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A survey of the induced seismic responses to fluid injection in geothermal and CO2 reservoirs in Europe

pubblicazioni - Articolo

A survey of the induced seismic responses to fluid injection in geothermal and CO2 reservoirs in Europe

The paper documents European case histories that describe the seismogenic response of crystalline and sedimentary rocks to fluid injection. It is part of an on-going study to identify factors that have a bearing on the seismic hazard associated with fluid injection. The data generally support the view that injection in sedimentary rocks tends to be inherently less seismogenic than in crystalline rocks, although the presence of faults near the wells that allow pressures to penetrate significant distances vertically and laterally can be expected to increase the risk of producing felt events. All cases of injection into crystalline rocks produce seismic events, albeit usually of non-damaging magnitudes, and all crystalline rock masses were found to be critically stressed, regardless of the strength of their seismogenic responses to injection. Thus, these data suggest that criticality of stress, whilst a necessary condition for producing earthquakes that would disturb (or be felt by) the local population, is not a sufficient condition. The present data are not fully consistent with the concept that deeper injections in crystalline formations tend to produce larger magnitude events. Injection at sites with low natural seismicity, defined by the expectation that the local peak ground acceleration has less than a 10% chance of exceeding 0.08g in 50 years, have not produce felt events. Although the database is limited, this suggests that low natural seismicity, corresponding to hazard levels below 0.07g, may be a useful indicator of a low propensity for fluid injection to produce felt or damaging events. However, higher values do not necessarily imply a high propensity.

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