As an increasing number of thermal wells are drilled in arctic and subarctic regions, such as the north slope of Alaska and northern Canada, there is an urgent need for lightweight cement systems with thermally insulating properties. Significant temperature changes resulting from activities such as shut-in, steam injection, and production can lead to increased temperatures in the wellbore. As the wellbore temperature rises, there is an increased risk of melting permafrost, which can allow the formation to move and result in costly damage to the well. Lightweight and thermally insulating cement would contribute to the life of a well by maintaining low thermal conductivity while providing structural support for the casing strings. This study compares the thermal and mechanical properties of water-extended, foam, and microsphere cements with densities of 1.32, 1.50, and 1.68 specific gravity (SG) (11, 12.5, and 14 lbm/gal).
To simulate several different conditions in a well, thermal conductivity of the foam system was measured for dried, as-poured, and saturated conditions. While the amount of air or fluid in the foam samples influenced the measured thermal conductivity, both microsphere and foamed systems appeared to be comparable.
Initial findings from mechanical properties testing demonstrated foamed slurries have higher tensile and compressive strengths. Under confining pressure, the foam cement system had a larger failure envelope and would be able to withstand greater downhole pressure increases compared to the microsphere design at the same density.
When designing wells in areas with permafrost, including a cement system with low thermal conductivity would help minimize the risk of melting the permafrost and maximizing the longevity of the well. This paper reviews several possible lightweight solutions and presents the thermal and mechanical properties of various foam and microsphere cement designs.