That is a common technique right? 

They use water to pump out the oil to fully exploit the oil field. Because oil floats on water.

Hi Livermore,

Thank you so much for the excerpt.

The Truth About Oil - This is just a small section from an article

JACKSON, WY -- According to the U.S. Department of Energy's special report, the world will face "peak oil" by 2015. But many of the world's best informed professionals think the end is much closer than that. Some, like Matthew Simmons, think that it has already passed as far back as 25 years ago. And their reasoning is disconcertingly solid.

Over in the Middle East the oil fields are already using water-flooding, a version of advanced oil recovery, to get out what oil they have left. That is a major sign that they have passed their peak of easily extractable oil.

Water, Water Everywhere

In Saudi Arabia, seawater is injected into oil fields to increase pressure and stimulate production.

Now, normally only 30% of the oil in a reservoir can be extracted. But water injection increases that percentage-known as the recovery factor-and maintains the production rate of a reservoir over a longer period of time.

Over time, however, the volume of water that is lifted along with the oil increases, decreasing the volume of oil proportionately until, eventually, what flows out of the reservoir is almost pure water and the field is no longer worth operating.