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Seeing beneath the surface
Extracting oil would be simple if it were found in huge underground lakes.
However it's always more complicated than that. Hydrocarbons are held in porous
rocks like water in a sponge, often in concentrations that are broken up and
spread across a large area, making them difficult to find.
Seismic surveys are the most powerful tool that exists to understand what
is going on beneath the surface of the earth. First used in the 1920s, the
technology uses sound waves generated by small explosions or vibrations at the
surface that reflect off underground rock layers. Interpreting the signals that
come back is key to understanding what is down there and how to reach it.
Today sophisticated software is combined with massive computing power to
translate the data to very high-resolution 3D images, or models, that reveal the
unique features of a reservoir. Over the years, Shell has developed, combined
and adjusted increasingly advanced programmes to help our geophysicists process
huge quantities of seismic data. During the processing, these programmes enable
them to filter out distortions caused by underground obstacles such as layers of
salt and volcanic rock – letting them see features in the subsurface that are
simply not visible on conventionally processed seismic.
With the models in place, geologists and engineers in different locations can
then view them simultaneously using Shell’s 12 interconnected virtual reality
centres around the world. The same 3D image appears to float in the air in front
of them allowing them to see above, behind and below the reservoir. This
real-time collaboration with such detailed imagery means faster and more
accurate decisions can be made on where to drill wells and the best way to
develop a reservoir.
Splitting the difference
Seismic data at sea is usually gathered using a single boat that both sends and
receives the seismic signals. When volcanic rock or salt is present under the
seabed, however, the signals become distorted and what’s below is hard to
interpret. By splitting the process and separating the signal sender and the
signal receiver between two boats, Shell has been able to shoot seismic at an
angle, getting underneath problematic structures. This technique helped Shell
win exploration rights for no less than 67 blocks in a Golf of Mexico lease sale
in 2007 which is a success rate of more than 70 %.
Electro-magnetic surveys
While seismic surveying and imaging are central to our success they are part of
a suite of technologies that we use to explore areas faster, more thoroughly and
with more certainty. In recent years, for example, we have had great success
with the new technology of electromagnetic surveying, providing increased
certainty that we will hit the right spot when we go in to drill an exploration
well.
The technology works by towing a powerful electro magnetic (EM) source close to
the seabed (rather than on the surface as with seismic). This source sends out
EM signals in to the subsurface which then bounce back and are captured by
receivers on the seabed. The type of signals that return change depending on how
strongly a material opposes the flow of electric current. While this technology
is available on the open market, we are able to apply our own processing
algorithms and techniques to the data to give us even more enhanced information.
Our approach of integrating technologies to optimize our exploration program has
enhanced our success rate in recent years - in deepwater Malaysia and Nigeria we
have made 19 discoveries from 25 deepwater wells drilled between 2001 and 2007.
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