June 29, 2017

Fossil Fuels – Where Oil Comes From (Part 1)

fossil fuels - fossilized fern leaf embedded in limestone

Fossil Fuels – fossilized fern leaf embedded in limestone.


You’ve heard it a million times, but have you ever truly considered the reality that fossil fuels are in fact derived from fossils? Fossilized plants and animals, to be exact, and contrary to popular belief, not from the fossilized remains of dinosaurs. Geologists and scientists within the petroleum industry largely acknowledge a “biogenic theory” for the development of oil, which states that fossil fuels are the byproduct of organic matter from microscopic marine plants and animals.

The fossilized remains of  algae and plankton mixed with mud and sand accumulate into a thick sludge on the bottom of oceans, swamps, rivers, lakes and inland seas. Compressed by extreme heat and pressure these sediment layers of sludge were transformed over millions of years into “kerogen,” a dark, waxy substance that over time disintegrates into a variety of molecular structures made up of mostly carbon and hydrogen atoms. As kerogen disintegrates it becomes either a solid, a liquid or a gas and depending on the specific geological conditions and elements present it can become coal – a carbon-based solid comprised primarily of woody plant material or hydrocarbons – the hydrogen-rich byproduct of aquatic plant life.

“It’s rather remarkable that we are so dependent on oil, and yet we really don’t understand how it is made in all its gory details.”

Everett Shock, Biogeochemist at Arizona State University

Source rock, reservoir rock and traps

Over thousands of years, these thick sediment layers of organic matter eventually mature and seep into “source rock,” which then requires a “reservoir rock” to soak up the oil like a sponge, holding it within the porous spaces between grains of sand. Oil can also be encapsulated into reservoirs between layers of impervious “trap rocks” such as shale. When there is enough space between layers, oil will accumulate into large extractable quantities. Whether a liquid or a gas, fossil fuels will always migrate to areas of less pressure, often upwards toward the surface through naturally occurring seeps.

It runs our world, but most people don’t fully understand where oil comes from

Dueling geological theories on how fossil fuels were produced

An alternative petroleum formation theory known as “abiogenic” was developed in the 1950’s by Russian scientists, suggesting that instead of petroleum being the byproduct of compressed organic matter, it is instead formed deep within the Earth and seeps to the surface through fissures formed by the impact of ancient asteroids. Currently the biogenic theory is the leading explanation for the formation of fossil fuels and it’s believed that the petroleum we most commonly use took anywhere from 1 million to 1 billion years to form and represents a wide spectrum of useful petroleum and natural gas products including methane, propane, butane, hexane, octane and others.

Oil and gas exploration

What was once a challenging and dirty pursuit often dependent on pure luck has now become a sophisticated and methodical process that employs highly technical explorative methods such as seismic surveying, gravitational surveying and geological mapping to locate deposits of oil and gas. Seismic surveys use sonar to bounce sound waves off of rock formations and sediment layers, which are then used to create 3D renderings of geological features indicating potential oil and gas deposits. Exploration technologies are constantly evolving to include 4-dimensional projections of the Earth’s interior and detailed maps of geological deposits. Once a viable deposit is located through the exploration process, extraction begins through primary, secondary and enhanced recovery processes.

The extraction process

Some conventional oil and gas deposits are easily extracted, while others, known as unconventional products are more difficult and costly to remove, requiring alternative extractive methods. The science of extraction has evolved immensely over the past few decades and whereas recovery once yielded as little as 10% of an available deposit, advanced modern technologies have increased yield significantly, sometimes as much as 60%. Primary recovery through drilling uses naturally occurring underground pressure to displace the oil to the surface. Pumps are often installed to boost the pressure and increase flow, and in some cases gas is pumped back into the well to expand and drive fluids toward the surface.

Secondary recovery through techniques such as hydraulic fracturing is the most common form of extraction where produced water, a byproduct of the initial drilling process is re-injected into the well to force more oil to the surface. Enhanced recovery techniques such as chemical flooding, thermal recovery and gas injection are then used to extract the remaining oil trapped within a well.

Contact an SCL Consultant today

In a wide range of industrial sectors, if there’s metal touching metal, oil is involved. At SCL, we’re here to protect and optimize the machines that keep our country moving and we pride ourselves on providing superior logistics and solutions, extensive product and industry knowledge and total performance satisfaction for our customers. Understanding the story and best-practice application of a wide spectrum of petroleum products is our job, and we hope you enjoyed this article about the fascinating origins of oil and fossil fuels. For information on how we can assist your fleet in choosing the optimal products at a competitive price, contact an SCL consultant today.