Shale oil most often refers to oil that is extracted from immature source rock containing high amounts of organic material called kerogen. Kerogen is essentially the remains of plant and microscopic sea life that was trapped in sediments that later became shale rock. There are literally trillions of barrels of oil (or potential oil from kerogen) trapped in U.S. shale deposits such as the Green River formation. This large rock formation is found primarily in Utah, Wyoming and Colorado. The Green river oil shale is the largest in the world, holding over 1.5 trillion barrels of oil. The problem is how to get that oil out. That is more than all of the reserves of light sweet crude in the world.
Oil shales provided some of the first petroleum used by humans. In the 1300′s shale derived oil was used to light street lamps in Austria. The traditional process for extracting oil from shale was to mine it, crush it and heat it. All of this was quite labor and energy intensive, to say the least.
It was coal however that was the first hydrocarbon to be widely used by man since it burned similarly to wood and was found in easy to mine deposits. When oil finally became important because of the internal combustion engine there were easier sources of crude for refining into gasoline. Shallow oil wells could be drilled by cable tool rigs such as the Drake well in Pennsylvania and because of this shale oil was largely forgotten. Once oil was discovered in large quantities in the Middle East in liquid form shale oil was largely dismissed as a source of energy. Small scale mining of deposits that contained high amounts of free oil, and required less energy to extract crude, continued up until the 21′st century in a few places around the world such as Estonia.
Now that conventional oil and gas reserves are dwindling oil companies are taking a closer look at oil shale as a resource. The problem with it is that extraction of shale oil costs energy. It is the EROEI, or end return on energy invested that determines if it is economical do extract oil from shale. Unlike some shales, as those in Estonia, oil shales in the United States are largely kerogen and not free oil.
What is kerogen? Kerogen is the precursor to oil and it is widely accepted that this is where most of the world’s oil comes from. Shales rich in kerogen are the “source rock” found beneath most oilfields. Pressure and heat over millions of years convert the kerogen into oil and it flows up into “traps” or layer of rock that are porous, such as sandstone, and which are capped with a hard rock layer. Getting crude oil out of American shale requires much energy.
In – situ shale oil recovery does not require mining but instead takes the heating process to the shale in the ground. Shell Oil has developed a process that they claim has an EROEI of three to four units of energy produced for every one unit of energy consumed. The Mahogany Project in Colorado uses as system of cooling pipes spaced eight feet apart around several square acres to create a barrier to contain the oil. Wells are drilled inside the barrier and the shale is heated using electric resistance heaters which are placed in wells spaced forty feet apart. This process speeds up a process that would normally take millions of years. Kerogen in the rock is converted into oil and pumped out of recovery wells.
The downside to this technology is that it uses fossil fuel energy and poses a risk of groundwater pollution to aquifers.
Will shale oil end the energy crisis? It is not likely. Although there are trillions of barrels of potential crude in the Green River formation it is not liquid oil and it is not easy to recover. As a last resort we may turn to shale oil in the future. Oil and gas are now being recovered from more mature shales deep underground. In shales such as the Eagle Ford shale, which may be the sixth largest discovery of oil in U.S. history, oil is is liquid form and can be extracted with horizontal wells without heating.