Making sense of seismic noise

How High-Throughput Compute helps scientists to correlate data from millions of calculations to unveil the rock structure of an oil field under the North Sea

Oil and mining companies use seismic waves to figure out the structure and type of rocks underground, so they can plan their work. Because they can’t wait for earthquakes, they artificially induce seismic waves with explosions. This is, however, expensive and has severe environmental consequences.

Aurélien Mordret, a seismologist based in France, is working on an alternative that puts the background seismic noise to good use. Thanks to a mathematical method called cross-correlation and to high-throughput compute, it is possible to collect meaningful seismic data from the rumble of waves as they travel across the seafloor.

As part of his research, Aurélien applied the cross-correlation method to the Valhall oil field in the North Sea to investigate the structure of the rocks underneath the ocean floor.

Armed with the data and the computational power of EGI’s High-Throughput Compute,  Aurélien was able to produce 3D models of the ground beneath the network of sensors.

At Valhall, the cross-correlation method is only sensitive to the first 500 meters, so the model does not reach the oil reservoir that is down at 2,500 meters. Even so, by computing the way the seismic waves propagated underground, Aurélien was able to draw some conclusions about the reservoir. He reported on a cluster of cracks in the rock in a paper for the Geophysical Research Letters.

“To sum up, even if it will never totally replace the use of explosions, the seismic noise correlation technique is very powerful to make high-resolution seismic images of the subsurface when it is coupled with the very dense seismic network of several hundreds of stations,” he concludes. “But it requires a huge amount of computation and this is where EGI becomes helpful.”

An oil and gas exploration platform in the North Sea. Image: JanChr / wikicommons

References

A. Mordret et al. (2013) Helmholtz tomography of ambient noise surface wave data to estimate Scholte wave phase velocity at Valhall Life of the Field. Geophysics 78:WA99-WA109 (abstract)

A. Mordret et al. (2013) Azimuthal anisotropy at Valhall: The Helmholtz equation approach.Geophysical Research Letters 40:2636-2641 (abstract)