Origin of Petroleum

Origin of Petroleum

In common English usage, the terms “oil and gas” refer to petroleum and its associated gases.  Petroleum, literally “rock oil”, is a mixture of hundreds of types of hydrocarbon molecules, formed by the thermal decomposition of organic matter that has been buried to significant depths and temperatures in the earth.

Living organisms flourish in the upper layers of lakes and seas, extracting energy from sunlight, and nutrients from the waters.  When these organisms die, their organic matter normally provides a food source for animals burrowing in the bottom sediments.  Sometimes, the bottom sediments are sterile, un-burrowed, lacking oxygen; then, the dead organisms rain to the sea floor, and accumulate in thick layers of organic-rich rocks, protected against scavengers, while being buried beyond their reach.

Continued burial to greater temperatures in the earth causes the buried organic matter to “cook” and liquefy to petroleum.  All petroleum forms in this manner, as does the methane gas generated with the oil.


Multiple Origins Of Methane Gas


Methane from petroleum

Most of the methane contained in subsurface accumulations of “natural gas” is thermal methane.  This particular variety of methane, a product of the thermal decomposition of organic matter, is generally found with its higher homologs, ethane, propane, and butane, and is isotopically “heavy”, compared to methane produced directly by life processes.

Bacterial methane

Methane produced by bacterial decomposition of organic matter is ubiquitous on the earth, and is readily distinguished from thermal methane by bacterial methane’s “light” carbon isotope. Methane is a major byproduct of the decomposition of plant material in swamps, oceans, rice fields, animals, and especially, from cattle. (%).  Such bacterial methane can pass directly into the atmosphere. Globally, the agricultural sector is the primary source of methane emissions to the atmosphere.  In the United States, when overall methane emissions decreased 8% in the period 1990-2011; US agricultural emissions increased, while those due to oil and gas activities decreased. (EPA)

Recovery of methane from large scale farm manure operations, and from organic decay in municipal waste sites provides a modest source of fuel for local electricity generation.

Subsurface gas accumulations containing bacterial methane are common, including the huge gas fields recently discovered near Cyprus and Israel.

On a pound for pound basis, methane in the atmosphere is over twenty times as effective as carbon dioxide in trapping radiation.  Methane is much lighter, however, and has a much shorter residence time in the atmosphere than does carbon dioxide.


Methane Hydrates

In the presence of water, within a narrow pressure and temperature range, methane forms a solid, ice-like substance called methane hydrate.  The substance was first recognized by Sir Humphrey Davy, and its common appearance in piping has created persistent flow problems for engineers.

In the 1960’s, Russian and American scientists discovered that methane hydrate occurs widely, abundantly, and naturally in the earth.  It is dominantly of bacterial origin and the solid hydrate occurs in two settings; at shallow depths in permafrost areas, and beneath deep ocean floor sediments.

Enormous quantities of methane hydrate exist in the earth as a solid, ice-like substance, each cubic foot yielding about .7 cubic feet of fresh water and 160 cubic feet of methane gas, when decomposed.  World-wide, the quantity of methane held in gas hydrates may exceed all other methane previously discovered.  No viable method for commercial production of methane from methane hydrate has ever been established.


Town Gas (Manufactured Methane)

London’s streets were lit by methane gaslights in the 1800’s.  That methane gas was CREATED by blowing water over hot carbon; carbon (C) plus water (H2O) gives methane and carbon monoxide and dioxide.  The created methane was manufactured locally in many cities and called “town gas”. Since the 1950’s, methane gas has been provided more cheaply from underground accumulations of “natural gas”, and the manufacture of “town gas” has ceased.

Is methane gas a renewable resource?  After all, anytime you must have it, it can be made from water and hot carbon.


Costs of Oil and Gas

Oil and gas costs benefit enormously from the prior energy input by the sun and the earth.  Our sun provided free energy to create organic matter; the earth’s heat converted organic matter to petroleum; gravity (buoyancy) collected the petroleum into underground deposits of oil and gas.  Creation of the earth’s oil and gas energy is free.  Locating the oil and gas, supplying the energy to convenient places, in a useful form, takes enormous amounts of money.  The energy business is the largest business in the world,

We will NEVER run out of oil and gas, as long as we can AFFORD oil and gas.  Every atom of hydrogen and carbon that was ever present on this earth,… is still present, and will remain on this earth.  It is child’s play for an able organic chemist to make methane from carbon and hot carbon, or to produce oil and gas from carbon dioxide and water.  These processes are well known, but are much more EXPENSIVE than simply extracting petroleum from the earth.

