oil
Oil
The
Basic Terms
The Origin of
Oil and Gas
Conditions
for Oil and Gas Formation
Occurrence
of Oil and Gas - four conditions
Types of Oil Traps
oil dome photo
oil dome section
fault trap
sand lens
salt dome
unconformity trap
see also Oil
Deposits - types
of traps (different file)
see also Bio Fuels
Fuels Oil and Gas Exploration Offshore Oil and Gas Refining Oil Spills
The Basic Terms
Petroleum
- A broad term which
includes both crude oil and natural gas
Crude Oil
- a liquid mixture of
naturally occurring hydrocarbons (compounds containing carbon and
oxygen).
Natural Gas
- A gaseous mixture of
naturally occurring hydrocarbons.
Oil and natural gas originate from organic matter in marine sediment. Microscopic organisms such as single-celled algae settle to the sea floor and accumulate in marine mud. This organic matter may partially decompose, using up the dissolved oxygen in the sediment. As soon as the oxygen is used up, decay stops and the remaining organic matter is preserved. Continued burial subjects the organic matter to higher temperatures and pressures, which cause physical and chemical changes in the organic compounds. These changes produce tiny droplets of oil and natural gas. As muddy sediments compact, the oil and gas are squeezed out and move into more porous and permeable sandy layers.
Conditions for Oil and Gas Formation
Anaerobic
- conditions under which
oxygen is not present. This is the condition necessary for the
formation
of oil and gas. Such conditions are found in a highly restrictive
environment
such as in a closed basin like the bottom of the Black Sea.
Aerobic
- conditions under which
oxygen is present to oxidize organic material and sulfur.
Four conditions or requirements are necessary in order for large accumulations of oil and gas to form. The requirements are:
Source Rock
- A shale must contain
organic material which has not been oxidized and which is converted to
petroleum by burial pressures and temperatures.
Reservoir Rock
- A sandstone or other
relatively porous rock is required to store and transmit the petroleum
when wells are drilled into the reservoir.
A Trap
- a set of conditions
to hold the petroleum in a reservoir and prevent its escape by
migration.
Deep enough burial but
not too deep - Temperatures and Pressures are required to "cook" the
petroleum
out of the organic matter. Of course, if the rock gets too hot the
petroleum
is all "burned" off.
Types of traps:
