Investigation of Asphaltene Onset Pressure (AOP) in Low Asphaltenic Light Oil Samples

Abstract

Asphaltene precipitation is a common problem in reservoir field during natural pressure depletion and gas injection process for enhanced oil recovery (EOR). Extensive field and laboratory data have proven that asphaltene precipitated more easily from light oil rather than from heavy oil. This study concerns with both experimental and simulation investigations on asphaltene precipitation condition during pressure depletion and gas injection. A series of isothermal depressurization experiments have been carried out using light oil samples with low asphaltene content to investigate its asphaltene onset pressure (AOP). In addition, precipitation onset condition induced by different carbon dioxide (CO2) concentration has been investigated over the pressure change. Besides, simulation studies have been carried out to understand asphaltene onset behavior over pressure change at reservoir temperature. Three light oil samples with low asphaltene content have been chosen to investigate precipitated asphaltene fraction induced by different CO2 concentrations over the pressure change. The results of this study have shown that asphaltene starts to precipitate in oil when approaching bubble-point pressure during depressurization. The precipitated amount increases and reaches the maximum around bubble-point pressure. After bubble-point pressure, part of the precipitated asphaltene re-dissolved back to the oil. By injecting higher CO2 mol percentage, bubble-point pressure increases and more asphaltenes precipitate in oil.