PARIS - It is a little-known fact that oil has been pumped out from underneath the Paris Basin for more than half a century. There are more than 2,000 wells operating in 52 oil fields, producing around 10,000 barrels per day, amounting to 0.5 percent of French national consumption.

With most conventional crude reserves already exploited, U.S. companies such as Toreador and Hess, and the Canadian branch of Vermilion have set their sights on non-conventional reserves, in particular shale oil. In the Paris Basin, a vast area that covers much of northern France, this crude oil substitute is found in bedrock some 2,750 meters below ground, which dates back to the Lower Jurassic period some 150 million years ago.

For the time-being, the full potential of these reserves is unclear: the French Institute of Petroleum (IFP) estimates they could amount to between 60 and 100 billion barrels of oil – equivalent to 90 and 150 years of French national consumption at the current rate.

These are theoretical numbers, to be distinguished from proven reserves that are economically feasible. But the more the price of oil soars, the more attractive French shale appears, despite the higher extraction costs and other obstacles such as local opposition on environmental grounds and state bureaucracy.

Local Opposition

US oil company Toreador is due to start exploration drilling for oil shale in the town of Doue, some 50 kilometers east of Paris on April 15, with the aim of mapping reserves in the area. Their plans, however, have met with stiff opposition from locals over environmental concerns. On March 3, Doue's city council approved a motion to suspend the exploration project. The following weekend, some 2,000 people joined a demonstration against the exploitation of shale oil in the area.

Doue's opposition followed similar protests in the regions of Languedoc-Roussillon and Rhone-Alps, where Toreador also plans to prospect for oil. Following a meeting with the Ministries of Industry and Ecology, the company agreed to suspend its exploration operations ahead of two reports by the government and parliament, due May 31 and June 8.

In the meantime, researchers at France's Bureau of Geological and Mineral Research (BRGM) recently combined a series of seismic studies of the area carried out by various petrol companies over the last 50 years (Marine and Petroleum Geology, April 2011). The institute's researchers have succeeded in putting together the first ever geological chart mapping of the entire 170,000-square-kilometer Paris Basin, which extends eastward into parts of Belgium, Luxembourg and Germany.

The seismic studies give an image of the basin's geological make-up to a depth of some four kilometers without having to drill. BRGM researchers were able to visualize the Triassic layers, dating back some 250 million years, and even reached the 400-million-year-old Variscan, or Hercynian, platform. The publication of the BRGM study coincides with the oil exploration projects to the east of Paris as well as growing affirmation from experts such as Roland Vially at the IFP that the basin could be home to important shale reserves.

"That's the conclusion made by the geo-chemists," says Charles Lamiraux, geologist with the National Office for Energy and Climate. "But first, exploration is needed to ascertain whether it is possible to gain access to the reserves, and if the technology exists for that"

Precious data

The BRGM study does not shed new light on potential hydrocarbon reserves, but it helps better retrace the geological history of the basin and its oil infrastructure. This information is precious for oil companies, a number of which have purchased the data compiled by the BRGM.

"The Paris Basin is relatively simple," says Franck Hanot, formerly of BRGM and now heads of the research office at CDP energy consulting. "We used to think there were lots of small fractures, but in fact there are relatively few fractures. A few big fractures have cut through a number of strata to form some very large structures."

One hundred and fifty million years ago, the Paris Basin looked nothing like it does today. "It was initially a vast lagoon. After that it was a relatively deep sea, intercut with small land masses, before becoming the vast sedimentary basin that it is today," explains Laurent Beccaletto, a geologist at BRGM. "The large fractures in the Paris Basin were formed well before the African landmass started pushing up against the European continent. The pressures which occurred later and coincided with the formation of the Pyrenees and the Alps made these fractures move, but they also prompted the formation of more recent fractures."

The migration of oil

The geology atlas of the Paris Basin's underground provides information on the formation and possible migration of hydrocarbons. It may also be useful for future geothermic and hydrological studies.

"It is the only document that allows us to have a profound understanding of what is buried beneath the surface," says Hanot. "Petroleum engineers often have a more localized vision of geology," explains Laurent Beccaletto. "It is their job to drill in order to see what exactly is there."

One thing is for sure – the Paris basin is no Saudi Arabia. "Nor is it Texas," adds Hanot. "There is no risk that oil will start flowing freely in France because the procedure for obtaining licenses and carrying out drilling is very strict here. The government requires operators to conduct serious preliminary environmental studies."

Read the original articles in French here and here.