Tectonic controls on maximum sustainable overpressure:fluid redistribution from stress transitions

摘要

Containment of overpressured fluids in areas of strong fluid release depends criticaly on the stress state and the brittle infrastructure within capping layers. Maximum overpressure is controlled by hydraulic extension fracturing only under low differential stress in the absence of throughgoing faults that are well-oriented for fricitional reactivation. Elsewhere, over pressure is bufferend by fault-valve action accompanying shear failure along existing or new-forming faults and is substantially lowere than that required for hydrofracturing, decreasing with increasing differential stress. For equivalent brittle failure modes at the same depth and differential stress, maximum overpressure is always higher compressional than in extensional regimes. Transitions in the tectonic stress state (e.g.positive or negative inversion),by changing mean stress (governed by critically stressed faults) and maximum sustainable overpressure, may thus induce regional episodes of fluid redistribution. Effects are likely to be most pronounced when the stress transition takes place rapidly.