A seismic shift

New innovations in seismic data gathering led to a major breakthrough in Maersk Oil’s Culzean field in the North Sea.

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This is how the new production facility at Culzean will look. Installation begins in 2016.

Deep beneath the turbulent North Sea waves, at a location almost equidistant between Denmark and the UK, a giant gas field capable of producing up to 5% of the UK’s domestic needs awaits development.

The field is called Culzean, a flagship project in the Maersk Oil portfolio and one of the largest gas discoveries of recent years in the North Sea. Development of the field recently took a leap forward with the announcement that USD 4.7 billion will be invested by Maersk Oil, and partners BP and JX Nippon, on the construction of the production facility. Installation begins in 2016 and drilling contractors have been signed, with first gas expected in 2019.

Dependent on the data

While Culzean could one day become a vital new energy resource for the UK, accessing the gas is no easy task. Operating in the North Sea is technically challenging, and with the reservoir located 4,300 metres below sea level, Culzean presents unique dangers related to high pressures and extreme temperatures.

Before taking the leap to develop in such an inhospitable environment, a massive amount of seismic data must first be accumulated.

In fact, the seismic data sets are so vast that the geophysical industry has earned a reputation for being the third most data-intensive industry globally after finance and defence.

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“Not only do geoscientists gather a vast amount of data, but we do complex calculations that would take several decades on an ordinary computer,” says Pierre Lanfranchi, head of Global Surface Technology at Maersk Oil.

Pierre Lanfranchi, Head of Global Subsurface Technology at Maersk Oil, estimates that if the data gathered in just one day during a typical seismic survey was stored on CDs, the pile would stretch almost as tall as the Eiffel Tower.

“Not only do geoscientists gather a vast amount of data, but we do some very intensive and complex calculations with it,” says Lanfranchi. “Processing the recorded data requires complex algorithms. An ordinary computer would need several decades to deliver the necessary information, so only by using the most advanced super-computers can we process the data in the required timeframe.”

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New innovations in seismic data led to a major breakthrough in Maersk Oil's Culzean field.

Geophysicists working on Culzean employed innovative technologies to acquire the seismic data, one of which involved placing 4,000 sensors directly on the seabed. The sensors were used to record reflections from acoustic waves being sent from a seismic vessel sailing above. The vessel covered a 20,000 square kilometre area, sending out a sound wave every 20 seconds for around two months, and the team worked intensively for eight months to transform this recorded data into a set of images of the subsurface.

More to be explored

The new technology – known as ‘ocean bottom cables’ – meant a much clearer picture could be formed for the Culzean team. “Placing sensors directly on the seabed provided a superior image of the subsurface,” says senior geophysicist Line Plouman Jensen. “The depths of the different geological formations are better understood and the data meant we could build a convincing geological model in a complex structural setting. This information is invaluable to drillers in such a high-pressure, high-temperature environment.”

There’s still much more information to be gleaned about what lies beneath Culzean from the seismic data, and this will be extracted in the years to come. “There is a wealth of information in the data set still to be extracted, analysed and understood. The data will work as an excellent baseline for future time-lapse seismic surveys used to monitor the depletion of the Culzean field,” says Jensen.

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The science behind seismic 

  • Seismic data provides geoscientists with the clue of where to drill for oil and gas. To gather seismic data, sound waves are sent into the earth’s subsurface where hydrocarbon accumulations could be trapped in the geological layers. The waves are reflected back to the surface where they are recorded by digital sensors. Computers process the raw data from the sound waves to reconstruct a 3D image of the earth’s crust. Those images are analysed to try and pinpoint where oil and gas reservoirs are located.
  • In offshore exploration, seismic data is usually generated by a vessel which sails slowly around the exploration area sending out acoustic waves. The vessel tows a high-tech array of ultrasensitive hydrophone sensors behind it on a series of streamers which can be up to 20 km long, making this device one of the largest-moving objects on the planet. In Culzean, the sensors were placed directly on the seabed, allowing a much larger hydrophone density and avoiding propagation noise in the water layer, which meant a much clearer picture could be formed.