12. salt & shale

7/30/2019 12. Salt & Shale

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12. VERTICAL12. VERTICAL--DISPLACEMENTDISPLACEMENT

STRUCTURESSTRUCTURES

ASSOCIATED WITH SALT ANDASSOCIATED WITH SALT AND

OVERPRESSURED SHALEOVERPRESSURED SHALE

Topics

• Habitat

• Mechanics

• Small Extension Style

• Classical Salt Tectonics: Vertical

• Salt Sheets

•

Pseudoextension• Big Extension Style

Habitat

passive

margininterior

basins

Major Salt Basins Mechanics

buoyancy

soft and ductile material

unbalanced

load

material properties

driving forces

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salt

coverstretching

over crest of

structure

Active diapir

arches the

overburden

VerticalDisplacements

active

passive

passive diapir

regional

regional

salt

top of diapir remains at

surface while sedimentssubside around it

Vertical

Large rotation due to flow of salt or shale

Pseudoextension

vertical movement

of salt is driven by

stretching and

thinning of cover

ductile material

cover

Extension

Reactive diapir

Small Extension Style

Primary salt weld on autochthonous salt

Salt rollers

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North Choctaw Ridge field Alabama

5 million

barrels of oil

produced

Sinbad Valley, Paradox basin

Classical Salt Tectonics: Vertical

Paradox Basin, western U.S.Sequential evolution of salt anticlines of Paradox Basin

passive diapir

Active diapir: growth of dome below overburden

Chinguetti field Mauritania deep water

RMS amplitude extraction

T u r b i d i

t e s s r e

s e r v o i t n

o t d e f l e

c t e d b y

d o m e 120 million

barrels oil

reserves

Active diapir

Chinguetti field Mauritania deep water

optical stack of 20 traces

OWC

top reservoir

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Evolution of active piercement structures

pillow

primary rim

syncline

secondary

rim syncline

piercement

diapir

salt

salt

relative ages of dome growth

determine the relative ages of dome growth

salt dome from the North Sea

explain the structural-stratigraphic relationships

Evolution of dome in seismic line

turtle

formation

of a turtle

structure

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Turtle structure

Bryan field, Mississippi interior salt basin

~25 million barrels oil producible from K ss.

Diapir flanks are commonly poorly imaged on seismic

Flank traps

Passive piercement traps

Cote Blanche dome, LA

138 million barrels

oil ultimate recovery

10 bcf gas reserves

Active piercement traps

Nash dome, TX

3.3 million barrels oil

from 4 separate traps

2-D seismic on steep flank

Precaspian basin, Kazakhstan

Stratigraphic-structural traps

South Liberty dome, TX

88 million barrels oil,

1.2 million barrels condensate,

32 tcf gas from 5 reservoirs

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Germany Salt geometry related to original salt thickness

Shale diapirs

Port Isabel fold belt trend, Texas

Scoter field

UK North Sea

200 bcf gas

Crestal traps

Extension above dome

Reitbrook dome northern Germany

Seismic response

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Active piercement

basic fault patterns

X Y

faults detached on salt

faults cut salt

Forward models

and restorationAfter displacement on Y and X pattern faults

faults cut salt

faults

detached

on saltfault

zone of high

strain in HW =

2nd-order fault

Structural styles of Y pattern faults

parallel

normal

faults cut top salt

Style as a function of direction

with respect to master fault

parallel

normal

faults detached

on top salt

Style as a function of direction

with respect to master fault

Half graben dome style

South Pierce diapir, Central Graben, North Sea

top Paleocene ss.

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Pierce field, North Sea

Top Paleocene ss.

showing oil and gas

40 million barrelsoil reserves

202 bcf gas

Flexural-slip

restoration

Restoration

Apparent stratigraphic thickness

changes

Pitfalls in RestorationGaps between fault blocks

result of out-of-plane transport

uncorrected

thickness corrected

length and thicknesscorrected

t = tv cos δ (1)

Map restoration

3-D

model

perfect

restoration

vertical

simple

shear

restoration

flexural slip

restoration

parallel

block

centerline

Interpret the profile from the southern North Sea

TJ

Tr

Pz = Zechstein

ST 12-1

Objectivesprimary rim syncline

secondary rim syncline

pregrowth sequence

subsalt sequence

faults

salt boundary

drilling targets

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Salt dome from Yorkshire coast, North Sea

Jim Lowell interpretation

Salt Sheets

Salt

glaciers

Formation of Allochthonous Salt

Sheets

Detached sheets

major discovery estimated to contain

100-200 million barrels oil equivalent

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Princess field

175 million barrels oil estimated recovery

truncation below salt sheet

Minibasins

MM

7

minibasin province

perched minibasin

sliding downslope and subsiding into salt

thrusts

salt

result of extension between minibasins

Reactive diapir

Large rotation due

to flow of ductile

substrate

Pseudoextension

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Regional dip

Regional dip

Structure above thick salt sheets

Roho = C. C. Roripaugh’s moho (Schuster, 1995)

Roho = thin band of high-amplitude discontinuous

reflectors that form the base of most of the

faults and allochthonous salt features

Roho system = major, listric, down-to-basin growthfaults that sole into intra-Tertiary salt

evacuation surfaces (tertiary salt welds)

Stepped counter-regional system = major, listric, up-

to-basin growth “faults” that sole into salt

evacuation surfaces

Roho fault systems

Roho

system salt =

green

evacuated

salt = tan

inferred

salt

feeders =

red

arrows

A

B

Dip profile of roho system

tertiary salt weldsalt

salt

lower Pliocenefeeder?

A

Strike profile of roho system

salt

lower Pliocene

B

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Strike-slip margin of roho block

Evolution of

dip profile of

roho system

fig 5

Stepped counter-regional

fault system

Counter-regional fault between salt diapirs

salt

2.8

Time slice, counter-regional fault between salt diapirs Connection between stepped counter-regional fault system and salt

domes

AB

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Connection between stepped counter-regional fault system

and salt domes

A

secondary salt weld at

diapiric stem

Connection between stepped counter-regional fault system

and salt domes

B

Evolution of stepped counter-regional fault system and salt domes

B Schematic summary

evolution of stepped

counter-regional fault

system

regional dip

Huge counter-regional fault system, Cabo Frio area Brazil

Huge counter-regional fault system, Cabo Frio area Brazil

apparent downlap caused by progressive salt evacuation

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vertical movement of cover driven by

horizontal displacement of salt

salt

cover

normal faults, without regional extension,

a consequence of lateral salt displacement

Big Extension

Rafting on the Angola continental margin

Mock turtle

Angola continental margin

Angola continental margin

Rise and fall of diapirs during extension Interpret seismic and locate traps

ST 12-2

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12. salt & shale

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