Impact of Asphaltene Nanoscience on Understanding Oilfield Reservoirs

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.

Petroleum Asphaltenes

“…The island architecture exhibits attractive forces in the molecule interior (PAH) and steric repulsion from alkane peripheral groups. These structures were also observed in oil reservoirs with extensive vertical offset, where gravitational effects are evident (Creek et al, 2010;Mullins et al, 2011). Results from analytical methods such as time-resolved fluorescence depolarization (TRFD) (Groenzin & Mullins, 2000), Nuclear magnetic diffusion (Freed et al, 2007); Fluorescence correlation spectroscopy (FCS) (Andrews et al, 2006), DC conductivity (Zeng et al, 2009;Goual et al, 2011) indicate that the size of asphaltene molecules is  1.5 nm.…”

Development of Nanofluids for Perdurability in Viscosity Reduction of Extra-Heavy Oils

“…Nevertheless, the physicochemical properties of EHO such as low API gravity and high contents of heavy components such as resins and asphaltenes lead to high viscosities through the formation of a complex viscoelastic network [4] and generate substantial technological challenges for production, transporting and refining operations [5][6][7]. The crude oil heavy fractions, particularly the asphaltenes, are high dipole moment compounds [8] due to its chemical structure which is composed by a polyaromatic core surrounded by aliphatic chains and may contain heteroatoms such as oxygen, nitrogen, and sulfur [9,10]. The high polarity caused by this chemical structure generates in this compounds a self-association characteristic, leading to the asphaltene arrangement in aggregates that, depending on their sizes, can be classified as nanoaggregates or clusters [11].…”

Nanotechnology-Assisted EOR Techniques: New Solutions to Old Challenges

“…According to that, it seems justifiable to consider most of the oil and gas production technologies, reservoir treatments and stimulation as nanotechnologies (Evdokimov et al, 2006;Mullins et al, 2011). Several studies have shown that asphaltene precipitation as a side effect of some EOR processes, mostly miscible gas injection, hinders the oil production from the wells.…”