Slurried solids injection is a procedure for placement of granular solid waste deep into porous and permeable geological strata. This technology is currently used by the petroleum industry in several countries (United States, Canada, North Sea, and Indonesia) to dispose of nonhazardous oil-field waste solids. Granular or ground solids of grain size less than 5 mm (0.19 in.) are mixed with waste liquids to form a slurry that is pumped down a deep well under conditions of continuous hydraulic fracturing pressure (pinj > σv).
This article discusses rock mechanics aspects and geological engineering criteria for deep slurry injection. Specifically, the geometrical, lithostratigraphical, and physical parameters that characterize a stratum as a suitable target reservoir for slurried waste placement are addressed. The most important criteria are permeability, porosity, reservoir thickness, depth, and structural geology (of the region). A geological assessment model was developed to serve as a screening process to select suitable reservoirs for slurried waste placement. The screening process to select suitable reservoirs is composed of two steps: a decision tree and a semiquantitative ranking system that provides a numerical score for the stratum. The apparently robust assessment model was tested on several sites representing diverse sedimentary geology in the United States, Canada, the North Sea, and Indonesia.