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A method has been developed to restore injection capacity to wells that have been damaged by plugging with iron sulfide and free sulfur. It consists of(1) making the plugging material water-wet with a non-ionic detergent, (2) acidizing to remove the iron salts, (3) making the remaining free sulfur oil-wet with a surfactant, (4) dissolving the free sulfur with a suitable solvent, and (5) flushing all fluids into the formation. The order of applying these steps should not be varied. However, the mechanics of applying the treatment and the necessary volume of chemicals depend on well characteristics, operating conditions and economics. Certain safety rules and precautions must be followed when these chemicals are used. This treatment was devised when standard methods such as acidization, fracturing, or recompletion were not successful in restoring injectivity to wells plugged with iron sulfide. The problem was approached on the theoretical basis of the chemistry of the injection fluids in the well. Field tests have proved the method to be practical, economical and successful. It should be emphasized that this is not a permanent cure. It will only restore injection capacity. Well plugging can be prevented by stabilizing the injection water before injection. Since it is difficult to stabilize waters containing iron sulfide, economics should determine whether stabilization is more desirable than repeated well clean-out. Usually, the most economical solution is partial stabilization to reduce the frequency of well treatment. Introduction The industry has always been plagued with plugging difficulties when injecting waters containing sulfides into waterflood or disposal wells. Ordinary remedial measures such as acidization, fracturing, reperforation, recompletion, or backwashing were partially successful for the first few treatments. Apparently a portion of the plugging material remained in the wellbore following these treatments because each successive treatment became less effective. This restricted injectivity forced curtailment of production. Therefore, we needed to determine the reasons for this ineffective clean-up in order to improve treatment or to design new methods. Extensive laboratory and field study led to a method which proved to be satisfactory in one type of injection well. During the past year, this method has been modified and improved to make it applicable to various types of injection wells.

A New Method of Restoring Water Injection Capacity to Wells Plugged with Iron Sulfide and Free Sulfur