Petroleum

Petroleum is hydrocarbon, with minor amount of Nitrogen, Oxygen and Sulfur as impurities along with heavy metal. Source of petroleum is organic. It contains CH4 chains that are linked together to form long chains of more complex molecules. Petroleum occurs in the earth in combination of any of the many states like gas, liquid (crude oil),
and solid(asphalt, tar, pitch). Today petroleum is found in vast underground reservoirs where ancient seas were located.
Petroleum can be found under the ocean as well as the land.

Generation of Hydrocarbon: –

The organic matter that accumulate within a basin suffers various stages of pre-burial oxidation/ reworking prior to deposition. The part of this animal that escapes destruction and oxidation when buried within an ever-increasing accumulation of sand, clays and more debris until the sediment is thousands of meter thick.

As the burial increases bacteria take oxygen from the trapped organic residues and gradually break down the matter into substances rich in carbon and hydrogen. This is accumulated in the rock called as source rock like carbonates shales and coals. Organic rich rock are potential for generating hydrocarbons. The qualitative and quantitative evaluation of source rocks are essential for the prediction of the type of hydrocarbons (gas/liquid), identification and spatial distribution of potential source rocks, variation or type of kerogen, thermal maturity etc.

Organic matter transformation on burial :-

Diagenesis	Catagenesis	Metagenesis
shallow subsurface Normal pressure and Temperature Released: CH4, CO2, H2O Overall decrease in O Overall increase in H & C	Deeper subsurface Increased pressure and temperature Released: oil and gas	Last stage of organic matter transformation

Types of Kerogen :-

Type -1	Formed mainly from proteins and lipids derived from cyanobacteria, fresh water algae etc. Forms mainly in anoxic lakes H/C ration highest Gives liquid hydrocarbons
Type -2	Sporinite: formed from the casing of pollen and spores Cutinite : formed from terrestrial plant cutical Resinite : formed from terrestrial plant resins and animal decomposition resins Liptinite : formed from terrestrial plant lipids and marine algae Produces mix of gas and oil
Type -3	Formed from cellulose (terrestrial plant matter) Tends to produce coal and gas
Type -4	No potential to produce hydrocarbons

Five ingredients of the petroleum :-

1) Source rock: Source rock is a sedimentary rock that contains sufficient organic matter such that
when it is buried and heated it will produce petroleum (oil and gas)

• Organic matter rich in soft and waxy tissues yields oil with associate gas on maturation of
  woody tissues yields only gas.
• Source rocks are associated with areas where high organic productivity is combined with
  those processes which preserve organic matterI. Deposition in anoxic environment
  II. Upwelling
  III. Rapid sedimentation

2) Reservoir rock : These rocks are porous and permeable contained on the trap, with petroleum and
some water in its pore spaces.

3) Seal rock : Seals tends to be fine-grained or crystalline, low permeability rocks ( shale, anhydrite,
chert, salts) which resists the migration of petroleum to the surface.

4) Traps : Traps is the description of geometry of the sealed petroleum bearing rock

5) Timing of petroleum migration :

• If migration has occurred before the deposition of a suitable reservoir petroleum will- not be trapped
• If petroleum migrates before structuring in basin creates suitable trap geometries, than the petroleum will not be trapped

Petroleum exploration :-

Because of the burial and temperature requirements needed for the maturation of organic matter, most petroleum will be found in sedimentary basins. The petroleum richness of sedimentary basin, or even the presence of petroleum is also highly dependent on source rock and reservoir development and the presence of good sealing lithologies.

There are mainly five phases of petroleum exploration –

1. It is the stage of early surface mapping and reconnaissance geophysics. It begins with the unexplored basin, there may also have been reports of surface indications to encourage the exploration. Surface evidence of petroleum has been important in the discovery of nearly every onshore petroleum province in the world. At this stage, a geologic analogue is often used to compare the unexplored basin to other producing “look-alike” basin which appear to have common
   geologic characteristics.
2. Phase 2 is the stage of seismic survey. During this stage, more data is obtained on the depth configuration of potential traps and hopefully some knowledge of the character and volume of the sedimentary fill is gained.
3. Phase 3 is the stage of exploratory or “wild cat drilling”, which establishes for the first time a detailed sampling of the sediment character (reservoir, source or cap rock potential), maturation, and geothermal regime.
4. Phase 4 is the discovery phase , follows the successful completion of some wild cat wells. At this stage, reservoirs are established and hydrocarbon types are linked to the particular stratigraphic units. Further wild cat drilling in less developed parts of the basin may be guided in part which are left. Many of the basin’s largest fields will have been discovered and exploration for more traps may commence.
5. It is the production phase, begins to provide exploration geologists with reserve estimates and a history of the hydrocarbons potential of the basin. There is enough information to work out field size distribution patterns

