Tectonic breaching

Although seal failure caused by fracturing results from the interplay of pore-pressure and tectonic deformation, it is useful from the point of view of risk analysis to consider them separately as tectonic breaching (caused by tectonically-induced dilation), and hydraulic breaching (caused by increase in pore-pressure). 

Tectonic breaching within the GEA is mostly related to Cretaceous to Tertiary compressional or tran-spressional deformation and is manifested by two processes. Firstly, extension occurs above the neutral surface of inversion folds (Fig. 8a), thereby creating a pattern of radial tension fractures, extending upwards from the seal into the overlying section. Radial fractures will not form below the neutral surface of the fold limb which is in compression. As a consequence, reservoir objectives lying above or close to the neu-... 

Fig. 8. Schematic illustration of tectonic breaching for (a) structural inversions and (b) footwall fault blocks. Tectonic breaching within inversions is caused by radial fractures and wrench faults. It is also possible that tectonic breaching may be caused by the re-activation of normal faults.

Cored Upper Jurassic claystones from a well located within the Lindesnes trend display both dila-tional and shear fractures (Fig. 9). Although both shear and dilational fractures can be produced by hydraulic fracturing (Lockner and Byerlee, 1977), the location of this well within a major wrench zone suggests tectonic breaching as the most likely cause. 

Hart S. R. and Zindler A. (1989) Constraints on the nature and development of chemical heterogeneities in the mantle. In Mantle Convection Plate Tectonics and Global Dynamics (ed. W. R. Peltier). Gordon and Breach, vol. 4, pp. 261-387. 

F.H. Busse Fundamentals of thermal convection, in W.R. Peltier (ed.) Mantle convection, Plate Tectonics and Global Dynamics, Gordon and Breach, p. 23 (1989)... 

The 2008 Wenchuan earthquake of Mw = 7.9 in the Sichuan Province of China affected mountainous area where body of moxmtains has been deteriorated by the tectonic action. Slope failures produced natural dams (Fig. 15). The problem of the natural dams is the possibility of breaching and flooding in the downstream area. Therefore, it is important after big earthquakes in mountain regions to find the formation of natural dams and if a dam is subject to overtopping, erosion, and breaching to drain water as soon as possible. Empirically it is known that seepage and piping failure is rather rare in natural dams (Tabata et al. 2002). 

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