18 structures petroleum

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Structural Geology inPetroleum Exploration

Topics: Petroleum System

Traps

Exploration Methods (seismic)

Maui Field Example

Salt Tectonics

Reading:• 1. Outline in website

2. Pdf file: Geology for Petroleum Exploration, Drilling, and Production by Norman J. Hyne, 1984, pages 173-197.

Oil Exploration Strategy:

Find the Traps

Most common traps are structures

So exploration often targets the structures in

hopes of finding oil

Origin of Petroleum

Oil forms from the decay and

transformation of dead organisms buried in

sedimentary rocks

Major

Hydrocarbon

Provinces in

North America

Sedimentary Basins

Factors required to make an Oil

deposit

• Source rock - rich in organic matter

• Burial heating- > maturation

• Reservoir rock - porous and permeable• Trap-

• structural trap

• stratigraphic trap



Petroleum system Source Rocks

Black organic-rich marine shales

Organic matter is preserved low-oxygenwater

Restricted marine basins and zones were

water rises from the deep

Maturation of Organic Matter

Organic matter in sediments is solid (kerogen)

At about 60o C transformation begins

• Liquid hydrocarbons begin to form

At 120o C gas begins to form

At 140o C organic matter is exhausted

Only gas forms at higher T

Migration of oil

Oil is less dense than water

Oil will move up by buoyancy

Oil needs a permeable bed to move

It will stop when it reaches an impermeable bed

MigrationEastern

Venezuela

Western

Canada



Oil traps

Permeable reservoir bed

Impermeable seal

Porosity

Stratigraphic Traps

Structural

Traps

Fault

Traps

Map of the

Murre Field

Newfoundland



Salt TrapsCompressional Traps

Traps in Strike-Slip settings

Positive Flower Structures

Trap Types How to image the subsurface?

Drilling

Structural Interpretation

Seismic Reflection Imaging• Send sound into the rock, and collect the

echoes



Seismic Acquisition

3D Seismic Image

Salt

3D Geological Model



Offshore Platform

Maui Field, New Zealand

Gulf of

Mexico

Salt

Salt moves driven by buoyancy

•Salt density= 2 g/ cm3

•Salt undergoes no compaction

•Shale Density is initially 40% water

•Initial Density = 1.8 g/ cm3

•Water expelled during compaction

• Final Density = 2.4 g/ cm3



Sequential Stages

of a Salt Diapir

Seismic Image of a Salt Dome 3D Seismic Interpretation of Salt

Structures

Sandbox Experiment

Relationship between diapirism and normal faulting

Extension Above Salt Diapir



Syn-sedimentary Salt Movement

18 structures petroleum

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