Toward Molecule-Specific Geochemistry of Heavy Ends: Application to the Upstream Oil Industry

Abstract

Detailed molecular analysis of the composition of petroleum is typically performed on only the light (volatile) fraction, using analyses involving gas chromatography (GC). Heavier (nonvolatile) components such as kerogen, bitumen, and asphaltenes, which are relevant to conventional reservoirs and particularly to unconventional gas shale and tight oil formations, are not amenable to analysis by GC and instead are typically studied by more phenomenological techniques. This report describes a suite of analytical techniques that can provide sufficient average molecular information on the heavy ends (defined as the nonvolatile fraction) to be useful for a variety of industrial applications, expanding the discipline of molecule-specific geochemistry into the non-GC amenable fractions of petroleum materials. Heavy ends are composed of the elements C, H, N, S, and O, and the bonding environments of each can be measured by various solid state spectroscopies: nuclear magnetic resonance (NMR) and infrared (IR) spectroscopies for C, H, and O; X-ray absorption near-edge structure (XANES) spectroscopy for S and N. Additionally, advances in mass spectrometry, including techniques such as laser desorption laser ionization mass spectrometry (L 2 MS), can be used to measure the molecular weight and dominant molecular architecture of asphaltenes. Moreover, higher-order structures can be measured: samples of kerogen with representative pore geometry can be prepared, and those pore systems are analyzed with techniques such as X-ray diffraction and neutron scattering. Colloidal structures of asphaltenes can be measured with a variety of techniques, which reveal a hierarchical aggregation structure. These analyses provide sufficient structural data to enable structure−property and structure− function relationships to be determined, which can be applied to the characterization of conventional and unconventional resources. In gas shale and tight oil formations, which contain abundant inorganic minerals as well as kerogen, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is used for simultaneous analysis of mineralogy, kerogen content, and maturity, typically performed at the wellsite. In conventional reservoirs, spatial variations in the asphaltene concentration measured by downhole fluid analysis logging tools are being interpreted with a recently developed equation of state to address upstream issues such as reservoir connectivity, tar mat formation, and fault block migration. As more heavy end analyses are developed, further scientific knowledge and industrial applications of heavy end geochemistry are anticipated.

Chemical, Molecular, and Microstructural Evolution of Kerogen during Thermal Maturation: Case Study from the Woodford Shale of Oklahoma

“…Raman spectroscopy − and 13 C NMR − are two techniques capable of probing the bonding environment of carbon comprising aliphatic and aromatic moieties, as well as their absolute abundance. Advanced 13 C NMR spectral acquisition and editing techniques now offer discrimination and quantification of specific C, CH, CH 2 , and CH 3 functional groups including their connectivity or proximity, from which parameters such as the average carbon number of aromatic clusters and of aliphatic chains can be estimated. ,, Infrared spectroscopy can routinely identify functions associated with C, H, and O, including aromatic CC and CH, aliphatic CH, CH 2 , and CH 3 , and oxygenated C–O and CO groups. ,,− Quantitative analysis of organic sulfur and nitrogen species is now established using sulfur- and nitrogen-XANES. ,− Solid-state XPS is capable of quantifying several functionalities in carbonaceous materials associated with carbon, oxygen, sulfur, and nitrogen. ,,− A recent review of several of these techniques and their applications in the analysis of kerogen and other complex carbonaceous materials is given by Pomerantz . Separately, methods such as scanning electron microscopy, − gas adsorption,…”

Structure-Solubility Relationships in Coal, Petroleum, and Immature Source-Rock-Derived Asphaltenes

“…This technique has been described previously and is summarized here . IR spectroscopy has been used to measure the composition of nonvolatile hydrocarbon mixtures such as soils and sediments, coals, − kerogens, ,− bitumens , asphalts, and asphaltenes. ,,, Numerous functional groups can be identified and quantified, including aliphatic CH, CH 2 , and CH 3 ; aromatic CH and CC; and oxygenated functionalities such as carboxyl, quinone, aldehyde, ketone, and ester. , The IR spectra were acquired on splits of the isolated asphaltenes prepared as KBr pellets. With this sample preparation, the mass ratio of sample and KBr matrix is controlled, yielding IR spectra that can be interpreted quantitatively according to the Beer–Lambert Law .…”

“…This technique has been described previously and is summarized here. 4 IR spectroscopy has been used to measure the composition of nonvolatile hydrocarbon mixtures such as soils and sediments, 53 coals, 54−57 kerogens, 33,58−60 bitumens 33,61 asphalts, 62 and asphaltenes. 4,59,63,64 Numerous functional groups can be identified and quantified, including aliphatic CH, CH 2 , and CH 3 ; aromatic CH and CC; and oxygenated functionalities such as carboxyl, quinone, aldehyde, ketone, and ester.…”

Fourier-Transform Infrared Proxies for Oil Source and Maturity: Insights from the Early Permian Alkaline Lacustrine System, Junggar Basin (NW China)

“…In this study, we chose the diffuse reflectance infrared fourier transform (DRIFT) mode of FTIR spectroscopy to analyze oil samples. This method has been widely used to analyze crude oil samples. , Compared to the attenuated total reflectance and transmission modes, the DRIFT mode requires simpler sample preparation and the resulting DRIFT spectra are similar to those obtained by the transmission FTIR technique. , Therefore, the DRIFT mode was used.…”