Fracture sealing and its impact on the percolation of subsurface
fracture networks
Abstract
Fractures play an essential role in formations with low permeability;
however, fracture sealing significantly reduces the permeability of
fractures. The mechanism of how fracture sealing impacts the macro-scale
fluid flow is rarely investigated. Here, we simulate sealing in two- and
three-dimensional orthogonal fracture networks and investigate the
impact of sealing on the percolation of these fracture networks. We find
that a small amount of sealing can prevent the formation of spanning
clusters, which suggests that global connectivity is rarely realized.
Without significant stress perturbations, most fractures are partially
sealed and non-critically stressed, and they usually do not contribute
much to the fluid flow. However, under a significant stress
perturbation, such as hydraulic fracturing, the well-connected and
critically oriented fractures become critically stressed and slide
because of the increased pore pressure. Partially sealed and
non-critically stressed fractures can also contribute to the fluid flow
by enlarging the stimulated reservoir volume (SRV). We estimate the
stimulated reservoir volume in two dimensions by dividing the target
distance (LSRV) into two parts. One is the distance limiting generation
of hydraulic fractures (ΔLh), and the other is the limiting distance of
making natural fractures slide (ΔLs). A rough estimation yields an
elongated shape of the SRV, which is consistent with observations from
microseismicity maps.