Dissertação
Caracterização multiescalar e modelagem geológica de carbonatos neoproterozoicos da Formação Lagoa do Jacaré, Grupo Bambuí, na pedreira GMD - Paraopeba - MG: uma contribuição à geologia de reservatório
Fecha
2020-05-11Autor
Alex Rodrigues de Freitas
Institución
Resumen
The present work features multiscale analysis of Neoproterozoic carbonate rocks
of Lagoa do Jacaré Formation (Bambuí Group) that outcrops in a deactivated
quarry in Paraopeba - MG. The Multiscale Reservoir Characterization
(CAMURES) methodology was partially applied, and it assumes as a premise the
characterization of analogue outcrops using different investigative tools, in
different scales of observation, ranging from basin scale, passing through
reservoir scale, until petrophysics microscale. The rocks in GMD quarry comprise
five sedimentary lithofacies: medium to fine grained massive calcarenites,
intraclastic breaches, fine calcarenites with asymmetric ripple marks, medium
grained calcarenites with hummocky cross-bedding, and finally, calcilutites and
siltstones (rares). Those lithofacies represent platform sedimentary environment,
in the shoreface-offshore transition. GPR (Ground Penetrating Radar) survey
revealed depositional geometries such as sigmoidal, hummocky and parallel
patterns. Petrographic analysis showed the presence of five carbonate
microfacies and one hybrid terrigenous-carbonate: ooidal intraclastic
grainstones, intraclastic grainstones, recrystallized grainstones, intraclastic
wackestones, mudstones and laminated siltstones. Depositional environment of
these rocks points to a deposition in a shallow marine carbonate platform, under
storm waves influence, as identified in many tempestite cycles in the quarry.
Structural analysis showed the presence of three fractures systems with principal
directions N-S, NE-SW and NW-SE, subvertical in general, cutting the huge
outcrop which present subhorizontal layers. Gamma-ray prospects allowed
laterally correlate the four profiles prospected in the base of the quarry, and
served as basis for a facies zoning that guided the 3D geological modelling of the
quarry outcrop. The modelling used a workflow that interpolate microfacies data
to define their spatial distribution and proportion along the entire outcrop. The
results showed the predominance of oolitic intraclastic grainstones with about
58% of presence, followed by intraclastic grainstones with about 15%, siltites with
13%, wackestones with 12% and recrystallized grainstones with 2%. Carbonate
lithofacies analysis, depositional architecture and geometry, in combination with
micropetrographic data in thin section and textures observed in Scanning
Electron Microscope (SEM), identified brittle structures, and modelled data suggests that the studied section of the Lagoa do Jacaré Formation in the GMD Quarry has a potential for a fractured non-conventional reservoir type.