Washing More Oil from Rocks
A lot of oil can be left behind after "primary production." Often, it is clinging tightly to the underground rocks, and the natural reservoir pressure has dwindled to the point where it can't force the oil to the surface.
Imagine spilling a can of oil on the concrete floor of a garage. Some of it can be wiped up. But the thin film of oil that's left on the floor is much more difficult to remove. How would you clean up this oil?
The first thing you might do is get out a garden hose and spray the floor with water. That would wash away some of the oil. That's exactly what oil producers do in an oil reservoir. They drill wells called "injection wells" and use them like gigantic hoses to pump water into an oil reservoir. The water washes some of the remaining oil out of the rock pores and pushes it through the reservoir to production wells. The process is called "waterflooding."
How effective is waterflooding?
Let's assume that an oil reservoir had 10 barrels of oil in it at the start (an actual reservoir can have millions of barrels of oil). This is called "original oil in place." Of those original 10 barrels, primary production will produce about two and a half barrels (2½). "Waterflooding" will produce another one-half to one barrel.
That means that in our imaginary oil reservoir of 10 barrels, there will still be 6½ to 7 barrels of oil left behind after primary production and waterflooding are finished. In other words, for every barrel of oil we produce, we will leave around 2 barrels behind in the ground.
That is the situation faced by today's oil companies. In the history of the United States oil industry, more than 160 billion barrels of oil have been produced. But more than 330 billion barrels have been left in the ground. Unfortunately, we don't yet know how to produce most of this oil.
Petroleum scientists are working on ways to produce this huge amount of remaining oil. Several new methods look promising. Oil companies, in the future, might use a family of chemicals that act like soap to wash out some of the oil that's left behind. Or possibly, they might grow tiny living organisms in the reservoir, called microbes, that can help free more oil from reservoir rock. Sound interesting?
To find out more about these new ways to produce oil....