Earthquakes and depleted gas reservoirs: which comes first?

Abstract

Abstract. While scientists are paying increasing attention to the seismicity potentially induced by hydrocarbon exploitation, so far, little is known about the reverse problem, i.e. the impact of active faulting and earthquakes on hydrocarbon reservoirs. The 20 and 29 May 2012 earthquakes in Emilia, northern Italy (Mw 6.1 and 6.0), raised concerns among the public for being possibly human-induced, but also shed light on the possible use of gas wells as a marker of the seismogenic potential of an active fold and thrust belt. We compared the location, depth and production history of 455 gas wells drilled along the Ferrara-Romagna arc, a large hydrocarbon reserve in the southeastern Po Plain (northern Italy), with the location of the inferred surface projection of the causative faults of the 2012 Emilia earthquakes and of two pre-instrumental damaging earthquakes. We found that these earthquake sources fall within a cluster of sterile wells, surrounded by productive wells at a few kilometres' distance. Since the geology of the productive and sterile areas is quite similar, we suggest that past earthquakes caused the loss of all natural gas from the potential reservoirs lying above their causative faults. To validate our hypothesis we performed two different statistical tests (binomial and Monte Carlo) on the relative distribution of productive and sterile wells, with respect to seismogenic faults. Our findings have important practical implications: (1) they may allow major seismogenic sources to be singled out within large active thrust systems; (2) they suggest that reservoirs hosted in smaller anticlines are more likely to be intact; and (3) they also suggest that in order to minimize the hazard of triggering significant earthquakes, all new gas storage facilities should use exploited reservoirs rather than sterile hydrocarbon traps or aquifers.

An Insight into Underground Hydrogen Storage in Italy

“…In a final step, the identified aquifers and depleted hydrocarbon fields were uploaded to a Geographical Information System (GIS) map, where we also plotted the location of potential sources of earthquakes larger than Magnitude 5.5 included in the Database of Individual Seismogenic Sources (DISS) of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) [55]. Two studies that addressed the anti-correlation between the occurrence of gas reservoirs and large seismogenic faults in Italy [56,57] found that large earthquakes cause large slips over large faults compared to smaller events where the associated slip is too small to potentially affect reservoir integrity. Therefore, sites located over or near these larger seismogenic sources were not considered as favourable for UHS.…”

Sources and migration pathways of methane and light hydrocarbons in the subsurface of the Southern Po River Basin (Northern Italy)

“…amounts of higher hydrocarbons) in the subsurface. In tectonically active basins, fracture and fault systems strongly enhance channeling and vertical migration of CH 4 -rich fluids from the source zone to reservoirs (Mucciarelli et al, 2015), ultimately allowing their seeping from terrestrial and submarine vents (Etiope, 2009;Capaccioni et al, 2015). Surface seepage of methane, light hydrocarbons and oil is a widespread phenomenon along the Alpine-Himalayan Orogen where mud volcanoes, dry gas vents and brackish/salt water seeps, mostly occurring in correspondence of suture zones between converging plates (e.g.…”