The Effect of Brine Concentration on Asphaltene Stability
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AbstractThe stability of asphaltenes is a critical parameter which may affect the flow in porous media significantly. This study investigates the change in the stability of asphaltenes after the interaction of asphaltenes originated from five different reservoirs with reservoir components? namely sand, clay, water, and brine. Asphaltenes are polar like water and brine. Hence, the initial lab-scale sensitivity studies were carried out first with asphaltene-water and asphaltene-brine systems. Then, the impact of porous medium has been investigated on asphaltene stability? asphaltenes are mixed with either sand or sand+clay mixture and then exposed to water or brine. Since, both sand and clay show water-wet behavior, the effect of water-wet rock surface on asphaltene stability has been aimed to understand. Moreover, different brine types and concentrations on asphaltene stability have been tested. A divalent and a monovalent salts were used to prepare brine solutions at 2%, 4%, 6%, and 8% concentrations. All laboratory tests were achieved under optical microscope and the interaction has been examined overtime. Our experimental results suggest that asphaltenes from all five crude oil samples are dispersed in water and they aligned themselves within water due to polar nature of asphaltenes and water. In asphaltene-brine systems, the monovalent salt (NaCl) interacts more with asphaltenes than divalent salt (CaCl2). This is due to higher water uptake capacity of CaCl2 than NaCl. The microscopic images revealed that a water layer is formed around CaCl2 inhibits the direct interaction of asphaltene-CaCl2. This behavior is enhanced within the porous media; salt crystals form bridges between the sand grains, clay and asphaltenes contribute to the formation of those bridges. The impact of brine has been observed more significantly at high concentration of the brine solutions. The asphaltenes-brine interaction also shows variations among different asphaltenes. Thus, all asphaltene samples have been analyzed for their elemental compositions to check if cation exchange is possible between the salts and asphaltenes. These experiments revealed that for the asphaltenes rich in calcium and sodium content, their interaction with brine is greater than for the asphaltenes poor in calcium and sodium content. Moreover, this interaction contributes to the formation of bigger asphaltene clusters which decreases the asphaltene stability and promotes more asphaltene precipitation. This study provides some general trends observed in asphaltene-water and asphaltene-brine systems and explains the reasons why some outliers do not fit the trends by examining the differences in the chemical composition of asphaltenes. Hence, this study enriches our knowledge towards asphaltene behavior in porous media.
