Laboratory Investigation of Asphaltene Instability in Low-salinity Waterflooding using a Hele-Shaw Cell

Document Type : Research Paper

Authors

Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran

Abstract

Low-salinity waterflooding is a practical method to maintain the pressure of reservoirs and increase oil recovery. However, an aspect that requires further investigation is the impact of water salinity on the instability and deposition of asphaltene in the reservoir that may lead to formation damage and injectivity loss. To investigate this type of damage and the associated mechanisms, dynamic tests were performed using a Hele-Shaw cell. Oil and water were co-injected to mimic the injection area condition around the well-bore, and the effect of brine salinity on emulsification and asphaltene precipitation/deposition was investigated. Moreover, two different scenarios were considered to localize the deposited asphaltene: i) in the presence of an asphaltene instability stimulator such as normal pentane, ii) in absence of normal pentane. Furthermore, two compositionally different crude oils were used: Ab-Timur and Koupal. The results for Ab-Timur oil showed that the brine salinity and the type of ions have a significant effect on in-situ emulsification and asphaltene deposition. For this oil, the most stable emulsion with a droplet size of 151 μm was obtained in twice-diluted-seawater and the amount of asphaltene precipitation was 18.3% of the cell volume in the presence of normal alkane. It can be concluded that there is a direct relationship between emulsion stability and asphaltene precipitation: the more stable the emulsion, the more asphaltene deposition. For both oils, it was observed that with ten-times-diluted seawater there are trapped oil areas which are bypassed by the flowing water. Areal microscopic observation showed that the oil-water interface remains unchanged even by increasing injection rate, due to formation of a rigid layer around the oil. Ultimately, this shows that in the actual process of low-salinity waterflooding in oil fields, there is a possibility of asphaltene instability at some salinity ranges that can cause oil trapping due to oil-brine interface hardening.

Keywords

Main Subjects

References

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Journal of Petroleum Research
Volume 34, 1403-2 - Serial Number 135
Special Issues on Water-based EOR
July and August 2024
Pages 3-16

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