For a long while the oil* buried deep beneath the ocean bed seemed to be impossible to exploit for two main reasons: firstly because existing technologies did not make it possible to drill 3,000 metres beneath sea level, and secondly because it was difficult to see how these deposits could be profitable in the long run given the means needed to acquire them in these conditions. Technological advances, ever greater demands for hydrocarbons, and the increase in the barrel* price mean that these impediments no longer seem quite so insurmountable. The oil majors are now turning to deep (between 500 and 1,500 metres beneath sea level) and ultra-deep offshore (beyond 1,500 metres) drilling. In 1978 the deepest offshore drilling was at 312 metres, but since 2007 it has been at 2,540 metres. To exploit a deposit at these depths the risers generally used in conventional offshore drilling are no longer appropriate as they would collapse under their own weight. The water temperature (4°C at 1,500 metres) is also a problem for bringing the oil* up to the surface, which gushes from the well at between 80°C and 100°C and needs to be kept as hot as possible to prevent deposits of paraffin or carbohydrate inside the pipes. Petrobras, the Brazilian oil company, has embarked in ultra-deep offshore drilling since the discovery in 2007 of vast submarine deposits off the coast of Brazil beneath 2,100 metres of water, 3,000 metres of sand, and 2,000 metres of salt. The deposits are estimated at somewhere between 5 and 8 billion barrels*, amounting to 40% of the country’s current reserves.

Closer to home, explorations have been carried out in 2,000 metres of water off the coast of Surinam since 2000.

The history of oil exploration off the coast of French Guiana goes back a fair way to the 1970s when Elf was prospecting off the coast at Sinnamary. The French oil giant, which was still state-owned at the time, drilled two 850 metre wells beneath 50 metres of water. Neither were put into production.

It was only in 2001, when the British company Tullow Oil bought an exploration licence from the French authorities for 32,000 square kilometres in the economic exclusion zone, that oil exploration off the coast of French Guiana started again.

The technologies and economic context for oil had considerably changed since the 1970s, and the explorations carried out by Tullow Oil concentrated on an ultra-deep deposit beneath 2,000 metres of water. Oil geologists hope to find exploitable deposits beneath the seabed off French Guiana because the geological system is analogous to that found off Surinam and in the Jubilee oil field off the coast of Ghana.

The uplift* of the Andes combined with the opening up of the South Atlantic when Pangaea broke up and the action of mega-rivers means that there are chances of finding mature “rock reserves” about 90 million years old at the foot of the continental slope off the coast of French Guiana.

In order to prove this theory the company initially worked with Gaz de France and carried out seismic testing at sea off the mouth of the Mana river, in a sector called Mata Mata in depths of 1,800 metres of water. The results suggested that there was little chance of finding any exploitable deposits of either gas or oil, so Gaz de France withdrew from the project.

A second fruitless attempt using the same seismic testing methods was carried out in 2005 on the eastern edge of the permit zone.

It was only in 2009 when more complex exploration techniques were used and a consortium set up with Total and Shell that Tullow Oil finally reckoned the chances of success to be sufficiently good to drill an exploration well.

And so today French Guiana is about to see an oil rig appear 160 kilometres off the coast of Cayenne. The GMES-01 well should be completed in May this year and it will be an ultra-deep one as it is beneath 2,050 metres of water and about 4,000 metres below the seabed. The latest hypotheses suggest reserves of between 500 million and 1 billion barrels*, about the quantity of oil* produced worldwide in ten days or so (or 300 years of consumption in French Guiana at the current rate). It comes as no surprise that oil* from French Guiana will not make any impact on the world market or even French self sufficiency given the distances involved. However, selling it on neighbouring markets could generate taxes and become a source of revenue for the State and perhaps the future single-tier authority. It is to be hoped that the catastrophe in May 2010 on the ultra-deep rig Deepwater Horizon, belonging to the British group BP, which provoked an unprecedented ecological catastrophe (5 million barrels were spilled into the ocean along the coasts of Louisiana and Florida) will act as a lesson for the future operator of the French Guianese field. What is more, following on from this traumatic experience, the American government has taken the precaution of decreeing a moratorium1 on offshore oil exploration and the European Commission has invited member states to implement the precautionary principle.2

1: On 2 December 2010 the US declared itself in favour of a 17-year moratorium on all new drilling in the Gulf of Mexico.

2: Communication by the EU Energy Commissioner to the European Parliament on 12 October 2010, seeking to enforce the applicable European legal framework. Whilst awaiting implementation of these legal improvements the Commission invited member states to apply the precautionary principle for all drilling projects, excluding exploration.

Seismic testing at sea

When carrying out exploration prior to any drilling, seismic vessels are used. Their role is to navigate the exploration zone to build up an image of the sub-surface. The method is relatively similar to that of an ultrasound scan, just on a far larger scale. A seismic wave is generated using air canons which fire air under high pressure into the water. The frequency of this wave can be modified depending upon the desired depth to be studied: the higher the frequency, the lesser the depth but the greater the resolution. For images of less than 200 metres beneath the surface (referred to as very high-resolution seismic testing) the wave frequency is between 300 and 2,000 Hertz, whereas frequencies of between 5 and 80 Hertz are used for so-called conventional seismic testing, which can build up an image of the sub-surface to depths of up to fifty kilometres. The wave generated passes through the water and then the marine sub-surface, according to the laws of reflection and refraction. Fixed behind the ship are streamers made up of hydrophones which record the echoes of the wave, thus making it possible to render a 2D image of the structure of the sub-surface, something that is referred to as a seismic profile. A seismic vessel normally tows ten or so streamers behind it. The quality of the profile depends on the wave sent out, the amount of information collected (the number of hydrophones receiving echoes of the wave), the geology and topography of the terrain, and the weather. The vessel explores the zone following a grid system so as to obtain a large number of parallel seismic profiles according to a predetermined acquisition line, thus providing a near-3D image of the sub-surface. On-board geophysicists carry out quality control on the data collected and perform a series of modifications so as to improve it. This process, called seismic processing, consists for example in filtering data and correcting it depending on the speed of the wave through the various layers, thus making it possible to eliminate as much useless information as possible without altering the useful information: this is known as increasing the signal-to-noise ratio. This is where the role of the explorer ends since interpretation is normally carried out by geologists in processing centres.