The injection of industrial wastewater into the subsoil is responsible for regular earthquakes in the Lacq basin, in the Pyrénées-Atlantiques. This is a “conclusive” finding established by an international study from the University of Toulouse.
The anthropogenic origin of the seismicity of Lacq, near Pau, had been known for a long time. However, this “cluster” of earthquakes has long been attributed to past intense gas extraction activities from the Lacq reservoir. The latter was, moreover, for sixty years, the largest natural gas deposit exploited in France.
Gas extraction exonerated
However, “the intensive extraction of Lacq gas ended in 2013 and the seismicity of the area has not decreased,” Jean Letort, teacher-researcher at Toulouse III-Paul University, told AFP. Sabatier, within the Research Institute of Astrophysics and Planetology.
The study published Thursday in Geophysical Journal International confirms the hypothesis, considered three years ago by a Franco-German research team, of a “major role” of industrial wastewater injected into the reservoir.
Since 1969, a few years after the start of the exploitation of gas reservoirs, the Lacq region has been regularly shaken by low magnitude earthquakes. “The majority of earthquakes are located very close to the limits of the reservoir and the seismic energy released is directly linked to variations in the volume of industrial water injected into the reservoir,” concludes the study, based on a network of sensors deployed for three years.
“The more we inject, the bigger the earthquake,” summarizes Jean Letort, who calls for the development of reliable models. “You have to understand what the risks might be in order to establish a ceiling,” he says. A “crucial issue” for the management of wastewater injections, but also for deep geothermal energy and carbon dioxide sequestration projects, the study further underlines.
Questions about the CO2 landfill project
The Lacq basin is in fact at the center of a CO2 burial project which plans to store five million tonnes of CO2 in the ground per year. A project led by the gas network manager Teréga, the French cement manufacturer Lafarge, the steel group ArcelorMittal and the Spanish oil company Repsol.
Involved in this study, German researchers from the German Research Center for Geosciences in Potsdam are also working on the case of the Groningen natural gas field, in the north of the Netherlands, where the numerous earthquakes caused by extraction have shaken homes. . In October, the Dutch Senate approved its permanent closure.