By Zach Hagadone
Reader Staff
Editor’s note: Brenden Bobby is taking a week off, but he’ll return soon.
Oil has been big in the news lately, and specifically the vast oil reserves in Venezuela. This is “Mad About Science,” though, so we’ll avoid the politics surrounding the topic and focus on a basic question: How come Venezuela is so rich in oil?
According to most sources, the South American country holds more than 300 billion barrels of proven crude oil reserves — more than Saudi Arabia, Iran, Iraq and the United Arab Emirates, which round out the top five countries with the largest known reserves.
The first thing that might strike an observer is what those latter countries have in common: they’re all in the Middle East, which is filled with a mix of vast deserts and arid coasts and highlands.
When we think of major oil-producing regions, we tend to (rightly) envision desertified landscapes — whether they be sandy and rocky (like the Middle East) or frigid and remote (like the North and South Poles, which also have enormous oil and gas reserves). Venezuela is unlike those places, so what gives?
Speaking with Scientific American for an article published Jan. 7, petroleum engineer Luis Zerpa, with the Colorado School of Mines, said, “From the geology side, it just has the perfect location” for the accumulation of huge quantities of fossil fuels.
One thing all oil-rich regions have in common is the interplay of plate tectonics — that is, how the continents have bumped into each other and shuffled around the globe over the eons. The formation of oil, gas and coal, collectively referred to as hydrocarbons, requires organic material to be swiftly buried underground — so swiftly and thoroughly that it’s trapped in places where there’s not enough oxygen to spur decomposition, known as “anoxic” burial.
This generally occurs in areas where continental drift has pushed up land, resulting in a lower-elevation area nearby (or a “basin”). Through the processes of erosion, sediments move from the higher- to the lower-lying regions and cover whatever plant and animal remains might be there. As those sediments build up over time, they turn to rock, trapping the organic materials beneath. This can happen both in terrestrial and aquatic environments. (Sadly, we don’t have the space to get into other formations like oil shale, but feel free to look it up yourself.)
Rather than rotting away in the presence of oxygen, this material keeps its bonds of hydrogen and carbon; and, under intense pressure and heat from plate movements over enormous spans of time, it turns into the highly concentrated hydrocarbons we burn for energy.
These “fossil fuels” would stay trapped underground, inaccessible for extraction, if not for plate tectonics. Sealed deep below the surface — with the “oil window” ranging from 4,000 to 12,000 feet — hydrocarbons like oil and gas are released when their rocky prison walls start to crack as plates crunch together. Being more buoyant than water, oil and gas migrate toward the surface once free, seeking out pathways into porous and permeable rocks, which then become subterranean reservoirs — the “reserves” that fossil fuel companies (and governments) covet.
The answer to why places like Saudi Arabia, Iran, Iraq and the UAE have so much oil and gas is precisely due to these tectonic processes, occurring over a period of time that dates back to the beginning of the Cambrian Period about 540 million years ago, when they (along with Africa, Antarctica, Australia, India and South America) were part of the Gondwana supercontinent.
Sedimentation, the proliferation of marine life, sea level changes and the breakup of Gondwana all created ideal conditions in certain places for anoxic burial and the formation of oil, gas and coal. In the most “recent” few million years, a number of geological faults, rifts, shelves and belts have developed throughout and surrounding the Arabian Peninsula, which is sandwiched between the African and Asian plates.
Which brings us to Venezuela. While Saudi Arabia is crunched between two plates, Venezuela is surrounded by three: the Caribbean, South American and Nazca plates. Over the hundreds of millions of years since Gondwana, the interaction of those plates forced up huge regions of land, resulting in Venezuela’s highlands and no less than the Andes Mountains.
All those high-elevation areas resulted in a trio of enormous basins around Venezuela, identified today as the Eastern Venezuela, Maracaibo and Barinas-Apure basins. Couple that with the fact that what we call Venezuela has remained a tropical region for far longer than places like Saudi Arabia, and you have a recipe for massive quantities of organic material getting trapped in a particularly active tectonic environment that, as we mentioned, is particularly politically active today.
Stay curious 7B.