Permafrost-sealant

Figure 15.3 shows a typical time versus consistency graph for a permafrost-sealant test composition. The low initial Be ensures a low yield stress and pumping viscosity. The increase in Be is gradual, indicating slow dissolution of MgO and wollastonite in the solution. As the Be increases, its rise to 70 is rapid, and the time versus Be curve is almost vertical. Such behavior ensures that the slurry, once placed, will set rapidly. 

Adding cenospheres and Styrofoam up to 10wt%, its thermal conductivity can be lowered to half that of conventional cement. When Ceramicrete-based permafrost sealant was cured in a CO2 environment, it set well, and when stored in CO2 for a week, it did not show any deterioration. Sugama and CarcieUo [8] predict that these sealants are durable up to 20 years in a downhole environment, compared to conventional cements that last for only a year. Unlike conventional cements, because CBS are neutral in pH and are not affected by downhole hydrocarbon gases, they are ideal for use in the gas hydrate regions in arctic climates. 

The worldwide cement composition is —1.6 billion metric tons per year [2], approximately 3% of which is consumed by the oil and natural gas industry. Thus, the annual cement consumption by this industry is —48 million metric tons. The industry, till now, has depended on modified portland cement, but there are niche areas where conventional cement is not reliable. Portland cement has several shortcomings for borehole sealant. It does not set easily in permafrost temperatures, because the water in it will freeze even before the cement sets. Its bonding to earth materials in the presence of oily surfaces is poor. Inherently porous, it cannot form a good seal. A major ingredient, calcium oxide, is affected by downhole gases such as carbon dioxide as a result, cement performance can be poor. These problems can be overcome by a range of CBPC formulations because of their above-mentioned superior properties. 

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