Poster Session - IFP Invited Poster

Hydrodynamics of waxy deposit accumulation in pipelines

A. Benallal (1), Ph.Maurel (1), J.F.Agassant (2).

(1) Applied Mechanics Division, Institut Français du Pétrole, Vernaison, France

(2) Centre de Mise en Forme des Matériaux, École des Mines Paris , Sophia antiplois, France

Pipelining crude oils that contain large quantities of paraffin can cause lots of difficulties. In the exploitation temperature range, wax crystals appear in waxy crude oil, which generate a deposit at pipe wall, reducing the flow section and so the production capability. Nowadays, the existing remedial procedures (insulation, mechanical scrapping, chemical treatment etc…) need important investments and operational costs. To optimize these installations design, oil industry needs to predict accurately, the location and dynamic of wax deposit.

Currently, models used by the oil industry are based on thermodynamics properties coupled with several Fick's diffusion mechanisms. Wax molecule solubility decreases with the temperature and wax crystallizes below a critical temperature called Wax Appearance Temperature (WAT). Usually, the pipe wall temperature is lower than WAT and paraffin crystals appear near wall pipe. Consequently, there is a wax molecule deficit in crude oil along the pipe wall which will induces a diffusion of the non solidified wax molecule towards the pipe wall and so increase the development of o paraffin layer along this pipe wall.

Unfortunately, these models overestimate the deposit and they need some parameters fitting to match computational data to experimental one. In fact these models do not account for the rheological properties of waxy crude oils when paraffin crystallization progressively develops and the consequence on the flow pattern within the pipe.

In this paper, a waxy crude oil is considered as a viscoplastic fluid. An extension of classical Bingham model in which both viscosity and yield stress depend on the temperature and wax crystals. The numerical results highlight the influence of temperature and wax crystals content on the flow pattern, especially in terms of yielded /unyielded regions. A static layer region appears near the pipe wall, representing the deposit.

Key Words: wax, diffusion, viscoplastic, hydrodynamics, unyielded regions.