Flow and solute transport around injection wells through a single, growing fracture

Abstract During deep-well injection of liquids, the formation around an injection well is often fractured due to an imbalance between the injection pressure and the minimum horizontal rock stress opposing fracturing. The resulting fractures can grow during injection, which may span over several months to years. Earlier studies reported on solute transport in a single fracture in low permeability fractured media, assuming that transport into the formation perpendicular to the face of the fracture is mediated by diffusion alone. This may be valid for flow under natural gradients through fractured formations of low permeability. In contrast, due to the high rates of injection through a fractured injection well, both advection and dispersion play an important role in the spread of contaminants around a fractured injection well. We present a model for the flow and reactive solute transport profiles around fractured injection wells, through a single, two-winged vertical fracture created by injection at high rates and/or pressures and growing with time. The fracture, of constant height and infinite conductivity, serves as a line source injecting fluids into the formation perpendicular to its face via a uniform leak-off, resulting in an elliptical water flood front confocal with the fracture. Flow and solute transport within the elliptical flow domain is formulated as a planar (two-dimensional) transport problem, described by the advection–dispersion equation in elliptical coordinates including retardation and 1st order radioactive nuclear decay processes. Results indicate that transport at early times depends strongly on location relative to the fracture. Retardation has a more pronounced influence on transport for the cases where advection is significant; whereas 1st order radioactive nuclear decay process is independent of advective velocity. Flow and transport around an injection well with a vertical fracture exhibits important differences from radial transport that neglects the presence of the fracture, and also from transport from a fracture of constant length. The model and findings presented have applications in the calculation of the fate and transport of contaminants around fractured injectors and modeling the resulting contaminant plumes down stream of the wells. Further, the model also serves as a basis for modeling enhanced remediation of contaminated rock via injection well fracturing, a recently demonstrated technology.