After 100 years of extraction, how much oil and gas remains undiscovered in the US?

After more than a century of drilling, a new federal science report says the Phosphoria rocks beneath southwest Wyoming and northwest Colorado are almost out of undiscovered oil. The same assessment still finds a noticeable pocket of natural gas, but the easy barrels are mostly gone.

A U.S. Geological Survey assessment finds that the Phosphoria system still holds undiscovered oil and gas. It estimates about 3 million barrels of oil and 666 billion cubic feet of gas remain to be found. 

Since about 1920, wells tied to this system have already pumped roughly 500 million barrels of oil and 2.5 trillion cubic feet of gas. That history makes the remaining oil well under one percent of what has already been produced.

What the new assessment shows

The work was led by the U.S. Geological Survey (USGS), a federal science agency that maps and analyzes Earth’s resources. Its teams study how energy, water, and minerals influence hazards, ecosystems, and the economy.

The survey treated the remaining oil and gas as technically recoverable, resources that can be produced with today’s tools even if profits are uncertain. Those kinds of estimates focus on what has not yet been drilled.

“Areas where science tells us there may be a resource that industry hasn’t discovered yet,” said Sarah Ryker, acting director of the USGS.

The Phosphoria Formation

The Phosphoria Formation is built from layers of mudstone, fine grained rock made from compacted clay and silt.

These seafloor sediments were later buried deep and heated, turning trapped organic matter into oil and natural gas over tens of millions of years.

Some Phosphoria layers contain up to 10 percent organic carbon, the leftover carbon from ancient life that fuels hydrocarbon formation.

Most rocks have less than 1 percent of this material, so the Phosphoria became a prolific source for nearby oil and gas fields.

As the rocks were buried deeper, they passed the temperatures needed to turn organic matter into oil and gas roughly 85 million years ago. 

Geologists refer to the connected source rocks, reservoirs, and traps as a total petroleum system, a linked set of formations that charge and hold petroleum together.

Oil and gas generated in the deep Phosphoria rocks migrated upward into shallower reservoir formations, where drillers later found them in structural traps. More than 1,000 wells in the Southwestern Wyoming Province have produced from these sub Cretaceous rocks, around the margins where oil dominates the mix.

More and more difficult

“The Phosphoria Formation is really deep in southwest Wyoming,” said Steve Degenfelder, a landman with Kirkwood Oil and Gas.

Even where gas remains, getting to it is difficult because the Phosphoria lies miles below the surface in much of southwest Wyoming. 

One major concern is that much of this remaining gas is sour gas, natural gas that contains toxic hydrogen sulfide and needs special handling.

Industry experts note that removing hydrogen sulfide requires costly treatment plants, and in some fields those costs erase the value of the gas.

Geologists stress that this does not mean southwest Wyoming is running out of oil, because shallower Cretaceous formations above the Phosphoria still produce strongly. 

Ring points out that the Phosphoria is the deepest major producing formation in the region. He notes that its oil has migrated into shallower reservoirs that are easier to reach, where drillers now focus much of their work.

From oil source to critical mineral target

As oil potential fades, scientists are turning to the Phosphoria for critical minerals, mineral resources vital to the economy but at risk of shortages.

The Earth Mapping Resources Initiative program, run by the USGS with state partners, is mapping where those minerals may concentrate in these rocks.

In Utah and Idaho, the Phosphoria supplies several million tons of phosphate rock each year from mines near Vernal and Diamond Fork.

That phosphate goes mainly into fertilizer, linking these ancient seafloor deposits to modern farms that depend on phosphorus rich soil amendments.

The same chemical conditions that concentrated phosphate also tend to enrich rare earth elements, metals used in magnets, batteries, and many high tech electronics. 

Finding out how much of these elements occur in the Phosphoria is a priority for researchers. They also want to know whether they can be recovered as by products from existing or future phosphate mines, instead of opening new deposits.

Lessons from Phosphoria

The Phosphoria update is one piece of a U.S. Geological Survey effort to track undiscovered oil and gas in the United States and beyond.

Through its Energy Resources Program the agency estimates conventional and continuous oil and gas may be technically recoverable in geologic provinces worldwide.

In the same Southwestern Wyoming Province, the USGS has finished several related oil and gas assessments that cover other rock units.

Those studies include the Niobrara Formation, the Lewis Shale, and the Mowry system, which together hold larger undiscovered resources than the Phosphoria system.

One Mowry system study shows that younger rocks in the same province still hold large undiscovered resources. It estimates 473 million barrels of oil and 27 trillion cubic feet of gas in that single system.

For planners and communities, these findings suggest that conventional oil from Phosphoria related traps will decline while gas and other systems carry more of the load.

They also underline why decision makers pay attention to continuous resources, oil and gas spread through tight rocks that require advanced drilling to produce.

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