Thermal Flow Properties of Heavy Oils

Abstract

A major flow assurance challenge in the near future is the production and transport of heavy oils: although these petroleum products represent very important reserves, their exploitation is limited by their high viscosity. The paper discusses the origin of this high viscosity in order to ultimately develop operating guidelines. It focuses on the relationship between the composition of heavy oils, in particular their asphaltenes and resins contents, and their flow properties. The structural analysis and rheological measurements that were performed revealed how strongly the transportability of heavy oils depends on thermal conditions, especially in deepwater ones. From this study, we conclude that the high viscosity of a heavy oil comes essentially from the overlapping of its asphaltenes. We observed that as temperature decreases, not only the viscosity increases but also the rheological behavior of heavy oils becomes non Newtonian. Dynamic tests carried out on several crudes show that at low temperatures, they develop a shear thinning behavior with no yield stress appearance. It was checked that this phenomenon comes from the particular structure of asphaltenes and that it is not due to the presence of waxy crystals. It is therefore recommended to take into account this non Newtonian behavior if heavy oils are to be transported in deepwater conditions. Introduction. A major flow assurance challenge in the near future is the production and transport of heavy oils. Despite very large reserves, their exploitation is limited by their high viscosity. Actually, the very low mobility of these petroleum products is making an as such pipeline transportation impossible. Advanced methods are necessary. They include upgrading, dilution, formation of oil-in-water emulsions and heating. These technologies imply high operational and investment costs so that optimized transport conditions have to be found. With this aim in view, a detailed study of the rheology of heavy oils was carried out. It deals with the link between the constitution and the flow properties of the crude, and lays emphasis on the role played by temperature. The understanding of the origin of the high viscosity of heavy oils will help to improve their methods of transportation, especially at low temperatures like in expected deepwater discoveries. The overlapping of asphaltenes inside a heavy oil and its consequence on viscosity. One main chemical characteristics of a heavy oil is its large content in asphaltenes. These molecules constitute a class of substances defined on the basis of their solubility in organic solvents: they are soluble in toluene but insoluble in alkanes such as n-pentane. Asphaltenes are the heaviest and most aromatic and polar fraction of a crude oil. These particular components are described as molecules composed of polycondensed aromatic rings carrying aliphatic chains that contain acid-base and polar groups at their edge. It is well recognized that thanks to these chemical characteristics, asphaltenes can self assemble through physical interactions and increase the viscosity of a medium in which they are added. Most of these studies were realized with simple organic solvents [Reerink and Lijzenga (1973), Sheu et al. (1991), Yudin et al. (1998), Acevedo et al. (1999).].

Flow Characteristics of Heavy Oil through Porous Media

“…The geologic reserves are much higher than conventional crude oil. A major flow assurance challenge in the near future is the production and transport of heavy oils (Henaut et al, 2003). Heavy oil has been repeatedly verified as suspensions of 348 H. Liu et al asphaltene colloids stabilized by resins (Yen and Chilingarian, 1994;Mullins and Sheu, 1998;Wong and Yen, 2000), which leads to the heavy oil representing some unusual flowing behaviors through pipes and porous media (Steinborn and Flock, 1983;Hasan et al, 2010;Luo and Gu, 2009).…”

Influence of heat transfer on two-phase flow behavior in onshore oil pipelines

“…However, as commented by Henaut et al (2003), "a major flow assurance challenge in the near future is the production and transport of heavy oils. Despite very large reserves, their exploitation is limited by their high viscosity".…”

Non-Newtonian flow characterization of heavy crude oil in porous media

“…However, the production and transport of these oils are challenging because of their non-Newtonian flow characterization in reservoir. The rheology of heavy crude oil plays an important role in the flowing process of oil through porous media, and the rheological behavior of heavy crude oil is directly related to the development indexes, like well productivity and oil recovery (Chen and Lu 1990;Henaut 2003;Prada and Civan 1999). High viscosity and high density are the most prominent properties of heavy crude oil, resulting in a major difference of rheology feature with the conventional oil.…”

“…First, the composition of heavy oils, particularly the content of asphaltenes and resins, plays an important role for the flowing process of heavy crude oil, it is the leading cause of their high viscosity (Argillier et al 2002;Schramm and Kwak 1988;Ovalles et al 2011;Steinborn and Flock 1983). Henaut et al (2003) and Argillier et al (2002) investigated the influence of asphaltenes and resins content on oil viscosity. Their experimental work revealed the existence of a critical concentration above which the asphaltenes particles overlap.…”