Acid corrosion inhibitors provide protection by adsorbing on metal surfaces, thus forming a barrier against acid attack. Upon entering the formation, the inhibitor is strongly adsorbed on clays and other minerals present within the matrix of the rock. In some cases, inhibitors contain acid-insoluble residues which can cause surface plugging of the formation face. Inhibitor adsorption and formation plugging by inhibitor residues can have a major influence on cleanup rate and the ultimate effective permeability of the treated zone. Consequently, acid corrosion inhibitors should be evaluated both for their ability to protect metal and for their potentially damaging effect on stimulation results.
Laboratory tests, using a computerized core test permeameter, demonstrate the strong influence of acid inhibitors upon acid injectivity, cleanup rate and stabilized long-term effective permeability. The adsorption characteristics of the inhibitor were shown to strongly influence test results. The beneficial effect of mutual solvent upon injection rate and, in some cases, well cleanup was also demonstrated.
Data are presented showing the influence of temperature, differential pressure and mutual solvent upon injectivity, cleanup rate and apparent stabilized oil permeability. Various types of inhibitors were evaluated under a variety of test conditions.
In general, it was found that damage resulting from the corrosion inhibitors was more pronounced at the lower temperatures and that mutual solvents reduced the magnitude of the problem.