Fluid conduction in closed fractures and implications for DFIT interpretation

In this post, I address a topic that seems esoteric, but it has critical implications for understanding how DFITs respond to closure. In turn, this directly affects how we estimate stress and permeability. The question under investigation: do fractures store and conduct fluid after they close? My answer: in most DFITs, yes. Two caveats: unless the formation is extremely soft or ductile (allowing residual aperture to be nearly zero) or the matrix permeability is sufficiently high (making the residual fracture conductivity so small relative to the matrix permeability that it is negligible). Note that as fluid pressure draws down after mechanical closure, conductivity decreases. So it is possible that fractures that are hydraulically conductive during a DFIT may effectively close when fluid pressure is drawn down during long-term production (this depends on the stiffness and strength of the asperities that allow the mechanically “closed” fracture to retain aperture).