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Geologists study earth history: Today we are concerned
about climate change. Many geologists are working to learn about
the past climates of earth and how they have changed across time.
This historical geology news information is valuable to understand
how our current climate is changing and what the results might be.
Oil and gas (hydrocarbons) are valuable resources hidden in the
subsurface of the Earth. Geologists and geophysicists use a myriad of
advanced techniques in order to find commercial accumulations of oil
and gas. The investigation of organic rich rocks (hydrocarbon source
rocks) and their geological history is important to understand the
petroleum system in a sedimentary basin. The basic elements of a
petroleum system consist of a source rock, a porous and permeable
reservoir rock and a tight cap rock.
When organic rich rocks (usually shales containing 4-20
weight % total organic matter (TOC) are buried, they are subjected
to increasing temperatures and pressures (typically 30 degrees
Celsius/km).At about 60 degrees Celsius, oil begins to form in the
source rock due to the thermogenic breakdown (cracking) of
organic matter (kerogen).
The oil window is a temperature dependant interval in the
subsurface where oil is generated and expelled from the source rocks.
The oil window is often found in the 60-120 degree Celsius interval
(aprox. 2-4 km depth), while the corresponding gas window is found
in the 100-200+ degree Celsius interval (3-6 km depth).
After expulsion from the source rock, the oil/gas (lighter
than water) migrates upwards through permeable rocks
(sandstones) or fractures until they are stopped by a tight, non-
permeable layer of rock, like shale. If hydrocarbons get trapped in
a subsurface, geological structure, they may be produced from a
hydrocarbon accumulation (reservoir) through an oil well. If not
trapped, the hydrocarbons may eventually migrate up to the
surface, where they can be seen as seeps.
Many geologists find employment in fields which are
focused on extracting useful resources from the Earth. Geologists

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