Resolved stress analysis, failure mode, and fault-controlled fluid conduits in low-permeability strata

Abstract

Failure behaviour can strongly influence deformation-related changes in volume, which is critical in the formation of fault and fracture porosity and conduit development in low permeability rocks. This paper explores the failure modes and deformation behaviour of faults within the mechanically layered Eagle Ford Formation, an ultra-low permeability selfsourced oil and gas reservoir and aquitard exposed in natural outcrop in southwest Texas, U.S.A. Particular emphasis is placed on analysis of the relationship between slip versus opening along fault segments, and the associated variation in 10 dilation tendency versus slip tendency. Results show that the failure mode and deformation behaviour (dilation versus slip) relate in predictable ways to the mechanical stratigraphy, stress field, and specifically the dilation tendency and slip tendency. We conclude that dilation tendency versus slip tendency patterns on faults and other fractures can be analysed using detailed orientation or structural geometry data and stress information, and employed predictively to interpret deformation modes and infer volume change and fluid conduit versus barrier behaviour of structures. 15 IntroductionFaults and fractures often serve as conduits for fluid in low permeability rock (Barton et al.

Influence of fluid pressure changes on the reactivation potential of pre-existing fractures: a case study in the Archaean metavolcanics of the Chitradurga region, India

“…Faults and fractures are most likely to accommodate repeated slip episodes over a period of time, especially if reactivated by fluids (Curzi et al 2020). However, whether a fracture will behave as a conduit or a barrier depends on its mode of reactivation (Ferrill et al 2017a(Ferrill et al , 2019b(Ferrill et al , 2020. The external stress field plays a key role in fracture formation/propagation.…”

“…The vein emplacement mechanism within pre-existing fractures depends on the availability of fluids and P f magnitudes high enough to generate slip/dilation. Thus, finding out the eminence of slip over dilation or vice versa can be effective for understanding the deformation behaviour in fractures (Ferrill et al 2020). Quantifying the failure mode in fractures that have been reactivated also helps to estimate the volumetric changes associated with vein emplacements.…”

“…Quantifying the failure mode in fractures that have been reactivated also helps to estimate the volumetric changes associated with vein emplacements. Slip versus dilation patterns can be functional for inferring the failure mode in fractures within a stress field, at the time of deformation (Ferrill et al 2017a(Ferrill et al , 2019b(Ferrill et al , 2020. Tensional failure and shear failure can be easily identified and thus segregated from field observations.…”