Field, experimental, and numerical studies of deformation localization bands



Characterization and Formation Mechanisms of Deformation Localization Bands(Shear, Compaction, and Dilatancy): Field and Experimental Data,Theoretical Analysis and Numerical Models;Montpellier, France, 9–10 May 2011. The origin of fractures and discontinuities in rocks has been for decades a subject of common interest in both the academic world and industry, as these features influence hydrocarbon reservoir production. Fractures (notably joints) and deformation bands are usually analyzed on a separate basis. Joints have commonly been interpreted as mode I fractures susing fracture mechanics, whereas the bifurcation theory has been used for deformation bands. This diversity was called into question by the research carried on by the Geo-FracNet consortium sponsored by Total and Shell International. New findings (A. I. Chemenda et al., J. Geophys. Res., 116, B04401, doi:10.1029/2010JB008104, 2011, and references therein) suggest that at least a part of joints could have been formed as dilatancy (dilation) bands, i.e., due not to the strong effective tensile stress concentration at the opening fracture tip but to the porosity increase and decohesion (perigranular and/ or intragranular grain breakage) of the material within a band several grains thick. The band (material damage and dilatancy within it) can propagate along the strike without opening and can eventually be opened.