liquid phase mol fraction becomes higher. At the standard temperature, the more is pressure applied to the gas, the more the liquid phase proportion is. As a result, in the gas storage tanks, the more the gas is compressed, the more the condensate (liquid phase) deposit will be noticed. While transporting the gas through pipeline, the higher the pressure undergone by the gas, the more is the amount of condensate to be counted in pipelines. Moreover, at the standard temperature, the condensate proportion unit variation as function of pressure unit variation is higher when the pressure is under 20 bar.