Ureolysis induced mineral precipitation material properties compared to oil and gas well cements
Beser, Guneycan Dicle
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Novel methods are needed to prevent or mitigate subsurface fluid leakage, for example stored carbon dioxide, fuels during unconventional oil and 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 and 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) x 5 cm (length) and 5 cm x 10 cm cylindrical molds with sand and injecting both microbial and plant-based enzymes with urea and calcium solutions to promote precipitation. Sources of urease included jack bean enzyme and S. pasteurii microbe, resulting in both enzyme and microbe induced calcite precipitation (EICP, MICP) specimens. For comparison, Class H well- and Type I-Portland specimens were made by mixing cement paste (API 10B) with sand (ASTM C305). Fine cement specimens were also included in the comparison and were made both by mixing and also injecting to match the process used to make the biocement specimens. For the 2.5 cm x 5 cm specimens, the addition of nutrient broth to the enzyme specimens (ENICP) resulted in increased compression strengths compared with specimens without nutrient (EICP). The average compression strengths of these ENICP specimens reached 77% and 66% of the compressive strength of the 28-day well cement and Type I cement mortars, respectively and were over two times larger than the 28-day strength of the fine cement specimens. For 5 cm x 10 cm specimens, compression strengths of MICP, ENICP, and EICP specimens reached 42%, 38%, and 16% of the 28-day injected fine cement specimens. The average modulus of elasticity of ENICP was 17,316 + or = 1,430 MPa with 8.3 + or = 1.8% CaCO3 content (g/g sand) and was approximately 30% larger than the average modulus measured for the fine cement specimens. The results of this study indicate that the UICP produced specimens may have adequate strength and stiffness for field applications.