Petroleum
Petroleum is basically
a mixture of some of the naturally occurring hydrocarbon compounds which are
found in rock. It exists in solid, liquid and gaseous states in accordance with
the surrounding pressure, temperature and composition. It could be with or
without impurities like sulphur, oxygen and nitrogen and can have considerable differences
in its physicochemical properties such as colour, gravity, odour, sulphur
content and viscosity in petroleum from varied areas.
Petroleum System:
Petroleum System is a vast term which includes geologic components and processes significant for the
generation as well as storage of hydrocarbons. It comprises of mature source
rock, migration pathway, reservoir rock, trap and seal.
To accumulate and preserve hydrocarbons, suitable
relative timing is required for the formation of these elements along with the processes
of generation, migration and accumulation. In the basins or regions, where a
complete petroleum system has certain likelihood of existence, exploration
plays and prospects are developed considerably.
Source rock, trap, seal & reservoir rock are key elements of petroleum system.A petroleum system mainly incorporates an active
source rock and all genetically related oil and gas accumulations. It further
incorporates geologic elements and processes that are significant if there is oil
and gas accumulation exists. The presence of Petroleum System must be
identified before initiating the exploration.
Source Rock
It is a subsurface sedimentary rock usually shale or limestone,
they have the ability of generating or already generated movable quantities of
hydrocarbons.
A rock must have three major features to be a source
rock:
Source rocks are mainly categorised into three basic
categories on the basis of kerogen they contain. They are described in the next
table.
1. Type1 source rocks:-Formed from algal remains
deposited in oxygen depleted conditions in deep lakes.These source rocks when
subjected to high thermal stress during deep burial produce waxy crude oil.
2. Type 2 source rocks:-These type of
source rock are produced by marine planktonic and bacterial remains preserved
under oxygen depleted conditions. Type 2 source rock tend to produce both oil
and gas when subjected to high pressure and temperature.
3. Type 3 source rocks:-These type of
source rocks are mainly formed by land plants that got decomposed by bacteria
and fungus .They tend to generate mostly gas and some associated light oil.
Discussion will be continued in next blog.......
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