Name: Luiz Fernando Rambalducci Dalla
Type: MSc dissertation
Publication date: 30/04/2018

Namesort descending Role
Edson Jose Soares Advisor *
Renato do Nascimento Siqueira Co-advisor *

Examining board:

Namesort descending Role
André Luiz de Castro Machado External Examiner *
Edson Jose Soares Advisor *
Fabio de Assis Ressel Pereira External Examiner *
Renato do Nascimento Siqueira Co advisor *

Summary: The restart of paraffinic oil flow is a problem of extreme severity in the scope of flow assurance. After a period of production stoppage, the paraffins precipitate and the oil begins to behave as a non-newtonian material. In fact, it behaves as a viscoelastoplastic and thixotropic material. In order to resume flow, the viscoplastic aspect is the most important. The minimum pressure required to restart the flow must be predicted. For that purpose it is common to use the relation, ∆P = 4τ0L/D, WHERE L and D are respectively the length and diameter of the pipe and τ0 is the yield stress. This work evaluates how realistic this expression is, since it does not consider, for example, slip phenomenon at the wall. An experimental apparatus is used, consisting of a piston that pushes the oil inside a tube. The critical stress to start flow is compared to the yield stress by using the sliping factor SF = (τ0 −τc)/τ0. For carbopol, the critical stress obtained on the bench was lower than the yield stress measured on the rheometer for the case of a smooth pipe. Nonetheless, using a rough inner surface, the SF reduces, being an indication that the slip effect isimportanttothecarbopolflowrestart.Inthetestswithparaffinicpetroleum,twoinitialheating temperatures were evaluated 50◦C and 60◦C. A good concordance was verified between the critical tension obtained in the bench and yield stress. The results indicated that the mechanism of gelled structure breaking is the adhesive failure and, in this case, the above equation provides a good estimate of the pressure required to restart the flow.
Keywords: Carpobol. Waxy crude oil. Yield stress. Start-up. Slip.

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