Particulate solids and/or colloids.
Bacterial growth on well screen and formation.
Emulsification of two fluid phases.
Precipitates resulting from mixing of injection and reservoir fluids.
Expansion and dispersion of water-sensitive clays
Migration of fines (very small particles) released by dissolution.
Reprecipitation of dissolved material (iron or calcium sulfate).
Change in wettability or reduction in pore dimensions by adsorption (organics with large molecular weight).
Flow of unconsolidated sands into bore.
Scaling on injection equipment by precipitation from injection fluid.
Filter before injection. Treat with bactericides.
Do not exceed solubility limits of organic wastes in water. Use pretreatment or buffer of non reactive water.
Avoid injection of low-salinity solutions in water-sensitive
(particularly montmorillonite) formations. Use clay stabilizers. Neutralize before injection.
Difficult to remedy.
Use gravel-pack well screen. Inject a slug of brine after every period of interrupted flow.
Use pretreatment; flush with solutions to remove accumulated scale.
Remove gases from waste before injection or treat to prevent gas formation in the injection zone.
Source: U.S. EPA, Assessing the Geochemical Fate of Deep-Well-Injected Hazardous Waste: A Reference Guide, EPA/625/ 6-89/025a, U.S. EPA, Cincinnati, OH, June 1990.
wastes will not migrate into the injection zone until permeability is reestablished by physical or chemical means (see Table 20.15). Partial reductions in permeability may allow wastes to move into the injection zone but at increased pressures. This latter situation may contribute to well-casing or confining-layer failure. Clay swelling, mobilization of fine particles by dissolution, and precipitation are the common causes of well plugging.
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