Organic flow assurance, pour point depressant development through experimental design
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Flow assurance is of great importance in the oil and gas industry, where the main objective is to provide and secure the transport of the well stream fluid from the reservoir to the process facilities. The main challenges in flow assurance are solid depositions in the pipelines, which can lead to reduction in the production, or in worst case completely block the pipelines. Wax deposition is a common problem in the oil industry, especially with cold and deep offshore fields. Waxes are long alkane chains found in the crude oil, which can begin to precipitate and form deposits in the pipelines when the temperature decreases during production. There are applied different methods for preventing and removing wax depositions, such as mechanical removing, heat application or chemical prevention. The application of wax inhibitors is an effective method to prevent wax depositions, and in this thesis a common group of chemicals called pour-point depressants (PPDs) are tested. The PPDs are polymers consisting of a polymer backbone with long alkyl side chains attached, which are meant to interfere with the wax crystals and prevent further growth. The focus of the thesis is to use a statistical method called design of experiments (DOE) to find the best formulation for a group of PPDs known as acrylate ester polymers. There were performed two analyses with one mixture containing acrylate ester polymers where there were synthesized different percentages of alkyl side chains of 16 carbons, 18 carbons, and 22 carbons length on the polymer backbone. The other mixture contains different percentages of acrylate ester polymers, which had alkyl side chains of either 16 carbons, 18 carbons or 22 carbons length. A software program called Design-Expert was used to perform the two DOE analyses. Design-Expert managed to quick and simple come up with a systematic plan for the minimum number experiments needed, to find the optimal formulations for the two mixture analyses. The performances of the different PPDs were measured by a viscometer, where the effect of the PPDs was how well they managed to displace the temperature for then the wax started to precipitate and cause gelling of the crude oil. The results from the viscosity measurements were analysed in Design-Expert, which provided a response surface graph where the optimum effects of the different PPDs combinations could be easily found from. The results from the response surface graphs and the optimization points for the two analyses showed similar results. The best interaction of the different alkyl side chains length on the polymers were in general found to be with different percentages of 16 carbons and 18 carbons, with an increasing optimum towards polymers containing only 18 carbons. The optimal formulations were made and their effect tested on the viscometer. However, none of the results corresponded well to what the response surface graphs had indicated, and were in general much lower than expected. Overall the different DOE analysis did not manage to find an optimal combination for the different components in the mixtures, which were any better than acrylate ester polymers with 18 carbons alkyl side chains alone.
Master's thesis in Environmental technology