-Unconventional oils -mainly heavy oils, extra heavy oils and bitumens -represent a significant share of the total oil world reserves. Oil companies have expressed interest in unconventional oil as alternative resources for the energy supply. These resources are composed usually of viscous oils and, for this reason, their use requires additional efforts to guarantee the viability of the oil recovery from the reservoir and its subsequent transportation to production wells and to ports and refineries. This review describes the main properties of high-viscosity crude oils, as well as compares traditional and emergent methods for their recovery and transportation. The main characteristics of viscous oils are discussed to highlight the oil properties that affect their flowability in the processes of recovery and pipeline transportation. Chemical composition is the starting point for the oil characterization and it has major impact on other properties, including key properties for their dynamics, such as density and viscosity. Next, enhanced oil recovery (EOR) methods are presented, followed by a discussion about pipeline and transportation methods. In addition, the main challenges to achieve viable recovery and transportation of unconventional oils are compared for the different alternatives proposed. The work is especially focused on the heavy oils, while other hydrocarbon solid sources, such as oil sands and shale oil, are outside of the scope of this review.

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This paper is aimed to an experimental study on the flow patterns formed by heavy crude oil (initial viscosity and density 488 mPa s, 925.5 kg/m 3 at 20°C͒ and water inside vertical and horizontal 2.84-cm-i.d. pipes. The oil-water interfacial tension was 29 dyn/ cm. Effort is concentrated into flow pattern characterization, which was visually defined. The similarities with gas-liquid flow patterns are explored and the results are expressed in flow maps. In contrast with other studies, the annular flow pattern (''core annular flow'') was observed in both horizontal and vertical test sections. These flow pattern tends to occur in heavy oil-water flows at low water input fractions. Because of the practical importance of core flow in providing an effective means for heavy oil production and transportation, this paper discusses criteria that favor its occurrence in pipes.

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