Understanding asphaltene precipitation and subsequent deposition during oil production is of great importance for the oil industry nowadays because of the potential risk associated with this heavy fraction in plugging wellbores and production equipment. Although water is commonly present in the produced fluids, because of instrument limitations and inadequate techniques, it is usually separated from the oil prior to any experimental analysis. Therefore, the effect of water on asphaltene stability and deposition tendency is not completely understood, and the information available in the literature is scarce. In this work, the effect of emulsified water on asphaltene instability in crude oil systems is investigated. Three crude oils and one bitumen sample were used in this study. The crude oils had American Petroleum Institute (API) gravities ranging from 26°to 40°and asphaltene content between 1.2 and 13 wt %. Model oils were also prepared with asphaltenes extracted from these crude oils. A total of nine systems were investigated with and without the presence of emulsified water. It was found that, for the crude oils from the Middle East and Canada and their corresponding model oils, the addition of water did not have a significant effect on either the detection of asphaltene precipitation or the amount of precipitated asphaltenes. However, the stability of asphaltenes in the crude oil from the Gulf of Mexico and the model oils from the Athabasca bitumen (containing n-C 5 and n-C 7 asphaltenes) was significantly affected by the presence of water. The experimental evidence suggests that some asphaltenes are more prone to interact with water at the oil−water interface. This work provides a simple technique to screen whether water has an effect on asphaltene stability for a given crude oil at ambient pressure and different temperatures. With this study, we aim to contribute to a better understanding of the interaction of water and asphaltenes in crude oil systems, which will eventually lead to the development of cost-effective strategies for the mitigation of this flow assurance problem.

Although multiple problems occur simultaneously in oil production, the solution strategy is typically presented by addressing one problem at a time. The objective of this work is to provide insight into the detrimental effect of iron ions, which are produced as a result of corrosion, on the asphaltene precipitation and deposition tendency during oil production. Furthermore, we aim to provide means to control these adverse effects by using chelating agents. In a series of experiments, a model oil system, which was prepared by dissolving asphaltenes in toluene, was put in contact with aqueous solutions of iron ions to study the effect of these species on the stability of asphaltenes using the indirect method. Also, a new experimental setup, consisting of a multi-section Teflon column packed with carbon steel spheres was built to quantify the deposition of asphaltenes under different operating conditions. This device was used to study the effect of the aqueous iron solutions on the asphaltene deposition tendency. It was found that the solubility of iron species is relatively high in the oil phase, compared to other cations, and that unlike other metals iron has a significant destabilizing effect on the asphaltene system. Furthermore, the multiphase systems that were analyzed in the column that is packed with carbon steel spheres, showed increasing deposition as the concentration of iron in the aqueous phase increased. A chelating agent was tried to reduce the adverse effect of iron and successful results were obtained. A systematic study was conducted to analyze the effect of different variables on the iron-induced asphaltene precipitation. Charge of metal ions, pH, and emulsified water do not seem to affect the asphaltene precipitation tendency as much as the iron concentration. In this work we account for the corrosion of pipelines and asphaltene deposition and the interrelation between them. According to the evidence that we have found, the corrosion of pipelines might be an aggravating cause for asphaltene deposition in wellbore and surface facilities. By addressing the corrosion problem, asphaltene deposition might actually subside.

In this work, the effect of carbon steel corrosion on asphaltene deposition tendency was investigated. A new experimental setup, consisting of a multi-section column made of polytetrafluoroethylene (PTFE), was built and packed with carbon steel spheres, which was then used to quantify the deposition of asphaltenes under different conditions. It was found that, in the presence of iron ions in a brine-in-oil emulsion, the amount of deposited material upon the addition of an asphaltene precipitant, such as n-heptane, was significantly higher than in the case of iron-free brine. In addition, it was observed that asphaltenes have a higher tendency to deposit on the rust-covered metallic surfaces compared to the clean and smooth carbon steel spheres. Also, increasing the surface roughness can lead to a higher asphaltene deposition rate. To reduce the extent of asphaltene deposition induced by the tube corrosion, a chelating agent, ethylenediaminetetraacetic acid (EDTA), was added to sequestrate the iron ions. The results obtained showed that EDTA is able to mitigate the extent of corrosion-induced asphaltene deposition on metallic surfaces. Consequently, when the corrosion problem is addressed, asphaltene deposition may actually subside. The deposition tests also revealed a surprising result: even though EDTA reduced the amount of asphaltene deposition on carbon steel spheres, it significantly increased the amount of deposit collected on the PTFE surface. With these results, we conclude that corrosion and asphaltene deposition are two problems that must be concurrently investigated and that strategies for their mitigation should account for the interactions between chemicals in the bulk phase and also with the exposed surfaces.

No abstract