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•Natural samples of different maturation from Vaca Muerta formation are studied.•They are compared with kerogens of obtained by closed non-hydrous pyrolysis.•Evolution of molecular ...structure of both sets are followed by 13CNMR, XPS and FTIR.•Most structural parameters showed an excellent correlation between sets.•Differences in the branched content and heteroatoms speciation have been found.
Artificial maturation of kerogen is a widely used technique to assess the hydrocarbon potential of shale rocks and to observe thermal transformations of organic matter in the laboratory. However, the degree of reproducibility of natural geological transformation at the molecular level is still not fully established. In the present work, a set of kerogens isolated from Vaca Muerta Formation core samples at varying levels of thermal maturity were studied. Another set of samples was obtained by anhydrous pyrolysis of kerogen in a closed system. Molecular structures measured by solid-state techniques (13C NMR, XPS and FTIR) were compared in natural and artificially matured samples at equivalent levels of thermal maturation. We observed that heating in an anhydrous closed system accurately reproduces most of the molecular structural changes observed during natural thermal maturation, with exceptions related to the branching degree and oxygen containing groups. The evolution of some parameters, such as N and S content, are highly variable in the natural samples because of differences in their deposition environments. In these cases, artificial thermal maturation changes are smaller and follow more clearly defined trends because variables other than thermal changes are not present. This is the first work comparing natural and artificial thermal maturation in the Vaca Muerta Formation and add valuable data regarding the limitation of artificial maturation that can be extrapolated to other formations.
•Rocks and kerogens from Vaca Muerta formation are studied by NMR and XPS.•Analysis is focused on the speciation of carbon, oxygen, nitrogen and sulphur.•Differences of aromaticity obtained by both ...techniques are related to C-O content.•Results are compared with programmed pyrolysis and solid bitumen reflectance.•Changes of nitrogen and sulphur content with maturity are discussed.
The Vaca Muerta Formation, located in the Neuquén.
Basin (Argentina), is one of the most important shale plays in the world. A detailed structural characterization of the formation and evolution of the organic matter during maturation is a must for the correct evaluation of the petroleum potential. The present work studied the molecular characteristics of the organic matter of samples from several wells within the formation. Speciation of organic carbon, oxygen, nitrogen and sulfur present in the rocks was analyzed by XPS and 13C solid-state NMR spectroscopy and compared to data from more typical geochemical analyses, including pyrolysis and solid bitumen reflectance. Samples present with high TOC and cover a wide range of maturity levels (%BRo between 0.7 and 1.6%). Differences in carbon aromaticity measured by 13C NMR and XPS are discussed. Carbon, nitrogen, and sulfur present in organic isolates were studied and compared to reported data for several other shale formations (Duvernay, Bakken, Woodford and from the Bohai Bay Basin). The results are a novel contribution to the understanding and modeling of organic matter in the Vaca Muerta Formation and can be used to support and improve the classification of kerogens based on their molecular structures.
One of the key parameters in assessing the production potential of unconventional oil and gas reservoirs is the quantification of organic matter, which is generally determined by pyrolysis. ...Laboratory nuclear magnetic resonance (NMR) is widely used in the oil industry; being a nondestructive method, it enables the possibility to perform several analyses on the same sample, which is desirable due to the heterogeneity of these types of geological formations. 13C spectra provide much information, from speciation to maturity determination. The main drawback of this technique is the inherently low signal obtained for these nuclei, rendering extremely long experimental times. A solution is using cross-polarization schemes that transfer the high polarization of nearby 1H nuclei to 13C ones, with the penalty that quantification is a priori not feasible. In this work, we analyze the cross-polarization evolution and conclude that quantifying the total organic content (TOC) is possible for a wide range of organic matter content and maturities for rock samples corresponding to the Neuquén and Cuyo basins in Argentina.
The trophic state is usually defined by the concentrations of total phosphorous and chlorophyll a. Besides the input of nutrients from catchment, the internal process can modify the trophic state in ...reservoirs and lakes. Embalse Río Tercero is a multipurpose reservoir that has been object of a limnological study since 1996, as a requirement of the Nuclear Power Plant that uses the water for cooling. Invasive species have been reported in this reservoir: the mussel Limnoperna fortunei Dunker 1857, since 1996 and the dinoflagellate Ceratium hirundinella (O.F.Müller) Dujardin 1841, since 1999. As a result of their successful colonization, some characteristics of water quality and plankton composition have been modified. Despite this, during a long time period, the trophic state has not been modified. However, since 2013 noticeable increases in phosphorous and clorophyll a have been detected, and C. hirundinella reached exceptional abundances and became the dominant algae. Coincidentally, L. fortunei almost disappeared without any apparent reason. We intended to interpret the long-term tendencies of main trophic variables, and hypothesized some explanations for the population changes of C. hirundinella.
Alternative sources of neutron production other than nuclear fission reactions are important priorities in medical and nuclear applications due to costs, safety and ease of operation. In this work,
...12
C
and
13
C
thick targets for neutron production through
12
C(d,n)
13
N
and
13
C(d,n)
14
N
, respectively, have been manufactured and characterized by different techniques. In order to evaluate the irradiation effects on these materials, the targets were irradiated with 150 keV proton beam. A complete characterization of these samples was performed using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, Auger electron spectroscopy, X-ray photoemission spectroscopy and Raman spectroscopy. The results of these studies allowed us to establish that even though the irradiated samples present microstructural and chemical structure changes on its surface, the
12
C
and
13
C
thick targets were stable and would maintain their performance after proton irradiation at a fluence of
2.0
×
10
18
ions/cm
2
and
3.7
×
10
18
ions/cm
2
, respectively.
Graphical abstract
Alternative sources of neutron production other than nuclear fission reactions are important priorities in medical and nuclear applications due to costs, safety and ease of operation. In this work, ...Formula omitted and Formula omitted thick targets for neutron production through Formula omitted and Formula omitted, respectively, have been manufactured and characterized by different techniques. In order to evaluate the irradiation effects on these materials, the targets were irradiated with 150 keV proton beam. A complete characterization of these samples was performed using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, Auger electron spectroscopy, X-ray photoemission spectroscopy and Raman spectroscopy. The results of these studies allowed us to establish that even though the irradiated samples present microstructural and chemical structure changes on its surface, the Formula omitted and Formula omitted thick targets were stable and would maintain their performance after proton irradiation at a fluence of Formula omitted and Formula omitted, respectively.
