Identification of magnetic minerals related to hydrocarbon authigenesis in venezuelan oil fields using an alternative decomposition of isothermal remanence curves |
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| Authors: | Milagrosa Aldana Vincenzo Costanzo-Álvarez Luis Gómez Carlos González Marisel Díaz Pedro Silva Myriam Rada |
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| Institution: | 1.Dpto. Ciencias de la Tierra,Universidad Simón Bolívar,Caracas,Venezuela;2.Coordinación de Ingeniería Geofísica,Universidad Simón Bolívar,Caracas,Venezuela;3.Centro de Física,Instituto Venezolano de Investigaciones Científicas IVIC,Caracas,Venezuela |
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| Abstract: | 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 H2S
at shallow levels, might allow the formation of secondary Fe-sulphides. |
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