SPE 146649 Impact of Asphaltene Nanoscience on Understanding Oilfield Reservoirs Oliver C. Mullins, 1 A. Ballard Andrews, 1 Andrew E. Pomerantz, 1 Chengli Dong, 1 Julian Y. Zuo, 1 Thomas Pfeiffer, 1 Ahmad S. Latifzai, 1 Hani Elshahawi, 2 Loïc Barré, 3 Steve Larter 4 1. Schlumberger Oilfield Services, 2. Shell Exploration and Production Company, Inc, 3. IFP Energies Nouvelles , 4. PRG, University of Calgary & Gushor Inc. Copyright 2011, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Annual Technical Conference and Exhibition held in Denver, Colorado, USA, 30 October–2 November 2011. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract Understanding asphaltene gradients and dynamics of fluids in reservoirs had been greatly hindered by the lack of knowledge of asphaltene nanoscience. Gravitational segregation effects on oil composition, so important in reservoir fluids, are unresolvable without knowledge of (asphaltene) particle size in crude oils. Recently, the “modified Yen model” also known as the Yen-Mullins model, has been proposed describing the dominant forms of asphaltenes in crude oils: molecules, nanoaggregates and clusters. This asphaltene nanoscience approach enables development of the first predictive equation of state for asphaltene compositional gradients in reservoirs, the Flory-Huggins-Zuo (FHZ) EoS. This new asphaltene EoS is readily exploited with “downhole fluid analysis” (DFA) on wireline formation testers thereby elucidating important fluid and reservoir complexities. Field studies confirm the applicability of this scientific formalism and DFA technology for evaluating reservoir compartmentalization and especially connectivity issues providing orders of magnitude improvement over tradional static pressure surveys. Moreover, the mechanism of tar mat formation, a long standing puzzle, is largely resolved by our new asphaltene nanoscience model as shown in field studies. In addition, oil columns possessing large disequilibrium gradients of asphaltenes are shown to be amenable to the new FHZ EoS in a straightforward manner. We also examine recent developments in asphaltene science. For example, important interfacial properties of asphaltenes have been resolved recently providing a simple framework to address surface science. At long last, the solid asphaltenes (as with hydrocarbon gases and liquids) are treated with a proper chemical construct and theoretical formalism. New asphaltene science coupled with new DFA technology will yield increasingly powerful benefits in the future. Introduction It is widely acknowledged that reservoir engineering is inextricably linked to the use of cubic equations of state to model compositional gradients and phase behavior. Cubic equations of state are modifications to the van der Waals equation which itself is derived from the ideal gas law. Cubic equations of state are derived to treat gas-liquid equilibria and are not a formalism to treat solids. Hence, they are grossly inadequate to handle molecularly or colloidally suspended solids. Crude oils contain not only gases and liquids but also solids, the asphaltenes. It is not proper to treat the solid asphaltenes with equations derived from the idea gas law. For example, cubic equations of state require knowledge of the critical point, the point at which the liquid and gas properties are identical while asphaltenes have no liquid phase, no gas phase and no critical point. Specifically, there had been no first principles method to model asphaltene gradients in reservoirs. Indeed, this led to a general misunderstanding of black oils. Condensates have relatively high GOR compared to black oils [1] and high GOR fluids generally exhibit large compositional gradients.[1-3] Cubic equations of state yield homogeneous compositions for black oils due to their characteristic low GOR.[1-3] Consequently, there has been the erroneous assumption that black oils are homogeneous because cubic equations of state give this result. Nevertheless, numerous geochemical studies indicate chemical compositional variations do exist laterally and vertically in many black oil reservoirs.[4] As mentioned above, cubic equations of state cannot model asphaltene gradients in any first principle approach. Moreover, black oils are best described by their asphaltene content, not their (low) GOR. Since viscosity depends exponentially on asphaltene content,[5] it