Natural gas plays critical role in reservoir pressure

Loss of reservoir energy can result in thickening as some oil changing from liquid to gas

As the Alaska Oil and Gas Conservation Commission approaches a decision on how much production to allow for a natural gas pipeline from the Prudhoe Bay oil field, the commission’s Cathy Foerster explained reservoir issues at stake in a presentation to the Alaska Natural Gas Development Authority’s board.

In a Jan. 23 presentation, Foerster said there are three things that can happen in the reservoir when gas is produced that could impede the long-term recovery of oil.
One is that as gas is withdrawn from the large gas “cap” overlying the oil-saturated rocks in the field, the reservoir pressure in the cap declines. That causes oil fluids to move up from the oil strata below the gas into rock that previously had not held oil.

“The previously ‘dry’ reservoir rock becomes coated with oil. Although some of this oil can be produced, a substantial portion – in some fields 20 percent to 30 percent – sticks to the rock and will never come out,” Foerster said. “In short, producing gas without replacing the gas cap fluids will cause some oil to stick to the rock and result in a decrease of ultimate recovery of oil.”

Alaska Journal of Commerce