Effect of Dilatancy in Weak Mechanical Discontinuities on Their Interaction with Fluid Driven Fractures

Fluid driven fracturing plays a key role in several industrial applications, such as stimulation of O&G reservoirs, development of enhanced geothermal systems, and geological carbon storage, to name a few.

In previous works we have introduced Y-FRAC^®, a fluid driven fracture and rock mechanics simulation platform which makes use of the Discontinuous Galerkin method and a cohesive zone model to describe the deformation and fracture processes that take place in the rock, and standard finite elements to model the corresponding fluid flow inside the fractures during stimulation.

In this work, we expand the previously used constitutive models in order to include the effects of dilatancy during shear deformation. We then evaluate the effect of dilatancy in some cases of practical interest, particularly for the hydraulic fracturing of unconventional reservoirs.

The role of fluid driven fractures and their interaction with weak discontinuities in subsurface phenomena is of significant interest for many industrial applications, such as geothermal energy production, O&G reservoir stimulation and CO₂ storage, among several others Kneafsey et al. (2018); Zimmermann and Reinicke (2010).

Shale formations are characterized by having an extremely low permeability, in the order of hundreds of nD.. For this reason, hydraulic stimulation is required in the O&G industry in order to generate conductive channels between the formation and the well, thus making extraction commercially viable. In the context of CO₂ geological storage, they are considered as seals.

Weak mechanical discontinuities play an important role in the development of O&G fields in Argentina due to the highly variable presence of sub-vertical and sub-horizontal natural fractures Rodrigues et al. (2009); Ukar et al. (2017, 2019a,b). It is known that these weak interfaces can potentially act as preferential propagation paths, locally altering the fracture propagation direction Gale et al (2018), or even restricting its height Weng et al. (2018); Xu et al. (2019); Celleri and Sánchez (2021).