Contradictory magnetic polarities in sediments and variable timing of neoformation of authigenic greigite

Jiang, Wei Teh; Horng, Chorng Shern; Roberts, Andrew; Peacor, Donald R.

doi:10.1016/s0012-821x(01)00497-6

Cited by 106 publications

(138 citation statements)

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“…Framboidal aggregates of greigite of authigenic origin, linked to hydrocarbon activity, have been previously reported by Jiang et al (2001). Post-depositional greigite and pyrrhotite, related to hydrocarbon microseepage, have been also detected over oil fields (e.g.…”

Section: Resultsmentioning

confidence: 60%

“…Different mechanisms have been proposed for hydrocarbon-related generation of sulphides. Jiang et al (2001) argue about the neoformation of greigite after pyrite formation, apparently related to a change in the physical chemical conditions possible induced by hydrocarbon migration. In this case, the initial formation of pyrite is favored by the presence of high concentrations of dissolved sulphide species with Fe available from reactive iron oxides.…”

Section: Resultsmentioning

confidence: 99%

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Identification of magnetic minerals related to hydrocarbon authigenesis in venezuelan oil fields using an alternative decomposition of isothermal remanence curves

et al. 2011

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In this work we try to better characterise the shallow magnetic signature of hydrocarbon microseepage in oil fields from eastern and western Venezuela. To get a better insight of the processes involved, we attempt to find out the main magnetic phases responsible for the observed oil-related shallow magnetic anomalies. In this way, a new and alternative numerical approach to decompose Isothermal Remagnetization (IRM) curves is introduced. The method is based on a Direct Signal Analysis (DSA) of the IRM curve in order to identify the number and type of magnetic components. Representative wells from western (La Victoria) and eastern (San Joaquín) Venezuelan fields are studied. The DSA approach, together with rock magnetic experimental results, indicates that in the well from western Venezuela the main magnetic mineralogy associated to hydrocarbon microseepage is magnetite. Conversely, in the well from eastern Venezuela, these MS anomalies are mainly caused by the presence of Fe-sulphides (i.e. greigite). These results support the hypothesis of two different authigenic processes. For the well at the western field, we propose that a net electron transfer from the organic matter, degraded by hydrocarbon gas leakage, should occur precipitating Fe(II) magnetic minerals (e.g. magnetite). On the other hand, in the well of the eastern field, high concentrations of H 2 S at shallow levels, might allow the formation of secondary Fe-sulphides.

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Section: Resultsmentioning

confidence: 60%

Section: Resultsmentioning

confidence: 99%

Identification of magnetic minerals related to hydrocarbon authigenesis in venezuelan oil fields using an alternative decomposition of isothermal remanence curves

et al. 2011

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“…Thus, preservation of intermediate magnetic iron sulphides like greigite, which did not transform completely into pyrite, can be related to an abundance of reactive iron relative to more limited production of dissolved sulphide (e.g., Kao et al, 2004). Third, slow reaction of more refractory iron-bearing phyllosilicate minerals with pore water sulphide over long periods of time can give rise to slow but continuous iron sulphide formation, which can have important consequences for authigenic magnetic mineral formation and for the paleomagnetic record of sediments (e.g., Jiang et al, 2001;Roberts and Weaver, 2005).…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Magnetic mineral diagenesis

Roberts

2015

Earth-Science Reviews

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313

347

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“…Framboidal aggregates of Fe-sulfides of authigenic origin, linked to hydrocarbon activity, were previously reported by Jiang et al (2001). Post-depositional greigite and pyrrhotite, related to hydrocarbon microseepage, have been also detected over oil fields (e.g.…”

Section: 2 O I L W E L Lmentioning

confidence: 53%

“…Different mechanisms have been proposed for hydrocarbon-related generation of sulfides. Jiang et al (2001) argue about the neo formation of Fe-sulfides after pyrite formation, apparently related to a change in the physical chemical conditions. In this case, the initial formation of pyrite is favored by the presence of high concentrations of dissolved sulfide species with available Fe from reactive iron oxides.…”

Section: 2 O I L W E L Lmentioning

confidence: 99%

Study of magnetic contrasts applied to hydrocarbon exploration in the Maturín Sub-Basin (eastern Venezuela)

et al. 2011

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We have studied near-surface magnetic contrasts in nine oil wells from an oil prospective area in eastern Venezuela (compressive deformation front of the northeastern Maturín Sub-Basin). Samples are drill cuttings taken at intervals of about 15 m within approximately the first 1200 m of most of these wells. Rock magnetic experiments, electron paramagnetic resonance (EPR), extractable organic matter (EOM), X-ray diffraction and scanning electron microscopy (SEM) are used to discriminate between two anomalies in magnetic susceptibility (MS), related to either a reducing environment caused by the underlying reservoir (Type A), or to primary lithological contrasts (Type B). Contour maps of MS, S-ratio and organic-matter-free radical concentrations (OMFRC), for the A-like depth levels, show a major central zone of anomalous high values. This area is probably associated with either maximum accumulation of hydrocarbons in the reservoir or with their southerly migration from the northern petroleum source towards the deformation front. We argue that such a result could be used, for future exploration and production ventures in the region, as a preliminary characterization of the reservoir. We also show in a Day plot, that saturation remanencesaturation magnetization ratio (M rs /M s ) and coercivity of remanence -coercive force ratio (H cr /H c ) stand as additional criteria to discriminate between these two types of magnetic contrasts. In fact, for the area of study, hysteresis ratios show three distinct trends corresponding to samples from A-like, B-like and non-anomalous depth levels.

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Contradictory magnetic polarities in sediments and variable timing of neoformation of authigenic greigite

Cited by 106 publications

References 32 publications

Identification of magnetic minerals related to hydrocarbon authigenesis in venezuelan oil fields using an alternative decomposition of isothermal remanence curves

Identification of magnetic minerals related to hydrocarbon authigenesis in venezuelan oil fields using an alternative decomposition of isothermal remanence curves

Magnetic mineral diagenesis

Study of magnetic contrasts applied to hydrocarbon exploration in the Maturín Sub-Basin (eastern Venezuela)

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