Geomechanical Forward Modelling of the Genesis of Polygonal Fault Systems

Abstract

Polygonal fault systems (PFS) are commonly encountered in the subsurface. Many of the key characteristics of PFS have been established using 3D seismic data and the potential impact of PFS on caprock integrity and hydrocarbon exploration has been realised for some time. However, a universal mechanism to explain their formation remains elusive. Understanding processes leading to natural fracturing and faulting in mudstones may have implications for a number of industrial activities, particularly in this case where tectonic forces are not thought to have played a significant role. The work presented here attempts to progress recent efforts examining a diagenetic trigger for polygonal fault genesis. More specifically, investigations of diagenetically sourced structure development in mudstones have been undertaken in order to formulate a geomechanical argument for the triggering of shear failure in scenarios of uniaxial consolidation. Data from the literature is used to populate material parameters for finite strain computational models using the geomechanical code ELFEN. Prediction of PFS in both two and three dimensions are presented that demonstrate that this modelling approach can predict realistic PFS geometries including the observed transition from random to preferential fault alignment with increasing degree of stress anisotropy.