Re-equilibrium of Asphaltenes by Repressurizing after Precipitation in Natural Depletion and CO2 Enhanced Oil Recovery Schemes

Abstract

In a series of isothermal depressurizing tests to measure asphaltene onset pressure (AOP), several depressurizing operations are usually conducted to multiple AOPs using the same lot of fluid subsamples. After one depressurizing operation is finished, the pressure/temperature condition is reset to the initial condition. Then, the next depressurizing run is performed. Before the next run, the fluid sample must equilibrate again by dissolving precipitated asphaltenes from the previous step. According to our many experiences with isothermal depressurizing tests for measuring AOPs, we know that redissolving asphaltenes depends highly upon the characteristics of a fluid sample. Some fluids redissolve asphaltenes quickly, while other samples need a lot of time. This study focused on fluid-dependent asphaltene re-equilibrium during a series of isothermal depressurizing tests. To investigate asphaltene re-equilibrium, the authors re-examined past experimental data for two types of crude oils. In the experiment, c...