Late 1970s-1980s
Paris Basin geothermal boom (late 1970s-1980s)
After the 1973 oil crisis, France pushed home-grown heating. The first doublet plants tapped the Dogger limestone under the Paris Basin in the late 1970s and early 1980s, using one well to extract hot water and a second to reinject it.
Then
The plants cut reliance on imported oil for heating, and the Paris Basin became one of Europe's busiest geothermal districts.
Now
The doublet design became the standard for deep geothermal heating, and many of those 1970s-80s plants fed French district heating networks for decades.
Why this matters now
Aulnay-sous-Bois uses the same Dogger aquifer and doublet design France pioneered in the 1970s, applied to a network that now runs on natural gas.
