The influence of subseismic-scale fracture interconnectivity on fluid flow in fracture corridors of the Brejões carbonate karst system, Brazil

The influence of subseismic-scale fracture interconnectivity on fluid flow in fracture corridors of the Brejões carbonate karst system, Brazil

Furtado, Carla P.Q. (Universidade Federal do Rio Grande do Norte)
Medeiros, Walter E. (Universidade Federal do Rio Grande do Norte; National Institute of Science and Technology of Petroleum Geophysics (INCT-GP/CNPq))
Borges, Sergio V. (Federal Institute of Education, Science and Technology of Rio Grande do Norte)
Lopes, Juliana A.G. (Universidade Federal do Rio Grande do Norte)
Bezerra, Francisco H.R. (Universidade Federal do Rio Grande do Norte)
Lima-Filho, Francisco P. (Universidade Federal do Rio Grande do Norte)
Maia, Rubson P. (Universidade Federal do Ceará)
Bertotti, G. (TU Delft Applied Geology)
Auler, Augusto S. (Instituto do Carste,Carste Ciencia e Meio Ambiente, Belo Horizonte)
Teixeira, Washington L.E. (Universidade Federal do Rio Grande do Norte)

2022

The present study used a multitool approach to characterize fractures of several orders of magnitude in large fracture corridors, caves, and canyons to investigate their impact on fluid flow in carbonate units. The study area is the Brejões carbonate karst system that is located in the Neoproterozoic Salitre Formation in the Irecê Basin, São Francisco Craton, Brazil. The approach included satellite imagery, used for interpreting the regional structural context, Unmanned Aerial Vehicle (UAV) and ground-based Light Detection And Ranging (LiDAR) imagery, used for detailed structural interpretation. Regional interpretation revealed that fracture corridors, caves and canyons occur along a N–S-oriented anticline hinge. An advanced stage of karstification caused fracture enlargement and intrabed dissolution, and the formation of caves and canyons. A river captured by the highly fractured zone along the anticline hinge played an important role as an erosive agent. Detailed characterization of fracture corridors comprised structural analysis, topological studies, persistence estimations, power-law fitting of fracture trace length distributions, and identification of network backbones. Our results indicate that fracture corridors comprise four subvertical fracture sets: N–S and E-W and a conjugate pair, NNE-SSW and NW-SE. Fractures observed in the caves show the same dominant directions. Fracture directions are consistent with a common origin associated with the anticline folding. Fracture traces range from 1.0 m to 300 m, comprising both subseismic (<50 m) and seismic scale fractures (>50 m). Networks have dominance of node terminations Y and X (notably Y), C_B values higher than 1.8, high P₂₀ and P₂₁ persistence values, and highly interconnected backbones. Fracture network connectivity is associated with power-law exponents greater than 2.5 for the fracture trace distributions, indicating large influence of subseismic-scale fractures on fluid flow. As the final result of folding and karstification, large volumes of secondary macroporosity were created, particularly in the zone of maximum fracture intensity around the hinge zone of the anticline. This scenario can be used to understand better oil reservoirs formed in similar structural controls in near-surface conditions.

Carbonate reservoirs
Carbonate rocks
Caves
Fracture corridors
Karst

http://resolver.tudelft.nl/uuid:7514afae-4569-42c5-acb3-3875d407686a

https://doi.org/10.1016/j.marpetgeo.2022.105689

2023-07-01

0264-8172

Marine and Petroleum Geology, 141, 1-21

Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.

Institutional Repository

journal article

© 2022 Carla P.Q. Furtado, Walter E. Medeiros, Sergio V. Borges, Juliana A.G. Lopes, Francisco H.R. Bezerra, Francisco P. Lima-Filho, Rubson P. Maia, G. Bertotti, Augusto S. Auler, Washington L.E. Teixeira