Well Casing and Confining Formation Failure

Interactions between corrosive wastes and casing and packing can threaten the integrity of a well if proper materials have not been used in construction. Of equal concern is the potential for failure of the confining zone due to physical or chemical effects. For example, dissolution of an overlying carbonate confining layer may allow upward migration of wastes. This process was observed when hot acidic wastes were injected in a Florida well.

Chemically active injected fluids can also have negative impacts on the mechanical properties of the reservoir rock. For example, adsorption of aluminum and iron hydroxides and ferric chloride on quartz and other silicates can weaken the surface silicon-oxygen bonds by hydrolysis, reducing the surface energy, surface cohesion, and breaking strength of the formation. In addition, stress changes caused by increased injection pressures can fracture rock, forming permeability channels in a confining formation through which injected fluids could escape.80

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