Stress magnitude and orientation in the Potiguar Basin, Brazil: Implications on faulting style and reactivation

Abstract

[1] We analyzed borehole breakout data and drilling-induced tensile fractures derived from resistivity image logs run at 10 oil wells to derive the orientation of the maximum horizontal stress S Hmax from the Potiguar Basin in the continental margin of Brazil. Stress magnitudes are derived from density logs for the vertical stress, mini-frac tests for the minimum horizontal stress S hmin , and rock strength laboratory analysis to estimate the S Hmax magnitudes. We compared these results with the stress regime and S Hmax orientation derived from nine earthquake series located in the crystalline basement, where seismicity is concentrated, and previous breakout data from the basin. In the basin, the S Hmax gradient is 20.0 MPa/km, and the S Hmax /S hmin ratio is 1.154, indicating a normal tectonic stress regime from 0.5 to 2.0 km, whereas the S Hmax gradient of 24.5 MPa/km and S Hmax /S hmin ratio of 1.396 indicate a transition from a normal to strike-slip stress regime at 2.5 to 4.0 km. The deeper stress regime in the basin is similar to that in the basement at 1-12 km depth. This transition of the tectonic stress regime is consistent with an incipient tectonic inversion in the basin. We note that the S Hmax orientation rotates from NW-SE in the western part of the Potiguar Basin to E-W in its central and eastern parts, roughly following the shoreline geometry, indicating that local features such as flexural stresses influence the local (scale < 100 km) stress pattern. We also conclude that the basement is critically stressed, but not the basin.

The impact of different aperture distribution models and critical stress criteria on equivalent permeability in fractured rocks

“…Five data sets were obtained from carbonate pavements located in Brazil, which we refer to as "Brazil I" to "Brazil V" . These pavements are part of a subhorizontal postrift carbonate sequence (the Albian Jandaíra Formation), deposited in the Potiguar basin in northeast Brazil [Reis et al, 2013]. Although these pavements are located in the same structural domain, they display fracture networks with different spatial distributions.…”

Some remarks on the earthquakes of Fennoscandia: A conceptual seismological model drawn from the perspective of hyperextension

“…We thus cast our eyes briefly towards the southeast margin of Brasil, where both the concepts of hyperextension (Zalán et al, 2011) and a strikingly similar seismological model (Assumpção et al, 2011) have recently been proposed. Lima et al (1997) suggested that offshore sediment loading on the continental shelf can produce the coast-parallel Sh max observed in borehole breakouts from the onshore parts of many marginal basins (see Reis et al, 2013). Lima et al (1997) also proposed that local sources of stress at the eastern continental margin may have been underestimated in the theoretical stress models of the South American plate.…”

The role of tectonics in the late Quaternary evolution of Brazil's Amazonian landscape

“…During this latest evolution, both the eastern and equatorial passive margins of the South American plate were under compression and strike−slip deformation (Ferreira et al, 2008;Reis et al, 2013). This stress regime is still effective at the present time (Bezerra et al, 2014).…”