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Microbial enhanced oil recovery (MEOR) Stimulating bacterial growth at an oil/water interface causes a substantial reduction in interfacial tension (IFT), which in turn can help to achieve improved oil recovery (IOR).

The prime consideration with MEOR is how much additional oil can be produced from reservoirs by stimulating the growth of indigenous or injected bacteria. This is accomplished by adding nutrients to injection water.

When certain types of microbes are stimulated in core samples of reservoir sandstone in the laboratory, they improve oil production by mobilising residual oil trapped in the pore space.

This is probably because the bacteria induce changes in the IFT between the oil and the water, and possibly also because they cause a change in wetting properties.

However, proving this experimentally on growing bacterial systems is notoriously difficult.

Researchers at Statoil and Norways Sintef foundation have made a significant advance by quantitatively monitoring changes in IFT at a simple oil/water interface using an advanced laser-light scattering technique.

Microbially induced reduction in interfacial tension with time.

The graph of IFT versus time shows that the bacteria induced a 6,000-fold exponential reduction in the IFT.

This development is thought to occur because the bacterial growth requires both carbon from the oil and nutrients from the formation water. Since they occur in the water, the bacteria need to penetrate the oil/water interface to access the carbon.

They achieve this by producing a biosurfactant (tenside), which reduces the IFT and thus lowers the energy needed for breakthrough.

Statoil is thought to be the only company in the world using MEOR on an offshore field, in this case Norne in the Norwegian Sea.

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