Review questions are highlighted in purple

Readings are in red

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Table of contents

A. Origin of Petroleum

1. Introduction

2. The petroleum system

3. What is Petroleum?

4. The subsurface environment

Temperature

Pressure

Fluids

 

5. Review of Sedimentary Basins and Sedimentary rocks
6. The source: How oil forms

Source rock characteristics
Maturation of Kerogen.

A. Origin of Petroleum

1. Introduction
Historical Review of Petroleum Exploration.

Petroleum= Rock Oil
Petroleum is known since antiquity but only in the late 1800’s it became an important resource.
Early uses: waterproofing, lubricant, medicinal
19th Century- kerosene for lamps
20th Century – fuel for internal combustion engines and then a huge number of other applications in all industries

What triggered the sudden growth of the oil industry in the second half of the 19th century?

Early explortion was based on the locations of oil seeps: places where oil flowed at the surface.

 


The future of the Petroleum Industry: When will we run out of oil?

 
 Petroleum is a large but finite resource.

• Reserves= Petroleum known to exist and which can be produced economically.
• Resource= Petroleum believed to exist on the basis of geological parameters.


Peak of oil discoveries was in 1962. Since then discovery of new reserves has been declining in spite of technological improvements. We are currently near the peak of production . This scenario implies that due to lack of new discoveries production will begin to decline by about 2010.

 



Discuss this scenario.



The price of oil has historically been closely tied to political events, particularly regarding the Middle East where half of the world's oil reserves are located.

Why has the price of oil tripled in the last year? Why has it not affected the economy to the same degree that it did in 1974 oil crisis?

Readings: Ch. 1, pp. 1-11, Selley., Ivanhoe, 1997, Get Ready for Another Oil Shock, in: http//dieoff.org/page90.htm

2. The petroleum system
Organic vs. inorganic origin of petroleum
 

Most scientific evidence shows that petroleum originates from the decay of organic matter buried in sediments.

What is this evidence?

Small amounts of hydrocarbons are also found in settings far from organic influence (meteorites, CH4 in Jupiter and Saturn, some metamorphic and igneous complexes, CH4 in volcanoes) so there must also be a minor inorganic source of petroleum.

The Carbon Cycle
 

Organic Carbon Cycle

Through photosynthesis plants and algae take CO2 from the air or water and turn it into organic molecules for their cells. These organisms support the food chain. Once a living thing dies it either is decomposed back to CO2 and H2O or is buried. If buried it may turn into hydrocarbons if all conditions are right. When we burn hydrocarbons CO2 returns to the atmosphere.

Make a diagram showing the organic carbon cycle.

In light of the carbon cycle, what are the environmental consequences of burning hydrocarbons?

Inorganic Carbon cycle

Most of carbon on earth is stored as carbonate ( CO3)- in rocks such as limestones and dolomites. Carbonate is in equilibrium with seawater, marine organisms take it from the water to make their skeletons.

Overview of the formation of a petroleum deposit from source to trap

These are necessary conditions for a petroleum accumulation:

1. Mature source rock.
2. Permeable reservoir rock.
3. Trap composed of structure, seal and reservoir.
4. Migration path from source to trap.
5. Right timing of all these elements.
6. Preservation

Make a sketch of an active petroleum system with all its elements.

Reading: Ch. 5 pp. 181-191, Selley

3 . What is Petroleum?

4. The subsurface environment

Temperature within the earth

Pressure

Why do we care about pressure?

P= pressure= force/area (units Pascals, or psi)

Not to be confused with stress which has same units, but is not a scalar quantity

P= rgz = density x accel. of gravity x depth
 

Lithostatic Stress= due to the load of the overlying column of rock