Abstract

A joint AAPG/Associación Mexicana de Geólogos Petroleros (AMGP) Hedberg Research Conference was held to examine issues associated with heavy oil in deep water. This article reports on the meeting highlights. Deep-water exploration has become increasingly important over the last three decades. For the deep-water environment to be economically viable, these accumulations need to be both volumetrically significant and capable of maintaining high production rates. Largely independent of the rise in crude oil price, there has been an increasing number of economically viable deep-water discoveries, where the resource base now exceeds 100 billion bbl oil equivalent. A significant percentage of this resource is heavy oil, with heavy oil dominating the resource base in such settings as offshore Mexico and Brazil. Economic success in both exploration and commercialization requires integration across disciplines as well as across the value chain, integrating the upstream, midstream, and downstream operations. Basin models were commonly used as the integration tool for exploration programs.

The exploration risks associated with the deep-water environment tend to be higher, in part as a result of oil quality. Risk reduction can be partially accomplished through a better understanding of the factors that control oil quality, including source rock facies, thermal maturity, and the alteration and migration histories. Although several factors may impact crude quality, the consensus was that biodegradation was the dominant factor controlling quality in most deep-water regions, Mexico being an exception, where source rock character has an important function. Biodegradation is controlled by such factors as charge and thermal history and the geometry of the oil-water contact. Where source facies is a key factor in establishing the presence of heavy-oil migration, distances tend to be more limited. Mixing of oils also appears to be an important factor in determining oil quality, often improving or maintaining oil quality, with the introduction of light oils into biodegraded oil.

The production of these heavy oils introduces several challenges above and beyond those associated with similar accumulations onshore and in shallow waters. Lessons learned from these settings can, however, be very useful when working in the deep-water setting. The value of continuous data collection and updating reservoir models was made clear in case studies from both Angola and Brazil, where phased development or reservoir model recycling permitted the more efficient use of capital. Also of importance is the need for long-term planning because of the long lives of heavy-oil accumulations.

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