Stress Effects on Flow and Transport in Three‐Dimensional Fracture Networks

Abstract

We investigate the effects of various external stress regimes on fracture apertures, fluid flow, and solute transport in three‐dimensional fracture networks. We use well‐established geomechanics equations coupled with discrete fracture network modeling to characterize changes in primary flow paths within a complex network as a function of stress magnitude and orientation. These changes manifest in the alterations of the fluid flow field and are measured in terms of Eulerian and Lagrangian flow observables including solute transport, which is a key problem in many hydrologic applications. Changes in primary flow paths affect the solute transport in the network by promoting anomalously early arrival or long tailing behavior. However, early time arrival is not ubiquitous in anisotropically stressed networks and in most cases there is a delayed arrival of solute, which is attributed to (i) the presence of low‐velocity zones normal to the flow direction, (ii) the angle between flow direction and major compressive principal stress directions, and (iii) changes in the primary flow paths (i.e., increases in tortuosity and active network structure). Overall, flows become more channelized in anisotropically stressed fracture networks than in unstressed and isotropically stressed networks.

From Fluid Flow to Coupled Processes in Fractured Rock: Recent Advances and New Frontiers

“…Although computationally expensive, the main advantage of discrete models is that they provide a more faithful representation of gradients between the properties of fractures and the rock matrix (de Dreuzy et al., 2002, 2012; Edery et al., 2016; Frampton & Cvetkovic, 2010; Hardebol et al., 2015; Hyman, 2020; Hyman et al., 2019a; Kang et al., 2019; Maillot et al., 2016; Painter et al., 2002; Selroos et al., 2002; Zou & Cvetkovic, 2020, 2021) across a wide range of length scales (Bogdanov et al., 2007; de Dreuzy et al., 2002, 2012; Frampton & Cvetkovic, 2010; Frampton et al., 2019; Hyman et al., 2019b; Joyce et al., 2014; Makedonska et al., 2016; Sweeney & Hyman, 2020; Wellman et al., 2009) and offer the ability to test hypotheses about the importance of one scale of heterogeneity against another. This aspect makes them better suited to inform field site operators about what data would be the most impactful to constrain predictive models.…”

Characterizing Reactive Transport Behavior in a Three-Dimensional Discrete Fracture Network

“…Additionally, it has been well studied that large, high velocity fractures form primary pathways which serve as a network's backbone and control conservative transport behavior at the network scale Viswanathan et al, 2018;Kang et al, 2019;Sweeney & Hyman, 2020). However, study of the network backbone's role in reactive transport behavior has been limited.…”

Modeling radial groundwater flow in fractured media using fracture continuum approach

“…Darcy law is applied for each fracture segment and the mass balance must be achieved at each fracture intersection. The DFN approach was studied by Cacas et al (1990), Sahimi (1995), Adler and Thovert (1999), Liu and Bodvarsson (2001), Park et al (2001), Zhang and Sanderson (2002), de Dreuzy et al (2002Dreuzy et al ( , 2004, Hyman et al (2015), Maillot et al (2016), Ahmed et al (2019), Frampton et al (2019), Jarrahi et al 2019, Khafagy et al (2020, Sweeney and Hyman (2020), and Khafagy et al (2021). On the other hand, the SC modeling approach depends on the representative elementary volume (REV) concept which represents the rock mass as an equivalent porous medium.…”