Undiscovered Oil and Gas in France's Paris Basin: A 2015 USGS Assessment

As part of a push to assess priority European basins, the U.S. Geological Survey estimated the undiscovered, technically recoverable oil and gas in the Paris Basin of France. The basin is part of the USGS's Anglo-Paris Basin Province, but only the Paris Basin itself was assessed, for both conventional resources and unconventional ones — shale oil, shale gas and tight gas.

The mean estimates

F95 means a 95 percent chance of at least that amount; F5, a 5 percent chance. The estimates are fully risked.

Conventional oil and gas

More than 35 conventional oil and gas fields have been found in the Paris Basin since the 1950s; the largest oil field, Chaunoy, was discovered in 1983. Given the fields' geology, their exploration history and what is known of the source rocks, estimating what conventional resources remain is straightforward.

The USGS drew one Mesozoic Reservoirs Assessment Unit around petroleum that formed in organic-rich Lower Jurassic shales, then migrated — across tens of kilometres from the areas where the source rocks were thermally mature — and was trapped in Triassic, Jurassic and Lower Cretaceous reservoirs.

Unconventional oil and gas

The study's focus was on source rocks that may still hold oil that never migrated. To count as a continuous source-reservoir system, a rock had to:

1. contain more than 2 percent total organic carbon by weight;
2. lie within the right thermal maturity window for oil or gas;
3. include more than 15 metres of organic-rich shale;
4. hold Type I or Type II organic matter.

For each candidate area, the region's tectonic and thermal history, and the timing of maturation and generation, were used to judge the risk that hydrocarbons had not been retained. Three units were defined:

Nearly all the unconventional gas is in the tight-gas unit — but whether the rifts, the tight river sandstones and the coal-sourced gas are there at all is highly uncertain, which is why the low (F95) estimate is zero. Across all units, the wide ranges reflect geological uncertainty, much of it over how much oil stayed in the source rocks after the rest migrated away.

What producing it would take

Well performance, drainage areas and success rates were borrowed from U.S. shale-oil and shale-gas analogues:

From these, the USGS estimates that a mean of about 6,400 hydraulically fractured wells would be needed to produce the continuous oil and gas.

Sources

• Schenk, C.J., Charpentier, R.R., Klett, T.R., Tennyson, M.E., Mercier, T.J., Le, P.A., Brownfield, M.E., Pitman, J.K., Gaswirth, S.B., Marra, K.R., and Leathers, H.M., 2015, Assessment of undiscovered oil and gas resources of the Paris Basin, France, 2015: U.S. Geological Survey Fact Sheet 2015–3016. https://pubs.usgs.gov/publication/fs20153016
• Method: Charpentier, R.R., and Cook, T.A., 2011, USGS methodology for assessing continuous petroleum resources: USGS Open-File Report 2011–1167. Results: USGS Energy Resources Program.
• The fact sheet's location map is drawn on an Esri basemap used under licence; it is left out.
• Rewritten in hubnx's own words.