Plant plankton Animal plankton
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.
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
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
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
If there are any animals on the
sea bed these will feed on the
Interpretation of Total Organic Carbon (TOC)
(based on early oil window maturity)
TOC in Shale
TOC in Carbonates
Organic Matter in Sedimentary Rocks
Disseminated Organic Matter in
Sedimentary Rocks That is Insoluble
in Oxidizing Acids, Bases, and
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.
As source rock is buried, it is heated.
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
Schematic Representation of the Mechanism
of Petroleum Generation and Destruction
(modified from Tissot and Welte, 1984)
Oil and Gas
Progressive Burial and Heating
Type of hydrocarbon
• The term "sweet" originates from the fact that a low level
of sulfur provides the oil with a mildly sweet taste and
• 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).
Producers of sweet crude oil include:
The Far East/Oceania:
The Middle East Kurdistan
North America: United States (Pennsylvania)
Petroleum containing higher levels of sulfur is called sour
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.
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
• 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.
Generation, Migration, and Trapping
Top of maturity
• Secondary migration is any movement in carrier rocks or
reservoir rocks outside the source rock or movement
through fractures within the source rock.
•Tertiary migration includes leakage, seepage, dissipation and
alteration of petroleum as it reaches the Earth’s surface