A new view of trapping pressure estimation using PVT simulation of hydrocarbon inclusions in petroliferous basins

Abstract

The trapping pressure of hydrocarbon inclusions can provide important information for fluid analysis in petroliferous basins. It can be obtained through PVT (pressure-volume-temperature) simulation, in which the gaseous filling degree (FV) of the hydrocarbon inclusion is a key parameter. Although it is believed that FV can significantly influence trapping pressure calculations, few studies have provided detailed numerical evidence. Here, we conducted a series of numerical experiments using thermodynamic simulation software to unravel the relationship between FV and trapping pressure. The results indicate that the influence is negligible when FV exceeds a certain value, while the FV can greatly influence trapping pressure when it is less than the certain value, especially a very low one. In addition, we discussed problems existing in the volumetric calculation of hydrocarbon inclusions based on Confocal Laser Scanning Microscopy, which is the predominant method. We find that a vapour bubble shrinks in the lateral plane and is stretched along the vertical axis under relatively strong monochromic or laser light, which is thought to be due to light pressure. Therefore, the vapour bubble can be regarded as a cylinder when it is restricted vertically due to the thin thickness of the inclusion, or an elongated ellipsoid when the inclusion is much thicker than it. Certain errors may be diminished or eliminated theoretically. Case studies are used to validate this novel approach. This view will help to improve the PVT simulation method and even develop new programs.