Origin of HydrocarbonsPresented by:

Waqas Javaid

Table of Contents:

Introduction to Hydrocarbons Theories about Origin of Hydrocarbons Postulates about in-organic origin of

Hydrocarbons Failure of in-organic theory Organic origin of hydrocarbons

Introduction to Hydrocarbons:

Hydrocarbons are the simplest organic compounds. It contains hydrogen and carbon as main constituents. Petroleum is formed by hydrocarbons, in addition with

some other substances. Carbon (93-94%) and hydrogen (10-14%) are the major

constituents of petroleum hydrocarbons having some other constituents in minor amount.

Theories about hydrocarbon origin:

Two school of thoughts exist about origin of hydrocarbons:

Western school suggests that it is of biogenic origin Russian school propose that it is a-biogenic with an

inorganic origin First suggestion implies an finite resource Whereas second implies an almost unlimited one.

Postulates for in-organic origin:

Deep Seated origin Dimitri Mendeleev proposed this theory. It said that at depth and high temperature. Metallic carbides react with water to produce acetylene. More heavier hydrocarbons are then derived from this acetylene.

Postulates for in-organic origin:

Postulates for in-organic origin:

Extra terrestrial origin Another Russian scientist, Sokoloff presented the theory of extra terrestrial origin in 1890. It stated that hydrocarbons were present in outer space long before the creation of our solar system. After creation of our solar system and Earth it was precipitated as rain and got deposited deep in Earth. Now it is subsequently ejected from Earths interior into surface rocks.

Postulates for in-organic origin:

Extra terrestrial origin It is supported due to two main discoveries. Firstly, the atmosphere of some celestial bodies are known to contain methane. Second discovery was of carbonaceous chondrites. Orgueil meteorite is one of the best example. It contains more than 6% organic matter. Simplest explanation for this is irradiation of light elements in a primeval dust cloud.

Postulates for in-organic origin:

Evidences for in-organic origin:

Hydrocarbon origin due to radioactive decay of heavier elements deep in Earth

Extra-terrestrial or primordial origin of hydrocarbons

Presence of hydrocarbons in basement/ crystalline rocks

Reservoir replenishments

Radioactive Origin:

Petroleum contains large concentrations of helium gas

Helium gas is chemically unconnected to biology i.e. no biological material can attract or produce it.

Its origin could be primordial radioactive decay or nuclear reactions

Extra-terrestrial Origin:

Astronomers have observed that hydrocarbons occur on many planetary bodies.

Such as meteorites, comets, particularly on Titan, a moon of Saturn.

They are also found in gas clouds (nebulas) which are origin of our solar system.

So it is reasonable to think that Earth has its hydrocarbons since its creation.

Extra-terrestrial Origin:

Deep Seated Origin:

In order to extend their search for hydrocarbons, different countries have drilled very deep boreholes.

These boreholes were drilled down to basement/crystalline rocks.

Finding hydrocarbons at such depth, in metamorphic and igneous rocks supports the inorganic origin of hydrocarbons.

Deep Seated Origin:

Some examples are:

Kola SG-3; world’s deepest petroleum well in Russia. White Tiger Vietnam Field Siljan deep well drill Syria Plateau basalt

Deep Seated Origin:

Kola Deep Borehole:

Deep Seated Origin:

The Vietnamese white tiger deep petroleum field is reported to have produced high quality crude petroleum from basalt rock more than 17,000 ft. below the Earths surface, at 6000 barrels per day per well :

Reservoir Replenishment:

Some petroleum reservoir engineers were puzzled Noticing that their estimated existing reservoir in old wells

were increasing rather than decreasing. It could be that their original estimates ere under

estimated. Later it was hypothesized that as petroleum is drawn out of

reservoirs its pressure decreases This decreased pressure allow more deep petroleum to

diffuse up from the mantle and recharge reservoir from below.

Reservoir Replenishment:Example is Eugene Island Oil Field Block 330

Drawbacks of In-organic theory:

Lack of evidence that the organic compound in chondritic meteorites is the result of a truly inorganic origin or was in an original parent material which was organically created.

Yet there is mounting evidence for an organic nature but not field evidence to prove that inorganic processes have occurred in nature.

Drawbacks of In-organic theory:

If an inorganic origin is the primary method for hydrocarbons origin then there should be large amounts of hydrocarbons emitted from volcanoes, magma, and other igneous rocks.

Petroleum accumulations are only restricted to sedimentary rocks mostly. Petroleum seeps are generally absent in igneous and metamorphic rock.

Theory for Organic Origin:

Organic origin theory of hydrocarbons is the most widely accepted.

According to organic theory, the oil and gas are formed from remains of prehistoric plants and animals.

Remains of plants have been transformed to coal and animals' to oil and gas.  

These remains were settled in to seas and lands along with sands and slits , mud and other minerals.  

As the rocks and slit settled, layer upon layer piled into rivers, along coastlines and on the sea bottom.

Theory for Organic Origin:

Geological shifts resulted  in some of these layers being buried deep in the earth.  

Over the time, the layers of the organic material were compressed under the weight of the sediment above them.  

The increase in pressure and temperature changed the mud, sand, slit in to rock and organic matter into petroleum.

The rock containing the organic matter that turned into petroleum is referred as SOURCE rock.   

Evidences for Organic Origin:

Analogy with Living Organisms:Composition of petroleum allies it with the material

(known as biomarkers) found in living organisms i.e. proteins, fats, fatty acids.

Analogy With Aquatic Life: The association of oil and gas with unaltered

sedimentary rocks containing marine fossils proved the analogy with aquatic life.

Evidences of Organic Origin:

Analogy With Coal:The presence of “bitumen” in both deep coal

seams and oil seepages proved the analogy with coal. It can be expressed that oil and coal both have the same origin but conditions under which they formed may vary.

Conclusion:

These analogies support that hydrocarbons have organic origin.

Hydrocarbons originate from microorganisms (planktons), when microorganisms died and buried in the sediments.

Due to overburden these dead organism get buried at depth, and at certain temperature/pressure conditions they convert into hydrocarbons.

This organic origin theory is the most widely accepted by scientists.

References:

Pg. 37-48, “Petroleum Geology by F.K North, Allen & Unwin” 1985.

Ragheb, M. "BIOGENIC AND ABIOGENIC PETROLEUM.“

Origin Of Petroleum by Petroleum Blog, thepetroleumblog.blogspot.com

Pg. 65-84. “ENCICLOPEDIA OF HYDROCARBONS” Volume 1.