Suggested workflows using MoveTM for structural ...

1 downloads 0 Views 2MB Size Report
Suggested restoration workflow in Move illustrated with adapted model of West Bison Field in the Gulf of Mexico. We would like to acknowledge Paul Mitchell.
Suggested workflows using Move for structural restoration when salt is present TM

Introduction •





The inherit instability and weakness of salt presents a number of unique challenges for any restoration Several important assumptions made about the behaviour of salt over geological timescales Suggested restoration workflow in Move illustrated with adapted model of West Bison Field in the Gulf of Mexico

We would like to acknowledge Paul Mitchell (BP) for kindly giving permission to use this data set in presentations

“Restore the sediment not the salt” 1. 2. 3. 4. 5. 6.

Establish baseline below section Decompaction Isostatic adjustment Thermal subsidence Adjustment of restoration template (regional) Restoring horizon to template

From Rowan (1993). •



Regional based on identifying areas unaffected by salt movement Preferable to use palaeo-water depth data to construct regional

“Restore the sediment not the salt” 1. How has the dynamic interaction between salt and sediment influenced the basin architecture and distribution of sedimentation through time? (In this interpretation) 2. Quantify salt thickness through time?

Adapted West Bison 3D model N

S

Horizon

Age

Seabed

0 Ma

Top Quaternary

3 Ma

Late Miocene

10 Ma

Top Oligocene

24 Ma

Top Eocene

34 Ma

Top Cretaceous

65 Ma

Top Jurassic

145 Ma

Salt

160 Ma

Basement

180 Ma

2D restoration Present-day

Seabed

Top Quaternary Late Miocene Top Oligocene Top Eocene Top Cretaceous Top Jurassic Salt Basement

2D restoration Uppermost unit removed

Seabed

Top Quaternary Late Miocene Top Oligocene Top Eocene Top Cretaceous Top Jurassic Salt Basement

Sediment decompacted; salt not decompacted

2D restoration Sediment touches basement - minimum salt modelled

Top Quaternary unfolded

Seabed

Top Quaternary Late Miocene Top Oligocene Top Eocene Top Cretaceous Top Jurassic Salt Basement

Space created by unfolding infilled with salt

Results of 2D restoration How has the dynamic interaction between salt and sediment influenced the basin architecture and distribution of sedimentation through time? (In this interpretation) •

Salt withdrawal created accommodation space and led to the development of mini-basins around the diapir – this process has been occurring since the Jurassic N

Top Jurassic Salt

S

Results of 2D restoration •

Late Miocene sag across diapir possibly indicates salt withdrawal from diapir – hypothesis can only be proved by 3D restoration

Seabed

Sag across diapir

N

Top Quaternary

S

Late Miocene Top Oligocene Top Eocene Top Cretaceous Top Jurassic Salt Basement

Results of 2D restoration •

Significant relief (1.7 km) on Top Eocene horizon and squeezing of the diapir potential suggests Oligo-Miocene compression

Seabed

Folded Top Eocene horizon

N

Top Quaternary

S

Late Miocene Top Oligocene Top Eocene Top Cretaceous Top Jurassic Salt Basement

Extent of diapir in the Top Eocene

Quantifying salt thicknesses Preferred method to quantify salt thickness is to use palaeo-water depth data (corrected for sea level changes) to define regional and adjust sub-salt units for isostasy and thermal subsidence. 50

0

350

0

J Eo

Q

500 1000 1500

K OG Mi

2000 2500

300 250 200 150 100 50 0 140

120

100

80

60

Time (Ma)

40

20

0

Haq (2005) sea level w.r.t modern (m)

Age (Ma) 100

150

Palaeo-water depth (m)

200

Quantifying salt thicknesses 1. Average Airy isostasy caused by Cretaceous sediments calculated.

2. Basement adjusted for thermal subsidence and isostasy.

3. Top Jurassic unfolded to regional based on palaeo-water depths, corrected for sea level changes.

Quantifying salt thicknesses Adjustment basement for thermal subsidence and isostasy.

-1

-2 -3 -4

Thermal subsidence (km)

0

1056 m

7m

-5 160

140

120

100

80

60

40

20

0

Time (Ma)

Predicted thermal subsidence following McKenzie (1978) • •

Rifting at 160 Ma (Bird et al., 2005) Beta factor of 2.1 (Pindell, 1985)

Predicted Airy isostasy uplift

3D pseudo forward model Top Jurassic (145 Ma)

3D pseudo forward model Top Cretaceous (65 Ma)

3D pseudo forward model Top Eocene (34 Ma)

3D pseudo forward model Top Oligocene (24 Ma)

3D pseudo forward model Late Miocene (10 Ma)

3D pseudo forward model Top Quaternary (3 Ma)

3D pseudo forward model Present

Results of 3D restoration Minimum

Top Quaternary Late Miocene Top Oligocene

Sediment thickness

Salt thickness

Present

Maximum

10 km

Basin depocentre

Results of 3D restoration Minimum

Maximum

Top Cret.

Top Jurassic

Sediment thickness

Salt thickness

Top Eocene

10 km

Basin depocentre

Results of 3D restoration S

N

Top Salt in Late Miocene

4.2 km

Top Salt at Top Quaternary

3.8 km

Quantifying salt thickness

Restored salt volumes through time 700

500 400 300 200 100 0 200

150

100 Age (Ma)

50

0

• Salt volume (km²)

600



Overall loss of salt through time (70% salt lost) Eocene (red point) is an exception; possibly relating to coincident Oligo-Miocene compression

Summary •



Workflow is flexible - can be tailored to particular problems and geological setting Palaeo-water depth is essential to quantify salt thicknesses through time

Horizon geometries and vertical salt thickness at Top Cretaceous

4411m

10m

How to get in touch: