This document discusses the origin and formation of oil and gas from plankton and other microscopic organisms. It explains that under low oxygen conditions on the seafloor, organic matter accumulates and is buried over time. Increased temperature and pressure converts the organic matter into kerogen and then into oil and gas. The hydrocarbons can then migrate from the source rock through porous carrier rocks until being trapped by an impermeable cap rock, forming an oil or gas reservoir. Sweet crude oil contains low sulfur while sour crude has higher sulfur levels, affecting refining.

1. Hydrocarbon Generation and
Migration

2. What is oil and gas? Where does it
come from?

3. Origin: Plankton
cache.eb.com/eb/image?id=93510
Plant plankton Animal plankton
en.wikipedia.org/wiki/Image:Ceratium_hirundinella.jpg en.wikipedia.org/wiki/Image:Copepod.
10,000 of these bugs
would fit on a pinhead!
• Most oil and gas starts life as microscopic plants and animals
that live in the ocean.

4. Introduction
 However, under certain conditions there may be very
little oxygen on the sea floor.
 This may be because the ocean is deep and stagnant and
oxygen has not been mixed down from the surface
waters.
 No animal life can survive where the sea bed is
completely lacking oxygen. Without animals to eat the
dead plankton, the organic mush builds up on the sea
bed.

7. On the sea bed
 When plankton dies it slowly settles to the sea bed where it forms
an organic mush. Usually there are lots of animals living on the
sea floor that feed on this material. One important group is the
polychaete worms. These are detritivores, which means they eat
the dead and decay remains of other organisms
upload.wikimedia.org/wikipedia/en/0/04/Plankton.jpg When the plankton dies it rains
down on sea bed to form an
organic mush
Sea bed
en.wikipedia.org/wiki/Image:Nerr0328.jpg
If there are any animals on the
sea bed these will feed on the
organic particles

8. Origin: Black Shale
upload.wikimedia.org/wikipedia/en/0/04/Plankton.jpg
• However, if there is little or no
oxygen in the water then animals
can’t survive and the organic
mush accumulates
• Where sediment contains
organic matter,
it eventually forms a rock
known as a Black Shale
© Earth Science World Image Bank

11. Interpretation of Total Organic Carbon (TOC)
(based on early oil window maturity)
Hydrocarbon
Generation
Potential
TOC in Shale
(wt. %)
TOC in Carbonates
(wt. %)
Poor
Fair
Good
Very Good
Excellent
0.0-0.5
0.5-1.0
1.0-2.0
2.0-5.0
>5.0
0.0-0.2
0.2-0.5
0.5-1.0
1.0-2.0
>2.0

12. Organic Matter in Sedimentary Rocks
Vitrinite
Reflected-Light Micrograph
of Coal
Kerogen
Disseminated Organic Matter in
Sedimentary Rocks That is Insoluble
in Oxidizing Acids, Bases, and
Organic Solvents.
Vitrinite
A nonfluorescent type of organic material
in petroleum source rocks derived
primarily from woody material.
The reflectivity of vitrinite is one of the
best indicators of coal rank and thermal
maturity of petroleum source rock.

17. Origin: Cooking
www.oilandgasgeology.com/oil_gas_window.jpg
As source rock is buried, it is heated.
Kerogen
Gas
Oil
Organic matter is first changed by the
increase in temperature into kerogen,
which is a solid form of hydrocarbon
Around 90°C, it is changed into a liquid
state, which we call oil
Around 150°C, it is changed into a gas
A rock that has produced oil and gas in
this way is known as a Source Rock

18. Schematic Representation of the Mechanism
of Petroleum Generation and Destruction
(modified from Tissot and Welte, 1984)
Organic Debris
Kerogen
Carbon
Initial Bitumen
Oil and Gas
Methane
Oil Reservoir
Migration
Thermal Degradation
Cracking
Diagenesis
Catagenesis
Metagenesis
Progressive Burial and Heating

19. Type of hydrocarbon
Sweet
• The term "sweet" originates from the fact that a low level
of sulfur provides the oil with a mildly sweet taste and
pleasant smell.
• High-quality, low-sulfur crude oil is commonly used for
processing into gasoline and is in high demand, particularly
in the industrialized nations.
• "Light sweet crude oil" is the most sought-after version of
crude oil as it contains a disproportionately large fraction
that is directly processed (fractionation) into gasoline
(naphtha), kerosene, and high-quality diesel (gas oil).

20. Producers of sweet crude oil include:
The Far East/Oceania:
Australia
Asia/Pacific:
Brunei
China
India
Indonesia
Malaysia
New Zealand
Vietnam
The Middle East Kurdistan
North America: United States (Pennsylvania)

21. Sour
Petroleum containing higher levels of sulfur is called sour
crude oil.
Sour crude oil is crude oil containing a high amount of the
impurity sulfur (level in the oil is more than 0.5% ).
The impurities need to be removed before this lower quality
crude can be refined into petrol, thereby increasing the cost of
processing - higher-priced gasoline than that made from
sweet crude oil.
Usually processed into heavy crude oil such as diesel and fuel
oil rather than gasoline to reduce processing cost.

22. The majority of the sulfur in crude oil occurs bonded to carbon
atoms, with a small amount occurring as elemental sulfur in
solution and as hydrogen sulfide (H2S) gas.
Sour oil can be toxic and corrosive, especially when the oil
contains higher levels of hydrogen sulfide, a t low
concentrations has the smell of rotten eggs.
Sour crude oil needs to be stabilized by having hydrogen
sulfide gas (H2S) removed from it before being transported by
oil tankers for safety reasons

23. • Since sour crude is more common than sweet crude in the
U.S. part of the Gulf of Mexico, Platts has come out in March
2009 with a new sour crude benchmark (oil marker) called
"Americas Crude Marker (ACM)".
• Dubai Crude (and Oman Crude) both sour crude oils have
been used as a benchmark (crude oil) oil marker for Middle
East crude oils for some time.
• The major producers of sour crude oil include:
North America: Alberta (Canada), United States' portion of the
Gulf of Mexico, and Mexico.
South America: Venezuela, Colombia, and Ecuador.
Middle East: Saudi Arabia, Iraq, Kuwait, Iran, Syria, and Egypt.

25. Generation, Migration, and Trapping
Migration route
Reservoir
rock
Seal
Oil/water
contact (OWC)
Hydrocarbon
accumulation
in the
reservoir rock
Top of maturity
Source rock
Fault
(impermeable)
of Hydrocarbons

29. • Secondary migration is any movement in carrier rocks or
reservoir rocks outside the source rock or movement
through fractures within the source rock.

30. •Tertiary migration includes leakage, seepage, dissipation and
alteration of petroleum as it reaches the Earth’s surface