Since oil and gas can be MADE, worries should focus more on AFFORDABILITY of our future oil and gas transportation fuel, and less about “running out of oil and gas”.

Petroleum Migration And Retention

As petroleum and its associated gases form in the earth, much of the oil and gas squirts out of the heated organic-rich layers into nearby reservoirs of porous limestones or sandstones, where the petroleum resides until located and produced.

Everywhere oil and gas have been found, a look beneath them will recognize the source beds that once generated the petroleum.   In the latter part of the 20th century, geologist recognized that those source beds still contained within them large quantities of petroleum.  It has been estimated that these “left-behind” hydrocarbons in source beds are as abundant as all the oil and gas previously discovered.

These hydrocarbons are tightly retained in the nano-porosity of the source rocks.  To recover these tightly held oil and gas molecules, geologists typically need to drill five to twelve thousand feet vertically, then turn the well trajectory horizontally for thousands of feet within the source rock layer.  Then the horizontal portion of the well bore is injected with a high-pressure mixture of water and sand (hydro-frack) to create hairline fractures in the source rock layer.  These created fractures provide flow paths between the nano-pores containing petroleum to the horizontal well bore.  The fracture dimensions are controlled by the rock type and the amount of fluid and sand that is injected as a proppant; vertical fracture height is rarely greater than 300 feet, horizontal lengths can be thousands of feet.

Within source rocks, the oil and gas molecules move very slowly, feet per year, and commercial recovery depends on the proximity of the newly created fractures to the oil and gas molecules tightly held within the rock.  It is the “fracture-touched-volume” that largely determines how much petroleum will be recovered.


Our Transportation Era Depends On The Petroleum Age

The use of petroleum fuels has revolutionized transportation and has powered the development of our modern world society.

For a million and a half years, humanity relied on muscle-power, sometimes aggregated into clans, tribes, and kingships.  Four or five thousand years ago, these agglomerations of manpower became assisted by horse-power, ox-power, and the mechanical advantages of the wheel and the lever.  Only three hundred years ago, the development of the English steam engine allowed the Industrial Revolution, with engines powered by coal able to move huge quantities of goods by land and sea.

Steam engines brought the benefits of transportation to areas touched by water, and the narrow strips of land crossed by railroads.

Recognizing the limitations imposed by the energy density of coal, in 1915, Winston Churchill saw to the conversion of the British battle fleet from coal-fired steam to petroleum.  He saw that much of the capacity of a battleship had been devoted to merely providing space for coal and the coal-handling crew.

Petroleum fuels have an extraordinary advantage for personal transportation; they contain enormous energy for little weight.  Gasoline, for example has more energy content, by weight, than the powerful explosive, TNT.

With the ready accessibility of petroleum provided by the huge early oil fields in Baku, the USA, and the Middle East, the great advantages of energy dense petroleum fuels became apparent, and our “Transportation Era” began in the 1920’s.

Now, for the first time in the history of human society, people could move around the earth, anytime, anyplace, and nearly effortlessly.  The great benefits of personal transportation are not uniformly available, but the desire for access to mopeds, automobiles, trucks and airplanes, appears to be irresistible and irreversible.  Petroleum, with its great energy content, and low weight, makes personal transportation cheap and effective over long distances.

Efforts continue to be made to make transportation more efficient, less costly; for example, the average automobile in the USA has improved mileage from ?/mile to ?/ mile in the past X years.

Frequently suggestions are heard to move our society to a petroleum and vehicle-free, Eden-like past.   Does anyone think many members of our society would want to live, could survive, with only those foods, products, and services available within a ten mile/day walking range?

For better, for worse, …for at least another fifty years, our comfortable modern society is firmly coupled to oil and gas and the Transportation Era.


Marlan W Downey