Magmatic events and sour crude oils in the Malargüe area of the Neuquén Basin, Argentina

Alberdi-Genolet, M.; Cavallaro, Adriana Noemi; Hernández, Norma Davila; Crosta, D.; Martı́nez, Luis

doi:10.1016/j.marpetgeo.2012.11.005

Cited by 11 publications

(7 citation statements)

References 21 publications

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“…This probably led to the generation of hydraulic fractures filled by bitumen and calcite (beef). It could be consistent with the study of Alberdi-Genolet et al (2013), who demonstrated a link between Tertiary volcanic activity and a pulse of hydrocarbon generation. However, we would admit that the presence of evaporite layers might have enhanced the overpressure and retained the hydrocarbons within the source rock.…”

Section: Discussionsupporting

confidence: 91%

Geological evidence for fluid overpressure, hydraulic fracturing and strong heating during maturation and migration of hydrocarbons in Mesozoic rocks of the northern Neuquén Basin, Mendoza Province, Argentina

Zanella

Cobbold

Ruffet

et al. 2015

Journal of South American Earth Sciences

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International audienceIn the northern Neuquén Basin of Argentina (especially in Mendoza Province), there is strong geological evidence for fluid overpressure in the past. The evidence takes the form of bitumen veins and bedding-parallel veins of fibrous calcite ('beef'). Such veins are widespread in the fold-and-thrust belt of the Malargűe area, where bitumen mining has been active for a century or so. So as to collect information on the development of fluid overpressure in this part of the Neuquén Basin, several old mines were visited and studied in the Malargűe area. Here the bitumen veins have intruded mainly the Late Jurassic to Early Cretaceous Mendoza Group, but also the Late Cretaceous Neuquén Group. The veins have the forms of bedding-parallel sills or dykes and they are especially thick within anticlines, forming saddle-reefs in several places. Beef veins are also numerous in the Malargűe area. They contain bitumen and therefore seem to have formed at the same time as the bitumen veins. Near many outcrops of bitumen and beef, we have found fine-grained volcanic intrusive bodies. The best examples are from the La Valenciana syncline. According to 39 Ar-40 Ar dating, these bodies are mainly of Mid-Miocene age. More generally, volcanism, deformation and maturation of source rocks seem to have reached a climax in Miocene times, when the subducting Pacific slab became relatively flat

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Section: Discussionsupporting

confidence: 91%

Geological evidence for fluid overpressure, hydraulic fracturing and strong heating during maturation and migration of hydrocarbons in Mesozoic rocks of the northern Neuquén Basin, Mendoza Province, Argentina

Zanella

Cobbold

Ruffet

et al. 2015

Journal of South American Earth Sciences

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“…As, for example, biochemical sulfate reduction (BSR) needs sulfate and sulfate-reducing bacteria in environments with temperatures lower than ≈ 60 to 80 °C 3 , thermal cracking of kerogen (especially type II-S), magmatic sources and possibly thermal alteration of oils 4,5,6 . Because H 2 S is a powerful poison and has great capacity for increasing corrosion, its presence can bring significant health and economic impacts for petroleum exploration and production.…”

Section: Introductionsupporting

confidence: 74%

H2S Risk in Presalt Reservoirs

et al. 2013

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Petroleum exploration in presalt reservoirs is reaching increasingly deeper carbonate reservoirs, more and more distant from coastline. Therefore, optimization of investments for a safe and profitable production is critical. Each possible concern on geological conditions that would govern fluid composition and that can bring impact in development cost of an accumulation must be taken into account. In some petroleum accumulations, within presalt reservoirs, along southeastern offshore Brazilian basins, H 2 S was found. Although H 2 S concentrations were significantly lower than most of carbonates worldwide, they are enough to be considered in economical evaluations. Therefore, it is important to identify the process that generated H 2 S and to constraint the main variables that govern its occurrence for a more precise evaluation of the "H 2 S risk", take into consideration possible pit falls during well intervention. In this way, H 2 S is precipitated on site as a salt (Ag 2 S) from the gas produced during the long lasting producing tests, shipped to laboratory and the 34 S/ 32 S ratio is measured. The corresponding δ 34 S value is the main tool for identifying H 2 S origin: if it was formed due to organic (BSR, δ 34 S < −10 ‰) or inorganic (TSR, δ 34 S > +10 ‰) sulfate reduction. Results of δ 34 S CDT obtained in H 2 S from presalt reservoirs of the Santos Basin spread between +10 ‰ and +20 ‰ typical of TSR. However, temperatures of the reservoirs are lower than that inferred for development of TSR (T > ≈120 °C) suggesting that H 2 S was generated in deeper intervals with significantly higher temperatures. More accuracy in the interpretation about the origin, and clues on migration pathways and accumulation are obtained integrating geochemical, geological and well data production. This integrated approach gives to the explorationist the best understanding about the "H 2 S risk" in a specific exploratory target. In this work it will be presented a discussion on the methodology for sampling and measuring δ 34 S for identification of H 2 S origin.

