3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Assessment of asphaltene stability at different temperatures using salicylic and iso-phthalic acids as inhibitors(2019) Agostinho, Luisa TuairaDuring crude oil production, processing, transportation and storage, the change in temperature, pressure and fluid composition can lead to the instability of asphaltene in the system. The posterior deposition of asphaltene can clog or completely close the production, processing, and transportation facilities, thus decreasing production and increasing maintenance costs. A cost-saving manner to prevent this problem is the use of processes such as addition of chemicals inhibitors, which prevent asphaltene precipitation. In this project, several experiments were performed to assess the stability of asphaltene in crude oil varying parameters as temperature, precipitant amount, inhibitors concentrations and time. The asphaltene behaviour and the reduction of the precipitated particles size in crude oil samples were controlled using an optical microscope. In order to propose a preventive method for the asphaltene deposition, different amount of Salicylic and Iso-Phthalic acids as asphaltene inhibitors and n-heptane as asphaltene precipitant agent were added at 35 ºC, 65 ºC, and 80 ºC. The results showed that the sizes of the asphaltene particles were reduced with increase in temperature. At almost room temperature such as 35 ºC, the inhibition of Salicylic acid was better for lower concentration (15%). While at higher temperature such as 65 ºC and 80 ºC, the best inhibition concentration for Salicylic acid was 25%. For Iso-Phathalic acid, at 35 ºC it was found that 25% was the best concentration, at 65 ºC, 20% was the best concentration, and at 80 ºC, small concentration of 2.5 % was sufficient to inhibite asphaltene in the crude oil. The precipitant agent n-heptane had an effect on the size of asphaltene aggregates. A minimum of 2 ml n-heptane was able to initiate the precipitation process at various temperatures (35 ºC, 65 ºC and 80 ºC). An increase in precipitant agent amount such as 3.5 ml increased the aggregates particle sizes. It was concluded that asphaltene is more stable at 80 ºC for Salicylic acid, showing the best inhibition capacity at this temperature, when compared to Iso-Phthalic acid which showed the best inhibition capacity at 65 ºC, for both inibitors asphaltene showed to be more instable at 35 ºC. The inhibition profile of Salicylic acid showed less variation with temperature than the inhibition of Iso-Phathalic acid.Item Assessing solvents effect for mitigation of asphaltene precipitation in South African Oilfields(2018) Saide, Alda Brigida JoaquimAsphaltenes molecules is one of the heaviest components in petroleum fractions that under reservoir conditions can be found either in colloidal form or dissolved in crude oil liquid phase. However, when variation in thermodynamic parameters such as temperature, pressure and fluid composition occur can lead to asphaltene precipitation phenomenon and posterior asphaltene deposition in oil wells, pipelines and processing facilities consequently, resulting in several damages along the petroleum chain as well as economical loss for oil and gas companies. Therefore, several studies have been developed to understand this phenomenon and eventually help to monitor and prevent its occurrence. In relation to the present work, an experimental study will be developed in the crude oil samples of one of the South African oilfields to evaluate the effectiveness of different concentrations of two solvents (Salicylic acid and Iso- phthalic acid) in the asphaltene precipitation onset time when variation in temperature and fluid composition occur. This procedure combined with laboratory experiments have helped to define a solvent with great inhibitor capability to prevent asphaltene precipitation in this field and also, estimate the solvent inhibitor concentration and quantity to be used. The results obtained in this study could thus allow the building of a clear picture about probable situations and/or stages to intervene for mitigation of asphaltene precipitation in South African oilfields.