08_salttectonics

GEOFÍSICA APLICADA À PROSPECÇÃO DE HIDROCARBONETOS

Leonardo Azevedo

Aula 8 – 12 Mar. 2013

Salt Tectonics

1 Leonardo Azevedo, 2013

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Salt Tectonics: Introduction

• Salt: mineral (Halite) and evaporitic rock (frquently

associated with siliciclastic, chalk, anhydrite).

• Both divergent (sin-rift/post-rift) and convergent

environments.

• Very ductile and low density.

• Halokinetis – deformation and movement of the sediments

above the salt layer.

• Sedimentary structures depend on the type of sediments

and the trigger event that lead to the salt movement.

Leonardo Azevedo, 2013

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Evaporties: origin and generation

• Marine precipitates, by the evaporation of the sea water;

• Evaporites are formed when the evaporation rate is higher than the precipitation;

• Short periods of comunications with less salty waters;

• Nowaday, the deposition of evaporites is constrained to tidal and estuarines

areas;

• Variable thickness and impermeable!

Leonardo Azevedo, 2013

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Salt Tectonics: introduction

• Various types of potential HC’s traps and

several types of morphologies.

• Very often associated with faults.

• Main Basins: Angola, Brasil e México

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Zagros Mountains

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Salt Tectonics: Buoyancy and deifferential compaction

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Salt Tectonics: Sedimentaitons

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7 Jürgen Adam, Zhiyuan Ge, Marianela Sanchez (2012). Salt-structural styles and kinematic evolution of the Jequitinhonha

deepwater fold belt, central Brazil passive margin. Marine and Petroleum Geology, 37 (1).

Salt Tectonics : Main Geometries

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Salt Tectonics : Diapirism

SALT

Reactive:

Extension creates room for diapir.

Stairstep faulting above.

Salt

Active:

Diapir creates room.

Thining and arching above.

Drag on flanks

Salt

Passive:

No room problem.

Diapir in equilibrium

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Offshore France

Salt Tectonics

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• Chaotic/transparent texture;

• Salt top with stronger reflection but hard spatial interpretation;

• Velocity anomalies beneath salt bodies;

• In post-stack migration there are no reflection beneath the salt bodies.

Seismic Interpretation

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Salt Geometries: Salt pillow

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Salt Geometries: Salt Diapirs

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Feda Graben - Dinamarca

Salt Geometries: Salt Diapirs

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Salt Geometries: Diapirs - Norway

VSA

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Salt Geometries: Salt Domes

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Paul J Valle, John G Gjelberg, William Helland-Hansen(2001). Tectonostratigraphic development in the eastern

Lower Congo Basin, offshore Angola, West Africa. Marine and petroleum geology 18 (8).

Salt Geometries: rafts

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Salt Geometries: rafts

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Salt Geometries: Canopy

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North Sea

Exercício

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Exercício Gabão – Delta do Congo

Angola

Courtesy – CGGVeritas Leonardo Azevedo, 2013

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Horizontal time slices

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Mar do Norte (Coerência)

Off W. Africa (Azevedo 2009)

Seismic Attributes

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