doctoralThesis
Silicificação hidrotermal ao longo de falhas em unidades carbonáticas e siliciclásticas e seu impacto na qualidade dos reservatórios, bacia potiguar, Brasil
Fecha
2019-07-15Registro en:
MENEZES, Cristiane Paulino de. Silicificação hidrotermal ao longo de falhas em unidades carbonáticas e siliciclásticas e seu impacto na qualidade dos reservatórios, bacia potiguar, Brasil. 2019. 62f. Tese (Doutorado em Ciência e Engenharia de Petróleo) - Centro de Ciências Exatas e da Terra, Universidade Federal do Rio Grande do Norte, Natal, 2019.
Autor
Menezes, Cristiane Paulino de
Resumen
We analyzed hydrothermal silicification along the Afonso Bezerra strike-slip
fault system in the Potiguar Basin, equatorial margin of Brazil, to assess the role
of Si-rich fluids in fault geometry, properties, and evolution. The fault cut across
the whole basin, including its crystalline basement, a late Cretaceous siliciclastic
unit and a lower carbonate unit, and a Paleogene-Neogene upper carbonate unit.
Intense fault-controlled silicification caused by the upward migration and diffusion
of hydrothermal fluids occurred repeatedly. The fault zone is characterized by
multiple events of syntectonic (dynamic) silicification with hydraulic brecciation at
all scales in the fault core and static silicification, in which no or little lattice
orientation or deformation occurred in the damage zone. In the carbonate units,
silicification resulted in the complete replacement of the carbonate mineralogy by
quartz, chalcedony and opal, and the SiO2 content increased from 3 to 15% in
the host carbonate units to as much as 94–97% in the silicified portions of the
fault. The silicified fault zone presents an abrupt widening from 150 m in the
siliciclastic unit to as much as 800 m in the lower carbonate unit. The matrix of
the siliciclastic unit exhibits a porosity reduction from 27% to 4%. By contrast, the
matrix porosity of the lower carbonate unit exhibits a primary porosity of
approximately 5–10%, which is either reduced to ~ less than 1% or increased to
more than 15% in the silicified zone. In the upper and lower carbonate units,
centimeter-scale vuggy porosity along fractures occurs in the silicified zone. This
anomalous vuggy porosity could serve as a reservoir pore space. The collective
field and petrological evidence suggests that volcanic intrusion plays an important
role in silicification. This work may shed light on the origin and likely geometry of
the fault-controlled silica distribution causing heterogeneities within carbonate
and siliciclastic reservoirs.