In today's oil and gas economic environment, oil and gas wellbores must remain competent for long-term production and injection use. Secondary recovery, waterflooding, and tertiary recovery methods of polymer and carbon dioxide injection have given new life to old wells, requiring even

longer use of existing wellbores. Wellbore integrity tests required by state and federal regulations, are designed to protect fresh water zones, prevent hydrocarbon migration into unwanted zones of porosity and insure that wellbores are not in communication with the strata behind the pipe. These integrity tests and the longer more demanding use of wellbores have contributed to oil and gas operators discovering that lengthy sections of the original casing string have disintegrated. Contributing factors of casing failures are external corrosion, electrolysis, and internal metal loss, due to hydrogen sulfide and carbon dioxide. "Retrievable" liner installations provide a method of ameliorating the casing problems, and restoring the old wellbore to service. Through the use of a gelatinous, thixotropic oil-base packer grease, instead of cement, placed in the annular area between the newly installed liner and the original casing string the liner become retrievable. When initially mixed the oil-base packer fluid is liquescent enough to be pumped into the annulus. In a quiescent state it develops the consistency of a stiff grease. Upon agitation, the packer fluid will alter to a consistency capable of being pumped, thus allowing the liner to be recovered.

The retrievable liner provides an alternative to squeeze cementing where the deteriorated casing length is too long to provide for adequate cement fill. The liner offers a method to protect the active production or injection zone from foreign fluid invasion and when needed, allows the installation of special alloy liner equipment to protect against hydrogen sulfide and carbon dioxide environments.

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