Underwater Archaeology and Oil Exploration Rely on Shared Technology
Technologies originally developed for oil exploration have helped to reveal the location of two ancient Egyptian cities buried for over a millennium beneath the seabed in the Nile Delta. Franck Goddio is a pioneering underwater archaeologist whose discoveries are the subject of 'Sunken Cities: Egypt’s Lost Worlds', the latest BP exhibition at the British Museum.
More than 1,000 years ago, floods, subsidence and seismic activity in the fragile landscape of Egypt’s Nile Delta caused two ancient cities to collapse into the surrounding water. Protected by cloudy seas and centuries of sediment, the ruins of Canopus and Thonis-Heracleion remained hidden until their story came to the attention of a pioneering underwater archaeologist. Franck Goddio began applying the principles and technologies of oil and gas exploration to the hunt for submerged treasures, and his discoveries are now the subject of a major exhibition.
Sound wave technologies
Goddio was on a research trip to Egypt in the 1980s when he first became fascinated by local stories of two cities said to have disappeared from the map centuries ago. From ancient texts and conversations with Egyptologists he concluded that the most likely location for the cities was a 110km2 span of open water in Abukir Bay, off the coast of Alexandria.
Faced with working in up to 10 metres of murky water to search an area of smooth, featureless seabed about the size of 16,000 football pitches, Goddio saw the potential in using sound wave technologies to narrow down his search – the same technologies employed in oil and gas explorations to identify geological structures associated with hydrocarbon fields and reservoirs. Goddio noted that the discovery of the lost cities was totally dependent on technology.
Magnetometry
Once such technology is nuclear magnetic resonance (NMR) magnetometry, which measures minute disturbances in the earth’s magnetic field. Interpretation of these disturbances can provide information about natural geological features or the presence of man-made objects.
NMR magnetometers were first developed for the oil and gas industry which was looking for vast geological structures, said Goddio. As he is looking for very, very tiny things, he needs the extreme sensitivity of the magnetometer.
Goddio found that it required a combination of four different NMR magnetometers to be sufficiently sensitive to distinguish the magnetic fields create by archaeological ruins and artefacts from the magnetic fields associated with earth, the stars and other sources.
Sidescan sonar
Towing this equipment beneath a boat he criss-crossed the search area in an organised pattern until the whole seabed had been surveyed. They also used other acoustic sensing technologies familiar to oil explorers, such as multi-beam bathymetry, sidescan sonar and a sub-bottom profiler, and fed all the results into computing systems to graphically display the data.
By studying the data for anomalies Goddio was able to target his divers’ exploratory excavations to very precise locations on the seabed. One particular feature in the data stood out. They saw a large, narrow, magnetic anomaly and Goddio directed the team to excavate right in the centre and at each end. In three small, focused excavations they characterised a 150m long wall beneath 1.8m of sediment.
Further targeted explorations revealed three further walls in the typical shape of an Egyptian temple, and by directing his divers to dig where he expected the centre of the temple to be, the divers discovered an immaculately preserved black stele. Subsequent translation of the hieroglyphs on the stele confirmed this was the great temple of Amun-Gereb in the city known as Thonis by ancient Egyptians, and as Heracleion by the ancient Greeks.
Keyhole surgery
Goddio compares what his team is doing to keyhole surgery. They are not doing big excavations of archaeological sites, like in the 19th century. The technology allows them to focus, to narrow, to zoom in and be very efficient.
Goddio draws a further parallel with oil and gas exploration: In underwater archaeology you start with a small team, two engineers, one or two divers. But when you know you have hit your target, then you can scale up the investment in the logistics, time and people.
The rewards of this approach are there for all to see at the British Museum in an astonishing collection of artefacts recovered from the two lost cities – and there is much more yet to come.
Pompeii is on land and has been excavated for centuries, says Goddio, but Thonis-Heracleion alone is bigger, and underwater. Goddio said he doesn’t think they have touched more than 5% of these sites yet, so they have a lot still to learn.
Seismic imaging
Further offshore and in much deeper water, BP has made several recent discoveries of its own in the Nile Delta.
The company’s main exploration technology for oil and gas is seismic imaging, explained BP distinguished adviser John Etgen. Just as the archaeologists are doing, they use sound waves to create a picture of the sub-surface, only they are looking for structures kilometres below the surface, rather than a few metres.
Seismic imaging has become increasingly sophisticated over the past 20 years and enables now the creation of detailed 3D images of rock structures that gives very good information about where they are likely to find oil and gas.
They also continue to use many of the tools that Franck Goddio talks about. For instance, side-scan sonar is very helpful in identifying where there may be faults in the sea bed – or where there are colonies of organisms that live on the ocean bottom. In this way they can make sure any structures they need to put on seabed are located safely and without harming important sea life.
Working with its partners, BP has been supplying Egypt with energy for over 50 years, and developments such as the West Nile Delta project, Atoll phase 1 in the East Nile Delta will help to provide the country with energy for many years to come.
The BP exhibition Sunken cities: Egypt’s lost worlds is now open at London’s British Museum and runs until 27 November 2016.
Source: BP Magazine, the international magazine of the BP group. BP Magazine brings regular reports from activities around the globe, the people who make them happen, and the challenges that face the oil and gas industry.
Images: Yann Bernard and Christoph Gerigk © Franck Goddio / Hilti Foundation
