Did Wastewater Disposal Drive the Longest Seismic Swarm Triggered by Fluid Manipulations? Lacq, France, 1969–2016 - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Bulletin of the Seismological Society of America Année : 2021

Did Wastewater Disposal Drive the Longest Seismic Swarm Triggered by Fluid Manipulations? Lacq, France, 1969–2016

Résumé

The activation of tectonics and anthropogenic swarms in time and space and size remains challenging for seismologists. One remarkably long swarm is the Lacq swarm. It has been ongoing since 1969 and is located in a compound oil-gas field with a complex fluid manipulation history. Based on the overlap between the volumes where poroelastic model predicts stresses buildup and those where earthquakes occur, gas reservoir depletion was proposed to control the Lacq seismic swarm. The 2016 M w 3.9, the largest event on the site, is located within a few kilometers downward the deep injection well. It questions the possible interactions between the 1955-2016 wastewater injections and the Lacq seismicity. Revisiting 60 yr of fluid manipulation history and seismicity indicates that the impacts of the wastewater injections on the Lacq seismicity were previously underevaluated. The main lines of evidence toward a wastewater injection cause are (1) cumulative injected volume enough in 1969 to trigger M w 3 events, onset of Lacq seismicity; (2) 1976 injection below the gas reservoir occurs only a few years before the sharp increase in seismicity. It matches the onset of deep seismicity (below the gas reservoir, at the injection depth); (3) the (2007-2010) 2-3 folds increase in injection rate precedes 2013, 2016 top largest events; and (4) 75% of the 2013-2016 events cluster within 4-8 km depths, that is, close to and downward the 4.5 km deep injection well. As quantified by changepoint analysis, our results suggest that timely overlaps between injection operations and seismicity patterns are as decisive as extraction operations to control the Lacq seismicity. The seismicity onset is contemporary to cumulative stress changes (induced by depletion and injection operations) in the 0.1-1 MPa range. The interrelation between injection and extraction is the most probable cause of the Lacq seismicity onset and is sustenance over time. The injected volume-largest magnitude pair for Lacq field is in the same range (90% confidence level) than wastewater volume-magnitude pairs reported worldwide, in a wide variety of tectonic settings. KEY POINTS • We highlight the role of wastewater disposal on seismicity in a context of gas reservoir depletion. • The interrelation between injection and extraction is the most probable cause of the Lacq seismicity. • The Lacq volume-magnitude pair is in the same range (90% confidence level) than pairs reported worldwide.
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hal-04476424 , version 1 (24-02-2024)

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Jean-Robert Grasso, Daniel Amorese, Abror Karimov. Did Wastewater Disposal Drive the Longest Seismic Swarm Triggered by Fluid Manipulations? Lacq, France, 1969–2016. Bulletin of the Seismological Society of America, 2021, 111 (5), pp.2733 - 2752. ⟨10.1785/0120200359⟩. ⟨hal-04476424⟩
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