Petroleum Geoscience

EAB -7- 151

Basin, structures and traps

Dr. Julie D. Bell RPG, PhD

bellj@lsbu.ac.uk

What is a sedimentary basin?A sedimentary basin is a depression filled with

sedimentary rocks.

Areas of basins can be 1 to 10 km plus

• A sedimentary basin is

– a depression filled with sedimentary rocks

– formed by any tectonic process

– filled with sediments, organics and water

– elements necessary to create a petroleum system are put in place

– traps are formed by tectonic processes.

• Reservoir models are made of the particular parts of basin that the company has located a play.

Classification of sedimentary basins

Sedimentary basins can be classified according to

structural genesis (or how they were developed)

evolutionary history (that can be linked to petroleum systems and play development)

• The foundations of sedimentary basins

• The mechanics of sedimentary basin formation

The foundations of sedimentary basins

Read Basin Analysis Principles and Applications Philip A. Allen

and John A. Allen page 3-- 218

Petroleum geologist - basin modelling

• At its most basic, a basin modelling exercise must include:

– burial history

– thermal history of the basin

– maturity history of the source rocks.

– expulsion, migration and trapping of hydrocarbons

Basin evolution

Number and variety of plays increases with basin evolution, as tectonics and sedimentary patterns become more complicated.

Different basin cycles can be present pre-rift

syn-rift

Transitional

Post-rift

Same or different petroleum systems can be present due to changes in cycles

How to understand evolution?

• Determine history of the basin fill including

– composition,

– primary structures, and

– internal architecture, can be synthesized into a model of stages of development, or a basin model

• Sedimentary basins are regions of prolonged subsidence of the Earth. The driving mechanisms of subsidence are principally driven by processes in the lithosphere. The earth consists of different zones.

Geometries in a basin

Geometries in sedimentary basins

Applied study for petroleum not academic, petroleum traps

Structural geology - study of 3D distribution of rock units with respect to their deformational histories

Planar features ○ bedding planes

○ foliation planes

○ fault planes

○ fold axial planes

Other features ○ joints

○ Stretching

Structures are present on all scale from macro to micro

Bedding planes - normal bedding

Bedding planes - folded beds

Fault planes

Bedding and normal and fold planes

Fold axial planes - Anticline

strike

plunge

Strike – the

direction that

the beds are

facing ie. NE

Plunge – the

angle that the

beds are from

the ground

surface ie 45

Fold axial planes - Synclines

Traps

Traps

Read Petroleum Geosciences Gluyas and Swarbrick Section 4.5 p 148-169

• Structural traps (fig 4.36 p149)

• Stratigraphic (fig 4.37 p150)

• Evaporites and salt domes (fig 4.47 p160)

Formation of traps and timing are critical

Structural traps

Read Petroleum Geosciences Gluyas and Swarbrick Section 4.5.3 p 151-163

What are the 6 types?

Salt dome traps

What are the 8 parts?

Wytch field is a synclinal fault basin with a

stratigraphic pinchout trap