Novel methods are needed to prevent or mitigate subsurface fluid leakage (stored carbon dioxide or fuels, during unconventional oil & gas resource development or nuclear waste disposal). Ureolysis-induced calcium carbonate precipitation (UICP) has been investigated as a method to plug leakage pathways in the near wellbore environment or in fractures. The enzyme urease catalyzes the hydrolysis of urea to react with calcium to form solid calcium carbonate (similar to limestone). UICP test specimens were prepared in triplicate by filling 2.5 cm diameter × 5 cm long molds with sand and injecting both microbial and plant- based enzymes with urea and calcium solutions to promote precipitation. For comparison, Class H well-, fine-, and Portland Type I- cement specimens were prepared by mixing the cement paste (API 10B) then mixing with sand (ASTM C305). Compression strengths of the plant-based enzyme specimens reached 77% and 66% of the compressive strength of the 28-day well-cement and Type 1 cement mortars, respectively. The specimens also reached 83% of the 14-day fine cement strength. The results of this study indicate that the UICP produced specimens may have adequate strength for field applications.

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