Experimental study of asphaltene precipitation prediction during gas injection to oil reservoirs by interfacial tension measurement

• Asphaltene precipitation occurs after the surface coverage beat a threshold value.
• Bond number (Bo) versus pressure is a tool for determining asphaltene precipitation.
• Three distinct regions could be identified in Bo curve for the CO2–oil system.
• In the Bo versus pressure for the CH4–oil, no major slope change is observed.
• There is no asphaltene precipitation when injecting CH4 to the asphaltenic oil.

The worldwide increase in energy demand dictates use of enhanced oil recovery (EOR) methods to recover more oil from depleted reservoirs. Displacement of oil by gas injection process is one of these methods. Carbon dioxide (CO2) and methane (CH4) are gases that are mostly used to inject into oil reservoirs. These gases under different reservoir conditions fulfill either miscible or immiscible displacement conditions. Asphaltene precipitation, which could take place during gas injection, would increase the minimum miscible pressure (MMP) of an oil–gas system. Hence, this could affect the economical aspect of the injection process.In this paper, prediction of asphaltene precipitation is studied by measuring the interfacial tension (IFT) between CO2 or CH4 (as the displacing gas) and various oil types with different asphaltene content. Also, the mechanism of CH4 solubility in oil containing asphaltene is analyzed. A proper tool, which is Bond number data versus pressure curve, is introduced to investigate asphaltene precipitation process in presence of different gases. When plotting Bond number against pressure for the CO2–oil system, three distinct intervals could be recognized. In the first interval, the oil-swelling occurs at a low pressure, in the second interval, because asphaltene accumulation happens at the gas–liquid interface, Bond number increases with a gentle slope as pressure increases; and in the third interval, more asphaltene accumulation happens when the surface coverage of the particles surpassed a threshold value (e.g., +60% surface coverage) and the rate of change in Bond number is much slower compared to the ones in the other two intervals. However, in the case of CH4–oil system, the Bond number increases linearly with pressure, and no significant slope change is observed.

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