Abstract
One of the possible fluid-fluid interactions during water-flooding in oil reservoirs, that is still debated, is the effect of injected brine salinity on asphaltene destabilization. If asphaltene precipitation is induced by salinity changes in the oil reservoirs and surface facilities, this could have a massive impact on the economy of a low salinity water-flooding project. Therefore, this study aims to investigate the effect of brine salinity on the amount of asphaltene precipitation and the governing destabilization mechanisms. Direct asphaltene precipitation measurements, along with the analyses of optical microscopy images and ion chromatography (IC), indicate that the asphaltene precipitation mechanism is dependent on brine salinity. At a high brine salinity, ions play the primary role as possible nuclei for asphaltene aggregates and might promote asphaltene precipitation through asphaltene-ions bonding. While at low salinity, the polarity of the brine-oil interface causes the asphaltenes to be adsorbed toward the brine-oil interface, and this also might disrupt the stability of asphaltenes in the oil bulk. Of all the brines investigated, the highest amount of asphaltene precipitation was observed for the case in which crude oil was in contact with formation water. Based on the IC results, sulfate and magnesium are the most active ions to play the role of the nucleus in the structure of asphaltene agglomerates. Results also showed that the presence of Naphthenic Acids (NAs) in crude oil composition can affect the amount of asphaltene precipitation. • The mechanism of asphaltene precipitation varies for different salinities. • At high salinity, asphaltene precipitates through asphaltene-ion bonding. • At low salinity, asphaltene precipitation is due to asphaltene self-aggregation. • Divalent ions are more effective for asphaltene precipitation than monovalents. • The presence of NAs reduces the amount of asphaltene precipitation.
Highlights
Low salinity/smart water injection, in addition to pressure mainte nance, can induce changes in the reservoir rock and fluids properties, to provide favorable conditions for further oil production
The results of this study suggest two main mechanisms for asphaltene destabilization in the presence of an aqueous phase: the well-known self-aggregation of unstable asphaltenes adsorbed toward the interface, and an apparent effect where electrolytes are incorporated leading to more associa tion
The polarity of the brine-oil interface causes the asphaltenes to be adsorbed toward the brine-oil interface, which indirectly might disrupt the stability of asphaltenes in the oil bulk
Summary
Low salinity/smart water injection, in addition to pressure mainte nance, can induce changes in the reservoir rock and fluids properties, to provide favorable conditions for further oil production. Different mechanisms (such as fines migration, pH change effect, multicomponent ion exchange, changes in surface-charge, and double-layer expansion, formation of micro-dispersions, variations in interface viscoelasticity and osmosis, mineral dissolution or slight variations and combination of all these mechanisms) have been proposed for the effect of low salinity/smart water in the literature, the Crude OilBrine-Rock (COBR) systems investigated in all these studies are different (Bartels et al, 2019) This may be the reason why no consensus on the dominant governing mechanism has been reached yet (Al-Shalabi and Ghosh, 2016; Derkani et al, 2018; Koleini et al, 2018; Mohammadkhani et al, 2021; Mokhtari et al, 2022). If asphaltene precipitation is induced by salinity changes in the reservoir and production facilities, this could have a major impact on the economy of a low salinity water-flooding project, especially in very tight carbonate reservoirs
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