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Scanline in the Kainer Formation and its Relationship with the Major Faults of the Edwards Group Limestones at Medina Lake, Texas

DOI: http://dx.doi.org/10.18190/1980-8208/estudosgeologicos.v24n2p149-158

https://www.ufpe.br/estudosgeologicos/ 

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Virgínio H. Neuman1,2, José A. Barbosa, Tiago S. de Miranda1,2, Rafael P. de Lima2, Ana C. da Silveira3, Flávia A. de A. Cabral2, Osvaldo J. Correia Filho2 & José A. Meneses Filho2

 

Resumo: O objetivo principal deste trabalho é avaliar as relações gerais entre os dados de fraturas coletados nos trabalhos de campo e as principais falhas ocorrentes nos calcários do Grupo Edwards na região do lago de Medina (proximidades de Santo Antônio), no Texas. Observações de campo incluíram as relações entre scanline e porosidade. As observações de campo, combinadas com a interpretação de análise gráfica, ajudaram na modelagem do padrão de distribuição das fraturas de um reservatório fraturado análogo. As principais direções dos calcários do Grupo Edwards é 60-80Az. Nos afloramentos estudados foram observadas uma grande falha de direção 70Az e outras duas menores de direção 75Az. Este conjunto de falhas esta formando um pequeno graben. Dois scanlines foram executados na superfície de uma camada cinza escura de um grainstone, na qual foram observadas porosidades tipo vugular grande (microcavernas). Outras porosidades do tipo vugular grande foram observadas nas interseções das fraturas nas paredes dos afloramentos estudados. Um cimento branco de calcita foi observado preenchendo fraturas nas camadas de coloração cinza-escura de grainstone. Os gráficos com as informações sobre a distribuição das aberturas das fraturas nos calcários do Grupo Edwards de ambos os afloramentos estudados, mostraram resultados semelhantes, indicando a continuidade do padrão de fraturamento neles. O padrão de faturamento e as falhas também apresentam uma boa correlação com os padrões regionais. Estas falhas são de cunho regional. As porosidades do tipo vugular se encontram nos cruzamentos das fraturas. A média de fraturas abertas por metro foi de 0.5 e o espaçamento das fraturas abertas variou de 5 a 7 fraturas por metro.

Palavras-chave: Calcários do Grupo Edwards, Scanline, fraturamento em carbonatos.

 

Abstract: The main purpose of this work is to evaluate the general relationships between collected field data of fractures and the major faults of the Edwards Group limestone at Medina Lake, Texas. Field observations include scanline relationships and porosity. These field observations, combined with the interpreted fracture distribution from graphic analysis, helped to modeling an analogous fractured reservoir. The major direction of faults in the Edwards limestones is 60 to 80Az. At the studied outcrop a big fault (70Az) and more two others small faults (75Az) was seen with the same range direction. These joint of faults are forming a small graben. Two scanlines were conducted at the surface of a dark bed of grainstone, in which some big vugs have been observed. Others big vugs, related to the fractures and to the intersection of them, were observed on the outcrop wall. Cement, white in color, fills the fractures in the dark bed grainstone. The graphics of aperture size distribution of Edwards limestone (fracture set trending 70Az) of both studied outcrops showed similar results, indicating the continuity of the fracturing pattern into them.

Key words: Edwards Group limestones, scanline, carbonate fracturing

 

1 Departamento de Geologia, Universidade Federal de Pernambuco, Brasil. neumann@ufpe.br
2 Programa de Pos-graduação em Geociências, Universidade federal de Pernambuco, Brasil.
3 Departmento e Engenharia do Petróleo, Universidade Federal de Alagoas, Brasil

 

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