Seashell waste as a complete substitute for metakaolin in high-performance and environmentally friendly geothermal well grouts: Fresh state behavior and rheology

In the face of challenging downhole conditions, the fresh state behavior of cement grouts employed for well cementation is as crucial as their mechanical properties. If not properly formulated, their primary purpose of providing zonal isolation of the steel casing from the surrounding formation may not be fulfilled. This study presents a rheological analysis of innovative lightweight slurry formulations utilizing finely ground seashell waste powder as a complete substitute for metakaolin. Replacing metakaolin with seashell waste powder aims to mitigate the environmental impact of well cementation and improve the fresh state behavior. Investigations are conducted using powders derived from various seashell wastes( Crassostrea gigas , Pinctada maxima , Pecten maximus , and Crepidula fornicata ) without the addition of chemical additives. The influence of elevated temperature on gelation, Yield Stress (YS), and Plastic Viscosity (PV) of the seashell slurries is compared with that of a conventional geothermal formulation containing metakaolin. The development of strength under elevated pressure and temperature conditions, similar to those found in downhole environments, is also examined using the ultrasonic cement analyzer (UCA) technique. All slurries demonstrated shear-thinning behavior, with apparent viscosity decreasing as shear rates increase. The findings further reveal a reduction in PV and YS of all seashell waste powder-based slurries relative to the traditional formulation. Moreover, gelation of the slurries formulated with seashell powder occurred more slowly at both ambient temperature and 55 °C. At 85 °C temperature and 18 MPa confining pressure, the compressive strengths obtained from UCA results meet the minimum industrial requirement of 24 h, and the ultimate UCA compressive strength of the seashell slurries surpasses that of the conventional formulation. • The rheology of slurries with seashell waste powder for geothermal cementation was studied. • Seashell waste powder reduces the yield stress and plastic viscosity of slurries. • Gel strength in seashell powder slurries developed gradually at both room temperature and 55 °C. • At 18 MPa and 85 °C, the seashell slurries develop strength beyond the 24-hour minimum requirement. • Seashell waste powder helps maintain slurry pumpability without the use of chemical additives.