Major Petroliferous basins of India :-

Assam-Arakan basin	Source rock : Kopili formation (Eocene ) Reservoir rock : Tipam sandstone (Miocene), Barail formation (Oligocene) Cap rock : Girujan clay, Kopili formation Major oil fields : Naharkatiya, Lakwa, Rudsagar, Digboi
Cambay basin	Narrow elongated rift basin Source rock : Cambay shale (Palaeocene- Eocene) Reservoir rock : Kalol formation , Ankhleshwar formation Cap rock : Tarapur shale
Cavery basin	Intracratonic rift basin formed as a result of fragmentation of Gondwanaland Source rock : Sattapadi shale (Cretaceous) Reservoir rock : Bhuvanagiri and Nannilam formation Cap rock : Sattapadi shale
Krishna-Godavari basin (1)	Extensive deltaic plane formed by Krishna and Godavari rivers in Andhra Pradesh Pre-Trappean petroleum system Source rock : Kommugudem formation (Upp. Early Permian) Reservoir rock : Mandapeta sandstone (Permo-Triassic) Cap rock : Tight layers within Mandapeta sandstone and the overlying argillaceous red bed
(2)	Late Jurassic-Cretaceous Petroleum system Source rock : Raghavpuram shale (Low. Cretaceous) Reservoir rock : Tirupati sandstone(Upp. Cretaceous), Gollapalli formation Cap rock : Raghavpuram shale and Razole formation
(3)	Post- Trappean petroleum system Source rock : Palakollu shale (Paleocene) Reservoir rock : Pasarlapuid Formation (Lower to Middle Eocene) Cap rock : Laterally persistent shales within pasarlapudi formation and Palakollu shale
Mumbai Offshore	Source rock : Panna formation (Paleocene -Eocene) Reservoir rock : Limestone (Miocene) Major oil fields : Heere, Panna, Bassein, Neelam, Mukta, Ratna
Rajasthan basin (1)	Jaisalmer basin Source rock : Baisakhi shales Reservoir rock : Baisakhi, goru, Sanu sandstone and fractured limestone of Jaisalmer
(2)	Bikaner-Naugaur basin Source rock : Karampur shales Reservoir rock : Jodhpur sandstone, Nagaur sandstone

Different Uses of Petroleum :-

When we talk about petroleum and its uses, most of the people generally think of it as fuel either petrol or diesel. However, petroleum has been used in one form or another. It is an important substance across society, politics, technology including in economy. Besides, apart from fuel there are a lot of petroleum by products that show up in our modern life. Let’s look at some uses of petroleum below.

• Agriculture
• Detergents, Dyes, and Others
• Plastics, Paints and More
• Pharmaceuticals
• Rubber

1. Agriculture
   When we talk about agriculture we are talking about fertilizers. Here, petroleum is used in the production
   of ammonia which serves a source of nitrogen. The Haber process is used in this case. Pesticides are also
   made from oil. All in all, petroleum based products are used extensively in agriculture as it helps in running
   farm machinery and fertilize plants.
2. Detergents, Dyes, and Others
   Distillates of petroleum that include toluene, benzene, xylene, amongst others are used to obtain raw
   materials that are further used in products like synthetic detergents, dyes, and fabrics. Benzene and
   toluene which gives polyurethanes is often used in oils or surfactants, and it is also used to varnish wood.
3. Plastics, Paints and More
   Plastics are mostly made of petrochemicals. Petroleum-based plastic like nylon or Styrofoam and other are
   made from this element. Usually, the plastics come from olefins, which include ethylene and propylene.
   Petrochemicals are also used to produce oil based paints or paint additives. Petrochemical ethylene is
   found in photographic film.
4. Pharmaceuticals and Cosmetics
   Petroleum by-products like mineral oil and petroleum are used in many creams and other pharmaceuticals.
   Tar is also produced from petroleum. Cosmetics that contain oils, perfumes are petroleum derivatives.
5. Rubber
   Petrochemicals are also used in manufacturing synthetic rubber which is further used to make rubber soles
   on shoes, car tire and others rubber products. Rubber is primarily a product of butadiene.
   Popular Products Made from Petroleum
   Some products made from or contain petroleum are; wax, ink, vitamin capsule, denture adhesive, toilet
   seats, upholstery, CDs, putty, guitar strings, crayons, pillows, artificial turf, hair colouring, deodorant,
   lipstick, heart valves, anaesthetics cortisone, aspirin.