Overview of Asphaltene Nanostructures and Thermodynamic Applications

Abstract

Previously, asphaltene science had been hindered by many significant uncertainties regarding molecular weight, molecular structure, and nanocolloidal characteristics in laboratory solvents and crude oils. These debates were of sufficient magnitude to forestall development and utility of asphaltene modeling for various applications. In the last 2 decades, advances in asphaltene science using many sophisticated techniques have greatly reduced corresponding uncertainties, enabling development of simple asphaltene models for a variety of applications. Here, we provide an overview of key findings in asphaltene science; dominant molecular and nanocolloidal structures are described. These structures with simple thermodynamic formalisms are shown to work well in oilfield reservoirs, specifically including light oils, black oils, and heavy oils. This novel thermodynamic approach using asphaltene nanostructures has enabled characterization of different processes that impact or preclude equilibration of reservoir fluids in geologic time. These processes combine to form the new technical discipline, "reservoir fluid geodynamics", that has proven value in many reservoir studies. In addition, these asphaltene nanostructures are shown to apply to interfacial tension of asphaltene solutions, using simple thermodynamics for surfaces. In addition, we contrast past and current debates in asphaltene science, especially regarding asphaltene molecular architecture, which has been largely resolved. Molecular structural characterization of asphaltenes reviewed herein shows that asphaltenes are dominated by island structures, but some asphaltenes also have a secondary content of structures with an "aryl-linked core", which we propose as a third class of molecular architecture along with island and archipelago designations. The aryl-linked core structure is defined as having a single, contiguous sp 2 -hybridized carbon network containing one or more aryl linkages, in which adjacent aromatic rings are directly bonded together but do not share a common bond in a ring. In contrast, a traditional island structure also has a single, contiguous sp 2 -hybridized carbon network but has adjacent aromatic rings exclusively fused (sharing a common bond in a ring) with no aryl linkages. The definition of archipelago remains unchanged and consists of multiple, discontinuous sp 2 -hybridized carbon networks, in which these different aromatic ring systems are connected by one or more sp 3 -hybridized carbons. This new classification, "aryl-linked core", has been assigned to both island and archipelago structures in different publications; thus, this new designation should reduce confusion and help resolve structure− function relations, especially regarding aggregation and reactivity. More broadly, the advances in asphaltene science have ushered in powerful, new applications that are continuing to expand.

Imaging Titan’s Organic Haze at Atomic Scale

“…This approximate size window is a result of the preparation method used. The molecules are sublimed by resistive flash heating from a piece of oxidized silicon wafer in ultra-high vacuum (UHV) (Schuler et al 2015(Schuler et al , 2020 onto the sample held at T = 10 K. Some of the small molecules (about two rings and less) are too volatile and thus might leave the wafer before the evaporation step. On the other side, large molecules (about 20 rings and more) tend to fragment before their sublimation.…”

Molecular Dynamics Analysis on Hydrogenation Process of Asphaltene Aggregate for Medium and Low Temperature Coal Tar

“…At present, it is considered that the molecular structure unit models of asphaltenes are mainly "group island type", "continental type" and "mixed type" (Fernando et al 2013). Schuler et al (2015Schuler et al ( , 2017Schuler et al ( , 2020) demonstrated the first direct observation of wide diversity of asphaltene molecular motifs with peri-and cata-condensed polycyclic aromatic hydrocarbons (PAHs). Various types of coal-derived asphaltene structures were obtained by the atomic force microscopy.…”

Analysis of Xinjiang asphaltenes using high precision spectroscopy

“…These breakthroughs have to a great extent provided answers as well as providing evidence to earlier debates on molecular weight and structural models of asphaltenes. [13][14][15][16] It's now generally accepted that "island" or "aryl linked core" models are more representative of asphaltenes whereas the archipelago model has been either redened or has been neglected entirely. 13 With this new information coming to light; in this paper we combine this microscopy information with results obtained using renown spectroscopic methods to characterize and assign chemical structures to these asphaltenes.…”

“…[13][14][15][16] It's now generally accepted that "island" or "aryl linked core" models are more representative of asphaltenes whereas the archipelago model has been either redened or has been neglected entirely. 13 With this new information coming to light; in this paper we combine this microscopy information with results obtained using renown spectroscopic methods to characterize and assign chemical structures to these asphaltenes. Various studies in the past have shown that these methods can be used to effectively characterize asphaltenes although did not answer the questions on the type of model.…”

“…Various studies in the past have shown that these methods can be used to effectively characterize asphaltenes although did not answer the questions on the type of model. 13,14 ESI FT ICR MS mass spectrometry This is an ionization technique that involves electrospray ionization coupled with Fourier transform-ion cyclotron mass spectroscopy (ESI FT-ICR MS). [17][18][19][20][21][22] Xinjiang oil contains considerable amounts of heteroatoms, 2 thus their analysis is warranted.…”