Asphaltenes Explained for the Nonchemist
- Oliver C. Mullins (Schlumberger) | Andrew E. Pomerantz (Schlumberger) | A. Ballard Andrews (Schlumberger) | Julian Y. Zuo (Schlumberger)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- June 2015
- Document Type
- Journal Paper
- 266 - 275
- 2015. Society of Petrophysicists & Well Log Analysts
- 6 in the last 30 days
- 493 since 2007
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Crude oils consist of dissolved gases, liquids, and dissolved solids—the asphaltenes. The chemical identity and thermodynamic treatment of gas and liquid components of crude oil have long been understood. For example, the cubic equation of state (EoS) is very familiar to the reservoir engineering community. In contrast, in years past, the asphaltenes were viewed as complex, enigmatic and without a thermodynamic foundation. Consequently, oilfield observations related to asphaltenes, such as asphaltene gradients in crude oil, heavy-oil gradients, viscosity gradients, tar mat formation, bitumen deposition and asphaltene flow assurance, were all viewed very much within a phenomenological context without a first-principles foundation. In the recent past, a simple molecular and nanocolloidal model of asphaltenes, the Yen-Mullins model, has been shown to apply broadly. This model, combined with the Flory-Huggins-Zuo Equation of State (FHZ EoS), accounts for asphaltene gradients in bulk oil and when combined with the Langmuir EoS accounts for oil-water interfacial properties. Such success establishes validation.
These new developments in asphaltene science have been closely linked with downhole fluid analysis (DFA) to address a wide variety of reservoir concerns. Consequently, petrophysicists and other geoscientists traditionally charged with the responsibility of formation evaluation are left with the task of understanding the asphaltenes. Here, we provide an overview of asphaltenes in order to make asphaltenes accessible to technologists who are not expert in petroleum and asphaltene science. The emphasis is on the simplicity of asphaltene chemistry. This discussion naturally leads to basic chemical precepts of solubility especially because asphaltenes are defined by their solubility characteristics.
IntroductionCrude oils consist of dissolved gases, liquids and dissolved solids: the asphaltenes. Figure 1 shows a schematic representing this composition. Gas-liquid equilibria have been treated for decades by petroleum and reservoir engineers using specific cubic equations of state accounting for many reservoir fluid properties, but only for gas-liquid equilibria.
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