Abstract
Ensuring the integrity of oil and gas wellbores critically hinges on cement binding. This paper presents findings of the untapped potential of Tanzanian natural pozzolans, namely, kaolin and pumice, as a feasible option for geopolymer cement, specifically tailored to enhance the structural integrity of oil and gas wellbores. Results from XRF, XRD and FTIR analyses confirmed that kaolin, modified kaolin (metakaolin), and pumice powder are composed mainly of SiO2 and Al2O3, while modified quartz with NaOH (metasilicate) is primarily composed of SiO2 and Na2O. The results revealed that 21% of metasilicate in a mixture of kaolin activated at 800 °C and pumice resulted in geopolymer pastes with the best compressive strengths. Compressive strengths of 35.94 ± 0.93 and 33.71 ± 0.37 MPa were obtained at 70 and 90 °C respectively, after 28 days of curing in brine baths (40 g/L NaCl and 40 g/L Na2SO4). XRD results on crystallinity showed that the formulated geopolymer pastes had amorphous phases (70.73%), indicating the presence of irregular, non-repeating atomic structure. The AFM results strongly supported the presence of amorphous phases and further revealed that the geopolymer pastes have few pores and no cracks. TGA results revealed that the formulated pastes were thermally stable up to 900 °C. MP-AES results showed an increase in the concentration of dissolved metal ions from the geopolymer pastes from the 7th to 21st days of curing that remained relatively constant until the 28th day. This observation suggests that the chemical stability of geopolymer paste increased with curing time due to the formation of more geopolymerization chains facilitated by the consumption of unreacted metal ions during curing. These results concurred with the compressive strength findings of this study. The water absorption result was 0.81%, implying that the geopolymer pastes were water-resistant. The overall results contribute to developing sustainable and eco-friendly cement options for the oil and gas industry, ensuring the integrity and longevity of wellbores.
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