The right mix to get more out

When a field ages, production declines. Engineers may inject steam, chemicals or gas to force more oil out and increase productivity. This is known as enhanced oil recovery (EOR).

STEAM (THERMAL)

Boosting oil recovery with steam injection.

Injecting steam heats the oil in a reservoir, thinning it and making it easier to produce. It also pushes the oil to wells where it can be better drawn to the surface.

Shell is working on several full-scale steam EOR projects with Petroleum Development Oman. For example, at Qarn Alam oil is drained through the reservoir’s rock fractures. But the natural process is slow because the oil is very thick. Injecting steam into the fractures is to raise recovery over the life of the field from 3-5% to 20-35%.

CHEMICALS

In this approach, chemicals are mixed with water before injecting it into an oilfield to drive the oil out of the rock. The mixture is tailored to the properties of the rock, the oil and the water it contains.

Chemicals can be polymers or surfactants. Polymers are long-chained molecules that thicken the water. At Marmul in Oman, for example, saline water is produced along with the oil. The water is unsuitable for any other purpose and can be re-injected it to help push out more oil. The water is too thin to push out the dense oil so we remove impurities like sand, add a

chemical polymer to thicken it and re-inject the mixture. This process began in February 2010 with the aim to increase production by 8,000 bbl/d and to raise the amount of oil recoverable from the field from 15 % to more than 25%.

Surfactants are chemical compounds that lower the surface tension of liquids. We inject these together with an alkali solution in water to spark a reaction with natural acids in the trapped oil. This results in a soapy lather which reduces the stickiness of the oil. The mixture flows out of the reservoir, in a similar way to laundry detergents shifting dirt from clothing.

We are testing chemical EOR with a mixture of polymer and surfactant – a technique known as alkaline surfactant polymer – at sites including in Russia and Oman.

GAS

Injecting gases that can dissolve in oil – known as miscible gas – into a reservoir creates a mixture that flows more easily through the reservoir to production wells.

Shell was one of the pioneers in injecting naturally produced CO₂ to boost oil recovery from the Permian Basin in Texas, the USA, in the 1970s. There we built one of the world’s largest CO₂ EOR projects. Now we are looking at ways of using man-made CO₂ from power plants for gas EOR.

We also plan to use contaminated natural gas produced with oil in a project at Harweel in Oman. Here a gas rich in hydrogen sulphide will be re-injected into the reservoir to force out more oil. Using this approach we hope to recover up to 50% of the oil, compared to 10% using conventional production methods.