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“…In some thin sections, pyrite abundance exceeds 15% of the bulk mineral composition (Figure ). Furthermore, other types of sulphurs, such as marcasite and pyrrhotite, have also been reported in the intrusions and their host rock in the RGV (Alberdi‐Genolet, Cavallaro, Hernandez, Crosta, & Martinez, ). Pyrite exhibits excellent electrical conductivity, which is usually comparable to, or even higher than, the conductivity of the formation water.…”

Section: Interpretation and Discussionmentioning

confidence: 98%

“…In the RGV oil field, Alberdi‐Genolet et al () argue that the growth of pyrite‐dominated sulphide aggregates in the igneous reservoirs can be associated with different processes, such as replacement of ferromagnesian minerals by reaction with free H 2 S (water soluble), cubic pyrite, typically of volcanic origin, pyrite filling secondary pores, indicating that free H 2 S (water soluble) reacted with soluble iron, framboidal aggregates associated with organic matter that can be interpreted as the precipitation of water‐soluble sulphates that were present in sedimentary connate waters after igneous intrusion and fracturing. In addition, Alberdi‐Genolet et al () proposed that H 2 S in the magmatic fluid reacts with zinc in hydrothermal fluids and iron in ferromagnesian minerals to produce pyrite and marcasite. This mechanism could be the main cause for massive sulphide mineralization in the CLRsZ, when intrusions are emplaced in organic‐rich formations.…”

Section: Interpretation and Discussionmentioning

confidence: 99%

Low resistivity zones at contacts of igneous intrusions emplaced in organic‐rich formations and their implications on fluid flow and petroleum systems: A case study in the northern Neuquén Basin, Argentina

Spacapan¹,

́Odorico²,

Palma³

et al. 2019

Basin Research

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Igneous sills and laccoliths emplaced in sedimentary basins may significantly impact petroleum systems, both positively and negatively. Igneous intrusions provide heat to maturate regionally immature organic-rich host rocks, act as fractured reservoirs hosting commercial accumulations of hydrocarbons, and form structures affecting fluid flow and trapping at different scales. Nevertheless, the petrophysical implications of igneous intrusions on their host rock are poorly known. In this study, we analyse 200 wells in the Río Grande Valley oil field, Neuquén basin, Argentina, where the main reservoirs are in fractured igneous sills. This dataset represents a globally unique possibility to characterize the igneous-host rock interaction using both wireline logs and core material. We identify a systematic Contact Low Resistivity Zone (CLRsZ) at both the upper and lower contacts of the sills emplaced in the organicrich Vaca Muerta and Agrio Formations. We characterize the nature of these CLRsZ and their petrophysical properties by integrating resistivity and gamma ray well logs, petrographic analyses, petrophysical tests and geochemical analyses. The low resistivity signal of the CLRsZ is dominantly carried by massive-sulphide deposits, mainly pyrite, observed both in the host rock and the chilled margin of the sills. Well log images and porosity-permeability analysis on core plugs show that both the sills and their associated CLRsZ can act as carrier for fluid flow and reservoir for hydrocarbons storage. The thickness of the upper and lower CLRsZ correlates linearly with the thickness of the sill, and the volume of both the upper and lower CLRsZ represents ca. 40% with respect to the volume of their associated sill. The thickness of the CLRsZ represents ca. 13% of the thickness of contact aureole induced by the sills. In the CLRsZ, a great proportion of kerogen was transformed to hydrocarbon, so that CLRsZ were restricted to the innermost contact aureole of the sills. Our results show that the CLRsZ can have major implications on fluid flow and should be considered in reservoir models in volcanic basins hosting sills emplaced in organic-rich formations. 4 | EAGE SPACAPAN et Al.

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Magmatic events and sour crude oils in the Malargüe area of the Neuquén Basin, Argentina

Cited by 11 publications

References 21 publications

Geological evidence for fluid overpressure, hydraulic fracturing and strong heating during maturation and migration of hydrocarbons in Mesozoic rocks of the northern Neuquén Basin, Mendoza Province, Argentina

Geological evidence for fluid overpressure, hydraulic fracturing and strong heating during maturation and migration of hydrocarbons in Mesozoic rocks of the northern Neuquén Basin, Mendoza Province, Argentina

H2S Risk in Presalt Reservoirs

Low resistivity zones at contacts of igneous intrusions emplaced in organic‐rich formations and their implications on fluid flow and petroleum systems: A case study in the northern Neuquén Basin, Argentina

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