Application of existing hydraulic fracturing technology to deep well injection of exempt and non-exempt wastes has been investigated. This new application involves disposal of wastes by controlled hydraulic fracturing of suitable deep geologic formations. The proposed process is similar to the widely accepted Class I injection, but allows subsurface placement of waste solids-bearing slurries. Subsurface slurry injection causes fracturing of injection zone rocks because solids-laden fluids (slurries) form relatively impermeable filter cakes when pumped under pressure. Reliable information on hydraulic fracture geometry and propagation has historically been lacking, and current methods of deep well disposal exclude fracture injection. For fracture injection to be accepted, a demonstration is necessary that migration of contaminants is limited to specific geologic formations or zones, or that injected materials undergo chemical transformation into non-toxic forms. This is a "no migration" demonstration, and is done by mathematically simulating transport of injected materials.
The present research involves mathematical simulation, or modeling, of deep well fracture injection of solids-bearing waste slurries. Basic analytical and numerical models were formulated for estimation of injected waste migration from a fracture system. Parameters are in ranges expected of realistic disposal conditions. Analytical and SWIFT II models address regional fluid gradients, reservoir permeability, and fracture orientation.