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Abstract

Petroleum represents an important source of energy. The different resources for energy are classified into renewable and non-renewable. Petroleum is the main source of the non-renewable energy where it is found in conventional and non-conventional reservoirs. Conventional oil production is started since the last century with a high oil and gas production using primary and secondary recovery. Now, the global demand is high compared to the supply from the existing produced fields. The production is declining from the conventional resources, so the production from the unconventional reservoirs is essential to cover the market demand. The unconventional resources are classified as shale oil, shale gas, heavy oil, extra-heavy oil and bitumen. The challenge is to find the best production method that will lead to high production with low cost. The reserves for unconventional resources are estimated by trillions of oil barrels. In this paper, we will review the heavy oil origin, classification, and the different production methods and the challenges in the different phases of the upstream (subsurface reservoirs) and downstream (refineries & transportation) to recover the heavy oil economically.

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