EFFECTS OF HYDROCARBON-INDUCED DIAGENESIS ON THE MAGNETIC SIGNATURE OF AN OIL WELL IN THE NORTHERN NEUQUÉN BASIN (VACA MUERTA FORMATION, SW ARGENTINA)

IGLESIA LLANOS, MARÍA PAULA; DIAZ, M; ALDANA, MILAGROSA; RAPALINI, AUGUSTO E.; WALTHER, ANA MARÍA; LUPPO, TOMÁS; COSTANZO-ALVAREZ, VINCENZO

Querétaro

Congreso; LatinMag 2017; 2017

Asociación Latinoamericana de Paleomagnetismo y Geomagnetismo

A rock magnetism and electronic paramagnetic resonance (EPR) combined study was performed in samplesfrom an oil well drilled in the Vaca Muerta Formation (northern Neuquén Basin, SW Argentina). The aimof this work was to characterize the diagenetic processes involved in the origin of the magnetic mineralogypresent in hydrocarbon-impregnated rocks. The primary magnetic minerals were affected by diagenesisdue to a little-biodegraded crude oil, with low to medium sulfur content. A first reducing stage probablydissolved such minerals, forming pyrite and siderite. Consequently, some depth intervals along the coreshow a decrease of the magnetic signature in inverse relation to the concentrations of extractable organicmatter (EOM) and organic matter free radicals (OMFR). On the other hand, for a specific section of the core,that appears to be a lithological microtrap, a second diagenetic stage reduced pyrite to framboidal authigenicpyrrhotite, increasing the magnetic signature in direct proportion to the EOM and to the OMFR content.This ?microtrap? seems to be framed by two small peaks of Mn2+, a proxy of the calcareous cementation,the porosity and the permeability of these rocks. Indeed, in the rest of the samples, the M2+ content showsnegative correlations with the EOM and the OMFR, and positive correlations with the magnetic parameters.Hence, the negative correlations between magnetic properties and both, the EOM and the OMFR, suggestthat, with lower porosity and/or permeability, there is less hydrocarbons infiltration and, consequently, lowerdiagenetic destruction of the primary magnetic signature