Cement attack by acids during acid stimulation is a serious problem as indicated by both field experience and lab tests. A new cost effective technique was developed to enhance cement resistance to full strength mud acid. This technique will not only protect cement from acid attack, but will also prevent side problems, such as released iron (III) that may damage the formation around the wellbore area

The new technique includes preflushing the cement in the wellbore area (bridge plugs and cement behind casing) with 10 wt% acetic acid + 1.5 wt% HF prior to mud acid stimulation. This preflush will provide a protective layer on the surface of set cement that will minimize acid/cement interactions.

Lab results showed that the new technique significantly reduced the weigh loss experienced by neat cement exposed to a full strength mud acid by 16-fold. Moreover, it was more effective in reducing acid attack on cement than acid resistant cements (latex and latex-expanding).

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