Experimental analysis on reservoir blockage mechanism for CO2 flooding

The slim-tube experiment, component analysis experiment and microscopic simulation experiment are used to analyze the phenomena of reservoir blockage and drop of oil production rate, and to find out the reservoir blockage mechanisms in the process of carbon dioxide flooding. The slim-tube experiment shows that the effect of carbon dioxide flooding was poor under low displacement pressure, and the higher the displacement pressure, the better the effect of flooding. When the displacement pressure exceeded the minimum miscibility pressure, reservoir blockage could occur, affecting the reservoir productivity significantly. Component analysis and microscopic modeling experiments show that oil component differentiation could occur after oil contacted with carbon dioxide. Under low displacement pressure, component differentiation was not significant, so reservoir blockage did not occur; but when the displacement pressure was higher, aromatics in oil were extracted rapidly by carbon dioxide, resulting in quick deposition of non-hydrocarbons and asphalt and the blockage of pore-throats in reservoirs. Therefore, controlling the displacement pressure is the main measure to prevent reservoir blockage. The best pressure of carbon dioxide flooding should be near the minimum miscible pressure, pressure, too high or too low, is not good for carbon dioxide flooding.