A Study of Asphaltene Onset Pressure during High-Pressure Gas Injection

In order to avoid asphaltene precipitation caused by gas injection for enhanced oil recovery, the asphaltene onset pressure (AOP) was tested in the laboratory. On the basis of the analysis of the asphaltene precipitation mechanism during gas injection, the asphaltene onset pressures under different temperatures were measured along with crude oil samples in the process of high-pressure gas injection, by using the self-developed laser solid detection system and the light transmission method, so as to determine the depth of asphaltene precipitation. The results demonstrated that the asphaltene onset pressure decreases with the increase of temperature, AOP are 44.1 MPa, 39.7 MPa and 35.2 MPa at the temperatures of 44 ℃, 80 ℃ and 123 ℃ respectively in the experiment;the asphaltene onset pressure increases 0.5-0.6 MPa when amount of substance fraction 1% of hydrocarbon gas is injected. According to the asphaltene deposition envelope and wellbore temperature-pressure curve, it is predicted that asphaltene precipitates at a depth of 1 800 m, which matched the field conditions very well. The study suggested that there is a linear correlation between the volume of gas injection and the asphaltene onset pressure, which could provide a theoretical basis for preventing and removing asphaltene precipitate in gas injection on site.