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Angles
on oil
Oil in hard rock types under the
ocean’s floor can be difficult to find. A new search method
may change all that.
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NEW
METHOD: Sound waves sent obliquely into the water
can determine whether undersea rock formations contain oil
or not.
Contact: Martin Landrø,
Department of Petroleum Engineering and Applied Geophysics,
NTNU
Tel: +47 73 59 49 73
Email:mlan@ipt.ntnu.no |
| Photo: Arvid Steen |
MORE THAN HALF OF THE WORLD’S OIL RESERVOIRS
are embedded in carbonate rocks. These rocks are hard, and it can
be challenging to determine if the carbonate contains oil or just
water. A research team lead by Professor Martin Landrø has recently
revised an existing method that may solve this problem.
NO MORE DRILLING IN THE DARK
Landrø’s method in itself is not new. The technique is known as
repetitive seismic, and is used for mapping geological structures
below the ocean floor with sound waves. The seismic creates images
of the reservoirs, both to determine the amount of oil, and, during
extraction, to control the amount of water that flows in. Repetitive
seismic has worked very well on reservoirs located in sandstone.
Statoil has used the method in about seventy of its oilfields in
the North Sea, and Hydro is not far behind. Using the technique,
drillers can see when they have emptied a reservoir of oil, or if
more oil remains. They no longer need to drill in the dark. Statoil
says their profits from using the method are about five billion
kroner.
A REWARD WORTH BILLIONS
Until now, however, the method has not worked with carbonates. Because
carbonates are much harder than sandstones, it has not been possible
to read the difference in the signals from carbonates containing
oil and carbonates containing water. Landrø hopes he can change
all that. Along with Anh Ket Nguyen, a SINTEF Petroleum Research
scientist, and Hosseinn Mehdizadeh, a PhD student at NTNU, Landrø
has found a new approach to the old technique.
The sound signal is sent obliquely into the
water and ‘slides’ along the ocean floor – on top of the layer where
the oil is – and then returns to the surface again. The key is that
carbonates that contain oil and carbonates that contain water return
the signal at different points, and this difference can be measured.
“If the new method withstands the test, it
is reasonable to think that the reward will be much greater than
the five billion Statoil saves now,” says Landrø. The method was
presented at an international conference in the USA in October 2004.
Tore Oksholen
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