The Effects of Multiple Interacting Fractures on Surface Deformation and Flow

Abstract:

In a number of topical contexts, the response of fluid-filled fractures is of fundamental importance. For example, hydraulic fracturing operations typically generate multiple sub-parallel fractures that may, in turn, interact with families of preexisting natural fractures. At the In Salah carbon sequestration site, space geodetic observations of surface deformation suggested opening of a fracture and leakage of fluids into the caprock. And hydrocarbon production is often facilitated by naturally occurring fractures that are typically depressurized through production or pressurized to enhance oil recovery.

Both the surface deformation and the fluid flow resulting from pressure variations in a fractured medium are qualitatively different for a fractured medium compared to a medium with isotropic properties. It is straightforward to calculate the responses of a medium with a single fracture, with analytical solutions available for simple geometries. Also, in the limit of very high fracture density, continuum representations of anisotropic poroelasticity can be used. However, as in the examples above, there are many applications where a finite number of fractures are spaced closely enough that their stress fields interact. I investigate this regime numerically. Observations of both surface deformation and inferences of permeability can be effective in constraining estimates of fracture density and aperture.