Fracture behavior of transversely isotropic rocks with discrete weak interfaces

HUMBERTO CELLERIHUMBERTO CELLERI; MARTIN SANCHEZ; ,JOSE LUIS OTEGUI,JOSE LUIS OTEGUI

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS

JOHN WILEY & SONS LTD

Lugar: LOndres; Año: 2018 vol. 42 p. 2161 - 2176

0363-9061

Anisotropic rocks have gained increasingattention due to the development of unconventional Oil&Gas reservoirs.Thistype of reservoir requires complex engineering procedures from drilling to completion,and the mechanical properties of the rocks play a significant role. One of themost important characteristics of unconventional formations is the presence ofwell-defined layers, which greatly modify both the elastic and fractureproperties of the rocks. Rock elastic response is directiondependent, commonly described as Vertically Transversely Isotropic (VTI),meaning that there is an isotropic plane of symmetry with respect to thevertical direction. Between layers, calcitic veins or ash beds alter the rock´sproperties substantially. These interfaces, which can have low or no cohesionat all, act as preferential planes for fracture nucleation and propagation,affecting the rock´s strength.In this work, the fracture behavior ofVTI rocks with weak interfaces is studied using numerical simulations ofBrazilian tests. A hybrid Discontinuous Galerkin (DG) - Cohesive Zone (CZ)model was used to simulate fracture initiation and propagation on discs in thepresence of weak planes. With this approach, we determined the effective Braziliantest strength of the rocks under different conditions, namely, relative angles betweenlayers and the loading direction, densities and cohesion of weak interfaces. Shearreactivation of the interfaces is analyzed using the Mohr-Coulomb failure criterionand Mohr circles.